United States Office of Radiation Programs ORP/LV-78-2
Environmental Protection Las Vegas Facility April 1978
Agency P.O. Box 15027
Las Vegas NV 89114
Radiation
vxEPA Above Ground
Gamma Ray Logging
for Locating Structures
and Areas Containing
Elevated Levels of Uranium
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Technical Note
ORP/LV-78-2
ABOVE GROUND GAMMA RAY LOGGING FOR LOCATING
STRUCTURES AND AREAS CONTAINING
ELEVATED LEVELS OF URANIUM DECAY CHAIN RADIONUCLIDES
Joseph M. Hans, Jr.*
Gregory G. Eadie*
Jack Thrall*
Bruce Peterson**
April 1978
*OFFICE OF RADIATION PROGRAMS - LAS VEGAS FACILITY
U. S. ENVIRONMENTAL PROTECTION AGENCY
LAS VEGAS, NEVADA 89114
**RADIATION CONTROL SECTION
IDAHO DEPARTMENT OF HEALTH AND WELFARE
STATEHOUSE, BOISE, IDAHO 83720
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DISCLAIMER
This report has been reviewed by the Office of Radiation Programs -
Las Vegas Facility, U.S. Environmental Protection Agency, and approved for
publication. Mention of trade names or commercial products does not constitute
endorsement or recommendation for their use.
11
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PREFACE
The Office of Radiation Programs of the U.S. Environmental Protection
Agency carries out a national program designed to evaluate population exposure
to ionizing and nonionizing radiation, and to promote development of controls
necessary to protect the public health and safety. This report describes a
mobile gamma ray logging system which was used to rapidly screen areas and
structures for elevated levels of uranium decay chain radionuclides, and
presents the results of surveys conducted in selected areas of the western
United States. Readers of this report are encouraged to inform the Office of
Radiation Programs of any omissions or errors. Comments or requests for
further information are also invited.
Donald W. Hendricks
Director, Office of
Radiation Programs, LVF
m
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TABLE OF CONTENTS
Page
LIST OF FIGURES v
LIST OF TABLES vi
INTRODUCTION 1
SUMMARY AND CONCLUSIONS 3
DETECTOR ASSEMBLY 4
Design Criteria 4
Carrier Van 4
Detector Electronics 6
Hoisting Cart Design 7
Hoist Design 7
System Calibration and Response 10
GAMMA LOGGING EXPERIENCES 15
Areas Using Phosphate Slag Material 15
Screening Surveys in Soda Springs, Idaho 17
Screening Surveys in Pocatello, Idaho 24
Areas Using Uranium Mill Tailings and Other 29
Miscellaneous Sources
Salt Lake City, Utah 29
Farmington, New Mexico 29
Shiprock, New Mexico 29
Miscellaneous Logs 33
REFERENCES 36
APPENDIX A - Estimation of Gamma Exposure Rates at Curbside 37
from Structures Containing Uranium Mill Tailings
or Phosphate Slag
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LIST OF FIGURES
Number Page
1 Relative shielding effects from building construction 5
with tailings or slag used as bedding material
2 Photographs of van and detector assembly 8 & 9
3 Detector sensitivity versus source position 11
4 Detector response versus distance from source 13
5 Detector directional response inside van 14
6 Gamma ray log of streets in Soda Springs, Idaho 18
7 Map of Soda Springs anomalies 20
8 Gamma ray log from Pocatello, Idaho (Street paved with slag) 26
9 Gamma ray log from Pocatello, Idaho (Street not paved with slag) 26
10 Gamma ray log of downtown Pocatello, Idaho 27
11 Gamma ray log of downtown Salt Lake City, Utah 30
12 Gamma ray log of Salt Lake City, Utah (Near the former Vitro 30
Uranium Mil 1 Site)
13 Gamma ray log of Farmington, New Mexico 31
14 Gamma ray log of Shiprock, New Mexico (Community Center) 31
15 Gamma ray log of Shiprock, New Mexico (Former uranium ore 32
buying station)
16 Gamma ray log of Shiprock, New Mexico (Uranium ore residue) 32
17 Gamma ray log from propane trucks 34
18 Gamma ray log from Gallup, New Mexico 34
19 Gamma ray log on Interstate 15 35
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LIST OF TABLES
Number Page
1 Major Radioactive Constituents of Idaho Phosphate 16
Ore and Slag Materials
2 Gamma Radiation and Working Level Evaluations at 21
Selected Locations in Soda Springs, Idaho
VI
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INTRODUCTION
Naturally occurring uranium is present throughout the earth's crust. The
most abundant uranium isotope, uranium-238, is radioactive and is the parent
of a long chain of radioactive daughters. Because of the relatively long
half-life of uranium-238, all of the daughters are in radioactive equilibrium;
however, they may not be at the same location because chemical and physical
processes may have separated them from their respective parents.
The normal concentration of uranium in the earth's crust is approximately
four grams per ton (about 0.00044 percent). Various ores (e.g., uranium,
phosphate, gold and copper ores) contain increased uranium concentrations up
to several thousand times the normal content. Ore mining and processing
enhances the contact and distribution of uranium decay chain radionuclides in
the biosphere.
Increased concentrations of naturally occurring radionuclides are also
found in coal, lignites and oil shales. Their combustion will further
increase the concentration of uranium decay chain radionuclides in the biosphere.
Several products and wastes, containing elevated levels of radioactivity,
from the various ore mining and processing industries are being used for
commercial purposes. Specifically, uranium mill tailings and phosphate slag
have been used for construction and road paving but their use has been sporadic
and widely scattered throughout entire communities and areas. In order to
evaluate the radiological impact from this use, it is necessary to locate and
identify these locations. One approach, used in the past, was to mount a
scintillation detector in a vehicle and traverse or "scan" areas in order to
locate anomalous count rates. The use of phosphate slag in road paving has
raised some problems in identifying structures containing slag because of
radiation interference from the road materials. A mobile gamma ray detector
was designed and built to locate structures and areas which have elevated
1
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radiation levels while in the presence of other interfering gamma radiation
fields. This report describes the complete scanner detection system. Gamma
ray logs, produced by the system at a variety of locations, are discussed in
detail. Additional applications and uses of the "mobile logger" are also
discussed.
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SUMMARY AND CONCLUSIONS
This report describes the construction and operation of a mobile gamma
ray logging system used to locate areas and structures containing elevated
levels of natural uranium decay chain radionuclides. The detector system
consists of a sodium iodide crystal coupled to four photomultiplier tubes and
associated electronic system which permits both an audible indication and a
strip chart recording of gamma ray photon count rates. The crystal is surrounded
by lead shielding, to reduce incident background radiation, with a collimator
port to define the area of observation. Under normal operations, the detector
assembly is mounted in a van at about two meters above the ground surface and
gamma ray logs are obtained while travelling at about 16 kilometers per hour
(10 mph). This system has been used extensively in the Pocatello and Soda
Springs, Idaho areas and identified about 1900 locations where phosphate slag
has been used for various construction purposes. The system has also been
used in several other communities to identify locations where uranium mill
tailings or pumice, containing slightly elevated concentrations of natural
radioactivity, was used for construction purposes. Although this mobile
system has proven very successful as a rapid screening method for identifying
areas or structures with slightly elevated radiation levels, only a more
specific radiation survey can determine the exact exposure rate and specific
construction usage of the building materials containing natural radioactive
materials.
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DETECTOR ASSEMBLY
I. Design Criteria
When used by the construction industry, uranium mill tailings and
phosphate slag have been primarily used as bedding materials for concrete
foundations and/or driveway slabs. Some slag has also been used as aggregate
in concrete. Gamma radiation emitted by the bedding material and/or slab
along the same plane as the slab is subject to self-absorption and to attenuation
by the building footing and adjacent earth, while gamma radiation emitted
above the slab plane is subject to some self-absorption and attenuation from
the slab as well as the structure (Figure 1). The gamma photon flux should be
higher above the slab plane; therefore, the best position for the detector
should be such that it can "look" down on the structure's slab. Ideally, it
is advantageous to mount the detector as high as possible in the transport
vehicle in order that the slabs may be "viewed" from above. Increasing the
operational height of the detector has two additional benefits. It is possible
to "look" over parked cars, and it reduces somewhat the elevated ambient
radiation levels which originate from streets paved with slag.
II. Carrier Van
The carrier vehicle chosen to transport the detector assembly was a
3/4 ton Chevrolet van with a camper shell roof. This roof extends the van's
height by 66 cm and permits the operation of the detector at an elevation of
about 2 meters above the road surface. Two electrical charging circuits are
used in the van. One circuit is for the electrical systems of the van and an
electrical winch which is used to raise and lower the shielded crystal assembly.
i
The other charging circuit is used for the operation of the detector's electronic
equipment. Each charging circuit has its own alternator. The vehicle operator
has a remote panel to view the status of the D.C. voltage, A.C. voltage, and
count rate being recorded on a strip chart. For normal transportation, the
crystal assembly remains lowered on the floor of the van but during "scanning"
operations, the crystal assembly is elevated as described below.
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GAMMA RADIATION
EARTH l^FOOTING
i,r •'••y.ut.i ' **Y/////////////
Figure 1. Relative shielding effects from building construction
with tailings or slag used as bedding material.
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III. Detector Electronics
The radiation detector used with the system is a sodium iodide
(thallium activated) crystal having the shape of a solid right cylinder with a
diameter of 23 cm and height of 10 cm. The crystal is hermetically sealed in
an aluminum can with a wall thickness of 0.048 cm. Light signals, produced by
the interaction of gamma ray photons within the crystal, impinge on four (7.6-
cm diameter) photomultiplier tubes optically coupled to the crystal. The
output signals from the photomultiplier tubes are fed into a battery operated
preamplifier.
High voltage from a Canberra Model 3002 high voltage power supply is
fed in parallel to each photomultiplier tube and the signal from each tube is
summed at the input to the preamplifier. The preamplifier is a modified
Technical Measurements Corporation unit. The preamplifier modifications were
made to improve pulse input shaping and internal battery operation. The
preamplifier is used only for signal shaping and for impedance matching to
drive low impedance signal lines (50 ohms). The electronic system consists of
a Nuclear Data Model ND512 Amplifier and Single Channel Analyzer, Nuclear Data
Model ND776 Linear Ratemeter, and a Hewlett Packard Model 7155 Strip Chart
Recorder.
The ND512 amplifier gain stability is very good and the unit offers
a wide variety of input-output functions needed for experimental operations.
The ND776 Linear Ratemeter measures count rates from 1 to 100,000 counts per
second (cps), selected on nine linear ranges. Decoder outputs are provided at
0-1 mV; 0-10 mV; .or 0-100 mV full scale. Other features include a 1 to 100
percent scale, suppression for background subtraction, and a standard error of
1, 3, or 10 percent referenced to full scale. An audible tone frequency
varies with the count rate. The strip chart recorder is operated from the
vehicle's 12-volt system and has a variety of input signal configurations and
various chart speeds.
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IV. Hoisting Cart Design
The basic concern in the design of the cart assembly was the size
and weight of the shielded sodium iodide crystal. The crystal and lead shield
assembly measured 41 cm in diameter with a weight of approximately 450 kilograms,
With these two features in mind, the cart was designed with a 2-cm thick
aluminum base plate and eight guide wheels. With this amount of weight being
supported, additional strength was provided by a 10-cm x 7.6-cm I-beam support
which was centered below the middle of the cart. All weight was supported by
this beam establishing a two-reaction one-load type system.
A guide system was developed to prevent any horizontal movement of
the crystal as a result of slippage while the cart was being raised or lowered.
Eight guide wheels were mounted to provide minimum deflection of the cart when
installed between the four I-beam cart supports. The wheels were mounted on a
3-cm diameter shaft with two bearings per wheel. The size of shaft and
bearing design was established by materials on hand and by the fact that
standard bearing sizes were readily available. Because the wheels are approxi-
mately 9-cm in width, two end thrust bearings were used to provide uniform
loading on each wheel.
V. Hoist Design
In order to achieve maximum crystal height during operation, a lift
or hoist system was constructed. To accomplish both stability and strength,
four equal length I-beams were used vertically. These I-beams measure 10-cm x
7.6-cm x 183-cm and were made from 6061-T6 aluminum. The inside portion of
the I-beams are used as guides for the eight wheels of the hoisting cart. The
I-beams are mounted securely to the van floor and with diagonal supports to
the side panels. With the rails mounted, it was possible to construct a
hoisting system using an ATV 1500 "Superwinch" and a simple pulley system.
With the winch located on the floor, centered beneath the cart, two cables are
run from the winch through a set of bottom pulleys to the top support where
the cables are guided through two more pulleys. From there, the cables were
attached to the cart assembly. As the winch motor is activated, the pulley
system raises or lowers the crystal to the desired operational position.
Figure 2 shows several views of the actual detector assembly mounted in the
van.
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STRIP CHART RECORDERS
OPERATORS CHAIR
• <, m I
Mobile Gamma Ray Logging System - Transport Vehicle
Pvv ^mj^nUm"
TRIP CHART RECORDER
Strip Chart Recorder and Operator
Figure 2. Photographs of van and detector assembly,
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4 EACH,
PHOTOMULTIPLIER TUBES
Nai CRYSTAL
£&& ft LEAD SHU -D
CART & PULLEY SYSTEM
Crystal in Lowered Position
(Thermal Shield Removed)
Crystal in Raised Position
(Thermal Shield in Place)
Figure 2. Photographs of van and detector assembly.
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VI. System Calibration and Response
Since an available detector had to be used, no choice concerning its
size or shape could be made. Several parameters, however, were manipulated to
some degree in order to increase the sensitivity of the detector:
A. Detector Orientation - A small radium-226 source was used
to check the relative detection efficiency with relation to the
detector's vertical axis in order to determine its most efficient
position. The source-to-detector axis distance was kept constant
and relative count rate measurements were made at 45° angle
intervals through 180° (Figure 3). The most efficient source-
to-detector position would be the position as indicated by the
highest relative count rate as listed in Figure 3. Since the
detector was to observe areas to the right side of the transport
van, position #3 (i.e., crystal facing downward) was selected
for the detector operation although it had approximately 20
percent decrease in efficiency compared to the more favorable
positions (#1 and #2). The reasons for not selecting positions
#1 and #2 were that possible stresses could be placed upon the
crystal assembly from shear forces by the photomultiplier tubes
in the horizontal position, and that shielding the detector
assembly for these positions would be more difficult.
B. Detector Radiation Shielding - Lead shielding, about 4-cm
thick, was placed around the bottom and sides of the detector
in order to shield it from terrestrial radiation. A side port
was cut in the shielding in order to "view" a typical 107
square meters (10.6 m x 10.6 m) house slab from a distance of
7.6 meters. Although additional shielding would be more
desirable, its extra weight would require a heavier detector
suspension system and would contribute to the instability of
the carrier vehicle.
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D
PHOTOMULTIPLIER TUBES
Nal(TI)
CRYSTAL ASSEMBLY
4^
SOURCE
POSITION
•
1
2
3
4
5
RELATIVE
COUNT RATE
1200
1200
960
1040
1100
I
VERTICAL AXIS IN THE PLANE
OF THE PAGE
Figure 3. Detector sensitivity versus source position.
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C. Energy Response - The gamma ray energy band selected for scanning
purposes was from 20 KeV to approximately 0.7 MeV. The lower
energy cutoff is due to gamma ray absorption by the aluminum
can covering the crystal. The upper limit of 0.7 MeV was
selected to eliminate the background count rate from natural
potassium-40 contained in the crystal, environment, and structures,
The upper energy level is set by slowly opening the single
channel window until the count rate exhibites a substantial
increase from the 0.66 MeV gamma ray photons from a cesium-137
check source. The window is opened until the count rate becomes
constant which indicates that the photo peak is fully contained
in the window.
D. Detector Thermal Shielding - Quick temperature changes can
cause the detector crystal to fracture. In order to moderate
temperature changes, a 2-cm layer of closed-cell plastic foam
was placed between the crystal and the lead shielding. The
upper part of the crystal assembly was protected with a 3-cm
thick plastic foam can. A portable insulated container was
constructed to transport and store the crystal when not in use.
During cold weather surveys, the carrier van was kept warm
overnight by using a catalytic heater.
Figure 4 indicates the response of the detector to an encapsulated
radium-226 source which was placed at various distances from and in line with
the detector port. The source could be conservatively detected at a distance
of 48 meters. With an ambient background of 400 counts per second, a source
which produced an exposure rate of 0.34 yR/h at the detector could be measured.
Gamma ray exposure rates at curbside were calculated for structures containing
uranium mill tailings used for bedding a slab, and for phosphate slag used in
concrete walls (Appendix A). The estimated exposure rate at curbside for mill
tailings use was approximately 3 yR/h, and that from phosphate slag use was
1 yR/h. These rates would produce count rates of 450 and 150 counts per
second above background, respectively.
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100000-
o 10000-
o I
UJ
w
ff
z.
o
o
UJ
111
DC
1000-
100-
SOURCE-RADIUM-226
0.78 mR/h @1m
BACKGROUND
8 12 16 20 24 28 32 36 40 44 48 52
DISTANCE-METERS
Figure 4. Detector response versus distance from source.
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Figure 5 depicts the relative directional response of the detector
for four equidistant radium-226 source positions. The source was positioned
at the same elevation as the detector for the port, rear, and front measurements,
The count rate for the underneath measurement was extrapolated to the same
distances (6 m) as the other measurements. Front and rear measurements were
about 30 percent of the port measurements and the underneath measurement was
about 15 percent of the port measurement. Since the major interfering source
(phosphate slag in the road bed) was at ground level, the shielding around the
crystal effectively reduced the count rate from this source by 85 percent.
10000<
8000-
7000—
5000-
3000-
1000-
o
I
I
£ 1000-
<0 900-
z aoo-
500-
400-
300-
200-
I
2
o
£
Figure 5. Detector directional response inside van.
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GAMMA LOGGING EXPERIENCES
I. Areas Using Phosphate Slag Material
Large quantities of slag material are generated each year as a by-
product of the thermal process of the phosphate industry. This slag material
is enriched in the naturally-occurring radioactive products of the uranium
decay chain series. Table 1 shows the typical radioactive constituents of
samples of Idaho phosphate ore and slag materials.
In the past several years, there has been an increasing use in
Idaho, Montana and several other states of this slag material for a number of
unrestricted construction purposes such as aggregate in concrete and asphalt,
roadbed fill, railroad ballast, and stabilization material for stock yards.
The most significant use in habitable structures of slag has been for use as
"fill" or as aggregate in concrete foundations, sidewalks and driveways.
In general, the phosphate industry is neither regulated nor monitored
for the possession, use, or discharge of radioactive materials associated with
phosphate rock (ore), its products, or by-products (e.g., slag). Recently,
the State of Idaho (June 1, 1977) has prohibited the use of phosphate slag
material in the construction of habitable structures only, but has permitted
the continued unrestricted use for other purposes. The discharge into waterways
of radioactive pollutants has been regulated by specific plant National
Pollutant Discharge Elimination System (NPDES) Permits. To date, the airborne
discharge of radioactive materials has not been included under the discharge
restrictions applicable under the Clean Air Act Amendments.
The following section discusses the use of the mobile sodium iodide
crystal detector system to conduct fairly rapid gamma radiation screening
surveys to locate structures and areas where phosphate slag has been used.
Once the magnitude of this problem has been assessed, more specific surveys
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TABLE 1. MAJOR RADIOACTIVE CONSTITUENTS OF IDAHO PHOSPHATE
ORE AND SLAG MATERIALS*
Average Radionuclide Concentration ± Two-Sigma Counting Error Term, in pCi/gram
Pocatello Pocatello Soda Springs Soda Springs
Radionuclide Plant-ORE
Ra-226
U-234
U-235
U-238
Th-230
Th-232
26 ±
22 ±
0.95 ±
22 ±
22 ±
0.43 ±
19
2.0
0.40
3.2
4.1
0.12
Plant-SLAG
32 ±
25 ±
1.1 ±
25 ±
26 ±
0.59 ±
13
6.7
0.58
7.0
11
0.29
Plant-ORE
47 ±
37 ±
1.5 ±
34 ±
38 ±
0.29 ±
1.3
3.2
0.48
3.0
1.3
0.12
Plant-SLAG
50 ±
38 ±
<1.2
29 ±
42 ±
0.48 ±
1.3
8.4
7.0
1.5
0.17
* All radiochemical analyses were completed using standard procedures
(Johns, 1975) at the U.S. Environmental Protection Agency,
Environmental Monitoring and Support Laboratory, (EMSL), Las Vegas, NV.
16
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may be conducted at the use sites to better define the radiological impact of
phosphate slag utilization.
A. Screening Surveys in Soda Springs, Idaho
Due to the scarcity of economical quantities of natural aggregate
materials in the Soda Springs area, phosphate slag has been
widely used in the local construction industry during the past
ten years. It has been estimated that for the period 1972 to
1974, a total of about 24 curies of radium-226 (one of the
major radioactive constituents of phosphate slag) has been
redistributed throughout the general environs of the Soda
Springs area (Boothe, 1977). The use of the mobile scanner was
limited to identifying locations of elevated gamma radiation
levels, regardless of the specific use of slag material at that
location. Only follow-up surveys using portable instruments
will be able to define the exact geometry and intensity of
radiation from slag materials incorporated as aggregate in
concrete foundations, driveways or sidewalks, or as "fill"
material under and around the structure.
The mobile scanner was operated in the Soda Springs area during
October 27 to 29, 1977. Figure 6 is a typical portion of the
gamma ray log for Soda Springs, Idaho. Areas of possible slag
use were observed to produce gamma ray photon peak rates greater
than 100 counts per second (cps). Structures presumed to have
no phosphate slag use are marked (f) on the strip chart. The
entire community was surveyed and 340 out of 1082 locations
(about 31 percent) were reported as having elevated gamma
radiation levels. An additional 25 to 30 anomalies were detected
in the outlying areas. Background measurements, using a
Pressurized lonization Chamber (PIC) outside the van, averaged
about 15 yR/h for this area. Several structures with elevated
gamma radiation levels (e.g., a church, hospital, and school)
were further surveyed, using portable instruments. Gamma
17
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1200>
PEAK RATE
ABOUT 550 cps
200
DISTANCE
Figure 6. Gamma ray log of streets in Soda Springs, Idaho.
18
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exposure rates as high as 100 yR/h were measured indoors,
thereby confirming the mobile scanner results. The shaded
areas on the map of Soda Springs, Figure 7, indicate the
relative locations of the observed anomalies.
So far, slag has not extensively been incorporated in the pave-
ment or roadbeds but has been used for seal coating. However,
it appears that slag has been used as "fill" material in most
of the public parking lots and also as fill and/or aggregate
material for residential driveways and sidewalks. The most
widespread use of slag has been for railroad track ballast and
radiation levels up to 100 yR/h were measured, using the
scintillometer, at one-meter height over the'track right-of-
way.
A few locations identified as having used slag in their construc-
tion were previously surveyed in 1975. Gamma radiation levels
and indoor radon progeny concentration evaluations are reported
in Table 2. Of the 340 locations identified by the mobile
scanner as having elevated radiation levels, the exact number
of habitable structures which utilized slag material as aggregate
for concrete foundations or walls, or as land fill under or
around the structure, can only be determined by additional
follow-up surveys using portable instruments.
Considering the results reported in Table 2 to be representa-
tive of the radiological exposure conditions due to the utiliza-
tion of slag for construction purposes, the following exposure
estimates have been made:
1. External Gamma Exposure Estimate
a. The assumption is made that the exposure rates
measured using the scintillator survey meter are
equivalent to the "true" gamma exposure rate.
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I SCCA SPRINGS, IDAHO 1
Figure 7. Map of Soda Springs anomalies.
20
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TABLE 2. GAMMA RADIATION AND WORKING LEVEL EVALUATIONS AT SELECTED LOCATIONS IN SODA SPRINGS, IDAHO
Location Description*
Highest Outside
Gamma Exposure
Rate (uR/h)+
Highest Inside Total Ambient Radon Progeny
Gamma Exposure Hours Concentration-Average
Rate (yR/h)+ Sampling Period Sampled Working Level (Range)++
Residence/non-masonry
(Slag used within/under)
Residence/non-masonry
(Slag used within/under)
Residence/non-masonry
(Slag used under & outside)
Residence/non-masonry
(Slag used within/under)
Public School (masonry)
(Slag used within/under)
Residence/non-masonry
(Slag used outside)
Residence/non-masonry
(Slag used outside)
30
35
45
50
30
29
35
65
4/21/76 to 9/22/76 1046.5 0.016 (0.014 to 0.018)
50 4/21/76 to 9/7/76 639.7 0.015 (0.0061 to 0.030)
65 9/23/75 to 4/4/77 2588.7 0.014 (0.0085 to 0.022)
55 4/21/76 to 6/15/77 2689.1 0.010 (0.0045 to 0.017)
35 8/12/75 to 6/15/77 3409.3 0.0086(0.00087 to 0.026)
10 9/23/75 to 6/15/77 3429.3 0.0086(0.0031 to 0.014)
20 4/21/76 to 10/1/76 787.4 0.0058(0.0039 to 0.0069)
* Slag was probably used as concrete aggregate material but may also have been used as fill underneath and
around the foundation. Slag used outside probably was for fill or in concrete driveway or sidewalk.
+ As measured using the Baird-Atomic NE148A- Gamma Scintillator Ratemeter.
++ A Working Level (WL) is defined as any combination of radon daughters in one-liter of air that will result
in the ultimate emission of 1.3 x 105 MeV of potential alpha energy. These results were obtained using
the Radon Progeny Integrating Sampling Unit (RPISU) (Schiager, 1971).
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b. The highest gamma exposure rate measured indoors was
65 yR/h.
c. The measured background exposure rate was 15 yR/h
(average of outdoor measurements). Therefore, the
net gamma exposure rate indoors was about 50 yR/h.
d. The minimum occupancy time for a residence is about 8
hours per day, or 2920 hours per year. The most
likely exposure condition would be for a housewife or
children occupying the structure on a fairly continuous
basis (i.e., exposure times much greater than 2920
hours). A reasonable estimate of the dose equivalence
received by an occupant of a structure for the
postulated minimum occupancy time is about 140 mrem
q
per year above background (50 yR/h x 2920 h/yr x 10~
mrem/yR) (assuming 1 yR/h = 1 yrem/h).
Hence, it appears that minimum occupancy of structures where
slag was used in their construction would not result in an
annual dose greater than the recommended guideline of 170 mrem
average for the general population (NCRP, 1971). However, the
most likely occupancy period would result in an annual dose of
about 440 mrem (i.e., 24 h/day x 365 day/yr x 50 yR/h x 10"3
mrem/yR). Such a maximum postulated exposure would just be
permissible under the provisions of the State of Idaho radiation
control regulations (State of Idaho, May 1973); i.e., less than
500 mrem/yr to any individual of the general population.
2. Exposure to Radon Progeny Concentrations
a. The highest measured average working level was 0.016
WL (Table 2).
22
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b. Since all of the dwellings surveyed for indoor
concentrations of radon progeny had some slag associated
with their construction, the best estimate of the
background value would be somewhat less than the
lowest measured value of 0.0058 WL (Table 2). However,
the value of 0.0058 working level will be used as the
background value for Soda Springs.
c. Therefore, an average net radon progeny concentration
of 0.01 working levels is possible for structures
containing phosphate slag.
A working level of 0.01 is the lower guideline value for possible
corrective remedial action for structures having uranium mill
tailings associated with their construction (U.S. Surgeon
General, 1970). On the assumption that radon-222 and its
progeny are present in the structure in ratios 1.0/0.9/0.5/0.35
(for living accommodations with normal ventilation) a working
level of 0.01 would correspond to a radon level of 2 pCi/1 or
about twice the level permissible under the State of Idaho
regulations for unrestricted areas (State of Idaho, May 1973).
No measurements of radon levels have yet been made in Idaho
structures which contain slag.
Several other population exposure pathways also exist due to
the "unrestricted" use of phosphate slag material in addition
to the increased exposures resulting from occupancy of structures
utilizing slag material in their construction. Such pathways
have not been evaluated but are mentioned here for future
consideration:
1. Increased gamma exposure rate received while driving or
walking on streets paved with slag material or while
occupying nearby structures.
23
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2. Increased risk of inhalation of fugitive dust containing
radioactive particulates from the resuspension of slag
materials used for road and driveway construction.
3. Increased risk due to inhalation of radon gas, and its
particulate progeny, emanating from slag materials dispersed
throughout the environment (e.g., paved roads or railroad
track ballast).
In summary, 340 locations in the Soda Springs area (nearly
one-third of the structures) were identified as having elevated
gamma exposure rates, as compared to a background level of
15 yR/h, using the mobile scanner. To confirm the mobile
scanner results, radiation exposure rates up to 100 yR/h were
measured indoors, using both the PIC and portable survey
instruments at several selected locations. Radon progeny
concentrations measured inside a few structures which had
elevated gamma exposure rates ranged from 0.0058 to 0.016
working levels. As a result of these preliminary findings, it
is recommended that further evaluations of the indoor gamma
exposure rates and radon progeny concentrations be completed in
order to fully determine the total radiological impact of the
use of phosphate slag in the construction of habitable structures
in the Soda Springs area.
B. Screening Surveys in Pocatello, Idaho
The major use of phosphate slag in the Pocatello area has been
for asphalt mix for paving of streets and parking lots.
During 1974, about 15 curies of radium-226 (one of the major
radioactive constituents of slag) were redistributed throughout
the general environs around Pocatello (Boothe, 1977). Fortunately,
there is an abundant supply of natural aggregate material in
this area; hence, very little slag has been used as aggregate
for concrete in the construction industry. The prime use of
24
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crushed slag on residential lots appears to be for "fill" in
driveways. There is also considerable use of crushed slag for
farm road construction in the outlying rural areas.
The average background gamma radiation exposure rate, as measured
by a Pressurized lonization Chamber (PIC) at one-meter above
ground surface, was 11 yR/h for the Pocatello area. Gamma
radiation levels at one-m height above road surfaces were as
high as 40 yR/h. One parking lot covered with 7.6 cm (3-in) of
crushed slag had a gamma exposure rate of 44 yR/h at a one-
meter height. Due to the widespread use of crushed slag for
driveway fill, it was impossible, using the mobile scanner, to
identify locations where slag was used solely in the construction
of the structure.
The mobile scanner was operated in the Pocatello area from
October 29 to November 3, 1977, covering approximately 75
percent of the entire city. Almost all of the area west of the
railroad tracks (the older section of town) and the few smaller
nearby communities (e.g., Chubbuck, Inkom and Cherry Springs)
were not surveyed. Figure 8 is a log made in Pocatello on a
street that was paved with phosphate slag. The count rate
peaks, for the most part, are indicative of a visually confirmed
use of phosphate slag outside of structures (driveways, planters,
yards, etc.). It was not, however, possible to verify that
these locations had not also used slag for construction purposes.
The large peaks at both ends of the log were caused by crossing
an intersecting street that was payed with phosphate slag.
Figure 9 shows a typical log from a street having no slag use
or any visible slag around the structures. The variation in
the log's count rate trace was less than 50 counts per second.
Figure 10 contains a portion of the Pocatell.o log made in the
downtown area. The peaks are generally larger than those caused
by residences and, for the most part, are due to parking lots
which were paved or gravelled with phosphate slag.
25
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1200
DISTANCE
Figure 8. Gamma ray log from Pocatello, Idaho (Street paved with slag),
1200 r
1000
§ 800
8
ill
(0
£ 600
w
200
DISTANCE
Figure 9. Gamma ray log from Pocatello, Idaho (Street not paved with slag)
26
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1200 r
1000
Z800
O
O
w
-------
Elevated gamma radiation levels were reported for 1550 locations
in those areas which were surveyed; however, the vast majority
of these locations had slag fill driveways. A total of 2000 to
2250 anomalies has been projected for the Pocatello area. To
date, an extensive evaluation of indoor concentrations of radon
progeny has not been undertaken in the Pocatello area.
In summary, because of the widespread use of phosphate slag
material in the Pocatello area for street pavement mix and for
driveway fill, the exact identification of structures built on
or with slag cannot be resolved by using the mobile gamma
scanner. Additional radiation surveys using portable survey
instruments must be completed in order to obtain this informa-
tion. Therefore, it is recommended that the radiological
evaluation of those structures built on or with slag which have
already been identified in the Soda Springs area should be
completed first. Then, if conditions warrant, further radiological
evaluations should be completed in Pocatello and nearby communi-
ties.
Until all aspects of the radiological impact of slag utilization
have been completed, it is also recommended that the "prohibited
use" of phosphate slag in the construction of habitable structures
should remain in effect (State of Idaho, June 1, 1977). The
continued use of slag material for road construction, railroad
ballast, and for other outdoor construction purposes, results
in the annual dispersal throughout the general environs of
curie quantities of long-lived natural radioactive materials
(e.g., radium, uranium, and thorium). Such a situation is
creating radiological and environmental risks which will be
extremely difficult to evaluate or to rectify in the future.
Therefore, the extension of the "temporary use approval" for
other construction purposes should be reconsidered. The use of
slag for purposes such as discussed above is also known to be
taking place in Twin Falls, Idaho; Butte, Montana; and in
several other communities in both States.
28
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II. Areas Using Uranium Mill Tailings and Other Miscellaneous Sources
A. Salt Lake City, Utah
While enroute to Idaho, the logging equipment was checked in
Salt Lake City, Utah. Figure 11 is a portion of the gamma ray
log made in the city's downtown area. The peaks were presumed
to be caused by the massive highrise buildings which emitted
radiation down through the unshielded top of the detector
system. Figure 12 is a portion of the gamma ray log which was
made near the former Vitro uranium mill tailings pile located
in the southern portion of the city. Three apparent tailings
locations are indicated on this log section. An overpass,
which is also labelled, appears to have some tailings use.
B. Farmington, New Mexico
Pumice, produced from open pits northwest of Santa Fe, New
Mexico, is widely used throughout the southwest as a lightweight
aggregate for making cement blocks. The pumice contains about
6 pCi/g of radium-226. After it is mixed with other materials
to form the blocks, the average radium concentration in the
blocks ranges from 2 to 3 pCi/g. Figure 13 contains a gamma
ray log of downtown Farmington, New Mexico and a motel known to
contain pumice in the construction block. Two peaks are indicated
for the motel because it was passed with the scanner twice in
a short period of time. The cause of the three peaks in the
downtown section was not verified, however, it is presumed that
they were caused by pumice block also.
C. Shiprock, New Mexico
Shiprock, New Mexico contains pumice block from the Farmington,
New Mexico area as well as an inactive uranium mill site and a
former uranium ore-buying station. Figure 14 contains a gamma
ray log of a community building containing pumice block. The
three peaks on the log were caused by driving past three
different sides of the building. Figure 15 is a log of the
29
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12001-
1000
Z 800
O
O
UJ
to
5 600
CO
§400
200
Figure 11
1200i-
1000
DISTANCE
Gamma ray log of downtown Salt Lake City, Utah.
800
O
O
ju 600
Q.
I
§400
200
DISTANCE
Figure 12. Gamma ray log of Salt Lake City,
Vitro Uranium Mill Site).
Utah (Near the former
30
-------
12001-
1000
DOWNTOWN AREA
Z 800
o
o
III
CO
u 600
&
CO
0400
200
DISTANCE
Figure 13. Gamma ray log of Farmington, New Mexico.
1200r-
1000 -
COMMUNITY CENTER
lm»tf***^
t
0400
200
DISTANCE
Figure 14. Gamma ray log of Shiprock, New Mexico (Community Center),
31
-------
1200 r
1000
FORMER
ORE BUYING STATION
0400
U
200
i .
DISTANCE
Figure 15. Gamma ray log of Shiprock, New Mexico (Former uranium ore
buying station).
1200 r
1000
Z 800
I
Si 600
CO
0400
200
ORE RESIDUE
^^^^
DISTANCE
Figure 16. Gamma ray log of Shiprock, New Mexico (Uranium ore residue),
32
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former ore-buying station. The peak is well pronounced although
the scanner to source distance was approximately 46 meters.
Figure 16 is a log of an area on which uranium ore was dumped
because of an ore truck breakdown. The ore was later picked
up, leaving no visible residue but apparently some contamination.
Miscellaneous Logs
Figure 17 contains three large well-defined peaks caused by
propane trucks passing the scanner vehicle. Figure 18 is a
gamma ray log made in Gallup, New Mexico. The large peak on
this log was presumed to be caused by a large propane tank on a
service station lot.
Figure 19 is a portion of the gamma ray log that was made along
Interstate 15 from Salt Lake City to the Nevada border. It was
noted that the gamma ray background exposure rate increased
from about 12 yR/hr to about 23 yR/h around the Cove Fort to
the Beaver exit area in Utah. The scanning vehicle was driven
off the highway onto a dirt road in order to confirm that the
elevated exposure rate did not originate from the highway.
Uncorrected pressurized ion chamber exposure rates, location
points, and peaks caused from highway cuts are also noted on
the log. A scale change was necessary midway through the
portion of the log in order to plot the higher count rates
experienced. A similar anomaly was observed to occur 48
kilometers east of Kingman, Arizona. No explanation for the
occurrence of these anomalies can be made except to postulate
that they were caused by natural radioactivity.
33
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PROPANE TRUCKS
1200
1000
800
600
200
DISTANCE
Figure 17. Gamma ray log from propane trucks.
1200
1000
I 1
PROPANE TANK AT
SERVICE STATION
200
DISTANCE
Figure 18. Gamma ray log from Gallup, New Mexico.
34
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BEAVER EXITH
OVER PASS
20pR/h •
EXIT-
24 pR/h
22 |iR/h
20pR/h -
RANCH EXIT-
SCALESWlfgH —
JCT INT 70-
17)iR/h -
COVE FORT -
15jiR/h —
§
COUNTS PER SECOND
10 w »
§ § §
O O O
Ul
O
§
I
00
§
10
o
O
Figure 19. Gamma ray log on Interstate 15.
35
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REFERENCES
Boothe, Gary F., (April, 1977), The Need for Radiation Controls in the
Phosphate and Related Industries. Health physics: Vol. 32, pp 285-290.
Fitzgerald, J., G. L. Brownell, F. J. Mahoney, (1967), Mathematical Theory of
Radiation Dosimetry. Gordon & Breach Science Publishers, Inc., 150 Fifth
Ave., New York, N.W. 10011.
Johns, Fredrick B., ed., (1975), Handbook of Radiochemical Analytical Methods,
EPA-680/4-75-001, Las Vegas, Nevada.
(NCRP, 1971), National Council on Radiation Protection and Measurements, NCRP
Report No. 39 - Basic Radiation Protection. Issued January 15, 1971,
Washington, DC.
State of Idaho (May, 1973), Idaho Radiation Control Regulations, Part C -
Standards for Protection Against Radiation.
State of Idaho (June 1, 1977), Technical Policy Memorandum No. 7 - Concerning
the Use of Radium - Contaminated Phosphate Slag in Idaho.
Schiager, K. J., (March 15, 1971), The Evaluation of Radon Progeny Exposures
in Buildings: A Report on Equipment and Techniques. Colorado State University,
Fort Collins, Colorado.
(U.S. DHEW, 1960), U.S. Dept. of Health, Education and Welfare, Public Health
Service, Division of Radiological Health, Radiological Health Handbook.
Washington, DC 20425, September 1960, pp 151.
U.S. Surgeon General, (1970), Recommendations of action for radiation exposure
levels in dwellings constructed on or with uranium mill tailings. In: Hearings
on the Use of Uranium Mill Tailings for Construction Purposes, Joint Committee
on Atomic Energy (1971), pp 51-54.
36
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APPENDIX A
ESTIMATION OF GAMMA EXPOSURE RATES AT CURBSIDE
FROM STRUCTURES CONTAINING URANIUM MILL TAILINGS OR PHOSPHATE SLAG
1. Gamma exposure rate estimate at curbside from uranium mill tailings used
for bedding material under a typical residential buildtng slab
Assumptions used to estimate exposure rates:
Building area - 107 m2
Slab - Square - 10.6 meter side
Slab to curbside distance - 7.6 meters
Tailings depth under slab - 15 cm
Radium-226 concentration of tailings - 500 pCi/g
Exposure rate calculations are based on a 30-cm x 15-cm tailings line
source behind a 20-cm stem wall and no self-absorption. The energy flux
along a perpendicular bisector of a line source is estimated by the
following equation (Fitzgerald et al., 1967).
IQ = (2.96 x 109) CL E n 2L/h2[l - 1/3 (L/h)2 + 1/5 (L/h)11 -1/7 (L/h)6 ]
Where: I = Unattenuated energy flux at curbside from the assumed
line source (Mev/cm2-sec)
C. = Radium-226 concentration per unit length of line
source (Ci/cm)
L = Length of line source (cm)
E = Energy of gamma radiation (Mev)
h = Perpendicular distance from line source to point
of measurement (cm)
n = Gamma ray photon abundance
(2.96 x 10*) = 3'7 x ™
37
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Assumed active volume of tailings behind footing stem wall
V = 1060 cm x 15 cm x 30 cm = 4.8 x 10b cm3
Total activity of
radium-226 in active = 500 pCi/g x 1.6 g/cm3 x 4.8 x 10s cm3 = 3.8 x 108 pCi
tailings volume
CL = 3.8 x 108 pCi x 1/1060 cm = 3.6 x 10s pCi/cm
I = 2.96 x 109ii n X n^ngV** MeV/dis)(2.18)(2)^ -V°x 1"I2""' [1-0.225+0.09]
0 I.U X IU plsl/Ll \/vc. ClNy
IQ = 7.0 MeV/cm2-sec
Unattenuated exposure _ lo 7/5 2 1Q5 _ 13 x i0-6R/h B 13
rate at curbside 5.2xlOsMeV/cm2-sec-R/h '/b^xlu IJ x IU K/n IJ
Correcting for attenuation by the 20-cm concrete stem wall, the transmission
factor is 0.2 (U.S. DHEW, 1960).
Estimated exposure rate = 13 yR/h x 0.2 = 2.6 yR/h
2. Gamma exposure rate at curbside from phosphate slag used as aggregate
in concrete
Assumptions used to estimate exposure rates
Building area - 107 m2
Exposed wall - 91 cm high
Wall to curbside distance - 7.6 m
Wall length - 10.6 m
Radium-226 concentration - 15 pCi/g in wall
Wall volume = 1.96 x 10" cm3
= 1'96 xl°6 cm3 x 15 pCi/g x 2t35 9/CI" s 6'91 x 10? pC1
Radium-226 concentration Q, In7 r-
per unit length of = ins x Q^ cm = 6-58 x ^ Pci/cm
stem wall T-06 x 10 cm
38
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing}
REPORT NO.
ORP/LV-78-2
2.
3. RECIPIENT'S ACCESSION NO.
TITLE AND SUBTITLE
Above Ground Gamma Ray Logging for Locating Structures
and Areas Containing Elevated Levels of Uranium Decay
Chain Radionuclides
5. REPORT DATE
April 1978
6. PERFORMING ORGANIZATION CODE
Josepn Hans, Jr.; Gregory Eadie; Jack Thrall and
Bruce Peterson
8. PERFORMING ORGANIZATION REPORT NO.
PERFORMING ORGANIZATION NAME ANO ADDRESS
Office of Radiation Programs - Las Vegas Facility
U.S. Environmental Protection Agency
P.O. Box 15027
Las Vegas, Nevada 89114
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
Same as above
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRAC^iis report describes the construction and operation of a mobile gamma ray
logging system used to locate areas and structures containing elevated levels of
natural uranium decay chain radionuclides. The detector system consists of a sodium
iodide crystal coupled to four photomultiplier tubes and associated electronic
system which permits both an audible indication and a strip chart recording of gamma
ray photon count rates. The crystal is surrounded by lead shielding, to reduce
incident background radiation, with a collimator port to define the area of observa-
tion. Under normal operations, the detector assembly is mounted in a van at about
two meters above the ground surface and gamma ray logs are obtained while travelling
at about 16 kilometers per hour (10 mph). This system has been used extensively in
the Pocatello and Soda Springs, Idaho areas and identified about 1900 locations
where phosphate slag has been used for various construction purposes. The system
has also been used in several other communities to identify locations where uranium
mill tailings or pumice, containing slightly elevated concentrations of natural
radioactivity, was used for construction purposes. Although this mobile system has
proven very successful as a rapid screening method for identifying areas or struc-
tures with slightly elevated radiation levels, only a more specific radiation survey
can determine the exact exposure rate and specific construction usage of the building
materials containing natural radioactive materials.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Held/Group
Gamma Radiation
Uranium Series
Radiation Detector
Radium
Phosphate Slag
Uranium Mill Tailings, Pumice
Environmental Surveys
Radiation Surveys
Phosphate Industry
Uranium Mill Tailings
T8W
1807
1808
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (ThisReport)
Unclassified
21. NO. OF PAGES
46
20. SECURITY CLASS (Thilpage)
Unclassified
22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
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