&EPA
United States
Environmental Protection
Agency
Office of Radiation and Indoor Air
National Air and Radiation
Environmental Laboratory
EPA402-R-09-008
June 2009
www.epa.gov/narel
          Radiological Laboratory Sample
          Screening Analysis Guide for
          Incidents of National Significance

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                                        EPA 402-R-09-008
                                          www.epa.gov
                                             June 2009
                                             Revision 0
         Radiological Laboratory
Sample Screening Analysis Guide for
   Incidents of National Significance
           U.S. Environmental Protection Agency
               Office of Air and Radiation
             Office of Radiation and Indoor Air
      National Air and Radiation Environmental Laboratory
                 Montgomery, AL 36115
                                          Recycled/Recyclable
                                          Printed wirh Soy/Canola Ink on paper that
                                          contains at ieast 50% recycled fiber

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         Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
This report was prepared for the National  Air and Radiation Environmental Laboratory of the Office of
Radiation  and  Indoor Air,  United States  Environmental  Protection  Agency.  It  was prepared  by
Environmental Management Support, Inc., of Silver Spring, Maryland, under contracts 68-W-03-038, work
assignment 35, and EP-07-037, Work Assignments B-33 and 1-33, all managed by David Carman. Mention
of trade names or specific applications does  not imply endorsement or acceptance by EPA.

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
                                        Preface

The document describes methods that may be applied by personnel at a radioanalytical labora-
tory for sample radioactivity screening following a radiological or nuclear incident, such as that
caused by a terrorist attack. The methods used for the screening of a large number of contamina-
ted samples, and the decisions regarding sample processing, will change based on the radionuc-
lides involved in the event and the incident priorities. The rapid assessment and prioritization of
individual sample activity concentrations for analytical processing require consistent application
of the method used for screening  the different types  of samples that will be generated during
such  an incident.  A quality assurance program that addresses this  screening process  from
instrument calibration through data reporting will also be  necessary to  provide  defensible
decisions and data.

The need to ensure adequate laboratory infrastructure to support response and recovery actions
following a major radiological incident has been recognized by a number of federal agencies.
The Integrated Consortium of Laboratory Networks (ICLN), created  in 2005 by  10 federal
agencies1, consists of existing laboratory networks across the federal government. The ICLN is
designed to provide  a  national  infrastructure  with a coordinated and operational  system of
laboratory networks that provide timely, high-quality, and interpretable results for early detection
and effective  consequence management  of acts of terrorism and other events requiring an
integrated laboratory response. It also designates responsible federal agencies (RFAs) to provide
laboratory support across  response phases for chemical, biological, and radiological  agents. To
meet its RFA responsibilities for environmental  samples, EPA has established the Environmental
Response Laboratory Network (ERLN) to  address chemical, biological, and radiological threats.
For radiological agents, EPA is the RFA for monitoring, surveillance, and remediation, and will
share  responsibility for overall incident response with the U.S. Department of Energy (DOE). As
part of the ERLN, EPA's Office of Radiation and Indoor Air is leading an initiative to ensure
that sufficient environmental radioanalytical capability and competency exist across a core set of
laboratories to carry out EPA's designated  RFA responsibilities.

EPA's responsibilities, as outlined in the National Response Framework, include response and
recovery actions to  detect  and   identify radioactive  substances  and to  coordinate federal
radiological monitoring and  assessment activities.  This document was developed to  provide
guidance to those  radioanalytical  laboratories that  will support EPA's response and  recovery
actions following a radiological or nuclear  incident of national significance (INS).

The calibration and screening methods outlined in this document provide guidance  in gross
sample radioactivity measurements to support the laboratory's efforts to process  a large  influx of
samples rapidly.  These methods  are  based upon  the  anticipated varied activity levels  that
incoming samples  probably would contain if they were impacted by a radiological dispersion
device into the atmosphere, water, or soil.
1  Departments of Agriculture, Commerce, Defense, Energy, Health and Human Services, Homeland Security,
Interior, Justice, and State, and the U.S. Environmental Protection Agency.

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
The use of a planned methodology to assess radioactivity levels of samples that contain signifi-
cant quantities of radioactive materials will ensure that the radioanalytical data produced will be
of known quality and appropriate for the intended incident response decisions.  This guide will
assist laboratories in  establishing  measurement quality objectives (MQOs) for the screening
instruments. This will allow laboratories to have greater confidence in screening measurements
as they potentially will be using radionuclides for calibration that are likely to be present in such
samples.

As with any technical endeavor, actual radioanalytical projects may require particular methods or
techniques to meet specific measurement quality objectives.  This document cannot address  a
complete  catalog of analytical methodologies or potential radionuclides nor does it intend to
proscribe particular methodologies. Laboratories that have screening techniques using alternative
methods or instruments in place to address the protocols identified in this guide should continue
to use them if they support the measurement quality objectives required  by the incident. Radio-
nuclide-specific  methods to support response and recovery actions following a radiological or
nuclear INS can be found in Standardized Analytical Methods for Environmental Restoration
Following Homeland Security Events, Revision 4.0.

Detailed guidance on recommended radioanalytical practices may  be found in the Multi-Agency
Radiological Laboratory Analytical Protocols Manual (MARLAP) referenced in this document,
which provides  detailed radioanalytical guidance for  project planners,  managers,  and radio-
analytical personnel based on project-specific requirements. Familiarity with Chapters 2 and 3 of
MARLAP will be of significant benefit to the users of this guide.

This document is one in a planned series designed to present  radioanalytical  laboratory person-
nel, Incident Commanders (and  their designees), and other field  response personnel with key
laboratory operational considerations and likely radioanalytical requirements, decision paths, and
default data quality and measurement quality objectives for samples taken after a radiological or
nuclear incident, including incidents caused by a terrorist attack.  Documents currently completed
or in preparation include:

•  Radiological Laboratory Sample Analysis Guide for Incidents of National Significance -
   Radionuclides in Water (EPA 402-R-07-007, January 2008)
•  Radiological Laboratory Sample Analysis Guide for Incidents of National Significance -
   Radionuclides in Air (EPA 402-R-09-007, June 2009)
•  Radiological Laboratory Sample Screening Analysis Guide for  Incidents of National
    Significance  (EPA 402-R-09-008, June 2009)
•  Method Validation  Guide for  Qualifying Methods  Used by Radiological Laboratories
   Participating in Incident Response Activities (EPA 402-R-09-006, June 2009)
•   Guide for Radiological Laboratories for the Identification, Preparation, and Implementation
    of Core Operations for Radiological Incident Response (in  preparation)
•   Guide for Radiological Laboratories for  the Control of Radioactive Contamination and
   Radiation (in preparation)
•  Radiological Laboratory Sample Analysis Guide for Incidents of National Significance -
   Radionuclides in Soil (in preparation)

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
Comments on this document, or suggestions for future editions, should be addressed to:

Dr. John Griggs
U.S. Environmental Protection Agency
Office of Radiation and Indoor Air
National Air and Radiation Environmental Laboratory
540 South Morris Avenue
Montgomery, AL 36115-2601
(334) 270-3450
Griggs.John@epa.gov
                                        in

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         Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
                               Acknowledgments

This manual  was developed by the National Air and Radiation Environmental Laboratory
(NAREL) of EPA's Office of Radiation and Indoor Air (ORIA). Dr. John Griggs was the project
lead for this document. Several individuals provided valuable support and input to this document
throughout its development. Special acknowledgment and appreciation are extended to Dr. Keith
McCroan, ORIA/NAREL;  Mr. Daniel  Mackney for  instrumental  sample analysis  support,
ORIA/NAREL; Ms.  Schatzi Fitz-James, Office of Emergency Management, Homeland  Security
Laboratory  Response  Center;  and  Mr. David Garman,  ORIA/NAREL. We also  wish  to
acknowledge the external peer reviews conducted by Lindley J. Davis and Carolyn Wong, whose
thoughtful comments  contributed  greatly to the understanding  and quality of the report.
Numerous other  individuals,  both  inside and outside  of EPA, provided peer review of this
document, and their suggestions contributed greatly to  the quality and consistency of the final
document. Technical support was provided by Dr. N. Jay Bassin,  Dr. Anna Berne, Mr. David
Burns, Dr. Carl V. Gogolak, Dr. Robert Litman, Dr. David McCurdy, and Mr. Robert Shannon
of Environmental Management Support, Inc.
                                      IV

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         Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
                                     Contents

Acronyms, Abbreviations, Units, and Symbols	vii
Radiometric and General Unit Conversions	ix
I.   INTRODUCTION	1
  A.   Purpose and Objectives	4
  B.   Scope of DQOs/MQOs for the Screening Process	4
  C.   Measurement Quality Objectives: Relationship of Derived Concentrations, AAL, ADL,
       Risk Levels, and MMRto Dose	5
II.  RADIONUCLIDES	7
III.  DISCUSSION	8
  A.   Sample Screening and Processing at the Laboratory	8
       Gross Activity Measurement Instruments	8
       Instrument Response Characteristic Determination	10
       Crosstalk: Detector Responses to Radioactive Emissions	10
       Detector Background	13
       Sample Geometry	14
       Laboratory Instruments	14
  B.   Calibration of Instrumentation for Screening Analyses	14
       Detector Type	14
       Geometry	17
       Crosstalk, Dead-Band, and Self-Absorption Factors	21
       Final Instrument Calibration and Method Validation	21
  C.   Calibration of Screening Instruments when Radionuclide Identities are Known	22
  D.   Measurement Quality Objectives (MQOs) for the Screening Process	24
  E.   Key Recommendations	25
Appendix I- Screening Instrumentation Initial Calibration	26
Appendix II - Radiological Event Screening for 241 Am	28
Appendix III - Screening Instrumentation Response Corrected for Different Radionuclide	30
Appendix IV - Additional Sources and References	32
                                       Figures

Figure 1  - Halogen-Quenched GM Detector Response to Gamma Radiation (A) with Shield
    Open (B) with Shield Closed	16
Figure 2 - Gamma Energy Response for a Na(Tl) detector	16
Figure 3 -  Shown Without Bricks Covering Top of Shielded  Geometry. Nal(Tl) Detector
    Example	19
Figure 4 - An Improved Orientation for Shielding. Active Detector Area Within Shielding	19
Figure 5 -Relative Size of Shielded Volume	20
Figure 6  - Sample Shielding and Detector Orientations for Gross Screening of Air Particulate
    Filters Using an Alpha/Beta Pancake Detector	20
Figure 7 - Survey Meter 12345 Energy Open Window Response Curve for Beta Emitters	23
Figure 8 - Gamma Energy Response Curve for a Nal(Tl) Detector	30

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
                                        Tables

Table 1 - Radionuclides of Concern	7
Table 2 -Detectors Used for Gross Sample Screening	9
Table 3 -Radionuclides Spanning the Energy-Calibration Range	15
Table 4 - Response and  Figure of Merit  for 60Co and  137Cs with Different Nal(Tl) Detector
     Configurations	18
Table 5 -  Screening Instrument  Conversion Factor  Based on  Sample Analysis of a 1-Liter
     Sample Geometry	23
Table 6 - Calibration Data for Screening Instrument Response	26
Table 7 - Response Factors (RF) for Radionuclides with Respective Screening Equipment	27
Table 8 - Gross Screening Measurement Results from Transportation Incident	29
Table 9 -Results of Screening Measurement Using Adjusted Response	31
                                       VI

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         Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
               Acronyms, Abbreviations, Units, and Symbols
                           (Excluding chemical symbols and formulas)

a	alpha particle
AAL	analytical action level
ADL	analytical decision level
AL	action level
P	beta particle
Bq	becquerel (1 dps)
CERCLA	Comprehensive Environmental Response, Compensation, and Liability Act of
               1980 ("Superfund")
cfm	cubic feet per minute
CFR	Code of Federal Regulations
cm	centimeter
cpm	counts per minute
d	day
DAC	derived air concentration
DL	discrimination limit
DOE	U.S. Department of Energy
DP	decay product(s)
dpm	disintegration per minute
dps	disintegration per second
DQO	data quality objective
DRP	discrete radioactive particle
e~	electron
Epmax	maximum energy of the beta-particle emission
EDD	electronic data deliverable
EPA	U.S. Environmental Protection Agency
ERLN	Environmental Response Laboratory Network
FOM	figure of merit
y	gamma ray
g	gram
Ge	germanium [semiconductor]
GM	Geiger-Muller detector
GP	gas proportional
GPC	gas proportional counting [counter]
GS	gamma spectrometry
Gy	gray
h	hour
H0	null hypothesis
HI	alternate hypothesis
HPGe	high-purity germanium detector
1C	Incident Commander [or designee]
ICLN	Integrated Consortium of Laboratory Networks
IND	improvised nuclear device
                                      vn

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
INS	incident of national significance
keV	thousand electron volts
L	liter
LBGR	lower bound of the gray region
LCS	laboratory control sample
LEPD	low-energy photon detector
LS	liquid scintillation
LSC	liquid scintillation counter
MARLAP	Multi-Agency Radiological Laboratory Analytical Protocols Manual
MARS SIM	Multi-Agency Radiation Survey and Site Investigation Manual
MCL	maximum contaminant level
MDC	minimum detectable concentration
MeV	million electron volts
mg	milligram (1CT3 g)
min	minute
mL	milliliter (1(T3 L)
MQO	measurement quality obj ective
mR	milliroengten (1CT3 R)
mrem	millirem (1CT3 rem)
|_ig	microgram (1CT6 g)
Nal(Tl)	thallium-activated sodium iodide detector
NORM	naturally occurring radioactive materials

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
                 Radiometric and General Unit Conversions
To Convert
years (y)
disintegrations per
second (dps)
Bq
Bq/kg
Bq/m3
Bq/m3
microcuries per
milliliter (|j,Ci/mL)
disintegrations per
minute (dpm)
cubic feet (ft3)
gallons (gal)
gray (Gy)
roentgen equivalent
man (rem)
To
seconds (s)
minutes (min)
hours (h)
days (d)
Becquerels (Bq)
picocuries (pCi)
pCi/g
pCi/L
Bq/L
pCi/L
|j,Ci
pCi
cubic meters (m3)
liters (L)
rad
sievert (Sv)
Multiply by
3.16xl07
5.26xl05
8.77xl03
3.65xl02
1
27.0
2.70xl(T2
2.70xl(T2
io-3
109
4.50xlO~7
4.50X10"1
2.83 x!0~2
3.78
IO2
io-2
To Convert
s
min
h
d
Bq
pCi
pCi/g
pCi/L
Bq/L
pCi/L
pCi
m3
liters
rad
Sv
To
y
dps
Bq
Bq/kg
Bq/m3
Bq/m3
|j,Ci/mL
dpm
ft3
gallons
Gy
rem
Multiply by
3.17xl(T8
1.90xl(T6
1.14x10^
2.74xl(T3
1
3.70xl(T2
37.0
37.0
IO3
io-9
2.22
35.3
0.264
io-2
IO2
Note: Traditional units are used throughout this document instead of SI units. Protective Action
Guides (PAGs) and their derived concentrations appear in official documents in the traditional
units and are in common usage. Conversion to SI units will be aided by the unit conversions in
this table.
                                       IX

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
I.   INTRODUCTION

Most laboratories do not routinely screen samples under conditions found during an emergency
response situation, such as from a radiological or nuclear incident of national significance (INS).
Many of these samples are higher in activity  and  need to be accurately surveyed and prioritized
for analysis based on  direction from the Incident Commander (1C).1  This  document describes
methods that may be applied  by personnel  at  a  radioanalytical  laboratory for screening  of
samples for radioactivity. The specific techniques described in this guide may be used to assess
the gross a, P, or y activity in samples that may have been contaminated as the result of a radio-
logical  or nuclear event,  such as a radiological  dispersion device (RDD), improvised nuclear
device (IND), or an  intentional release of radioactive materials into the atmosphere or a body of
water or aquifer, or to terrestrial areas via mechanical or other methods. In the event of a major
incident that releases radioactive materials to the  environment, EPA will turn to selected radio-
analytical laboratories to support its response and  recovery activities. In order to expedite sample
analyses and data feedback, the laboratories will need guidance on EPA's expectations.

A response to a release of radioactivity to the environment likely will occur in three phases that
are generally defined in this  document  as:  "early"  (onset of the event to about day 4), "inter-
mediate" (about day 4 to about day 30), and "recovery" (beyond about day 30). Each phase of an
incident response will  require  different and  distinct  radioanalytical  resources to address  the
different consequences, management, priorities, and requirements of a phase. Some of the more
important radioanalytical laboratory issues germane to an incident response consist of radionuc-
lide identification and quantification capability, sample  load  capacity, sample processing turn-
around  time, quality of analytical data,  and data  transfer capability. This guide emphasizes the
laboratory screening of samples from the end of the early phase, through the intermediate phase,
and into the recovery phase (but does not address the screening by initial responders).

Although not the focus of this document,  during the  early phase, analytical priorities need to
address the  protection of the  public and field  personnel due to potentially high  levels  of
radioactivity and the need to  provide for qualitative identification of radionuclides.  During this
phase, the Protective Action Guides (PAGs) for radiological emergencies require evacuation of a
population if the projected short-term total  effective radiation  dose equivalent2 (TEDE) exceeds
1 rem.3 The nominal trigger for sheltering is 1 rem  over  four days (projected avoided inhalation
dose). The radioanalytical resource requirements  (field or fixed laboratory) for this  early phase
may vary significantly depending on the time frame, source-term nuclide, and the extent of the
contamination.

During  the intermediate phase, the radionuclides and matrices  of concern are  known qualita-
tively., and the quantitative levels suitable for making decisions based on action levels need to be
1 Throughout this guide, the term "Incident Commander" (or "1C") includes his or her designee.
2 The sum of the effective dose equivalent (for external exposure) and the committed effective dose equivalent (for
internal exposure). TEDE is expressed in units of sievert (Sv) or rem.
3 The common unit for the effective or "equivalent" dose of radiation received by a living organism, equal to the
actual dose (in rads) multiplied by a factor representing the danger of the radiation. "Rem" stands for "roentgen
equivalent man," meaning that it measures the biological effects of ionizing radiation in humans. One rem is equal
to 0.01 Sv.

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
rapidly  determined.  For the  intermediate phase, PAGs have  been established  to limit  the
projected radiation doses for different exposure periods, not to exceed 2-rem TEDE over the first
year, 500-mrem TEDE during the second or any subsequent year, or 5 rem over the next 50 years
(including the first and second years of the incident). In  addition, radionuclide concentration
limits for food and water as regulated by the Food and Drug Administration and EPA would be
applicable.

The final, or "recovery," phase occurs as part of a radiological incident site-remediation effort.
During this phase, when site atmospheric characterization and remediation cleanup  effectiveness
are determined, there is potential for more extensive radiochemical analyses at the lowest radio-
nuclide concentrations.

The analytical resources needed during any phase of a radiological event will depend on the
radionuclide  analytical action level  (AAL)4 developed for the various media that may affect
human exposure.  The radionuclide AALs, which are derived radionuclide concentrations for the
different media types based on the PAGs or risk values, may change depending upon the phase
of the event.

The time period of an incident where this document will find its greatest utility is early in the
intermediate  phase  through the  end of the  recovery  phase.  Laboratories performing analyses
must focus on  optimizing  sample analyses  so that the initial qualitative aspects  and concen-
trations  related to the  appropriate AALs can  be determined quickly  (i.e., rapid turnaround of
sample  results). Radioanalytical  screening  by laboratories during these phases  will include
methods for all three radioactive emissions. During the recovery phase, however, the screening
techniques used for samples will be more focused because  the radionuclides from the event are
likely to have already been identified and chemically characterized.

During all phases of an incident response, radioanalytical resources  are  needed for the  gross
radiation screening of samples for prioritization of sample processing or for information related
to the general  level of contamination, identification of  the  radionuclide  source term, and
quantification of the radionuclides  in  a variety of sample  media. This document has been
developed to provide  guidance during  an  incident on  techniques to  enhance the  ability to
differentiate  radioactivity in samples  near  action levels and optimize the  calibration of the
screening  equipment used for gross sample activity measurement. Using these techniques should
help laboratories to prioritize samples in a timely fashion based on the request of the 1C.

The process of screening samples using a survey instrument can be described  in two stages. The
first stage deals with the receipt of the bulk sample shipment and assessment of the radiation
dose rate (mrem/h) or gross activity (cpm) from the shipment and the individual samples, prior
to opening any samples. The main purpose in this stage is to identify any immediate radiological
hazard to  the receipt personnel and  sample analysts.  This screening  measurement typically is
made using  an  instrument that does  not discriminate particle energies or  assess total dose rate
from the sample. For example, an instrument like a Geiger-Mueller (GM) detector is sensitive to
4 The term "analytical action level" (AAL) is used in this publication series as a general term denoting the radio-
nuclide concentration at which action must be taken by incident responders. The AAL should always correspond to
a PAG or risk-based dose.

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
all gamma and beta particles with enough energy to pass through the container walls without
identifying which is which. At this time, no assessment of alpha particle or low-energy beta
particle contamination can be made. The measurement should not take more than 5 to 10 seconds
to complete per sample. Important aspects of the outcome of this  measurement are  that the
samples can be appropriately shielded and labeled for both radiation protection and prioritization
purposes,  and that the  sample mass and integrity remain unchanged (this is a non-destructive,
non-invasive test).

The  second stage of screening is more  substantive in that it examines  the total  radionuclide
activity for a  particular type of particle emitted from the radionuclides  contained within the
sample. Ideally, if 90Sr, 14C, and  99Tc were all contained in a sample, the instrument used for
screening  would measure the  total contribution as the sum of the  three, even if it could not
identify them individually.  Unfortunately, the instruments used for screening are  not  ideal:
detector response tends to be proportional to the characteristic energy of the radiation emitted by
a radionuclide and the detection is also impacted by sample self-shielding. It is very important to
ensure that a  screening test will provide a conservative  estimate of the total activity of the
radionuclides present to  ensure that the screen does not underestimate the total amount of a
radionuclide present. If the  identity of the radionuclides is known,  a different response factor
should be applied when measuring the medium-to-high energy beta from 90Sr/90Y than for the
lower energy 14C in samples where mass attenuation may be significant.

Using  gas proportional counting  (GPC) or  liquid scintillation counting (LSC) to perform the
screening  process has several important  consequences. First, when the sample container itself is
opened, the potential exists for contaminating  both the sample and the  laboratory.  Second, a
portion of the sample may be sacrificed for the screening process, which  may require judicious
sub-sampling. Third, chain-of-custody  must be  established for open sample containers  and
aliquanting prior to actual analysis. This will prevent questions later on regarding the sample
integrity.

This document provides technical information and recommendations for a laboratory faced with
screening  samples received following a radiological INS.  Screening samples deals with the
detector responses to radiation and the effects of different forms of radiation on different detector
types.  Three appendices  provide detailed scenarios that use the information in  the technical
section of the document. These scenarios illustrate when to change calibration and screening
techniques based upon what is  known about the sample's radioactive  contaminants  and the
instrument detection efficiency. The methods demonstrated by these scenarios are:

   •   Preparation of laboratory screening equipment for an INS event;
   •   Receipt of samples from an INS event with known radionuclides for which the  laboratory
       screening instruments are calibrated; and
   •   Receipt of samples from  an INS  event with known radionuclides,  but the  laboratory
       screening equipment must use a detection correction factor because the instruments were
       not calibrated with radionuclides present in the event samples.

Facility personnel should use these examples as guidance to prepare the  screening instruments
that are commonly used in their laboratories to analyze gross activity in samples from an INS.

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
A.  Purpose and Objectives

This document describes  how to  develop laboratory methods to perform gross radioactivity
analysis  for samples resulting from an  INS. It discusses  technical issues  associated with
screening measurements, provides  the suggested methodologies to determine correction factors
for these instruments, offers  a consistent methodology for  measuring sample gross activity
concentrations, and provides guidance on the calibration of screening equipment commonly used
by laboratories.

Although the list of potential threat radionuclides is relatively short, instrument responses to the
different particle  energies  may  vary  significantly  depending upon the type  of screening
instrument used. It is important to be able to use screening instrumentation to support the overall
laboratory process of sample prioritization and analysis that will support decisions to protect the
health and safety of the public.

This document provides guidance for a user to select appropriate  methods  for screening at
different points in the analytical process. The critical points in the process are sample receipt,
sample prioritization, and rapid feedback to the 1C on samples exceeding action levels.

The specific objectives for response  personnel to  accomplish  in preparing  their laboratories for
such an event include:

    •   Performance  of method validation for each  instrument/sample geometry combination
       used in screening;
    •   Identification of consistent methods of screening for various media;
    •   Screening instrument configurations that streamline the screening process;
    •   Screening measurements that will aid in prioritizing samples for analyses; and
    •   Methods for calibration of screening equipment that will have the widest applicability to
       those radionuclides most likely to result from an INS.

B.  Scope of DQOs/MQOs for the Screening Process

The use of screening instrumentation to prioritize  samples based on the amount of activity in an
individual sample  should be consistent  for all laboratories responding to  an INS. This should
allow the processing of samples and return of results to the 1C  based on the measurement quality
objectives (MQOs) of the event in the timeliest manner. During the early phase of an event when
the identity and extent of radioactive contamination are unknown, the screening instrumentation
should be calibrated with radionuclides that are routinely used for gross screening calibrations,
but in a  geometry that should support the best discrimination of activity  levels. As the  event
progresses and the specific radionuclides are identified, either  the calibration may be changed to
reflect the known radionuclides or an interpolated correction factor for instrument response due
to other radionuclides based on energy should be used.

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance


Other guides in this series5 identify Protective Action Guides (PAGs) as associated concentra-
tions and AALs that  are critical measurement limits. The  screening instruments used in the
laboratory to support the rapid and organized evaluation of sample priority should be calibrated
for gross activity measurements at these critical measurement limits in order to achieve the
established MQOs stated in the other guides.

Samples that have the potential for considerations in  a criminal investigation must be handled
separately, and the laboratory should receive information from the Incident Commander on how
to process these samples.

C.  Measurement Quality Objectives: Relationship of Derived Concentrations,
    AAL, ADL, Risk  Levels, and wMRto Dose

MOOs External to the Laboratory

Gross activity screening of samples is  the first step  to assessing whether or not a particular
sample exceeds a PAG's derived radionuclide concentration for the matrix that is being assessed
for radioactive materials. PAGs establish radiation dose limits applicable to different phases of
an  incident response.  The PAG (expressed  as  a numerical dose level)  indicates a level of
exposure at which  protective action should  be  taken to prevent, reduce, or limit a person's
radiation dose during  a radiological incident. The measurements that are made with screening
instruments in the  radioanalytical  laboratory should be correlated to the PAGs  expressed as
concentrations (or other AALs) for  each matrix defined by the incident.

A derived concentration of a radionuclide that corresponds to  a PAG or risk-based dose in a
specific matrix can be calculated and used to facilitate the application of these radioanalytical
action  levels in the laboratory  for decision-making  purposes. For  example, the derived air
concentration  (DAC, in units of pCi/m3) of an individual radionuclide in air corresponds to a
radiation dose (PAG)  to  a specific population. For each matrix that undergoes screening, there
should be a derived radionuclide concentration that may be directed by regulation or selected
based on the specific incident.

Screening instruments, when configured properly, can be used to conservatively determine if a
sample  has or has  not exceeded an AAL. However, when the total gross screening activity
exceeds an AAL, it  may not be possible to determine if the AAL for an individual radionuclide is
actually exceeded until radionuclide-specific methods are performed. In cases  where it is not
possible to determine  if an individual radionuclide AAL has been exceeded, screening provides
the laboratory with the information  to  prioritize samples that  need to be analyzed  first. The
priority for sample analyses will be decided based upon the incident phase and the specific needs
of the  1C. For example,  the order of analysis could be based on  highest activity first,  lowest
activity first, gamma response first, or any such logical priority.
 See Appendix IV for further references to how measurements are used to make decisions regarding PAGs and
action levels.

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
MQOs Internal to the Laboratory

The laboratory also needs the screening equipment to correlate  to MQOs  established in the
laboratory and thus facilitate sample processing. The screening MQO will likely change as the
event progresses and the known concentration of the radionuclides involved  becomes more
certain and their concentration diminishes due to radioactive decay, dilution, or dispersion. Using
Radiological Laboratory Sample Analysis Guide for Incidents of National Significance-Radio-
nuclides in Air as an example, four different levels are assessed over the course of an event: 2
rem, 500 mrem,  10~4 risk, and 10~6risk. As the event progresses towards samples being analyzed
at the  level  of  10~6 risk, the method detection capability may need to improve in order to
continually and  efficiently prioritize  samples.  The feedback to the 1C will be slowed down
because the  decreased sample activities will result in longer screening times for samples and
longer count times for samples following analytical  separations.

The changing  MQOs  will have a "domino effect" on laboratory QC analyses,  such  as spikes,
duplicates, laboratory control samples (LCSs),  and blank samples, processed in  a batch. The
activity levels for  spikes  and LCSs may  become  lower as the event  progresses, and the
acceptance criteria for the QC samples also may change. Changes to the required measurement
uncertainties for these QC samples will require  longer counting times and also may slow down
reporting to the 1C.

The required method uncertainty (MMR) may have default values for each radionuclide and matrix
(other guides in  this series identify these default values; see references in Appendix IV) or may
have incident-driven values.  In either case,  the laboratory should be prepared  to adjust these
values when  required by  the incident MQOs for  both  the screening instruments and the
radionuclide specific methods. The value of Z/MR and the acceptable error rates  for Type I and
Type II errors  are used to determine the analytical decision level (ADL). The ADL is a  value that
is less than the AAL.  When the ADL is exceeded, it is concluded that the AAL has  also been
exceeded, guarding against a decision error that  would allow a sample exceeding the AAL to go
undetected. The  ADL  concept is also used for both screening instruments and laboratory-specific
methods. For  more details  on these  concepts,  see Appendix VI  to Radiological Laboratory
Sample Analysis Guide for Incidents of National Significance-Radionuclides  in Water (EPA
2008a).

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           Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
II.      RADIONUCLIDES

The list in Table 1 is specifically for an RDD event and the major (non-inclusive) dose-related
radionuclides that might be released during the detonation of an IND. In the case of an IND,
numerous short- and long-lived radionuclides will be present, requiring proper identification and
quantification. Several of the radionuclides on the list have progeny that coexist with the parents.
Thus, if 228Th were to be found, 224Ra also would be present (although it is not listed). Several
different radionuclides may be present even if only one RDD is used.

                             TABLE 1 - Radionuclides of Concern
Alpha Emitters
Radionuclide
241Am
242Cm
243Cm
244Cm
237Np
2iopo [i]
238Pu
239Pu
240Pu
226Ra[2]
228Th[2]
230^
232^
234U
235U
238U[3]
U-Nat[3]






Half-Life
432.6 y
163d
29.1 y
18.10y
2.14xl06y
138.4 d
87.7 y
2.41xl04y
6.56xl03y
1.60xl03y
1.912y
7.538xl04y
1.405xl010y
2.455xl05y
7.038xl08y
4.468xl09y
—






Emission Type
cc, Y, [X-ray]
a.
a, Y
a.
a, Y, [Y, X-ray]
a
a, [Y, X-ray]
a, [Y, X-ray]
a, [Y, X-ray]
a, Y
a, Y
a, Y
a
a
a, Y
a
a






Beta/Gamma Emitters
Radionuclide
227Ac[2]
141Ce[l]
144Ce[3]
57Co[1]
60Co[l]
134Cs[l]
137Cs[4]
3H[1]
125j[l]
129j[2]
131j[l]
192Ir[l]
"Mo[2]
32p[l]
103pd[l]
241Pu
228Ra[2]
103Ru[2]
106Ru[2]
75Se[1]
89Sr[1]
90Sr[2]
99Tc[l]
Half-Life
21.77 y
32.51 d
284.9 d
271.7 d
5.271 y
2.065 y
30.07 y
12.32 y
59.40 d
1.57xl07y
8.021 d
73.83d
65.94 h
14.26 d
16.99 d
14.29 y
5.75 y
39.26 d
373.6 d
119.8d
50.53d
28.79 y
2.11xl05y
Emission Type
P,Y
P,Y
P,Y
e, Y, X-ray
P,Y
P,Y
P,Y
P only
e, Y, X-ray
P, Y, X-ray
P,Y
P,Y
P,Y
P only
P,Y
P, [a, y]
P only
P,Y
P only, (P, y
from progeny)
8, Y
P only
P only
P only
     Notes:
     The half-lives of the nuclides are given in years (y), days (d) or hours (h).
     [1] No radioactive progeny or progeny not analytically useful.
     [2] Radioactive progeny with short half-lives, and the progeny may be used as part of the detection
         method for the parent.
     [3] Radioactive progeny not used for quantification, only screening.
     [4] Radioactive progeny used for quantification only, not screening.
     Brackets [ ] indicate minor emission probability. If large quantities of these radionuclides are present,
     these  minor emission modes may contribute significantly to any screening measurements made on the
     sample.

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance


Instruments available for screening should provide a consistent measure of sensitivity6 to allow
detection of as many radionuclides as possible. However, some radionuclides (depending on total
activity levels) likely will evade detection with routine screening instrumentation (solid scintil-
lators or gas detectors). Generally, those radionuclides that decay by electron capture, positron
emission,  or very-low beta particle emission (and no gamma emission) should be analyzed with
radiochemical-specific methods to determine their presence. The radionuclides from Table  1 in
this group are: 3H, 99Tc, 125I, 228Ra, 241Pu, and 106Ru. However, it should be noted that if liquid
scintillation is used as  a screening technique, a measurable response to these  radionuclides  will
occur.

III.     DISCUSSION

The  discussion section of the document is divided into five parts. Part A  deals with  sample
screening  and different instruments that are commonly used to make these measurements. This
section also provides  some insight into technical  issues  encountered when performing gross
sample activity measurements when the radionuclide being measured is unknown.

Part  B  deals with the calibration of screening equipment  and the effects  on the calibration
process as a function of the particle type emitted by the calibration source and its  energy It  also
discusses the responses of different types of detectors and provides figures demonstrating detec-
tor and sample configurations  that may be  advantageous for screening of samples  for gross
activity.

Part  C deals with the use of screening  equipment for  prioritizing samples when  the  radionuc-
lide(s) present are known.

Part D discusses the MQO process, and Part E provides key recommendations for the laboratory
in establishing a screening protocol for samples resulting from radiological incidents.

A. Sample Screening and Processing at the  Laboratory

Guidance  on using both the  screening instrumentation  and  the radiation-specific detectors for
emergency response sample screening is discussed in this section.

Gross Activity Measurement  Instruments

If the  sample screening process at the  laboratory is  organized  properly, it  can significantly
improve the turnaround time for results and minimize risk of the spread of contamination in the
laboratory, as well as the chance for sample cross-contamination.

Gross activity measurements can be made using two general types of instrument—a ratemeter or
a sealer.
6 In this context, sensitivity refers to the ability of the screening equipment to detect different particles.

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
The ratemeter measures the radiation emission per unit time in real time, but not all instruments
have a summation function that would allow total decays to be measured over a defined time
period. The overall sensitivity and ability of these instruments to discriminate radiation types are
generally low. Although these are portable instruments that are  often used  for general area
surveys,  for the purposes of this guide these instruments are used in a fixed geometry relative to
the samples.  These instruments have time constants whose duration can be changed so that an
average  response to general radiation measured is more easily  determined.  A shorter time
constant  display has more frequent readings with the subsequent result of a "jumpy" needle or
scale  display  when activity levels are close to  the background level. By  increasing the time
constant, these measurements are averaged out internally and the display becomes more constant.
This is more  of a benefit to  the application where the sample and the detector are in a fixed
juxtaposition. When using a ratemeter for assessing gross radiation levels, it will be necessary for
the laboratory to establish a  protocol to  determine the measurement value  when meter/display
readings  are not constant (e.g., average the values of the high- and low-meter readings during a
20-second observation).

The sealer measures  individual events and  records  them  during  a specified  time period.
Instrument outputs are generally in terms of total counts. The assessment of the gross activity
generally takes longer with the sealer than with the rate meter, but the interpretation of the values
obtained  is  somewhat more  definitive.  Some of these  instruments  have  modest energy
discrimination capabilities.  However, these capabilities  are severely limited when a mixture of
radionuclides  of varied decay modes is present.  Laboratories should  have  a protocol that
describes how to use the gross count data  obtained by these types of instruments.

Table 2 identifies general descriptions of gross activity measurement instruments and laboratory
screening instruments that can be used for sample screening and specific emission types to which
they are most sensitive.

                 TABLE 2 - Detectors Used for Gross Sample Screening
Type of Detector
Geiger-Mueller (GM) Detector
[lonizable Gas]
Open-end GM Detector
[lonizable Gas]
GM Pancake Style Detectors
[lonizable Gas]
Micro-R meters [Nal(Tl)]
Cylindrical Probe [Nal(Tl)]
Thin Window (Alpha Scintillator)
Thin Window (Beta Scintillator)
Dual Phosphor Detectors
First Layer [ZnS]
Second Layer [Organic]
Portable Gamma Detectors [HPGe]
Small Article Monitors [Nal(Tl)]
Small Article Monitors [Organic Scintillator]
Liquid Scintillation [Liquid Fluor]
Sensitive to:
Gamma (X-rays)
Beta, Gamma, X-rays
(some high activity alpha)
Beta and Gamma
(some high activity alpha)
Gamma and X-rays
Gamma and X-rays
Alpha
Beta (low response to photons)
Alpha and Beta
Gamma (X-rays)
Gamma (X-rays)
Beta and Gamma (X-rays)
Beta, Alpha, and Gamma

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance


Instrument Response Characteristic Determination

The  first factor to  consider when performing  a  sample survey is  the  actual response by the
instrument to the potential radionuclides plus any decay progeny in the  sample. Not only is the
response of these instruments different for each type of radiation, but it may  also vary in a
complex way with respect to the energy of decay. A couple of examples that demonstrate these
differences in response are:

   •  The response  of  a Nal(Tl) micro-R meter will  be different for  high-energy photons
       compared to low-energy photons (i.e., it over-responds to low-energy photons).
   •  A GM pancake detector will respond to both alpha and beta radiation. However, for equal
       activities  of 32P (beta-emitter)  and 242Cm (alpha-emitter), the instrument will yield a
       greater response (i.e., higher counts per minute) from the betas of 32P.
   •  An open-end GM detector will respond to both beta and gamma radiation. However:
           o  The response to 10 nCi of  9Sr (Epmax at 1.49 MeV) will be greater than that for 10
              nCi of "Tc (Epmax at 0.294 MeV).
           o  The response to 50 nCi of 137Cs (gamma energy 0.662 MeV) will be smaller than
              that for 50 nCi of 57Co  (gamma energies at 0.136 and 0.122 MeV) because the
              lower energy gamma rays interact more favorably due to the photoelectric effect.
These  examples illustrate that the type and energy of radiation,  as well as branching ratios,
abundance values, and other physical properties of the radionuclide and the detection system are
significant factors in assessing the total activity of a sample during the screening process using
survey meters when the exact types of radionuclides present are unknown. Radionuclide-specific
detection parameters are explained in detail in Knoll.

Crosstalk: Detector Responses to Radioactive Emissions

In addition  to  the individual particle energy  providing  a different response in a particular
detector, one type of particle may yield a response indicative of another type of particle. This is
particularly  true with gross alpha-beta detection devices  that rely on pulse  size to determine
whether an individual event represents an alpha, beta, or gamma detection.
                                                                            9/11
One instance of this type of incorrect identification occurs with measurement of   Am using a
gas proportional detector. Although 241Am is principally an alpha-emitter, it also emits a low-
energy photon at  59  keV. A photon of this low energy may yield a response in the beta channel
because of the  high  probability of secondary interaction of scattered radiation with the instru-
ment components (including  electronics,  detector casing, instrument housing) via the photo-
electric and  Compton effects. Thus, if the total activity of the  241Am is  high, an incorrect
assumption regarding beta activity could be made.

Care must also be used to evaluate and interpret the results with respect to possible beta-to-alpha
and alpha-to-beta crosstalk effects when screening air filters (or other solid materials) for gross
alpha and beta activities by instruments  using gas  proportional  counting. The type of effect
7 Knoll, Glen F. 1979. Radiation Detection and Measurement, New York: John Wiley and Sons, Inc.
                                        10

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
depends on the instrument mode of operation, setup, voltage plateaus, and discriminator settings.
For most modern gas proportional counting instruments, the mode of operation may include:

    1)  Simultaneous measurements of alpha and  beta  activities based  on a single operating
       plateau and beta-to-alpha and alpha-to-beta discriminator settings; or
    2)  Independent  analysis of alpha and beta plus alpha activities on two separate voltage
       plateaus.

The second mode of operation, for most practical purposes, eliminates the beta-to-alpha crosstalk
effect. However, the alpha response on the beta plateau must be estimated and the beta results
adjusted accordingly. The remainder of the discussion that follows here will address the simul-
taneous alpha- and beta-counting mode.

The instrument voltage discriminator setting8 should be adjusted when operating in the simultan-
eous alpha and beta  counting mode to maximize the alpha detector efficiency and minimize the
beta-to-alpha response crosstalk. These settings should be established using a source with matrix
characteristics similar to the samples received from the incident response since absorption of the
alpha particles in the matrix will decrease the alpha energy available with a proportional decrease
in the  signal voltage for processing. Typically, nominal instrument settings can be established
that allow  for an acceptable alpha counting efficiency and a beta-to-alpha crosstalk of <0.1 %.
However, depending on the sample matrix and instrument settings, the actual crosstalk value can
vary widely from this value. For air filter matrices, the  alpha detector efficiency may be as low
as 5 to 10%, and the  beta-to-alpha crosstalk may contribute significantly to this value.

When  evaluating gross alpha and beta activity results of sample  analyses  for the purpose of
sample prioritization (for  subsequent radionuclide-specific analyses), it is important to consider
the possible effect of the beta-to-alpha crosstalk on deciding if the instrument alpha results have
been  artificially  increased.  The beta-to-alpha  crosstalk  effect may be most important either
during the  initial phases of an incident (when the radionuclides  of interest are unknown) or when
the composition of the mixture of alpha- and  beta-emitting radionuclides is known. For the latter
case,  the  beta-to-alpha crosstalk effect  should  be  addressed.  This can  be done,  once the
radionuclides have been identified, by  performing instrument calibrations for crosstalk using the
actual radionuclides  of concern, and corrections can be made that are both accurate and of known
uncertainty.

A general observation of the AALs for those  alpha- and beta-emitting radionuclides identified in
Table  1 indicates that the AALs for  the beta-emitting  nuclides are at  least a factor of 500 or
greater than for the alpha-emitting nuclides. For example, the 500 mrem AALs for 90Sr and 137Cs
are 110 and 550 pCi on  the air filter for a  68 m3 air sample. For the same dose and volume
                       941         9^Q
sampled, the AALs  for   Am and   Pu are 0.17 and 0.14  pCi.  For gross screening sample
prioritization,  the AALs for the 90Sr and 241Am should be used. Note that when the actual beta-
                                                                         on
to-alpha crosstalk discrimination is 0.1%, the alpha response observed  from  Sr activity at the
AAL may be > 0.1 cpm. With an alpha detector efficiency of 10%, the reported activity would be
8ASTM International (ASTM D7282-06). Standard Practice for Set-up, Calibration, and Quality Control of
Instruments Used for Radioactivity Measurements, ANNEX X2. West Conshohocken, PA. Available for purchase
from: www.astm.org/Standards/D7282.htm.
                                         11

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
near the gross alpha screening AAL. Therefore, when evaluating gross alpha results when the
beta result is greater than 500 to 1,000 times the alpha result, care must be taken to avoid the
false conclusion that the screening alpha AAL has been exceeded. When screening air filters that
have a beta-emitting radionuclide whose AAL is greater than the 90Sr AAL,  the beta-to-alpha
crosstalk effect may be  greater (depending  on the beta particle energy),  and the gross alpha
screening AAL may be artificially exceeded more often when the radionuclide beta activity is
near its own AAL.

                       on                                   ^
As an example, suppose   Sr at the 500 mrem AAL (110 pCi/m ) had deposited on an  air filter.
The activity would be the sum of 90Sr + 90Y = 220 pCi/m3 for a 68 m3 sample9 (a total activity of
3.32* 104 dpm). The measured beta activity for a 30% efficient detector would be

                    beta dpm = 0.3  x 3.32xl04 dpm beta = 9.96xl03 cpm.

The alpha response from beta-to-alpha crosstalk would be based on the  crosstalk factor, which is
relatively small (about 0.1%). Thus, the apparent alpha activity counted  would be

                            cpm =  9.96xl03 x 0.001 = 9.96  cpm.

Alpha background on a GPC will be small at ~ 0.05 cpm. Thus, with an alpha efficiency of 0.1
(10%), the net count rate for alpha would yield a calculated alpha activity of

                     alpha = (9.96-0.05) / (0.1) = 99.1 dpm = 44.7 pCi.

This would yield a false indication of alpha activity when none is present.

Using the same reasoning, example AALs can be applied to the evaluation of air  filters with
elevated alpha activity. The effects of alpha-to-beta crosstalk (versus beta-to-alpha crosstalk) can
be calculated, and the potential impact on artificially exceeding the beta  AALs can be deter-
mined.

When operating a gas proportional counter in the  simultaneous alpha  and  beta  counting mode,
the initial adjustment of the voltage discriminators  is intended to minimize  the beta-to-alpha
crosstalk. Crosstalk, however,  is more dependent on the specific radionuclide present in the
sample  and its physical  decay and  emission properties, than on the  instrument discriminator
settings. Actual alpha-to-beta crosstalk can vary from less than 3% to more than 30%, depending
on the radionuclide and other factors.

Alpha-to-beta crosstalk correction factors should  be determined  during the initial instrument
efficiency calibrations. These factors can be useful in making corrections to the  beta count rate,
based on the alpha count  rate,  but only when the radionuclide present has been  correctly
identified and the instrument has been calibrated accordingly.
9 The volume of 68 m3 is used as a reference volume as described in the Radiological Laboratory Sample Analysis
Guide for Incidents of National Significance-Radionuclides in Air (2009, In Preparation).
                                        12

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
When  performing gross screening analyses, however,  where the radionuclide has not been
identified and the instrument has not been appropriately calibrated, making a crosstalk correction
based on the initial instrument calibration can result in significant errors in the measurement of
the beta activity in the sample. Depending on the project  MQOs and event circumstances, it may
be preferable to make  no crosstalk correction and to potentially overestimate the  sample beta
activity. Because the beta AALs are typically much higher than the alpha AALs, this overesti-
mate should result in  artificially  exceeding the beta AALs only when the alpha activity is
extremely elevated.

In the previous example for beta-to-alpha crosstalk, the 500-mrem AAL for 90Sr is 110 pCi for a
68 m3  air sample. An  241Am activity of 2,200  pCi would be required to yield a beta  channel
signal that would correspond to the 110 pCi activity for 90Sr, or nearly 13,000 times the 241Am
AAL. For other alpha-emitting radionuclides, the alpha activity required to cause this beta AAL
to be artificially exceeded could be greater than 100,000 times the  AAL of that  other radio-
nuclide.

In these unusual cases, the apparent beta activity should be confirmed by an appropriate tech-
nique,  such  as recounting the sample with an alpha-attenuating barrier in place and comparing
the beta count rates from the two  analyses. For screening analyses, however, these techniques
assist only in estimating the degree of bias in the results, and do not correct for all sources of
crosstalk.

This effect can be illustrated by calculating the quantity of alpha activity from 241Am that would
yield an indication of beta activity  at the AAL for 90Sr. Given the 10~6 risk AAL for 90Sr of 0.29
pCi/m3 and an assumed sampled air volume of 68 m3:

   •   A beta activity from (90Sr +  90Y) on a filter at the AAL would be approximately 88 dpm;
   •   The beta counts recorded (with a detector efficiency of 30%) would be -26 cpm beta; and
   •   A normal beta background of 1 cpm yields a net beta count rate of-25 cpm.

Assuming 30% alpha-to-beta crosstalk and 10%  counting efficiency for 241Am, the alpha activity
required to produce alpha-to-beta crosstalk equivalent to the 90Sr AAL would be

                Alpha activity = 267(0.3x0.1x2.22), or approximately 390 pCi.

Thus, an activity of 241 Am of 390 pCi can cause  an apparent beta activity equivalent to the AAL
of 90Sr even when there is none present.

Detector Background

A second factor to consider  during  sample screening is the background. Background can  be
divided into the  categories of instrument (intrinsic or  electronic), environmental  (laboratory
location), and sample container/sample. These should be minimized when possible to achieve the
best signal to background ratio for the sample.  As will  be  shown further on in this document,
reduction of background is one of the most important limiting factors for detection  of low level
sample activity during the screening process.
                                        13

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
Some examples of potential background concerns are:

   •   Proximity of one screening instrument to another when samples or groups of samples
       contain enough activity to have an impact on a neighboring instrument.
   •   Presence of radionuclides with multiple emissions that can be detected by the instrument.

Since the level of background is crucial to the measurement, the shielding of the detector is an
important consideration.

Sample Geometry

The third factor that should be considered when using survey meters is the consistency of the
sample-to-detector geometry. The method of calibration of the survey meter and the method used
to screen samples using the  survey meter should match as closely as possible to obtain the best
estimate of absolute activity in the samples.

Finally, sample  self-absorption should be  evaluated  when  assessing the results  of sample
screening. This effect is most critical with  alpha- or beta-emitters, but for low-energy photon-
emitters it also will be a contributing factor to misidentification of particles. The loss of particle
energy as it travels through the sample medium will cause it to yield a smaller ionization pulse in
the detection device. As described earlier, this can register a false count for the wrong type  of
emitted particle.

Each of these three factors will be considered in the sections below that address the calibration of
screening detection equipment.

Laboratory Instruments

Hand-held  devices are not the only types of instrumentation that can be used for performing a
gross  radiological screen on  a sample. Consideration should also be given to using three
mainstays of the radiochemical laboratory for screening analyses. Gas proportional  counters
(GPC),  Nal(Tl) detectors,  and liquid  scintillation counters (LSC) normally  are used  for
radionuclide-specific analyses, and in such  applications radiochemical purity of the sample test
source (STS) is imperative.  These instruments can be used to assess total activity as well. This
may require a modification  or re-configuration of laboratory instrumentation to dedicate some
portion of the laboratory resources to emergency response rapid screening.

B. Calibration of Instrumentation for Screening Analyses

Detector Type

Examples of different types of gross screening survey meters and laboratory screening  instru-
ments are summarized here:
   •   Gross Alpha
       O  ZnS(Ag) scintillation detector with a thin aluminum or Mylar  window
                                        14

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
       o   Open-end GM detector
       o   Gas-filled pancake probe with a thin window
       Gross Beta
       o   Plastic organic scintillator with a thin aluminum or Mylar window
       o   Gas-filled GM detector (with slide-window allowing gamma detection in the presence
           of beta)
       Gross Gamma
       o   Gas-filled GM detector
       o   Sodium iodide (NaI[Tl]) or cesium iodide (CsI[Tl]) detector (well or flat type crystal)
           with sealer for open discrimination counting
       o   Micro-R meter using Nal(Tl) or CsI(Tl) detector
       o   HPGe detector (may be flat or well type) set for gross counts using summation of all
           channels
It would not be practical to maintain calibrations for each of the radionuclides, or mixtures of
radionuclides,  shown  previously in Table 1. However,  a straightforward  process can  be
performed to  relate the response  of  each detector to decay particle  energy.  While the
measurements are not as precise as more extensive laboratory measurements, it allows increased
accuracy for a longer list of radionuclides when making an estimate of the total activity. This can
be accomplished by selecting at least two (but preferably three or more) radionuclides that emit
characteristic decay particles with distinct energies that span the usable range of the instrument.
Table 3 identifies a list of radionuclides that  can be obtained as standards for calibration of
detector energy. Their emissions and energies for calibration are also included.

             Table 3 - Radionuclides Spanning the Energy-Calibration Range
Radionuclide
Emission Type
Energy, MeV
57Co
y
0.122,0.136
60Co
y
1.173, 1.332
137Cs
y
0.662
"Tc
Pmax
0.29
90Sr/90Y
Pmax
0.545, 2.28[2]
230^1]
a
4.69
241Am
a
5.49
[1]  This is the primary alpha for thorium; thorium has progeny that emit alphas as well.
[2]  This energy belongs to 90Y, which is in secular equilibrium with the 90Sr.

Next, the net instrument response for each of the  radionuclides is measured in a standard
configuration (i.e., a "geometry": matched quantities of sample, containers, and position relative
to the active  volume of the detector). For each type of decay particle and geometry, instrument
response should be plotted against the average decay energy10  of the particle emitted.  Using
these data, a table of response factors (i.e., efficiencies) is prepared that correlates to each of the
radionuclides in Table 1 based on decay type and respective  average decay energy. An example
of this application can be  seen in Figure 1, which shows the energy response to different energy
gamma radiation for a halogen quenched GM  detector, and  in Figure 2 for  a Nal(Tl) detector.
Note the significant, relative effect that using the GM shield has on the detection of the lower-
energy versus the high-energy gamma emitters. This also can  be used in a qualitative sense to
assess the overall energy profile of the gamma emitters.
10 See example in Appendix III for 192Ir.
                                         15

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance















Energy Response for Model 44-6
(Shield Open)
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c,«
























































1O 3CJO 1000 10000
fianutiii Kocrgj- ffcuVI
   FIGURE 1 - Halogen-Quenched GM Detector Response to Gamma Radiation (A) with
                           Shield Open (B) with Shield Closed

The maximum in detector response for the commonly used Nal(Tl) detector is about 100 keV
(see  Figure 2). For  a comparable  sized Csl detector, the response would be more efficient
overall, and the maximum in the efficiency curve would be at a slightly higher energy. This is
due to the difference  in physical properties of the CsI(Tl) crystal material.

                                Energy Response for Ludlum Model 44-10
J w -


S
S
1
9
X
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ai
























ta










-*










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                                                          10000
                                  Gamma Energy (k«V)
                FIGURE 2 - Gamma Energy Response for a Na(TI) detector

The response for an alpha-beta survey meter,11 using a halogen quench fill gas and a thin mica
window pancake probe, may have the following characteristics:

   •   Efficiency (2-pi geometry): 5%-14C; 22%-90Sr/90Y; 19%-"Tc; 32%-32P; 15%-239Pu
  The response curves and characteristics for these instruments were taken from information provided by Ludlum
Measurements, Inc., at www.ludlums.com.
                                        16

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance


   •   Sensitivity: Typically 3,300 cpm/mR/h (137Cs gamma)
   •   Energy Response: Energy dependent

From these few examples, it can be seen that the response of a survey instrument to different
types and energies of radiation is a complex function of not only the radiation emitted but also of
the survey instrument used.

Geometry

The  relative  geometry of sample to screening instrument and shielding can take on  several
different configurations. It is very important to ensure that the sample measurement matches the
calibration geometry.  Some of the considerations that will affect the optimal configuration of
sample to detection device are:

   •   Shielding (detector). The detection capability of the screening method will be optimized
       by shielding the detector to reduce  ambient background and minimize response to
       external sources of radiation. The  detector and detector shielding configurations should
       remain fixed so that the background count rate is reasonably constant.
   •   Shielding (container).  The sample container material can be made of glass, polyethylene,
       Teflon, or other non-reactive material.  The effect that these different  materials have on
       shielding the radioactive emissions from the detector varies with particle type and energy.
       Also,  the thickness of the container walls can increase the average distance of the center-
       of-activity of the sample to the detector. Both of these  sample container characteristics
       can affect the net screening result.
   •   Volume/shape/density. The sample volume must be consistent with gross measurements
       made  during the calibration of the  screening equipment so that the relative configuration
       of sample-to-detector  is maintained. Thus, it is important that the sample container be
       virtually identical to the container used for calibration purposes. Sample  density (or for
       solids, the degree of compaction) has a significant effect on the potential self-shielding of
       the sample from the detector. The  mass of the calibration source and the sample should
       be relatively close in value to  achieve consistent configuration.
   •   The figure of merit12 (FOM) for the  configuration of the  shielding may need to be
       optimized (i.e., a larger FOM is better). For example, it may  be advantageous to have a
       relatively large shielded volume  with  the sample centrally located,  versus a shielded
       volume that exactly fits the sample geometry.
   •   Location of the sensitive detection area in the screening equipment. The manufacturer's
       detailed diagram  for the  specific model of screening equipment should be available so
       that the optimum position of the detector with the sample can be achieved (See Figure 3).
   •   Size and shape of the detector with respect to the sample geometry. The sample shape
       and detector juxtapositioning can  have  significant effects  on the measurement.  One
       measure of this is the FOM.

An example illustrating the effects of the size and shape of the detector on the FOM can be seen
in Table 4, which  identifies some data taken using Nal(Tl) detectors of various sizes (none of
12                       ?
  FOM= [(detector efficiency) ^ackground] (Mann et al., 1991).
                                        17

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
these were well detectors). The sample container was a 1 liter plastic bottle. The data were
recorded using a detector and shielding as shown in Figure 3. The configuration of the detector
and shielding actually used in this case was not optimal: In the bottom orientation position, the
detector is partially unshielded, and the flat  surface of the Nal(Tl) detector can is facing the
sample bottle. Figure 3 also  shows the side orientation where again the detector is partially
unshielded, and the curved detector cover is parallel to the sample. Also, note the actual position
of the detector crystal in both cases. It is clear in either case,  however, that detector size  and
positioning  with respect to the sample will have  a significant effect  on  the measurement
sensitivity (based on the FOM).
 TABLE 4 - Response and Figure of Merit for   Co and   Cs with Different Nal(TI) Detector
                                      Configurations
Radionuclide

Background (BO)
137Cs (BO)
60Co (BO)
Background (SO)
137Cs (SO)
137Cs (SO)
137Cs (SO)
60Co (SO)
Activity
pCi/L

-
5.038xl05
3.317xl04
-
5.038xl05
5.038xl04
1.242xl04
3.317xl04
Net
cpm
l"xl"
2.80xl02
2.22xl03
5.5xl02
2.7xl02
5.03xl03
3.1xl02
l.SxlO2
5.8xl02
2"x2"
1.65xl03
1.34xl04
9.5xl02
l.lxlO3
1.66xl04
9.0xl02
3.0xl02
2.2xl03
3"x3"
2.4xl03
1.3xl04
7.5xl02
1.75xl03
1.78xl04
6.0xl02
1.2xl02
1.5xl03
Figure of Merit
l"xl"
-
6.93xl(T8
1.67xl(T7
-
3.69xl(T7
1.4xl(T7
5.40xl(T7
1.13x10^
2"x2"
-
4.28xl(T7
4.97x1 (T7
-
9.87xl(T7
2.90x1 (T9
5.30xl(T7
3.99x10^
3"x3"
-
2.77xl(T7
2.13xl(T7
-
7.13xl(T7
8.1xl(T8
5.33xl(T8
1.17xl(T6
Notes:
SO = Side Orientation (see Figure 3)
BO = Bottom Orientation (see Figure 3)
Example Calculation: For the Cs bottom orientation (BO) and the l"x 1" detector
FOM = [net cpm/pCi/L]2/[Background] = [2.22xl03/5.038xl05]2/(2.8xl02) = 6.93x10^

The  data indicate that the biggest detector volume does not always give the highest count rate,
nor  does it always yield  the highest value FOM.  Thus, it is  imperative that the detection
equipment used be  assessed in a similar fashion to determine which screening equipment is best
suited  for each combination  of matrix and  geometry. Two  factors to be  considered in deter-
mining this are:

   •  Location of the mean sample activity relative to the location of the detector, and
   •  Shielding (covering) of the screening equipment.

There are different  considerations for samples that need to be screened for gamma radiation. An
example is using a Nal(Tl) well detector. Many  different sample types  can be accommodated
into  this well for screening purposes. For example, a 47-mm air particulate filter may be rolled
and inserted into a container, such that the container will fit reproducibly into the well of the
Nal(Tl) detector,  improving overall efficiency for detection. When doing this, care must be taken
to avoid contaminating the detector. That specific geometry for calibrating  this style of detector
can be accommodated by most laboratories.
                                         18

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
                  Detector Perpendicular
                    to Sample Bottle
                       Detector Parallel
                       to Sample Bottle
                        Lead
                        Bricks
   1 Liter
Sample Bottle
Detector
 Crystal
 L
Detector
Housing
 FIGURE 3 - Shown Without Bricks Covering Top of Shielded Geometry. Nal(TI) Detector Example
Figure 4 shows another way to configure
the  detector  and  the  sample  bottle  to
achieve a better FOM for the measurement.
In this configuration, the active area of the
Nal(Tl) detector is inside the shielding and
thus has a lower net background from room
and ambient background contributions.

Figure 5 shows two different configurations
of shielding with respect to the detector that
will  provide different  backgrounds.  Note
that  the thickness of the shielding walls is
the  same but  that the  internal cavity  in
which the detector is held is larger in Figure
5B. The larger volume ultimately leads to a
better FOM since any Compton scattering
from the shielding in 5B will impinge to a
lesser  degree  on the detector  than  in  5A
solely  due  to  distance. In Figure  5B, a
sample stand  has been added to  put  the
sample  in  the  middle  of the shielded
volume, and the detector has been raised slightly to yield the same orientation as  in 5A, thus
maintaining the same detector efficiency.
           (The front shielding has been omitted
          so the detector and sample can be seen.)
          FIGURE 4 - An Improved Orientation for Shielding.
               Active Detector Area Within Shielding.
                                        19

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
                  5A. Smaller Volume
                      (The front shielding has been omitted so the detector and sample can be seen.)
CD  i       w i       Sample
5B. Larger Volume  stand
                        FIGURE 5 - Relative Size of Shielded Volume
Figure 6 shows a configuration for a pancake-style screening instrument (could be gross alpha-
beta or beta-gamma). The air particulate filter is slid into place beneath the detector, which is
maintained in a fixed position using a small stand. The presence of shielding allows reduction in
background for the detector and for the sample,  and provides a fixed geometry for consistent
results.
                                                       _ __ i
                             Air Particulate -
                             Filter
                                       Plan View (Sample drawer out)
                                     Front View (Sample drawer inserted)
                           (The front shielding has been omitted so the detector and sample can be seen.)
    FIGURE 6 - Sample Shielding and Detector Orientations for Gross Screening of Air
                 Particulate Filters Using an Alpha/Beta Pancake Detector
                                           20

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
Crosstalk, Dead-Band, and Self-Absorption Factors

The degree of crosstalk as determined under routine instrument calibration conditions may not be
significant. However, when the activity being measured is two and three  orders of magnitude
greater than normal sample test sources, crosstalk that was once obscured in the background may
provide a signal that is indicative  of a  particle  type that is absent.  Thus, it is important to
challenge the screening instrumentation with standards of high activity  so that the level of cross-
talk can be  assessed. One such application  involves  GPC  systems  that are  simultaneously
counting gross alpha and beta activity. An assessment of crosstalk should be made in the beta
channel response when the alpha activity is large compared  to the beta activity  and compared
with  the  same beta activity  response  with  no corresponding  alpha activity. The  inverse
assessment should also be made. These measurements may lead the lab to  apply  a "dead band"
between the lower level beta  and upper level  alpha  discriminator settings  that normally would
not be used. This dead band would  minimize the  crosstalk, but would  also lower the efficiency
for both types of particles.  Thus, the use of a dead band should be used  judiciously to avoid
abnormally long count times when screening time  is at a premium.

It  should  also be  recognized that elevated  activity  of radionuclides  that  decay only by beta
emission may result in counts above background when using  a sodium iodide detector for gross
count assessment (e.g., as when using a  small article monitor). The  bremstrahlung radiation,
emitted as a result of the beta interaction with  matter, yields low-energy photons  that produce a
signal in the sodium iodide detector.

Self-absorption factors  are  significant for alpha- and beta-emitters. Determining how  sample
mass affects the efficiency of detection can be  estimated using calibration sources and absorbing
materials of known areal density (measured in units of mg/cm2) placed between the  sample and
the detector. This intervening material would simulate the sample mass when the sample is not
ideal  (i.e., the  sample is not "massless"  and will  absorb  some of the contained radiation).  This
mass attenuation correction for  self-absorption is  similar to determining unknown beta particle
energy using  the Feather Method.13 For  alpha particles, this may mean using  a thin  film of
aluminized Mylar, while for betas, varied thicknesses of aluminum metal may be used. The  areal
density  effect  for each detector should be  semi-quantitatively identified  so that estimates of
activity correction can be made  when samples  of  observable mass are measured using detection
techniques such as GPC.

Final Instrument Calibration and Method Validation

Once the detectors to be used for screening have been selected and the considerations for sample
to detector configuration  and efficiency have  been  assessed, a method  should be written. The
13A technique that has been used successfully to determine the energy of beta-only emitters is to measure the range
of the beta particles in a pure material ("Feather analysis"). The ranges of beta particles in several pure materials
(such as aluminum) have already been established. The units of thickness are expressed as areal density, or mg/cm2.
A set of aluminum absorbers of varying thickness is used, and the activity versus the absorber thickness is plotted on
a semi-log scale. The linear portion of this curve is then extrapolated to find the "zero" activity thickness. This is
then related to the Epmax of the beta particle, which will be characteristic for a particular radionuclide. A discussion
of this technique can be found in Chase, G.D. and J.L. Rabinowitz (1967). Principles of Radioisotope Methodology,
3rd Edition. Minneapolis: Chase and Burgess.
                                         21

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
method should  incorporate the  laboratory's  best estimate  of the potential  geometries and
plausible radionuclides into the  procedure. Specific instructions  regarding the receiving and
storing of the samples, recording of data, and  sample aliquanting for particle-specific screening
should be included in this method. Once the method is written, a method validation process that
follows the Method  Validation Requirements for  Qualifying Methods Used by  Radiological
Laboratories Participating in Incident Response Activities (EPA, 2009b)  should  be followed.
The method validation process requires the  use of proficiency  test  samples to validate the
detector response to achieve the MQOs established for the project or by the laboratory. Once the
method has been  validated,   the  procedure  should  be implemented  routinely for  sample
processing by all staff members, which will reinforce training on the procedure.

C.  Calibration of Screening Instruments when Radionuclide Identities are  Known

Screening equipment that is  calibrated for overall response to decay particles will have its
accuracy challenged if the radionuclide  in the  sample to be measured has a different particle or
energy.

During the initial phases of an emergency, before the identity of the radionuclide(s) associated
with the event has been established, a response factor for the screening equipment presumably
will be based on a single radionuclide,  such as 137Cs. As  the radiological event progresses, the
                                                                         1 Q9
radionuclide(s) associated with the event should be identified. For  example, if  Ir is identified,
the factor used to convert cpm/sample to pCi/sample should be changed so that the screening
equipment more accurately characterizes the  sample activity level, and the laboratory will be
able to characterize the activity of the  samples more accurately.  This  change in  the response
factor can be implemented in several ways:

  1. The  laboratory has already  established a response factor on  the screening equipment for
     this radionuclide in this  geometry. In this case, receipt instructions need to be  updated to
     include the identity of the radionuclide(s) of concern. For example, consider a beta/gamma
     survey meter that has been calibrated with a 137Cs  source that had a measured response
     factor  for a 1-L  liquid sample of S.lxlCT4 mR/h per pCi. This factor has been entered into
     the electronic database for the meter used (identified by  serial number). Knowing now that
     the radionuclide of interest is 192Ir, with  a response factor of 2.8>
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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
           pCi/(microR/Hr)

           35
           30
           25
           20
           15
           10
                                  Beta Response Curve
            o t
                        100
200
300
                                           Biergy, keV
400
500
600
     FIGURE 7 - Survey Meter 12345 Energy Open Window Response Curve for Beta Emitters

     In Figure 7, the radionuclide energies represented are approximately  one-third of Epmax.
     Thus, as an example, the effective beta particle energy for 14C is 156 keV/3 = 55 keV.15

  3.  The laboratory may take a sample that is to be analyzed, and determine  a conversion factor
     based on a comparison of the screening value and radionuclide-specific analysis results. In
     this case, it would likely be best to take an average conversion factor from several samples
     to ensure the most accurate representation of the factor. This is because the factor can be
     affected by non-uniform distribution  in the sample. Consequently, the laboratory should
     consider the potential for significant uncertainty in this conversion factor,  which may be
     estimated by the standard deviation of the individual measurements used to calculate the
     average conversion factor.

As an example,  a data table like the  one below could be constructed. Note that the information
shown is not based on actual data but is used for illustrative purposes only.

Table 5 - Screening Instrument Conversion Factor Based on Sample Analysis of a 1-Liter
                                    Sample Geometry
Sample
Background
Sample 1
Sample 2
Sample 3
Screening
Value,
(mR/h)/L
2
55
78
41
Radionuclide-
Specific Analysis
Results, 137Cs
u€i/L
-
1,601
2,005
1,448
Conversion
Factor
[u€il/(mR/h)
-
30.2
26.4
37.1
Estimated
Conversion Factor
Uncertainty
[u€i]/(mR/h) [1]
-
-
-
-
Average Conversion Factor: 3 1 ± 5
[1] The method used to estimate the screening equipment uncertainty must be decided upon by the laboratory. The
   column is included here so that it is clear that this should be one aspect of this process.
  It is important to note that the use of this type of curve is not necessary for alpha instruments since the alpha
response would be mostly independent of energy.
                                         23

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
In this example, the samples have already been screened using a micro-R meter. The samples are
then analyzed using a radionuclide-specific method, and the values obtained are specifically for
137Cs. The final analytical values  for the samples are divided by the original exposure rate
measurements to obtain a conversion factor for the radionuclide contained in the event-specific
samples. The average conversion factor  and the associated uncertainty estimate are rounded to
the  appropriate number of significant digits. In this case, the conversion factor would allow the
laboratory to estimate the concentration of 137Cs in the subsequent samples, based on the micro-
R meter screening results.  This simplified example uses a single radionuclide with no ingrowth
considerations. In cases where one or more radioactive progeny  may be present, care must be
taken to ensure that the screening conditions, especially the degree of progeny ingrowth, are
reasonably consistent. In all cases, the  counting geometry  for sample screening should be as
consistent as possible.
During the latter phases of an event (when the radionuclide content of the samples is expected at
the  10~4 risk level  for air filters and the maximum contaminant levels for  drinking water), the
screening of lower activity samples may  be performed using a different technique. For example,
if both alpha- and beta-emitters are present, rather than using GPC to screen the samples for both
alpha- and  beta-emitters  simultaneously,  it  may  be  advantageous  to perform each  screen
separately and extend the count time to ensure better discrimination between  those samples
where analysis is required immediately and those that may be delayed.

D.  Measurement Quality Objectives (MQOs) for the  Screening Process

Screening of samples as they arrive significantly impacts the laboratory's decisions about which
samples to analyze first. The 1C should have decided how the samples are to be prioritized and
communicated this to the laboratory. The laboratory  may confidently screen these samples for
gross activity so  that they can be processed in a timely fashion based on the needs of the
incident.

General guidance  on how to establish an  MQO for the required method uncertainty can be found
in MARLAP (2004) and  specifically for radionuclides in water (EPA 2008a, Appendix VI).
Additional MQOs for screening should  be established by the laboratory based on the type of
instrumentation available.

In order to illustrate the typical decisions and  actions  to be taken  by a laboratory for  calibration
and gross sample  screening, three examples using theoretical samples and measurement results
are  provided in Appendices I-III. These examples demonstrate  an acceptable method  for the
calibration  of instruments and measurement  of samples, but each example is one  of  several
different possible variations of calibration and measurement techniques.  The examples here
should not be construed as  limiting.

The first scenario  (Appendix I) illustrates how a laboratory may prepare its screening equipment
to be ready  to receive samples from a radiological incident. The  instrumentation and standards
used are limited to what is available to the  laboratory, which demonstrates how  some basic
planning can assist in being prepared for  such an event. In the second scenario (Appendix II), the
same laboratory has received samples from a radiological transportation accident and has been
asked to rapidly assess the spread and degree of contamination.  The calibration of the screening
                                       24

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
equipment is optimized to assess the contamination levels in the samples that have been sent.
The third  scenario (Appendix III) discusses how instrument calibrations may be adjusted during
the latter  phases of an event when  the radionuclide(s)  identity(ies) is (are)  known.  In this
instance, the screening process will be looking at lower overall activity in the samples so that re-
calibration with the  same radionuclide will enhance  the  detection capability of the screening
equipment.

E. Key Recommendations

Laboratories  should be prepared for potential radiological events where large  numbers of
samples at much higher activity concentrations than normal arrive suddenly. To assist laboratory
personnel  in promptly receiving, prioritizing, and analyzing samples, the following is a summary
of the key recommendations for sample screening:

  •  Screening equipment should be calibrated with traceable sources that match geometries for
     anticipated emergency response samples.
  •  These calibrations should  have associated direct reading conversion factors  for ease of
     reporting results in the appropriate units.
  •  Laboratories should have written procedures  (or instructions) for the process of screening
     emergency response samples.
  •  Shielding for the  screening equipment should be configured to  maximize the signal to
     background ratio, providing the analyst with smaller uncertainties of the measurement.
  •  A plan that provides for the calibration adjustment of the screening equipment based on the
     incident radionuclide(s) should  be  prepared  for that time when  the  activities are much
     lower, and better discrimination between lower level activities will be required.
                                        25

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
Appendix I - Screening Instrumentation Initial Calibration
   It is assumed that laboratories will have properly calibrated their instrumentation prior to an
   event.  The data provided in the following three scenarios (Appendices  I-III) are  used for
   illustrative purposes only. Each laboratory should consider using the general techniques modeled
   here for its laboratory-specific methods to be used for sample screening. In addition, uncertainty
   values  have  been  omitted  from these examples.  For actual calibration and screening,
   uncertainties should always be included in the expression of the final results.
Background
ABG Laboratory, Inc., has decided to set aside certain instruments for radiological events where
sample gross  screening  will be necessary. A GM pancake detector and an old 3"x3", planar,
Nal(Tl) detector with a sealer have separate, shielded geometries for samples of 47-mm filters, a
1-L  liquid,  and  a  250-g solids  container. The equipment is to  be located near the sample-
receiving area of the laboratory  facility. Once the equipment is set  up,  the laboratory  staff
performs background counts on the instruments while waiting for the new calibration sources to
arrive. The calibration sources are 99Tc, 90Sr, 241Am, 57Co, 230Th, and 60Co. Each source has been
ordered for each  geometry identified above and is traceable to a national standards body, such as
the National Institute of Standards and Technology in the United States.
Discussion
The Nal(Tl) detector was set up to accumulate total  counts in  a two-minute count. The GM
pancake detector was  set up  in rate mode for cpm. The following table identifies the detector
background and response from the standards for each of the instruments.

              TABLE 6 - Calibration Data for Screening Instrument Response
Detector
Nal(Tl)



GM
Alpha



Beta



Radionu elide
Source
"Co

bUCo


Z41Am

232^

yyTc

yuSr

Total
Background*
5,840 cpm

5,840 cpm


0.05 cpm

0.05 cpm

0.8 cpm

O.Scpm

Activity
pCi
8.0x10'
2.0x10'
8.0x10'
2.0x10'

40
10
32
8.0
4.5xl03
1.2xl03
300
80
Air Filter,
Net Counts
8.88xl04
2.22xl04
1.24x10'
3.11xl04
Air Filter,
Net cpm
8
2
6.5
1.6
509
136
133
35.5
250 g Can,
Net Counts
5.33xl04
1.33xl04
9.59xl04
2.40xl04
250 g Can
(open)
Net cpm
0.18
0.04
0.14
0.04
10
2.5
67
18
1 L Bottle,
Net Counts
2.13xl04
5.33xl03
3.66xl04
8.88x10"
1 L bottle
(closed, side
measurement)
Net cpm
0
0
0
0
0.1
0.03
20
5.3
 For the sodium iodide detector, background counts were summed over the energy range of 50 to 2500 keV. For the
GM detector, the background represents an average measurement performed at several times of the day. Each
instrument background measurement was made  using an empty  sample container  in the position for sample
measurement, and the sample plus detector were shielded with 4" of lead brick.
                                         26

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
The laboratory staff has made separate calibration factors for low- and high-energy gamma-ray
emitters. Similarly, for the 90Sr and 99Tc, the efficiency of detection of the 9 Sr is much better due
to a smaller degree of self-absorption in the sample and better penetration  of the GM detector
beta shield when used. The response factors for both the 241Am and the 232Th  are the same. The
laboratory staff has made the following response factor table for its instruments:
      TABLE 7 - Response Factors (RF) for Radionuclides with Respective Screening
                                         Equipment
Radionuclide
Nal(Tl) Detector, Gamma
57Co
60Co
GM Detector, Alpha
241Am
GM Detector, Beta
"Tc,
90Sr
Energy,
keV

121, 135
1,173; 1,332

5,449; 5,440

210
546; 2,280
Abundance
Factor*

1.003
2.0

1.0

1.0
2.0
Air Filter,
pCi/cpm

17.5
6.45

5.01

8.83
1.13
Open Tuna
Can, pCi/cpm

29.9
8.34

2.25xl02

4.50xl02
2.25
Bottle,
pCi/cpm

74.8
22.5

1.5xl05

4.50xl04
7.5
*The abundance factor is the number of particles that are produced per decay of the radionuclide and can be detected
by the detector listed. The value for 60Co is 2.0 since it yields two gamma rays for each decay (the gamma rays are
in full coincidence). For 90Sr, the value is 2.0 since it is in secular equilibrium with its progeny 90Y, also a beta-
emitter.
The response factors in the table are calculated as follows:
                              RF
                                           Source pCi
                                   (net cpm) • Abundance Factor

Thus, for the air filter geometry on the Nal(Tl) detector for 60Co:
               RF,
                                   8xl05
                 Co-60
                        (1.24xl05 counts/2 min)-2.0
= 6.45 pCi/cpm
                                          27

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance


Appendix II - Radiological Event Screening for 241Am

Background
The date is November 15, and steady winds from the northwest at about 20-25 mph are expected
through tomorrow. A truck is carrying used 99mTc generators16 and 241Am smoke detectors (as
the bulk of its shipment, but other radioactive waste materials of smaller volume were on board).
The truck overturns and slides into a rock embankment, bursting into flames along a small two-
lane  highway between towns, and burns down to the  tires. Air sampling equipment  has been
stationed  in  several locations in both  towns and along several  roadsides. Air samples are
expected to  arrive at the laboratory by 1800  hours  this evening (it is currently 1300 hours).
Additionally, several hundred soil and crop samples are expected over the next week so that the
plume can be tracked.

The 1C has requested that the highest activity samples be identified and analyzed first so that the
recovery phase can focus on:

   •   Determining how much material has become airborne, and
   •   Cleaning up high activity areas first to remove the bulk of the source term.

Discussion
ABG Laboratory, Inc., has been contacted and told to expect the samples shortly. It will be using
the calibrations it has made for its screening equipment to accommodate the influx of samples.

Table 8 identifies the sample activity measured for each of the matrices received at -1800 hours.
Knowing the truck's  cargo  makes use of the calibration factors  straightforward.  The air
particulate filters have been transmitted  in glassine envelopes, and the soil samples were stored
in solids  (tuna)  can geometry  with a  removable lid.  The laboratory has verified that these
geometries match the geometries it used  for its gross screening calibration of the instruments.

The spreadsheet  it is using has the following equations for the analysis:
   •   Air Filters
          o  Gross Alpha Activity = (meter reading, cpm - 0.05, cpm)x(5.01pCi/cpm)
          o  Gross Beta activity = (meter reading, cpm - 0.8, cpm)x(8.83  pCi/cpm)
          o  Gross Gamma  Activity17 = (Total counts  - 5,840 cpm)x(17.5 pCi/cpm)
   •   Solids Can
                                 1 &
          o  Gross Alpha Activity  =  (meter reading,  cpm - 0.05, cpm)x(225pCi/cpm)
          o  Gross Beta activity = (meter reading, cpm - 0.8, cpm)x(450 pCi/cpm)
          o  Gross Gamma  Activity =  (Total counts - 5,840 cpm)x( 8.34 pCi/cpm)
16 Although the 99mTc (ty2 = 6 hours) and its 99Mo (ty2 = 66 hours) precursor have decayed, the progeny 99Tc has a
half-life of 2.1 x 105 y, and will thus be present in the environmental samples exposed during the accident.
17 Note that the energy of 241Am (59 keV)  is  somewhat lower than that of 57Co (122 and 135 keV) and will be
significantly affected by the aluminum shielding on the Nal(Tl) detector.
18 The laboratory homogenized the samples by shaking prior to opening and performing the gross screen. The values
will be affected due to sample self-shielding.
                                        28

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
      TABLE 8 - Gross Screening Measurement Results from Transportation Incident



Sample
Air Filter- 1
Air Filter-2
Air Filter-3
Soil-1
Soil-2
Soil-3
Alpha
GM
Detector,
cpm
4.7
0.085
0.10
0.550
0.16
0.07

a Gross
Screening
Estimate, pCi
23.3
0.175
0.25
113
24.8
4.5

Beta
Open Window
Probe, cpm
1.77
5.82
2.88
1.46
3.9
0.7

P Gross
Screening
Estimate, pCi
8.57
44.3
18.4
297
1,395
-45

Nal(Tl)
Detector,
cpm
5,750
5,900
5,880
6,050
8,120
6,000

Y Gross
Screening
Estimate, pCi
-1,580
1,050
700
1,750
19,000
1,330
The laboratory reports back to the 1C that the sample results, bolded above, have the highest
concentrations based on gross  screening results, and the  analyses for 241Am and 99Tc are in
progress.  The  laboratory supervisor queues the samples  according to activity. The highest-
activity samples are to be analyzed first. The supervisor also notifies the separations chemists
about the levels of activity they will find in these samples.

The laboratory protocol  has established a limit of 100 pCi per aliquant. Normally, the sample
size processed is 2.0 g. However, for Soil-2, there is 250 g of sample, and in order to be less than
100 pCi, only 1.0-1.3 g of sample will be aliquanted for this analysis.19
  The gross gamma estimate for the entire sample is 19,000 pCi. This gives about 19,000/250g = 76 pCi/g. Taking a
2-g sample would result in 152 pCi, exceeding the laboratory limit. An aliquant of 1.3 g yields 98 pCi.
                                         29

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
Appendix III - Screening Instrumentation Response Corrected for Different
Radionuclide

Background
A suspected  terrorist  event involving  explosive  devices  has occurred.  Several  different
radioactive materials suppliers have reported thefts of large quantities of radionuclides in the past
three months. The missing radionuclides were  210Po and 192Ir.  Preliminary evidence  from the
scene of the incident identified the presence of radioactive materials. It is suspected that the
materials that were reported missing are related to this event.
Radiochemistry Analysts of America has been  contacted  to  screen, then analyze about 200
                 1Q9       910                                                  	
samples a day for  Ir and   Po, and any other radionuclides that may be present. The samples
will be air particulate filters (47 mm) and soil (-0.200 kg). It is Day 1 at 1100 hours, and the first
sample shipment will  arrive at 0600 hours  on Day 2.  The 1C  has  indicated that the sample
priority is to analyze those samples with the highest activity first. The laboratory has neither a
710         1Q9
  Po nor a   Ir source/standard.

Discussion
The laboratory has selected a Nal(Tl) well detector to screen the air particulate filter samples for
the 192Ir. Its current calibration factor used 60Co, but it has a response curve based on energy as
shown below.20
pCi/cpm
o OOF +04
1 ROF+04
1 ROF+04
1 40F+04
1 OOF +04
•t OOF +04
Q nnp+rn
R nnp+rn
4 nnp+rn
o nnp+rn
n nnp+nn
c

Nal Response Curve for Gamma Rays
(Air Particulate Filter)
	 t
^ *
^-"-"^
j^
^
S




) 200 400 600 800100012001400160018002000
^eV —•— Response pCi/cpm
            FIGURE 8 - Gamma Energy Response Curve for a Nal(TI) Detector


The  average energy21 of the 192Ir is  approximately 390 keV.  This corresponds to a factor of
1.30* 104 pCi/(net cpm) as estimated using the curve in Figure 8. A similar curve was made for
the solid geometry and a response factor of 6.1 x 103 pCi/(net cpm) for 192Ir was estimated.
20 Calibration points for the curve were 88, 320, 662, 1115, and 1836 keV. The standards were counted for 5 minutes
each in a shielded geometry. The standards used were individual radionuclides (i.e., not a mixed gamma ray source).
21 Ir-192 has several different gamma rays. The average energy per decay event is approximately 390 keV based on
the sum of the gamma ray abundances multiplied by their respective energies.
                                        30

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance
The laboratory staff is using a GM pancake-style detector for alpha screening of the  samples.
The corresponding response factors for alpha particles are:
                                Air filter
                                  5.01
Solid 200 g
 2.25xl02
The following day, several hundred samples are received, and the screening process begins. An
example dataset is shown below:

         TABLE 9 - Results of Screening Measurement Using Adjusted Response
Sample ID
NalOTl), cpm
GM Detector, cpm
Air
Filter 1
4,630
2.80
Air
Filter 2
4,550
1.56
Air
Filter 3
4,480
0.23
Soil
Sample 1
6,100
0.13
Soil
Sample 2
4,700
0.14
Background
4,500
0.12
Screening Results
Gross gamma, pCi
Gross alpha, pCi
1.7xl06
13.43
6.5xl05
7.21
-2.6xl05
0.55
9.8xl07
2.25
1.2xl06
4.5
-
-
Based on the results of these screening measurements, air filter 1  and soil 1 have the highest
activities and should be analyzed first for 192Ir and 210Po.
                                        31

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          Radiological Laboratory Sample Screening Analysis Guide for Incidents of National Significance


Appendix IV - Additional Sources and References

U.S. Environmental Protection Agency (EPA).  1992. Manual of Protective Action Guides and
   Protective  Actions for  Nuclear Incidents.  Washington,  DC. EPA 400-R-92-001, May.
   Available at: www.epa.gov/rpdwebOO/rert/pags.html.
U.S. Environmental Protection Agency (EPA). 2008a. Radiological Laboratory Sample Analysis
   Guide for Incidents of National Significance-Radionuclides in Water. Revision 0. Office of
   Air and Radiation, Washington, DC.  EPA 402-R-07-007,  January. Available at: www.epa.
   gov/narel/recent_info.html.
U.S. Environmental Protection  Agency  (EPA). 2008b.  Standardized Analytical Methods for
   Environmental Restoration Following Homeland Security Events, Revision 4.0. Office of
   Research and  Development, Washington, DC. EPA/600/R-04/126D, September. Available
   at: www.epa.gov/ordnhsrc/sam.html.
U.S. Environmental Protection Agency (EPA). 2009a. Radiological Laboratory Sample Analysis
   Guide for Incidents of National Significance-Radionuclides in Air. Revision 0.  Office of Air
   and Radiation, Washington, DC. EPA 402-R-09-007, June.  Available at: www.epa.gov/narel/
   recent_info. html.
U.S. Environmental Protection Agency (EPA). 2009b. Method Validation Guide for Radiologi-
   cal Laboratories Participating in Incident Response Activities. Revision 0. Office of Air and
   Radiation,  Washington,  DC.  EPA 402-R-09-006, June. Available at: www.epa.gov/narel/
   recent_info. html.
U.S. Environmental  Protection Agency (EPA).  (In preparation). Guide for Radiochemical
   Laboratories for the Identification, Preparation, and Implementation of Core Operations
   Unique to Radiological Incident Response. Revision 0. Office of Air and Radiation, Wash-
   ington, DC.
Mann,  W.B., A.  Rytz, and A.  Spernol  (1991). Radioactivity Measurements: Principles  and
   Practices. Pergamon Press, p. 65
Multi-Agency Radiological Laboratory Analytical Protocols Manual (MARLAP). 2004. EPA
   402-B-04-001A, July. Volume I, Chapters 6, 7, 20, Glossary; Volume II and Volume III,
   Appendix G. Available at: www.epa.gov/radiation/marlap.
                                       32

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