&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 instrumenta ratemeter or
a sealer.
6 In this context, sensitivity refers to the ability of the screening equipment to detect different particles.
-------
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
-------
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)
10 -I
K
6
2
"S
|
Vrr
2* i
10
Co-57
^
V
V
\
N^
la
"
1- 3
v
iOO
C s-I37
Co-6O
HJOO
ioooo
Energy Response for Model 44-6
(Shield Closed)
10 -T
!*
s
"S
1
i
T.
,
"
Co-S7
f . «^^
^X
S
Ma
<
,
3
< »-137
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
1
§
ai
ta
-*
1!
r *
Co-57
""""N,
\
X
1:1
S
Cs
1
\
I
3
t?s
s
\
Co-60
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.
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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.
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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
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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.
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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
ui/L
-
1,601
2,005
1,448
Conversion
Factor
[uil/(mR/h)
-
30.2
26.4
37.1
Estimated
Conversion Factor
Uncertainty
[ui]/(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
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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.
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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.
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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
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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.
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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.
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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.
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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.
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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.
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