NIST Technical Note 1808

Report of Special Nuclear Material 

Validation Measurements for 

Backpack Type Radiation Detectors

L. Pibida

C. Ward
NIST Technical Note 1808

Report of Special Nuclear Material 

Validation Measurements for 

Backpack Type Radiation Detectors

L. Pibida 

C. Ward

Radiation Physics Division 

Physical Measurement Laboratory

August 2013

U.S. Department of Commerce 

Rebecca Blank, Acting Secretary

National Institute of Standards and Technology 

Patrick D. Gallagher, Under Secretary of Commerce for Standards and Technology and Director 
Certain commercial entities, equipment, or materials may be identified in this

document in order to describe an experimental procedure or concept adequately.

Such identification is not intended to imply recommendation or endorsement by the

National Institute of Standards and Technology, nor is it intended to imply that the

entities, materials, or equipment are necessarily the best available for the purpose. 

National Institute of Standards and Technology Technical Note 1808

Natl. Inst. Stand. Technol. Tech. Note 1808, 19 pages (August 2013) 

CODEN: NTNOEF
1

Report of Special Nuclear Material Validation Measurements for

Backpack Type Radiation Detectors

L. Pibida1 and C. Ward2

1 National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD 20899-8462 2 Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN 37831

1. Introduction

This report provides results and recommendations from the validation testing for the different source 

configurations and radiation fields produced by special nuclear materials (SNMs) and depleted uranium 

(DU) listed within the Technical Capability Standard (TCS) for backpack type radiation detectors (BRDs).

Testing took place at Oak Ridge National Laboratory (ORNL). Test planning, data analysis, and reporting 

were performed by the National Institute of Standards and Technology (NIST).

2. Measurements Setup

All sources used for testing, including shielding containers, were measured using a calibrated high purity 

germanium (HPGe) detector. Before beginning testing, a 500 s (live time) background spectrum of the 

facility was obtained. The sources were then placed at a distance of 1.25 m from the front face of the 

HPGe detector (same as HPGe calibration distance). A 500 s (live time) gamma-ray spectrum was

acquired for each source configuration using the HPGe detector. Measurements of the exposure rate

produced by each source configuration were performed at a distance of 35 cm from the left side of the 

Victoreen 451P-DE-SI1 (38.8 cm from the reference point of the instrument). A total of 10 independent 

readings were acquired to determine the mean and standard deviation of the radiation field for each 

source configuration as well as for the radiation background level. 

All the test configurations, testing parameters, and shielding thicknesses used in the tests were

recorded. The calculated testing distances were based on the measured emission rates for each source. 

A summary of these values are listed in Table 1.

 1 Mention of commercial products does not imply recommendation nor endorsement by the National Institute of 

Standards and Technology, nor does it imply that the products identified are necessarily the best available for the 

purpose.
2

Table 1: Summary of calculated and required test parameters 

Source Shielding 

material

Source 

thickness 

(mm)

TCS required 

fluence rate of 

the source at 

reference point 

(s-1 cm-2)*

Actual Shielding 

thickness (cm) †

Calculated 

Testing 

Distance

(cm)

Calculated

Testing 

Speed 

(m/s)

HEU None NA 0.94 ± 10 % NA 228.5 1.37

HEU Lead #1 NA 0.94 ± 10 % 0.04 (1/64”) 228.5 1.37

HEU Lead #2 NA 0.94 ± 10 % 0.08 (1/32”) 228.5 1.37

HEU Steel NA 0.94 ± 10 % 0.48 (3/16”) 228.5 1.37

HEU HDPE NA 0.94 ± 10 % 4.71 (2”) 228.5 1.37

HEU Steel + HDPE NA 0.94 ± 10 % 0.32 (1/8”) Steel/ 

2.53 (1”) HDPE

228.5 1.37

WGPu None NA 2.30 ± 10 % NA 47.0 0.28

WGPu 5 mm copper NA 2.30 ± 10 % 5 mm copper 47.0 0.23

WGPu 4.5 mm steel NA 2.30 ± 10 % 4.5 mm steel 47.0 0.25

WGPu 8.2 mm steel NA 2.30 ± 10 % 8.2 mm steel 47.0 0.19

WGPu Lead #1 NA 2.30 ± 10 % 0.24 (3/32”) 47.0 0.28

WGPu Lead #2 NA 2.30 ± 10 % 0.32 (1/8”) 47.0 0.28

WGPu Steel NA 2.30 ± 10 % 0.95 (3/8”) 47.0 0.28

WGPu HDPE NA 2.30 ± 10 % 7.98 (3”) 47.0 0.28

WGPu Steel + HDPE NA 2.30 ± 10 % 0.48 (3/16”) 

Steel/ 

3.78 (1.5”) HDPE

47.0 0.28

DU None 3.175 0.34 ± 10 % NA 217.3 1.30

* Uncertainties have a coverage factor, k, of 1

† The shielding thickness has an uncertainty of ± 10 % (k=1). Shielding material in the USA is purchase in inches; therefore values in 

parenthesis provide the actual thickness needed when purchasing this material. Values in SI units are rounded up and based on the 

actual measured values.

The ORNL sources used for these measurements were:

• 4 Depleted Uranium (DU) plates – source number: U-238-3618, U-238-3621, U-238-3622, U-238-

3624

• Highly Enriched Uranium (HEU) sphere – source number: U-234-5879

• Weapons Grade Plutonium (WGPu) cylinder – source number: Pu-239-FP22R9R87

In an effort to reduce the 241Am contribution of the WGPu source, three cylindrical shielding containers 

were also tested (4.5 mm steel, 5 mm copper, and 8.2 mm steel). 

Three BRDs were used for the measurements, two with gross count detection capabilities (refer to here 
3

as BRD1 and BRD2) and one with radionuclide identification capabilities (refer to here as BRD3). 

According to the BRD TCS, the testing parameters depend on the instrument’s operational mode. The 

following parameters were used for these tests:

1. Static Mode: collection time for radionuclide identification was set for 60 seconds. 

2. Dynamic Mode: the source was mounted at the back of the vehicle (Kubota), see Figure 1. The 

vehicle speed could not be easily controlled but the two available speeds were 2.14 ± 0.08 m/s 

and 1.07 ± 0.07 m/s. 

A phantom was placed behind each backpack, see Figure 2. The phantom dimensions were 40 cm wide, 

60 cm high and 15 cm thick. Measurements were performed with the front part of the BRD facing the 

source; the BRD was not rotated relative to the source direction.

The static measurements were performed indoors. The BRDs were mounted on a stand in front of the 

phantom with the center of the BRD placed at a distance of 1.5 from the floor, see Figure 2. The source 

was mounted on a table and the source center was aligned with the BRD center. Each source was 

placed in front of each BRD at the required distance, see Table 1. For each test, the instrument was 

exposed to a source listed in Table 1, the gamma and neutron readings were obtained (10 readings 

each), and when applicable, identified radionuclides were recorded. For BRDs with spectrometric 

capabilities, one 60 second spectra for each source configuration was acquired and saved. 

The dynamic measurements were performed outdoors. The BRDs were mounted on a stand in front of 

the phantom with the center of the BRD placed at a distance of 1.2 m from the floor. The source was 

mounted at the back of the vehicle (Kubota) and the source center was aligned with the BRD center, see 

Figure 1. The vehicle speed could not be easily controlled but the two available speeds were 2.14 ± 0.08 

m/s and 1.07 ± 0.07 m/s. The required speeds are listed in Table 1. Only 5 trials were performed for the 

BRD radionuclide identification capabilities due to impending weather conditions. The testing distance 

for the WGPu sources was 80 cm at a speed of 1.07 m/s. The HEU and DU sources were tested at 

2.14 m/s. The testing distances for HEU and DU were 228 cm and 217 cm respectively; same distances as 

used for the static measurements. 

For dynamic measurements only, three sheets of gauge 28 galvanized tin were used in an attempt to 

reduce the 241Am contribution to the total signal.
4

Figure 1: Source mounting for dynamic tests

Figure 2: BRD mounting on phantom and source location relative to BRD
5

The measured environmental conditions during testing are listed in Table 2.

Table 2: Environmental conditions during testing

Measurement location Temperature

(°C)

Relative humidity 

(%)

Atmospheric pressure 

(mm of Hg)

Indoor minimum value 22.9 52.0 740.6

Indoor maximum value 24.0 60.8 741.0

Outdoor minimum value 29.5 54.5 734.8

Outdoor maximum value 32.2 65.5 736.7

3. Shielding

The shielding thicknesses specified in the BRD TCS (see Table 3) could not be acquired from any material 

manufacturer. Therefore, it was decided to either purchase commercial available material closest to 

thicknesses as specified in the TCS or purchase thicker material and machine it to the required TCS 

value. In order to reduce the cost of the tests, it was decided to purchase commercial available material 

with the closest thicknesses as specified in the TCS. However, this meant the material thicknesses 

changed by a significant amount for both the lead and the high density polyethylene (HDPE). For the 

lead shielding, the difference was between 12 % and 21 % depending on the source and shielding 

thickness, therefore two different thicknesses were acquired for each source in order to assess the 

differences in response. Due to the properties of the HDPE, the material was welded together to form 

boxes. Table 3 also lists the actual thicknesses used for the testing. 

Table 3: Shielding thicknesses

Source Shielding 

material

TCS Shielding 

thickness (cm) †

Actual Shielding thickness 

(cm) *†

HEU Lead 0.05 0.04/0.08

HEU Steel 0.53 0.48

HEU HDPE 5.37 4.71

HEU Steel + HDPE 0.26 Steel/2.68 HDPE 0.32 Steel/2.53 HDPE

WGPu Lead 0.27 0.24/0.32

WGPu Steel 1.00 0.95

WGPu HDPE 7.18 7.98

WGPu Steel + HDPE 0.5 Steel/3.59 HDPE 0.48 Steel/3.78 HDPE

† The shielding thickness has an uncertainty of ± 10 % (k=1)

* Values in SI units are rounded up and based on the actual measured values.

In addition to the TCS specified shielding materials and thickness, ORNL built three cylindrical shielding 

containers intended to be used to reduce the 241Am contribution of the WGPu source. The containers 
6

included a 4.5 mm thick steel, a 5 mm thick copper, and an 8.2 mm thick steel cylinders. These cylinders 

were also used with the WGPu source.

4. Calculations and Measurements

4.1 Attenuation Factor

The HPGe measurements for each source configuration were used to obtain the attenuation factors 

produced by the different shielding materials and thicknesses as well as the corresponding fluence rates. 

The attenuation factor is defined as the ration between the emerging photon beam intensity, I, after 

going through a layer of material with thickness, x, and density, ρ, divided by the incident photon beam 

intensity, I0, see equation 1. 

I

I0

= exp�−�

μ

�ρ�xρ� (1)

where μ/ρ is the mass attenuation coefficient. The BRD TCS standard requires an attenuation factor of 

0.5 for all sources but the actual attenuation values varied between 0.40 and 0.58 depending on the 

source and shielding material thickness. These values were obtained for the 185.72 keV line for HEU, 

413.71 keV for WGPu, and 1001.03 keV for DU sources. Figure 3 for HEU and Figure 4 for WGPu show 

the required (0.5) and the actual attenuation factor for each shielding material.

HEU Lead #1

HEU Lead #2

HEU Steel

HEU HDPE

HEU Steel+HDPE

0.40

0.45

0.50

0.55

0.60

Attenuation Factor

Source

Figure 3: Attenuation factors for 185.72 keV photopeak from HEU source. Uncertainties are one 

standard deviation.
7

WGPu copper 5 mm

WGPu steel 8.2 mm

WGPu steel 4.5 mm

WGPu Lead #1

WGPu Lead #2

WGPu Steel

WGPu HDPE

WGPu Steel+HDPE

0.4

0.5

0.6

0.7

0.8

0.9

Attenuation Factor

Source

Figure 4: Attenuation factors for 413.71 keV photopeak from WGPu source. The points to the left 

of the vertical line are the measured values using the ORNL cylinders. Uncertainties are one 

standard deviation.

In Figure 4 the measured attenuation factors, calculated as the ratio of the measured fluence rate for 

the shielded WGPu source divided by the fluence rate for the bare WGPu source rate, for the cylindrical 

steel containers (4.5 mm and 8.2 mm thick) do not follow the expected exponential attenuation law. 

This can be explain by the fact that the source does not fit tightly within the cylinders so the source-todetector distance cannot be precisely set when using these shielding containers.

4.2 Fluence Rate

The TCS defines the fluence rates based on the emission of specific photon energies for the various 

sources; it does not define the total fluence rate of the source based on all the emitted photon energies. 

The fluence rates reported here are based on the emission of specific photon energies for the various 

sources. 

The fluence rates were measured at a source-to-detector distance of 1.25 m using the HPGe detector for 

all shielding configurations. The HPGe measurements can be performed at any distance as long as the 

full-energy peak efficiency of the HPGe detector is known at the measurement distance. The measured 

fluence rate values are shown in Figure 5 for HEU and in Figure 6 for WGPu. The measured fluence rate 

for the bare DU source (4 plates) was 1.028 gammas/s/cm2

. All fluence rate values were obtained for the 

185.72 keV line for HEU, 413.71 keV for WGPu, and 1001.03 keV for DU sources. However, the 59.54 keV 

line for 241Am in the WGPu spectra was always measureable except when the source was placed inside 

the lead shielding containers. The measured fluence rates for the different WGPu source containers are 

listed in Table 4. Figure 7 and Figure 8 show the 500 s live time spectra for the WGPu source shielded by 

different materials and material thicknesses. From these figures; the reductions of the 241Am 59.54 keV 
8

peak relative to the 413.71 keV peak of the 239Pu is displayed. The 241Am 59.54 keV peak is not 

measureable when shielded with lead. When shielded by HDPE, the 241Am 59.54 keV peak displays a 

large low-energy tail mainly due to scattering within the shielding material. 

HEU bare

HEU Lead #1

HEU Lead #2

HEU Steel

HEU HDPE

HEU Steel+HDPE

1.5

2.0

2.5

3.0

Fluence rate (s-1cm-2)

Source

Figure 5: Fluence rates for HEU source. Uncertainties are one standard deviation.
9

WGPu bare

WGPu copper 5 mm

WGPu steel 8.2 mm

WGPu steel 4.5 mm

WGPu Lead #1

WGPu Lead #2

WGPu Steel

WGPu HDPE

WGPu Steel+HDPE

0.10

0.15

0.20

0.25

0.30

0.35

Fluence rate (s-1cm-2)

Source

Figure 6: Fluence rates for WGPu source. Uncertainties are one standard deviation.

Table 4: Measured fluence rates and ratios for WGPu gamma-ray lines at 1.25 m

Source Shielding

Fluence rate of 

59.54 keV

(s

-1 cm-2

)

Fluence rate of 

413.71 keV

(s

-1 cm-2

)

Ratio

(59.54/413.71 keV)

WGPu None 73.51 ± 3.68 0.325 ± 0.008 226.2

WGPu 5 mm copper 0.096 ± 0.006 0.215 ± 0.006 0.448

WGPu 4.5 mm steel 1.77 ± 0.09 0.265 ± 0.005 6.691

WGPu 8.2 mm steel 0.028 ± 0.004 0.149 ± 0.007 0.186

WGPu Lead #1 0 0.158 ± 0.005 0

WGPu Lead #2 0 0.137 ± 0.005 0

WGPu Steel 0.016 ± 0.003 0.166 ± 0.005 0.098

WGPu HDPE 17.09 ± 0.86 0.138 ± 0.005 123.51

WGPu Steel + HDPE 0.504 ± 0.026 0.169 ± 0.006 2.989

Uncertainties have a coverage factor, k, of 1
10

:

Figure 7: HPGe spectra showing the plutonium source placed inside different shielding materials 

used to reduce the emission from the americium peak
11

Figure 8: HPGE spectra showing the plutonium source placed inside different shielding materials

4.3 Ambient Dose Equivalent Rate

The ambient dose equivalent rate for HEU and WGPu measured by the Victoreen 451P-DE-SI at a 

distance of 35 cm from the left side of the instrument (38.8 cm from the reference point of the 

instrument) is plotted in Figure 9 and Figure 10. The main contribution to the ambient dose equivalent 

rate for the WGPu is coming from the 241Am content in the source.
12

HEU bare

HEU Lead #1

HEU Lead #2

HEU Steel

HEU HDPE

HEU Steel+HDPE

0.0

0.1

0.2

0.3

0.4

0.5

Ambient dose equivalent rate (uSv/h)

Source

Figure 9: Ambient dose equivalent rate measured for the HEU source. Uncertainties are one 

standard deviation.
13

WGPu bare

WGPu copper 5 mm

WGPu steel 8.2 mm

WGPu steel 4.5 mm

WGPu Lead #1

WGPu Lead #2

WGPu Steel

WGPu HDPE

WGPu Steel+HDPE

0.01

0.1

1

Ambient dose equivalent rate (uSv/h)

Source

Figure 10: Ambient dose equivalent rate measured for the WGPu source. Uncertainties are one 

standard deviation.

5. BRD Measurement Results

The results of the gamma and neutron readings, and radionuclides identified (when applicable) for the 

static and dynamic measurements are summarized in Table 5 through Table 9. The uncertainties are the 

standard deviation of the mean value of the 10 static trials or 5 dynamic trials. The results of the static 

60 second dwell measurements for the BRD with radionuclide identification capabilities are summarized 

in Table 8. In Table 7 and Table 9 the numbers in parenthesis represent the number of trials for which a 

given radionuclide was identified. When there were no radionuclides identified it is summarized as “No 

ID”.
14

Table 5: Results of gamma and neutron readings for BRD1 - Static

Source Actual Shielding thickness 

(cm) †

Gamma 

Level* 

Neutron 

Level*

Background None 0 ± 0 1.0 ± 0.7

HEU None 1 ± 0 1.8 ± 0.4

HEU + Lead #1 0.0397 0 ± 0 0.9 ± 0.7

HEU + Lead #2 0.0794 0 ± 0 0.8 ± 0.9

HEU + Steel 0.4763 1 ± 0 0.8 ± 0.4

HEU + HDPE 4.7142 1.1 ± 0.3 0.5 ± 0.5

HEU + Steel+ HDPE 0.3175 Steel/ 2.5286 HDPE 0 ± 0 0.2 ± 0.6

WGPu None 4 ± 0 0.3 ± 0.7

WGPu None (with 5 mm copper) 2 ± 0 0.7 ± 0.7

WGPu None (with 4.5 mm steel) 2 ± 0 1.2 ± 0.4

WGPu None (with 8.2 mm steel) 2 ± 0 1.3 ± 0.7

WGPu + Lead #1 0.2381 1 ± 0 0.9 ± 0.9

WGPu + Lead #2 0.3175 1 ± 0 1.2 ± 0.9

WGPu + Steel 0.9525 1.9 ± 0.3 0.5 ± 0.5

WGPu + HDPE 7.9794 4 ± 0 1.4 ± 0.5

WGPu + Steel+ HDPE 0.4763 Steel/ 3.7833 HDPE 2 ± 0 1.3 ± 0.5

DU None 1 ± 0 0.7 ± 0.7

Uncertainties have a coverage factor, k, of 1

† The shielding thickness has an uncertainty of ± 10 % (k=1)

* The ranges of the levels are 0 to 10
15

Table 6: Results of gamma and neutron readings for BRD2 - Static

Source Actual Shielding 

thickness (cm) †

Gamma 

Level*

Neutron 

Level*

Net Gamma 

reading (cps)

Net Neutron 

reading (cps)

Background None 0 ± 0 0 ± 0 41.1 ± 10.6 0.9 ± 0.16

HEU None 4.8 ± 0.9 0 ± 0 130.9 ± 15.7 1.0 ± 0.16

HEU + Lead #1 0.0397 2.9 ± 0.7 0 ± 0 62.5 ± 9.6 1.6 ± 0.7

HEU + Lead #2 0.0794 2.1 ± 1.1 0 ± 0 43.7 ± 9.1 1.26 ± 0.13

HEU + Steel 0.4763 3.5 ± 1.1 0 ± 0 68.5 ± 7.3 1.09 ± 0.11

HEU + HDPE 4.7142 5.5 ± 0.5 0 ± 0 114.9 ± 16.5 1.19 ± 0.17

HEU + Steel+ HDPE 0.3175 Steel/ 

2.5286 HDPE

3.5 ± 0.8 0 ± 0 80.9 ± 7.4 1.15 ± 0.14

WGPu None 9 ± 0 0 ± 0 10058 ± 336 1.23 ±0.17

WGPu None (with 5 

mm copper)

8 ± 0 0 ± 0 399 ± 24 1.54 ± 0.16

WGPu None (with 

4.5 mm steel)

8.8 ± 0.4 0 ± 0 632 ± 49 1.20 ± 0.13

WGPu None (with 

8.2 mm steel)

8 ± 0 0 ± 0 319 ± 27 1.05 ± 0.18

WGPu + Lead #1 0.2381 5.1 ± 0.7 0 ± 0 112.5 ± 19.2 1.08 ± 0.12

WGPu + Lead #2 0.3175 4.9 ± 0.74 0 ± 0 108.6 ± 13.5 1.84 ± 0.39

WGPu + Steel 0.9525 7.6 ± 0.52 0 ± 0 300.5 ± 12.6 1.17 ± 0.20

WGPu + HDPE 7.9794 9 ± 0 0.2 ± 0.6 8491 ± 148 1.55 ± 0.66

WGPu + Steel+ 

HDPE

0.4763 Steel/ 

3.7833 HDPE

8 ± 0 0.4 ± 0.70 578 ± 31 1.84 ± 0.68

DU None 5.6 ± 0.5 0 ± 0 140.1 ± 12.4 1.33 ± 0.27

Uncertainties have a coverage factor, k, of 1

† The shielding thickness has an uncertainty of ± 10 % (k=1)

* The ranges of the levels are 0 to 9
16

Table 7: Results of gamma and neutron readings, and radionuclides identified for BRD3 - Static

Source Actual Shielding 

thickness (cm) †

Gamma 

Level*

Neutron 

Level*

Net Gamma 

reading

(cps)

Net 

Neutron 

reading

(cps)

Radionuclides 

Identified

Background None 0 ± 0 0 ± 0 230 ± 5 3.8 ± 1.1 No ID (10)

HEU None 7 ± 0 0 ± 0 337 ± 7 3.8 ± 1.2 U-235 HE (7), No ID (3)

HEU + Lead #1 0.0397 5 ± 0 0 ± 0 162 ± 3 4.4 ± 1.1 Co-57 (1), No ID (9)

HEU + Lead #2 0.0794 4 ± 0 0 ± 0 91.2 ± 1.1 3.7 ± 0.9 No ID (10)

HEU + Steel 0.4763 5.5 ± 0.5 0 ± 0 177 ± 4 4.3 ± 1.2 U-235 HE (3), U-238 

(2), Co-57 (1), No ID 

(4)

HEU + HDPE 4.7142 6 ± 0 0 ± 0 266 ± 23 3.1 ± 0.9 U-235 HE (3), No ID (7)

HEU + Steel+ 

HDPE

0.3175 Steel/ 

2.5286 HDPE

6 ± 0 0 ± 0 202 ± 7 4 ± 1 U-235 HE (7), No ID (3)

WGPu None 9 ± 0 0 ± 0 15860 ± 549 3.6 ± 1.2 Am-241 (1), No ID (9)

WGPu None (with 

5 mm copper)

9 ± 0 0 ± 0 1260 ± 102 3.4 ± 1 WGPu (2), Pu-240 (1), 

No ID (7)

WGPu None (with 

4.5 mmm steel)

9 ± 0 0 ± 0 1693 ± 19 4.1 ± 0.7 Am-241 (9), No ID (1)

WGPu None (with 

8.2 mmm steel)

9 ± 0 0 ± 0 1385 ± 78 4.2 ± 0.9 No ID (10)

WGPu + Lead #1 0.2381 8 ± 0 0 ± 0 582 ± 6 4.2 ± 0.8 WGPu (1), No ID (9)

WGPu + Lead #2 0.3175 7.7 ± 0 0 ± 0 487 ± 7 3.5 ± 1.4 No ID (10)

WGPu + Steel 0.9525 9 ± 0 0 ± 0 936 ± 11 4.3 ± 1.4 No ID (10)

WGPu + HDPE 7.9794 9 ± 0 0 ± 0 12809 ± 50 3.1 ± 0.9 No ID (10)

WGPu + Steel+ 

HDPE

0.4763 Steel/ 

3.7833 HDPE

9 ± 0 0 ± 0 1210 ± 15 3.9 ± 0.7 Am-241 (7), No ID (3)

DU None 8 ± 0 0.1 ± 0.3 581 ± 8 4.1 ± 1.4 U-238 (3), No ID (7)

Uncertainties have a coverage factor, k, of 1

† The shielding thickness has an uncertainty of ± 10 % (k=1)

* The ranges of the levels are 0 to 9
17

Table 8: Results of radionuclide identification for BRD3 – Static (60 s)

Source Actual Shielding 

thickness (cm) †

Radionuclides 

Identified

Confidence 

Indication

Filename

Background None No ID NA 2013-06-12T13.00.37.7768.n42

HEU None U-235 (HE) (SNM) 97 2013-06-12T13.58.43.1483.n42

HEU + Lead #1 0.0397 Co-57 (Ind)

U-235 HE (SNM)

97

73

2013-06-12T14.07.34.7167.n42

HEU + Lead #2 0.0794 U-235 (HE) (SNM) 72 2013-06-12T14.35.58-6786.n42

HEU + Steel 0.4763 U-235 (HE) (SNM) 92 2013-06-12T14.51.57.0532.n42

HEU + HDPE 4.7142 U-235 (HE) (SNM) 78 2013-06-12T14.45.38.3634.n42

HEU + Steel+ 

HDPE

0.3175 Steel/ 

2.5286 HDPE

U-235 (HE) (SNM) 93 2013-06-1T14.57.41.6714.n42

WGPu None Am-241 (Ind) 90 2013-06-12T13.38.14.1531.n42

WGPu None (with 5 

mm copper)

No ID NA 2013-06-12T15.41.44.9130.n42

WGPu None (with 

4.5 mm steel)

Am-241 (Ind) 87 2013-06-12T15.47.43.3741.n42

WGPu None (with 

8.2 mm steel)

Not measured

WGPu + Lead #1 0.2381 No ID NA 2013-06-12T15.11.26.0190.n42

WGPu + Lead #2 0.3175 No ID NA 2013-06-12T15.16.03.4703.n42

WGPu + Steel 0.9525 No ID NA 2013-06-12T15.21.32.5335.n42

WGPu + HDPE 7.9794 Am-241 (Ind) 72 2013-06-12T15.27.07.7509.n42

WGPu + Steel+ 

HDPE

0.4763 Steel/ 

3.7833 HDPE

Am-241 (Ind) 91 2013-06-12T15.34.52.9391.n42

DU None U-238 (NORM) 97 2013-06-12T13.52.21.5490.n42

† The shielding thickness has an uncertainty of ± 10 % (k=1)
18

Table 9: Results of gamma and neutron readings, and radionuclides identified for BRD3 - Dynamic

Source Actual Shielding 

thickness (cm) †

Gamma 

Level*

Neutron 

Level*

Net 

Gamma 

reading

(cps)

Net 

Neutron 

reading

(cps)

Radionuclides 

Identified

Background None 0 ± 0 0 ± 0 233 ± 6 3.7 ± 0.9 No ID (5)

HEU None 5 ± 0 0 ± 0 178 ± 6 NA U-235 HE (4), 

No ID (1)

HEU + Lead #1 0.0397 3 ± 0 0 ± 0 81.9 ± 2.4 NA No ID (5)

HEU + Lead #2 0.0794 1.2 ± 0.5 0 ± 0 46.3 ± 1.1 NA No ID (5)

HEU + Steel 0.4763 3.8 ± 0.5 0 ± 0 96.1 ± 2.1 NA No ID (5)

HEU + HDPE 4.7142 4.4 ± 0.5 0 ± 0 134 ± 3 NA No ID (5)

HEU + Steel+ 

HDPE

0.3175 Steel/ 

2.5286 HDPE

4 ± 0 0 ± 0 95.3 ± 1.6 NA No ID (5)

WGPu†† None 9 ± 0 0 ± 0 955 ± 57 NA Am-241 (4), 

Ba-133 (1)

WGPu None (with 5 mm 

copper)

6 ± 0 0.2 ± 0.5 219 ± 8 NA Am-241 (1), 

No ID (4)

WGPu None (with 

4.5 mm steel)

7 ± 0 0 ± 0 337 ± 6 NA Am-241 (4), 

No ID (1)

WGPu None (with 

8.2 mm steel)

6 ± 0 0 ± 0 211 ± 8 NA RG Pu (1), No 

ID (4)

WGPu + Lead 

#1††

0.2381 3 ± 0 0 ± 0 77 ± 3 NA No ID (5)

WGPu + Lead 

#2††

0.3175 3 ± 0 0 ± 0 72.9 ± 1.7 NA Ba-133 (1), No 

ID (4)

WGPu + Steel†† 0.9525 5 ± 0 0 ± 0 147 ± 6 NA Co-57 (1), No 

ID (4)

WGPu + HDPE†† 7.9794 9 ± 0 0 ± 0 664 ± 43 NA No ID (5)

WGPu + Steel††

HDPE

0.4763 Steel/ 

3.7833 HDPE

5.8 ± 0.5 0 ± 0 194 ± 5 NA No ID (5)

DU None 6 ± 0 0 ± 0 261 ± 8 NA No ID (5)

Uncertainties have a coverage factor, k, of 1

† The shielding thickness has an uncertainty of ± 10 % (k=1)

††The WGPu was surrounded by 3 sheets of gauge 28 galvanized metal

* The ranges of the levels are 0 to 9
19

6. Recommendations 

Based on the present validation measurements the following should be considered:

• The copper, steel or cadmium shielding used to reduce the 241Am present in the WGPu source 

shall be used for all bare and shielded test configurations. The testing distance and speed for 

WGPu shall be calculated based on the shielded source with the reduced 241Am emission.

• The shielding thicknesses that can be purchased without alteration of the material do not 

produce a 50 % reduction in emission rate. The purchased shielding thicknesses produce 

attenuation factors that vary between 0.40 and 0.58. Therefore, the purchased material without 

alteration could be used for the measurements if the standard specifies that the attenuation 

factor can range between 0.40 and 0.60. 

• From the four commercially available lead thicknesses, it is suggested to use the 0.04 cm (1/64 

inch) for HEU and 0.24 cm (3/32 inch) for the WGPu sources. These provide an attenuation 

factor closer to 0.5.

• It is recommended that the steel and HDPE shielding be made in a cylindrical shape. Welding the 

material into boxes or removing material from a solid cylinder has a similar cost. 

• Two out of the three BRDs didn’t have any issues in detecting the sources. Therefore, the

fluence rates specified in the standard can be reduced and still be detectable by these BRDs. 

• A track or linear motion system will be required to provide an adjustable testing speed.

• The BRD and source height of 1.5 m from the floor represents very tall users. Suggest reducing 

the testing height to 1.3 m from the floor to represent average height users.

• Due to possible presence of large amounts of 241Am in the WGPu source, it will be necessary to 

have the WGPu source be placed inside a copper, steel or cadmium shielding to reduce 241Am

contribution to the required levels. This new shielded source configuration (i.e., WGPu plus 

copper, steel or cadmium) shall be considered the bare source and it shall then be used to 

calculate the fluence rate and testing distance for all the test configurations.

• When the WGPu source was shielded with lead (both thicknesses) the 241Am peak at 59.54 keV 

was not observed in the spectrum. For all other shielding types, the 241Am peak was clearly 

visible.

• The BRD2 was automatically updating background when the WGPu was placed at the required 

testing distance of 47cm due to the large 241Am signal.