NIST Technical Note 1789

Validation Testing of Standard 

Requirements for Backpack-type 

Radiation Detectors

L. Pibida

B. Norman 

http://dx.doi.org/10.6028/NIST.TN.1789
NIST Technical Note 1789 

Validation Testing of Standard 

Requirements for Backpack-type 

Radiation Detectors

L. Pibida 

B. Norman 

Radiation and Biomolecular Physics Division 

Physical Measurement Laboratory

http://dx.doi.org/10.6028/NIST.TN.1789

March 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 1789 

Natl. Inst. Stand. Technol. Tech. Note 1789, 39 pages (March 2013) 

http://dx.doi.org/10.6028/NIST.TN1789

CODEN: NTNOEF
1

Validation Testing of Standard Requirements for Backpack-type 

Radiation Detectors

L. Pibida and B. Norman

National Institute of Standards and Technology, Gaithersburg, MD 20899-8462

Abstract

Two gross count and one radionuclide identification backpack-type radiation detectors (BRDs) 

were used to validate radiological test requirements listed in the Domestic Nuclear Detection 

Office (DNDO) Technical Capability Standard (TCS) for BRDs. For this purpose, a linear 

motion system was used to simulate the relative movement between the backpacks and the 

radioactive sources. Data was analyzed to evaluate the standard requirements for this type of 

instrument. It was observed that applying a scaling factor to the testing distance (equivalent to 

changing the testing radiation field) based on the measured background radiation can carry a 

large uncertainty as the measured values will strongly depend on the instrument used to perform 

the measurement. Therefore, testing parameter might not be reproduced in different laboratories. 

The emission rate and testing distance defined in the BRD TCS for the 252Cf source seems to be 

close to the limit of detection for this type of instrument. The fluence rate values produced by the 

different gamma-ray emitting sources required for testing the BRDs seem appropriate. If 

required to be closer to the limit of detection of the BRDs, the fluence rate values could be 

further reduced. 

Key words: gamma-ray detection, neutron detection, backpack-type radiation detectors, standard 

validation.

1. Introduction

Backpacks containing radiation detectors are used for localization of radioactive sources in a 

variety of areas, from buildings to ships. Several government agencies (Federal, State, and 

Local) have acquired different backpack-type radiation detectors (BRDs) for detection and 

interdiction of radioactive and nuclear materials. In general, there are two different types of 

backpacks currently available: one with gross count gamma-ray detection capabilities and the 

other with additional radionuclide identification capabilities with optional neutron detection. The 

Technical Capability Standard (TCS) document addresses both types of BRDs. While this 

standard was written primarily to address government needs, it requires validation based on 

testing of commercially available instruments. This work covers testing of the main parameters 

and requirements discussed by the TCS working group during the document standard 

development.

The following tests were performed to assess the TCS document requirements:
2

 Scaling of source emission with gamma-ray and neutron background measurement at test 

location

 BRD response as a function of increasing gamma-ray background level

 Suitability of fluence rate values used for testing BRDs

 Calculations of emission rates and/or fluence rate for SNM and DU sources

 Neutron measurement requirements

The results of these measurements were used to modify the test requirements and associated test 

methods of the draft version of the TCS document in order to produce the final version of the 

TCS document.

2. Experimental setup

Two gross count BRDs and one radionuclide identification BRD were used to validate a subset 

of the radiological test requirements listed in the TCS document standard. In this work, testing 

parameters used to assess the applicability of the requirements for the BRDs were broader than 

those specified by the TCS standard. The measurements were designed to assess the validity of 

the test methods and requirements described in the TCS and not to assess the goodness of the 

individual BRD response.

Backpacks were placed on an aluminum stand with the center line of the backpack located 1.2 m 

from the floor. The backpacks were positioned with the front face at several fixed distances from 

a horizontal track along which radioactive sources could move past the backpacks. All sources 

were transported along the track in front of the backpacks at two different speeds of 1.2 m/s and 

2.2 m/s. The source was transported past the backpacks at a height of 1.2 m from the floor. These 

tests were performed with the front of the BRD facing the source (referred to as the “Front” 

position) as it would be worn in the field (the backpack straps were facing away from the 

source). Measurements were performed without and with a phantom. In the latter case, the 

backpack was mounted with the back against the phantom to mimic the presence of a human 

body, see Figure 1. For each source different combinations of distance, speed and height were 

selected. At least 10 measurements were repeated for each source and for each setting 

combination. 
3

Figure 1: Diagram of BRD and phantom mounting

As this type of instrument is designed to be carried on a person’s back, tests were performed both

without a phantom and with two different types of phantoms (especially for the neutron tests). 

One phantom was a cubic-shaped block filled with water with dimensions of 30 cm High (H) 

30 cm Long (L)  15 cm Wide (W) and made of polymethyl methacrylate (PMMA), with a mass 

density, , of  = 1.19 g/cm3. The other phantom was a cubic-shaped block (40 cm (H)  40 cm 

(L)  15 cm (W)), made out of solid PMMA. Some standards do not require the use of phantoms 

when testing with gamma-ray emitting sources, phantoms are only required when testing with 

neutron sources. To investigate the difference in the gamma-ray response of the BRDs tests were 

carried out with and without phantoms.

Table 1 shows the activities for the gamma-ray and neutron sources used for testing. These 

radionuclides were selected to test the energy range covered by the TCS document. As can be 

observed in Table 1, some of the sources used in this work have activities that are different than 

the ones proposed in the TCS document standard. These additional sources were used 

exclusively to test the detection limits in addition to the TCS requirements for the backpacks. For 

the neutron tests, two different sources were used. One was a 252Cf source with an emission rate 

of 2  104neutrons per second placed inside a 1 cm steel encapsulation. The second one was a 

252Cf source with an emission rate of 4.2  105

neutrons per second placed inside a thin 

aluminum encapsulation and moderated by a 2 cm, 4 cm or 8 cm thick high density polyethylene 

(HDPE) sphere as well as a 5 % borated 8 cm thick HDPE sphere. This shielding was not 

specified by the standard, it was used to assess differences in detection for additional neutron 

moderation. Table 1 also lists the calculated fluence rate, , using equation (1) with a cut-off 

energy of 40 keV, these values were obtained using the gamma-ray emission probabilities listed 

in reference [6]. 

 

 

 

 ∑ (1)
4

where p(E) is the emission probability of a gamma-ray at energy E, A is the source activity, and r is the 

radius of the sphere from the point source.

Table 1: Activity values for gamma-ray and neutron sources

Radionuclide Activity (kBq)/ Emission 

rate

Calculated fluence rate 

(photons/s/cm2) at 2m (cut-off 

energy 40 keV)

241Am 1890 1.35

133Ba 508 1.38

57Co 674 1.29

60Co 1480 5.87

137Cs 504 0.85

DU 630 g 

(surface area 100 cm2)

0.08 

(for 1.001 MeV line)

237Np 2540 (~ 90 mg) 3.76

226Ra 294 4.87

232U 694 10.5

252Cf †

2  104neutrons/s -

252Cf *

4.2  105neutrons/s -

The uncertainty in the activities and neutron emission rate is 10 %, assuming a coverage factor of (k = 1). 

The activity values shown in the table are the ones used at the time of the measurements.

† The 2  104

neutrons/s 252Cf source was shielded by 1 cm of steel, the gamma-ray emission of this source was 

very low so there was no need to add the lead shielding for the neutron tests.

* The 4.2  105

neutrons/s 252Cf source was considered a bare source; it was placed inside a 0.762 mm thick 

aluminum holder.

For these tests, the backpacks are referred to as BRD-1, BRD-2 and BRD-3. The BRD’s 

characteristics are listed in Table 2. The backpack’s alarm thresholds used during testing were 

the default values set by the manufacturers.

Table 2: General characteristics of backpacks used in tests

Characteristics BRD-1 BRD-2 BRD-3

Gamma-ray detector 

type

Six CsI scintillators Plastic scintillator (PVT), 

Geiger-Muller GM) 

gamma-ray detector, 

NaI(Tl) detector

One plastic scintillator 

(Natural Background 

Rejection [NBR]-detector)

Gamma-ray detector 

dimensions

Four modules facing back: 

Diameter = 1.3 cm

Length = 3.8 cm

Two modules facing 

sideways:

Diameter = 1.3 cm

Length = 3.8 cm

Plastic scintillation (PVT) 

147cm2active area.

NaI(Tl) detector:

Diameter = 5 cm

Length = 5 cm

Volume ~ 770 cm3

Diameter = 9 cm

Length = 12 cm

5.08 cm diameter PMT tube

Neutron detector type Seven 3He tubes 3He detector Two 3He tubes

Neutron detector 

dimensions

Diameter = 5.08 cm 

Length = 35.81 cm 

Tube pressure: 270.89 kPa 

(39.3 psi) 

Information not provided 

in instrument manual

Diameter = 5.08 cm Length 

= 35.56 cm 

Tube pressure: 250 kPa 

(36.27 psi) 

Display 5.7 cm  5.7 cm LCD 

display with backlight

Provides:

Gamma-ray and neutron 

Wrist mounted LCD 

backlight display

Provides:

Gamma-ray and neutron 

LEDs for gamma-ray and 

neutron detection. Provides:

LEDs for gamma-ray and 

neutron signal level (scale 1
5

Characteristics BRD-1 BRD-2 BRD-3

count rate, gamma-ray and 

neutron alarm level, 

gamma-ray and neutron 

alarm trip level, active plot 

of gamma-ray and neutron 

alarm level versus time and 

operating status.

count rate, gamma-ray and 

neutron alarm level, 

gamma-ray and neutron 

alarm, active plot of 

gamma-ray and neutron 

count rate versus time, 

exposure rate, battery life

and radionuclide 

identification, including 

confidence indication.

to 10), gamma-ray and 

neutron alarm acknowledge, 

LEDs for artificial and natural 

radiation. Manual provides a 

conversion table for the LED 

display in mrem/h or Sv/h 

for gammas and in counts per 

second for neutrons.

Battery life 40 hours (without 

backlight) replaceable 

battery.

9 hours to 20 hours

rechargeable battery pack.

60 hours to 70 hours

rechargeable battery pack.

Gamma-ray alarm 

threshold

4 standard deviations from 

background

Different values for the 

different displayed levels. 

Level 1 is 4.3 sigma from 

background

5 standard deviations from 

background

The BRDs have different types of displays. Therefore, based on the BRDs display capabilities 

the following displayed parameters were recorded for the measurements:

 BRD-1

o Gamma-ray level (unit-less display from 0 to 9)

o Neutron level (unit-less display from 0 to 9)

o Gamma-ray count rate readings (unit = counts per second (cps))

o Neutron count rate readings (unit = counts per second (cps))

 BRD-2

o Gamma-ray level (unit-less display from 0 to 9)

o Neutron level (unit-less display from 0 to 9)

o Gamma-ray count rate readings (unit = counts per second (cps))

o Neutron count rate readings (unit = counts per second (cps))

o Radionuclide identification

 BRD-3

o Gamma-ray level (unit-less display from 1 to 10, and 0 corresponds to no LED 

illuminated)

o Neutron level (unit-less display from 1 to 10, and 0 corresponds to no LED 

illuminated)

Two gamma-ray handheld instruments were used to measure the background and source 

exposure rate (in units of roentgen)1and dose equivalent rates (in units of Sv). The gamma-ray

ambient dose equivalent rate ( ̇

 

 ) and exposure rate was measured using the Victoreen 

 

1 NIST does not endorse the use of non-SI units. This paper uses non-SI units because it addresses the requirements 

listed in the TCS published standards and the units displayed by the test equipment. 1 R = 2.58×10-4C/kg.
6

451P-DE-SI-RYR2and the Thermo FH40G-L respectively. The Thermo unit allows for 

integration of the gamma-ray field reducing the uncertainty in the background exposure rate 

measurements. The neutron measurements were performed using the Thermo Eberline ASP 2e 

neutron handheld survey meter.

3. Results and discussions

3.1 Scaling of source emission with gamma-ray and neutron background 

measurement at the test location

Different Department of Energy (DOE) testing programs make use of scaling rules to determine 

the appropriate value of the source activity or source emission rate to be used in testing grosscount radiation portal monitors. These scaling rules allow adjusting the source activity or 

fluence rate according to the gamma-ray or neutron background radiation levels present at the 

location were the test is being conducted. The need for this adjustment or scaling of the source 

activity or emission rate results from the fact that:

 The instrument minimum detection limit depends on the radiation background at the 

location.

 The gross-count radiation portal monitors alarm threshold is calculated as a multiple of 

the square root of the background radiation level ( √ ).

 The sources used for testing produce radiation fields are close to background levels. 

The use of these scaling rules ensures that the same minimum level of detection performance is 

met for gross-count portal monitors across different testing locations, only for monitors that 

calculate the alarm threshold as a multiple of the square root of the background radiation level. 

Furthermore, this guaranties that the same number of gamma-rays or neutrons are measured 

above background. 

During the development of the BRD TCS the applicability of these scaling rule methods for the 

testing of BRDs was discussed. The BRD TCS specifies the fluence rate of the testing sources 

instead of their activities or emission rates. This allows the use of any source quantity and shape 

as long as it produces the required fluence rate at the location of the instrument under test. 

Therefore, when specifying the source fluence rate for a given test condition, the background 

radiation level scaling methods (for a given source quantity) will be applied to the source-todetector distance. 

If the BRD does not set the alarm threshold as a multiple of the square root of the background 

radiation level, then the use of the scaling rule would adversely affect the results of the test. It is 

important to specify the range of the source activity, fluence rate or exposure rate for which this 

scaling rule is valid. In order to reduce the uncertainty determination of the testing radiation 

field, this scaling rule should not be applied to large radiation sources producing a field more 

than 100 times larger than background levels. 

 

2 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.
7

During the BRD TCS document development, it was suggested that the testing fluence rate 

values for all the sources were specified at a reference background radiation level of 20 μR/h. It 

was proposed that if testing is performed at a different facility or location where the background

radiation level is lower than the reference value of 20 μR/h the testing distance, d, shall be scaled 

by the square root of the ratio of the background radiation levels at both facilities. Scaling the 

distance in this way will adjust the fluence rate (above background) delivered to the detector so 

that the sensitivity of the instrument under test is approximately the same at any facility 

regardless of changes in radiation background levels (from the specified reference value of 

20 μR/h). 

As an illustration of the implementation of the scaling rule, consider a test being performed at a 

facility were the gamma-ray background radiation level is 10 μR/h. In order to ensure that the 

fluence rate (above background) delivered to the detector at this facility is the same as the 

fluence rate delivered at a different testing facility were the background level is 20 μR/h, the 

source-to-detector distance needs to be scaled as follows: 

 

√ 

√ 

(1)

where and are the source-to-detector distances at a laboratory where 

the radiation background are l0 μR/h and 20 μR/h respectively. Table 3 lists the distance at 

which the detector should be placed from a gamma-ray source for a test conducted at 3 different 

locations each with a different radiation background level of 5 μR/h, l0 μR/h and 20 μR/h. In 

Table 3 the testing distances for background levels of 5 μR/h and 10 μR/ h were derived from the 

distance of 1.5 m specified for the reference background value of 20 μR/h as described in the 

TCS document. Similarly, the scaling rule followed for neutron sources is the same as for 

gamma-ray sources given by Equation 1. Table 3 also shows testing distances for a neutron 

source placed in a location with three possible neutron background levels of 150 neutrons s

-1

m

-2

,

300 neutrons s

-1

m

-2

and 600 neutrons s

-1

m

-2

.

The scaling rule, from Equation 1, used to adjust the testing distances to account for the different 

possible background radiation levels results in differences in the fluence rate of up to 30 %. The 

determination of the background level at different laboratories can be performed using different 

types of radiation detection instruments. This adds an additional variable to the scaling process, 

as differences in the background determination (in a given location), when using different types 

of instruments, can be larger than 30 %. 

Table 3: Example of testing distance, d, for different radiation background levels

Source Radiation 

Type

Background 

Level

Testing 

Distance (m)

237Np Gamma rays

20 μR/h 1.5 

(reference value)

10 μR/h

2.1 

(scaled value)

5 μR/h

3.0 

(scaled value)

252Cf Neutrons 600 neutrons s-1 m-2 1.0 

(reference value)
8

300 neutrons s-1 m

-2 1.4 

(scaled value)

150 neutrons s-1 m

-2 2.0 

(scaled value)

To investigate the applicability of the proposed scaling method several measurements were 

performed to validate the requirements. Radiation background measurements were performed in 

two different locations at NIST using different types of instruments to evaluate the 

reproducibility in the determination of the gamma-ray exposure rate. 

The measurements of the gamma-ray radiation background at location 1 performed under the 

same conditions on the same day using the two handheld instruments are shown in Figure 2. The 

average dose equivalent rate and exposure rate values measured with each of these instruments 

were:

 Ambient dose equivalent rate (Victoreen 451P-DE-SI-RYR) = 0.057 μSv/h ± 42 % (1 

standard deviation)

 Exposure rate (Thermo FH40G-L) = 10.14 μR/h ± 10 % (1 standard deviation).

The average was obtained from 20 300-s integrated exposure values. Exposure rate 

values were divided by a factor of 100 in order to plot them together with the Victoreen 

451P-DE-SI-RYR measured ambient dose equivalent rate values.

The determination of the background ambient dose equivalent rate using the Victoreen 451P-DESI-RYR was performed by taking 20 independent dose equivalent rate readings (each 

independent reading consists of the average obtained from recording 10 displayed values). The 

determination of the background exposure rate using the Thermo FH40G-L was performed by 

taking 20 independent exposure readings integrated over 300 s. The uncertainties are the 

standard deviation of the 20 readings (1-standard deviation). The difference in the background 

determination using these two instruments is approximately 78 %.
9

0 5 10 15 20

0.02

0.04

0.06

0.08

0.10

0.12

0.14 Victoreen Thermo Background (uSv/h)

Measurement Number

Figure 2: Background exposure rate measurement in location 1 using different instruments; uncertainties are 1-standard 

deviation. 

Figure 3 shows measurements of the gamma-ray radiation background at location 2 performed 

under the same conditions over several years using five different ionization chambers.
10

1 2 3 4 5

0

1

2

3

4

5

6

7

8

9

10

11 Background Measurements Exposure Rate (uR/h) Pressurized Chamber Non-pressurized

Figure 3: Background exposure rate measurement in location 2 using five different ionization chambers. Uncertainties 

are smaller than the size of the symbol; uncertainties are 1-standard deviation. 

The variability in the background exposure rate determination through an extended period of

time using the same pressurized chamber is small. As expected when using a non-pressurized 

ionization chamber this variation is large. The variability in the determination of the background

exposure rate measurements using different types of ionization chambers is very large, including 

the pressurized chamber where there is a difference of approximately 44 %. Due to this large 

variability it would not possible to accurately determine the source scaling factor for testing at 

different locations with different background levels when using different instruments to 

determine the gamma-ray radiation background. 

3.2 BRD response as a function of increasing gamma-ray background level 

Testing of the BRDs in accordance with the ANSI/IEEE N42.53 standard requires verifying the 

instrument performance at two different radiation background levels. During the development of 

the BRD TCS document the need to modify or extend this requirement was discussed. Several 

measurements were performed to evaluate the BRD response to increasing background radiation. 

Natural occurring radioactive materials (NORM) can be used to increase the background

radiation level during testing. In the ANSI/IEEE standard, testing is carried out in a “low” 

radiation background condition defined as 10 R/h ± 50 % (k = 1) and in a “high” radiation 

background condition defined as 30 R/h ± 20 % (k = 1). In order to assess the BRD response to 

different background conditions a 226Ra and a 232U source were placed inside a 9 cm thick 
11

PMMA container to simulate a NORM [5] and increase the radiation background level. The 

Victoreen 451P-DE-SI-RYR was used to measure the background dose equivalent rate. The 

background dose equivalent rate was set by placing the 226Ra and 232U sources inside the PMMA 

at different distances from the BRD, the dose equivalent rates used for the measurements were 

0.1 Sv/h, 0.2 Sv/h, 0.3 Sv/h, 0.4 Sv/h and 0.5 Sv/h. 

For each one of these fixed background levels, a 57Co and a 133Ba source producing a fluence rate 

of 0.68 photons/s/cm2and 1.1 photons/s/cm2 respectively were moved past the BRD-2 at 1.2 m/s 

and the alarm level as well as the radionuclides identified were recorded. The PMMA phantom 

was placed behind the BRD-2. The BRD-2 was allowed to reset its background each time the 

background dose equivalent rate was increased. When the BDR-2 detects a source it produces an 

alarm, displays the alarm level (a number between 1 and 9) and displays the radionuclides 

identified. There was a total number of 10 trials per source, see the results for the 133Ba and 57Co 

sources in Figure 4 through Figure 7. These figures show the alarm levels and radionuclides 

identified for the 10 trials as a function of the different background dose equivalent rates. From 

these figures it can be observed that the BRD-2 is not capable of identifying the sources, as there 

was no radionuclide identified, when the background dose equivalent rate is increased above 

0.1 Sv/h. The BRD-2 alarm level is reduced when the background dose equivalent rate is 

increased. The BRD-2 sensitivity is reduced with increased background dose equivalent rate.

0.1 0.2 0.3 0.4 0.5

0

1

2

3

4

5

6

7

8

9

10

Level 1 Level 1

Level 2

Level 2 Level 2

Level 3 Level 3 Level 3 Level 4

level 1 level 2 level 3

level 4 level 5 Trial Number Background Dose Equivalent rate (Sv/h)

Level 5

Figure 4: Alarm levels for BRD-2 produced by 57Co source for different background radiation levels
12

0.1 0.2 0.3 0.4 0.5

0

1

2

3

4

5

6

7

8

9

10

No ID

No ID

No ID

No ID

241Am+Sr 137Cs

133Ba Trial Number Background Dose Equivalent rate (Sv/h)

 No ID Co-57 Am-241+Sr

 Cs-137 Ba-133

57Co

Figure 5: Radionuclide identification for BRD-2 produced by 57Co source for different background radiation levels

0.1 0.2 0.3 0.4 0.5

0

1

2

3

4

5

6

7

8

9

10

Level 4 Level 4

Level 3

Level 2

Level 1 Level 3

Level 2

Level 4 Trial Number Background Dose Equivalent rate (Sv/h)

level 1 level 2 level 3

level 4 level 5

Level 5

Figure 6: Alarm levels for BRD-2 produced by 133Ba source for different background radiation levels
13

0.1 0.2 0.3 0.4 0.5

0

1

2

3

4

5

6

7

8

9

10

133Ba No ID No ID No ID Trial Number Background Dose Equivalent rate (Sv/h)

No ID Ba-133

No ID

Figure 7: Radionuclide identification for BRD-2 produced by 133Ba source for different background radiation levels

3.3 Suitability of fluence rate values used for testing BRDs 

Currently, there are several requirements for different types of radiation detection systems 

including BRDs. The ANSI N42.53 [1] standard requires testing the BRDs alarm response 

function using a field of 4 photons/s/cm2 (± 5 %, 1-standard deviation) for 241Am, 57Co, 137Cs and 

60Co. It also requires the identification of several radionuclides (i.e.,

57

Co, 

60

Co, 

67

Ga,

99m

Tc, 

131

I, 

133

Ba, 

137

Cs, 

201

Tl, 

226

Ra, 

232

Th, 241Am, HEU, DU, and WGPu) producing an exposure rate of 5 

μR/h (±20%, 1-standard deviation) above background at the reference point of the BRD. The 

DNDO Radioisotope Identification Devices (RIIDs) TCS document [3], specifies that these 

instruments shall identify the bare and shielded sources listed in Table 4 through Table 6

depending on the category of use, (e.g., Conveyances/ Pedestrians, Containerized Cargo). In 

turn, the DNDO Traceability Memo [2] requires different source quantities to be used for testing 

of radiation detection systems used for homeland security applications. Based on the DNDO 

Traceability Memo [2] and the results of the measurements presented in this work, the draft 

version of the BRD TCS proposes the use of the sources listed in Table 6 and Table 7. 

Table 4: HEU, WGPU and DU Shielded and Bare Sources – RIIDs Conveyances/Pedestrians Category

Source Shielding material Minimum source 

thickness (mm)**

Fluence rate at 

reference point 

(photons/s/cm2)*†

HEU None 1 0.68 ± 10 %
14

Source Shielding material Minimum source 

thickness (mm)**

Fluence rate at 

reference point 

(photons/s/cm2)*†

HEU Steel 1 0.68 ± 10 %

HEU HDPE 1 0.68 ± 10 %

WGPu None 5 1.1 ± 10 %

WGPu Steel 5 1.1 ± 10 %

WGPu HDPE 5 1.1 ± 10 %

DU None 3 0.22 ± 10 %

DU Steel 3 0.22 ± 10 %

DU HDPE 3 0.22 ± 10 %

* Uncertainties have a coverage factor, k, of 1.

** Thickness are based in the 95% of infinite thickness emission rate, see Reference 15. The DU thickness 

is based on commonly available standard reference materials.

† Fluence rates correspond to a radiation background level of 20 μR/h

Table 5: DU, HEU and WGPU Shielded and Bare Sources – RIIDs Containerized Cargo Category

Source Shielding material Minimum source 

thickness (mm)**

Fluence rate at 

testing point 

(photons/s/cm2)* †

HEU None 1 1.6 ± 10 %

HEU None 1 0.18 ± 10 %

HEU Steel 1 0.18 ± 10 %

HEU HDPE 1 0.18 ± 10 %

WGPu None 5 3.8 ± 10 %

WGPu None 5 0.30 ± 10 %

WGPu Steel 5 0.30 ± 10 %

WGPu HDPE 5 0.30 ± 10 %

* Uncertainties have a coverage factor, k, of 1.

** Thickness are based in the 95% of infinite thickness emission rate, see Reference 15. The DU thickness 

is based on commonly available standard reference materials.

† Fluence rates correspond to a radiation background level of 20 μR/h

Table 6: 237Np Test Cases – All Instrument Categories

Target 

Source Quantity Distance (m) Shielding material

Shielding 

thickness

Masking 

source

Masking 

ratio

237Np 90 mg* 1.5 None None None None

* shielded by 1 cm of steel
15

Table 7: BRD HEU, WGPu and DU shielded and bare sources

Source Shielding material

Minimum 

source 

thickness 

(mm)**

Fluence rate of the 

source at reference 

point 

(photons/s/cm2)*

Shielding thickness 

(cm) †

HEU None 1 0.94 ± 10 % NA

HEU Lead 1 0.94 ± 10 % 0.05

HEU Steel 1 0.94 ± 10 % 0.53

HEU HDPE 1 0.94 ± 10 % 5.37

HEU Steel + HDPE 1 0.94 ± 10 % 0.26 Steel/2.68 HDPE

WGPu None 5 2.30 ± 10 % NA

WGPu Lead 5 2.30 ± 10 % 0.27

WGPu Steel 5 2.30 ± 10 % 1.00

WGPu HDPE 5 2.30 ± 10 % 7.18

WGPu Steel + HDPE 5 2.30 ± 10 % 0.5 Steel/3.59 HDPE

DU None 3 0.34 ± 10 % NA

* Uncertainties have a coverage factor, k, of 1.

** Source thickness values are based on the 95% of infinite thickness emission rate, see Reference 15. The DU thickness is 

based on commonly available standard reference materials.

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

Several tests and calculations were performed to investigate the suitability and differences in 

requirements proposed for testing of the BRDs. 

Calculations were performed to determine the fluence rate and activities of several sources when 

placed at a distance of 2 m from the BRD producing an exposure rate 5 μR/h and 50 μR/h above 

background at the reference point of the BRD, results of these calculations are shown in Table 8. 

These calculations assume the emission coming from a point source [7], uses a cut-off energy of 

40 keV and includes all gamma-rays with their emission probability. 

 

Table 8: Fluence rate and activities for several sources when placed at a distance of 2 m producing an exposure rate 

5 μR/h and 50 μR/h above background at the reference point of the BRD

Source Activity (MBq) 

for 5 μR field

Fluence rate at 

reference point 

(photons/s/cm2)

Activity (MBq)

for 50 μR field

Fluence rate at 

reference point 

(photons/s/cm2)

241Am 60.1 42.9 600.7 429

57Co 15.4 29.6 154.4 296

237Np 7.83 11.6 78.30 116

133Ba 3.90 10.6 38.97 106

137Cs 2.13 3.6 21.27 36

60Co 0.578 2.3 5.78 23

The exposure rate values used for testing the radionuclide identification capabilities of the BRDs 

in the ANSI N42.53 standard are orders of magnitude larger than those specified in the TCSs.

Measurements were performed using different source activities listed in Table 9. The source 

activity is given at the time of the measurements, the uncertainty in the source activity is ±10 % 

(k = 1). The measured dose rate at 2 m from the source as well as the calculated exposure rate 
16

(using the point source approximation described in reference [7]) and fluence rate at 2 m (for a 

cut-off energy of 40 keV), are listed in Table 9. These source activities were selected because 

they are used for testing BRDs in the ANSI N42.43 standard [4] and they provide a wide range 

of gamma-ray fields.

Table 9: List of sources used for BRD testing

Source

Average 

Energy 

(keV)

Source 

activity 

(μCi)3

Source 

activity (Bq)

Measured Dose 

equivalent rate 

with Victoreen 

(μSv/h) at 2m

Unc (%)

Calculated 

exposure rate 

(μR/h)/100 at 2m†

Calculated 

fluence rate 

(photons/cm2/s) 

at 2m

241Am 59.5 51.05 1.89E+06 0 31.86 0.0016 1.35

57Co 124.5 18.21 6.74E+05 0.0010 42.61 0.0022 1.29

237Np 251.7 68.65 2.54E+06 0.0283 37.03 0.0162 3.76

133Ba 266.4 13.74 5.08E+05 0.0120 22.09 0.0065 1.38

137Cs 661.7 13.62 5.04E+05 0.0133 43.74 0.0118 0.85

60Co 1252.8 39.89 1.48E+06 0.1160 17.18 0.1276 5.87

Uncertainties are 1-standard deviation.

† The calculated exposure rate values are divided by a factor of 100 in order to have them in the same scale as the ambient dose equivalent rate 

measurements. No conversion coefficients were applied to the calculated exposure rate values. 

The sources listed in Table 9 were used to determine the total count rate peak efficiency per 

Becquerel (Bq) at a distance of 2 m for BRD-1 and BRD-2. The results of these measurements 

are shown in Figure 8 and Figure 9, in these figures the x-axis represents the average energy for 

each source. The measured efficiency for BRD-2 is larger than that of BRD-1. 

 

3 NIST does not endorse the use of non-SI units. This paper uses non-SI units because it addresses the requirements 

listed in the ANSI/IEEE published standards.
17

100 1000

1E-5

1E-4

1E-3 Total count rate efficiency/Bq

Energy (keV)

BRD-1 Measurements

Figure 8: Total count rate efficiency per Bq for BRD-1 at 2 m; uncertainties are 1-standard deviation.

100 1000

1E-5

1E-4

1E-3 BRD-2 Measurements Total count rate efficiency/Bq Energy (keV)

Figure 9: Total count rate efficiency per Bq for BRD-2 at 2 m; uncertainties are 1-standard deviation.
18

The sources were moved passed the BRD-1 and BRD-2 at a speed of 1.2 m/s and 2.2 m/s with 

and without the presence of the PMMA phantom for total of 10 trials for each source, with a 

distance of closest approach of 2 m. The BRD-1 and BRD-2 can display a count rate or a level 

when detecting a radioactive source besides the alarm. For the BRD-1 the results are given based 

on the alarm and radiation level indication, see Figure 10 through Figure 12. From these figures 

it can be observed that the BRD-1 did not alarm to the 137Cs producing a fluence rate of 

0.85 photons/s/cm2at the reference point of the BRD. The presence of the PMMA phantom 

seems to increase the radiation level response for all sources. For the 241Am source the BRD-1 

response is lower than that of the 133Ba even when both sources produce a similar fluence rate, 

this can be explained by the drop in counting efficiency for the 60 keV gamma-ray emitted by 

241Am. 

Am-241 Ba-133 Co-57 Co-60 Cs-137 Np-237

0

2

4

6

8

10 Number of alarms

Source

No Phantom With Phantom

Figure 10: BRD-1 alarm indication with and without PMMA phantom, source speed 1.2 m/s, distance 2 m
19

Am-241 Ba-133 Co-57 Co-60 Cs-137 Np-237

0

1

2

3

4

5

6

7

8

9

10

Level 7

Level 6

Level 5

Level 4

Level 4

Level 3

Level 3

Level 3

Level 3

Level 1 Level 1 Level 2

Level 2

Level 2 Trial Number

Source

level 1 level 2 level 3 level 4

level 5 level 6 level 7

Level 2

Figure 11: BRD-1 level indication with PMMA phantom, source speed 1.2 m/s, distance 2 m
20

Am-241 Ba-133 Co-57 Co-60 Cs-137 Np-237

0

1

2

3

4

5

6

7

8

9

10

Level 7

Level 5 Level 5 Level 5

Level 4

Level 4

Level 4

Level 3

Level 3 Level 3 Level 1 Trial Number

Source

level 1 level 2 level 3 level 4

level 5 level 6 level 7

Level 2

Figure 12: BRD-1 level indication without PMMA phantom, source speed 1.2 m/s, distance 2 m

For the BRD-2 the results are given based on alarm, radiation level indication and the 

radionuclide identification information, see Figure 13 through Figure 17. The BRD-2 has no 

problems detecting any of the sources but it seems to have some difficulties identifying 60Co. 

There seems to be small difference in response with the presence of the PMMA phantom. For 

some sources the BRD-2 was not able to correctly identify the radionuclide present 10 out of 10 

times. 
21

Am-241 Ba-133 Co-57 Co-60 Cs-137 Np-237

0

2

4

6

8

10 Number of alarms

Source

Number of alarms With Phantom

Figure 13: BRD-2 alarm indication with and without PMMA phantom, source speed 1.2 m/s, distance 2 m

Am-241 Ba-133 Co-57 Co-60 Cs-137 Np-237

0

1

2

3

4

5

6

7

8

9

10

Level 6

Level 7 Level 7

Level 2

Level 4 Level 4 Level 4 Trial Number

Source

level 1 level 2 level 3 level 4

level 5 level 6 level 7

Level 3

Figure 14: BRD-2 level indication with PMMA phantom, source speed 1.2 m/s, distance 2 m
22

Am-241 Ba-133 Co-57 Co-60 Cs-137 Np-237

0

1

2

3

4

5

6

7

8

9

10

Level 6 Level 6

Level 7 Level 7

Level 4 Level 4

Level 4

Level 2

Level 3

Level 3

Level 3 Trial Number

Source

level 1 level 2 level 3 level 4

level 5 level 6 level 7

Level 3

Figure 15: BRD-2 level indication without PMMA phantom, source speed 1.2 m/s, distance 2 m

Am-241 Ba-133 Co-57 Co-60 Cs-137 Np-237

0

1

2

3

4

5

6

7

8

9

10 No ID

No ID

No ID

No ID

137Cs+

238U)

51Cr

137Cs

57Co

No ID

241Am Trial Number

Source

No ID Cs-137+U238 Cr-51 Np-237 Cs-137 Co-60 Co-57 Ba-133 Am-241

133Ba

Figure 16: BRD-2 radionuclide identification indication with PMMA phantom, source speed 1.2 m/s, distance 2 m
23

Am-241 Ba-133 Co-57 Co-60 Cs-137 Np-237

0

1

2

3

4

5

6

7

8

9

10

No ID

No ID

No ID

No ID

51Cr

137Cs

57Co

No ID

241Am Trial Number

Source

No ID Cr-51 Np-237 Cs-137 Co-60 Co-57 Ba-133 Am-241

133Ba

Figure 17: BRD-2 radionuclide identification indication without PMMA phantom, source speed 1.2 m/s, distance 2 m

For the 237Np source several additional measurements were performed to evaluate the BRD 

response based on the differences in source specifications in the ANSI/IEEE standard and TCS. 

The ANSI/IEEE N42.43 standard requires testing with a 90 mg 237Np shielded by 1cm of steel. 

During the development of the TCS it was suggested the use of a 90 mg 237Np without the steel 

shielding. Therefore, measurements were performed with and without the steel shielding. Figure 

18 shows the BRD-2 radiation level indication results without the presence of the phantom with 

the source placed at 2 m from the BRD-2, with and without the steel shielding. The radionuclide 

identification of 237Np was not changed by the use of the shielding. The BRD-2 net gamma-ray

count rates for the static measurements were reduced from 570 ± 13 cps to 292 ± 9 cps from the 

bare to the shielded source configuration at a distance of 2 m and from 286 ± 12 cps to 

144 ± 10 cps when the source was placed at a distance of 3 m. All uncertainties have a coverage 

factor, k, of 1.
24

Np-237(1.2m/s) Np-237(1.2m/s,1cm steel) Np-237(2.2m/s) Np-237(2.2m/s,1cm steel)

0

2

4

6

8

10

Level 6

Level 7 Level 4 Level 6

Level 5 Trial Number

Source

level 1 level 2 level 3 level 4

level 5 level 6 level 7

237Np (1.2 m/s) 237Np (1.2 m/s, 1 cm Steel) 237Np (2.2 m/s) 237Np (2.2 m/s, 1 cm Steel)

Level 5

Figure 18: BRD-2 level indication of 237Np without PMMA phantom, source speed 1.2 m/s and 2.2 m/s, distance 2 m

Similar 237Np source measurements were performed using the BRD-1 and the BRD-3 without a 

phantom. The BRD-1 net gamma-ray count rates for the static measurements were reduced from 

90 ± 20 cps to 42 ± 22 cps from the bare to the shielded source configuration at a distance of 

3 m. For the shielded configuration the gamma-ray count rate for the static measurements at 2 m 

was 67 ± 23 cps. All uncertainties have a coverage factor, k, of 1.The results of the dynamic 

measurements using the shielded 237Np source at 2 m are shown in Figure 19.
25

Np-237(1.2 m/s,1 cm steel) Np-237(2.2 m/s,1 cm steel) 0

1

2

3

4

5

6

7

8

9

10 Level 4

Level 1

Level 3

Level 4

Level 1 Trial Number Level 2

Source

level 1 level 2 level 3 level 4

Level 2

Figure 19: BRD-1 level indication of 237Np without PMMA phantom, source speed 1.2 m/s and 2.2 m/s, distance 2 m

The BRD-3 did not respond to the shielded 237Np source at a distance of 2 m at a speed of 

1.2 m/s. For the static measurements the gamma-ray reading level was equal to 1. 

From these measurements it can be observed that the source activities specified in Table 9 are 

detectable for most BRDs at a distance of 2 m. The 90 mg 

237Np shielded by 1cm of steel seems 

to be a strong source for testing the BRDs with the source placed or moving pass the BRD at a 

distance of 2 m. 

3.4 Calculations of emission rates and/or fluence rate for SNM and DU sources 

A depleted uranium (DU) source was measured using three different HPGe detectors. Two of the 

detectors were located at the National Institute of Standards and Technology (NIST) and one was 

placed at Oak Ridge National Laboratory. For each HPGe detector, the detector response was 

modeled using the Gamma Detector Response Analysis Software (GADRAS) developed by 

Sandia National Laboratory. A set of NIST traceable sources, emitting gamma-rays between 

60 keV and 2.6 MeV, were used to build the detector response function using GADRAS and to 

determine the full-energy-peak efficiency for each detector. The DU source consist of a plate 

with a surface Area ≈ 103.23 cm2(≈ 10.16 × 10.16 cm), and a thickness ≈ 0.32 mm

(approximately 630 g). The DU fluence rate measured by the three different HPGe detectors 

using the full-energy-peak efficiency for the 1001 keV line was 0.4576 photons/s/cm2(± 8.5 %), 

0.4386 photons/s/cm2(± 3.9 %) and 0.4467 photons/s/cm2(± 5.0 %). All uncertainties have a 

coverage factor, k, of 1.
26

Based on these three measured fluence rate measurements testing using the BRD-2 and BRD-3 

were performed at 3 distances in order to obtain a fluence rate at the reference point of the BRDs 

of 0.22 photons/s/cm2as specified in the RIIDs TCS. Measurements were performed at 1.2 m/s 

and 2.2 m/s, 10 trials for each speed and distance. For the BRD-3 the number of alarms was 

recorded (due to the type of the BRD-3 display). For the BRD-2 the count rate, radiation level 

and radionuclides identified were recorded, the background radiation level for BRD-2 was 

approximately 230 cps, results are shown in Table 10 and Table 11. For the BRD-2 additional 

static measurements were performed to determine the response to this DU source, results are 

summarized in Table 12. From these dynamic measurements it can be observed that the fluence 

rate for the DU source specified in the RIIDs TCS is barely detectable by the BRDs.

Table 10: BRD-2 dynamic test results for DU plate measurements

Radionuclide Distance 

(m)

Speed 

(m/s)

Phantom 

(Y/N)

Average net 

gamma-ray

count rate 

(cps)

Average 

gammaray level

Radionuclides 

Identified

DU plate 1.55 1.2 N 92.2 3.9 No ID (9), ?(1)

DU plate 1.55 2.2 N 71.4 3.4 No ID (10)

DU plate 1.83 1.2 N 78.1 3 No ID (10)

DU plate 1.83 2.2 N 60.7 2.9 No ID (10)

DU plate 2.29 1.2 N 55.7 2.2 No ID (10)

DU plate 2.29 2.2 N 39.1 1.9 No ID (10)

Table 11: BRD-3 dynamic test results for DU plate measurements

Radionuclide Distance 

(m)

Speed 

(m/s)

Phantom 

(Y/N)

Number of 

gamma-ray

alarms

DU plate 1.55 1.2 N 0

DU plate 1.55 2.2 N 0

DU plate 1.83 1.2 N 0

DU plate 1.83 2.2 N 1

DU plate 2.29 1.2 N 0

DU plate 2.29 2.2 N 0

Table 12: BRD-2 static test results for DU plate measurements

Radionuclide Distance 

(m)

Speed 

(m/s)

Phantom 

(Y/N)

Net average 

gamma-ray

count rate 

(cps)

Unc.

(%)

Average 

gammaray levelRadionuclides Identified

DU plate 1.55 0 N 225.4 1.29 6 K-40 Norm 99, U-238 Norm 99.

DU plate 1.83 0 N 186.2 3.19 5 K-40 Norm 100, U-238 Norm 97.

DU plate 2.29 0 N 118.1 2.90 4 K-40 Norm 100, U-238 Norm 97.

Uncertainties are 1-standard deviation.

A 1-Dimensional model (1-D model) was created for the DU plate using GADRAS. For two of 

the HPGe detectors, the measured count rate for the 1001 keV line was compared to the value 

obtained using GADRAS. For the NIST detector, the measured count rate was 0.723 cps and the 
27

calculated one was 0.684 cps, this corresponds to a percent difference of -5.4 %. For the ORNL 

detector, the measured count rate was 1.3 cps and the calculated one was 1.4 cps, this 

corresponds to a percent difference of 7.7 %. From these calculations it can be observed that 

source modeling is a usable tool (within approximately ± 12 %) to predict emissions from 

different DU source geometries.

Two additional 1-D models were created to compare the emission of one DU plate with that of 

two DU plates and a 4.5 kg DU sphere. The calculated count rate for the two DU plates was 1.2 

cps and for the 4.5 kg DU sphere was 0.756 cps, see Figure 20.

Figure 20: DU plate measurement graphed together with GADRAS 1-D models for two DU plates and one sphere

The DU, HEU and WGPu sources used by ORNL were measured using an HPGe detector. The 

gamma-ray emission rate and the testing distance to obtain the RIIDs TCS fluence rates were 

calculated using the measured HPGe full-energy-peak efficiency, results are shown in Table 13.

This table also shows the fluence rate produce by the sources at a distance of 1 m. These sources 

are going to be used in the future by ORNL to measure the BRD response under different test 

conditions specified in the TCSs.

A 1-Dimensional model (1-D model) was created for the sources specified in the DNDO 

traceability memo using GADRAS. From the model for each of the sources the emission rate and 

the expected testing distances for the RIIDs TCS fluence rates were calculated. For these 

calculations, GADRAS makes use of the following densities for uranium and plutonium: 

uranium - 18.95 g/cm3, and plutonium (delta) - 15.75 g/cm3. In addition calculated values 

 HEU #2 NTS 75cm 300s Jan 25 2012 live-time(s) = 300.00 

 Energy (keV) 

 200 400 600 800 1000 1200 

 Counts / keV 

1 00

1 01

1 02

1 03

1 04

1 05

- Measurement NIST source

- Calculation of DU 630 g slab (103 cm

2

)

- Calculation of DU 1.2 kg slab (200 cm

2

)

- Calculation of DU 4.5 kg sphere
28

provided by Los Alamos National Laboratory (LANL) are reported. These calculations used a 

density for uranium of 18.861 g/cm3and for plutonium of 16.9 g/cm3. Results are shown in 

Table 14. The difference between the calculated LANL and GADRAS emission rate values are 

within 9 %, that is within the ± 12 % estimated uncertainty of the GADRAS calculations. 

Table 13: Emission rate calculations for ORNL sources

ORNL 

Source

Energy 

(keV)

Emission rate 

(gammas/s)

unc (%) 

(k=1)

Fluence rate 

(photons/s/cm2) 

at 1 m

Fluence rate 

(photons/s/cm2) 

RIIDs TCS 

requirement

Testing 

Distance 

(cm)

DU 1 plate 1001 4.15 × 1047.0 0.33 0.22 123

3.9 29

DU 4 plates 1001 1.69 × 1053.0 1.35 0.22 247

3.9 59

HEU 186 5.66 × 1052.0 4.50 0.68 257

1.6 169

WGPu 414 5.50 × 1049.0 0.47 1.1 52

3.8 28

WGPu 

shielded 

5 mm steel

414 3.90E× 1044.0 0.31

1.1 53

3.8 29

Table 14: Emission rates and distance calculations for the RIIDs TCS fluence rates for traceability memo sources

Traceability Memo 

Sources

Energy 

(keV)

GADRAS 

calculated 

emission rate 

(gammas/s)

LANL calculated 

emission rate 

(gammas/s)

Emission rate 

(gammas/s) Distance (m)

1 kg HEU 186 4.70 × 1054.62 × 1050.68 2.35

1.6 1.53

400 g WGPu (delta) 414 1.15 × 1061.06 × 1061.1 2.89

3.8 1.55

Measurements were performed using 57Co and 133Ba as simulants for the HEU and WGPu 

sources. The 57Co and 133Ba sources were producing a fluence rate of 0.68 photons/s/cm2and 1.1 

photons/s/cm2 respectively. These sources were used to test the BRD-2 and BRD-3. These 

fluence rate values are consistent with the HEU and WGPu Conveyances/Pedestrians Category

requirements in the RIIDs TCS. For these measurements the following sources were used:

 677 kBq (18.3 μCi ± 5 %, 1-standard deviation) 57Co source placed at a distance of 

2.62 m from the reference point of the BRD

 507 kBq (13.7 μCi ± 5 %, 1-standard deviation) 133Ba source placed at a distance of 

2.22 m from the reference point of the BRD.

Static measurements were also performed using 57Co and 133Ba producing a fluence rate of 

0.18 photons/s/cm2and 0.3 photons/s/cm2 respectively using BRD-1 and BRD-2. These fluence 

rate values match the HEU and WGPu Containerized Cargo Category requirements in the RIIDs 
29

TCS. For these measurements the same 57Co and 133Ba sources were used, placed at a distance of 

4.3m and 4.2 m from the BRD respectively.

The sources were moved passed the BRD at a speed of 1.2 m/s and 2.2 m/s without the presence 

of a phantom for total of 10 trials for each source and speed. The background count rate as 

measured by the BRD was approximately 230 cps. The results of the measurements are 

summarized in Table 15 and Table 16. In Table 15 the number in parenthesis next to the 

radionuclides identified represents the number of trials for which this identification as displayed 

by the BRD. The results of the static measurement using the BRD-1 and BRD-2 are summarized 

in Table 17 and Table 18. For the static measurements the radionuclides recorded were those 

displayed by the BRD in the main screen (automatically updated radionuclide identification). 

From these measurements it can be observed that sources producing these fluence rates are close 

to the limit of detection and identification for the BRDs.

Table 15: Results of BRD-2 dynamic measurements for 57Co and 133Ba source

Source Distance 

(m)

Speed 

(m/s)

Phantom 

(Y/N)

Average net

gamma-ray

count rate (cps)

Std dev 

(%)

Average 

gammaray level

Radionuclides 

Identified

133Ba 2.22 1.2 N 85.7 2.68 2.9 Ba-133 (6), No ID (4)

133Ba 2.22 2.2 N 70.6 2.65 2.7 Ba-133 (2), No ID (8)

57Co 2.62 1.2 N 50 2.21 3 Co-57 (10)

57Co 2.62 2.2 N 42.3 3.44 2 Co-57 (8), No ID (2)

Uncertainties are 1-standard deviation.

Table 16: Results of BRD-3 dynamic measurements for 57Co and 133Ba source

Source Distance 

(m)

Speed 

(m/s)

Phantom 

(Y/N)

Number of 

gamma-ray

alarms

Average gammaray level

133Ba 2.22 1.2 N 5 NA

133Ba 2.22 2.2 N 4 NA

57Co 2.62 1.2 N 1 NA

57Co 2.62 2.2 N 0 NA

Table 17: Results of BRD-1 static measurements for 57Co and 133Ba source

Source Distance 

(m)

Speed 

(m/s)

Net average 

gamma-ray

count rate (cps)

Std dev 

(%)

BRD average 

gamma-ray

level

133Ba 4.2 0 27 33 1

57Co 4.3 0 16 35 1

Uncertainties are 1-standard deviation.

 
30

Table 18: Results of BRD-2 static measurements for 57Co and 133Ba source

Source Distance 

(m)

Speed 

(m/s)

Net average 

gamma-ray

count rate (cps)

Std dev 

(%)

BRD average 

gamma-ray

level

Radionuclides Identified

133Ba 2.22 0 127.6 3 4.5 Ba-133 Ind 100, K-40 Norm 97.

57Co 2.62 0 71.9 10 3.5 K-40 Norm 99, Co-57 Ind 93.

133Ba 4.2 0 56 5 1.5 Ba-133 (display intermetent)

57Co 4.3 0 7 15 0.5 Co-57 (display intermetent)

Uncertainties are 1-standard deviation.

The fluence rates specified in the BRD TCS for HEU 0.94 photons/s/cm2, WGPu 

2.3 photons/s/cm2and DU 0.34 photons/s/cm2were also used to test the BRDs. For these 

measurements the following sources were used:

 440 kBq (11.9 μCi ± 5 %, 1-standard deviation) 57Co source placed at a distance of 

1.94 m from the reference point of the BRD

 492 kBq (13.3 μCi ± 5 %, 1-standard deviation) 133Ba source placed at a distance of 

1.55 m from the reference point of the BRD

 DU plate placed at a distance of 1.13 m from the reference point of the BRD

The sources were moved passed the BRD at a speed of 1.2 m/s without the presence of a 

phantom for total of 10 trials for each source and speed. The results of these measurements are 

plotted together with the TCS fluence rate values used for RIIDs testing, see Figure 21 and 

Figure 22. There seems to be an observable variation in the BRD-2 response for the different 

fluence rate values. The results of these measurements for all the BRDs are shown in Figure 23.

From Figure 23 it can be observed that BRD-3 barely alarmed to all 3 sources. The fluence rates 

specified in the BRD TCS for HEU, WGPu and DU are above the detection limits for two of the 

BRDs.
31

Ba-133(1.1p/s/cm2) Co-57(0.68p/s/cm2) DU(0.22p/s/cm2) Ba-133(2.3p/s/cm2) Co-57(0.94p/s/cm2) DU(0.34p/s/cm2)

0

1

2

3

4

5

6

7

8

9

10

Level 5

Level 3

Level 3

Level 3 Level 3

Level 4 Level 4

Level 4

Level 5

Level 2 Level 4

Level 3 Level 2 Level 2 Trial Number

Source

level 1 level 2

level 3 level 4 level 5

57Co (0.68 s-1cm-2)

133Ba (1 s-1cm-2) DU (0.22 s-1cm-2)

133Ba (2.3 s-1cm-2)

57Co (0.94 s-1cm-2) DU (0.34 s-1cm-2)

Level 2

Figure 21: BRD-2 level indication for different fluence rate values without PMMA phantom, source speed 1.2 m/s. The 

fluence rates (in units of photons/s/cm2) are given in parenthesis.

Ba-133(1.1p/s/cm2) Co-57(0.68p/s/cm2) DU(0.22p/s/cm2) Ba-133(2.3p/s/cm2) Co-57(0.94p/s/cm2) DU(0.34p/s/cm2)

1

2

3

4

5

6

7

8

9

10

238U

57Co

57Co 133Ba

133Ba

No ID

No ID

No ID

No ID

133Ba (1 s-1cm-2) Trial Number

Source

 No ID U-238 Co-57 Ba-133

133Ba (1 s-1cm-2)

57Co (0.68 s-1cm-2) DU (0.22 s-1cm-2)

133Ba (2.3 s-1cm-2)

57Co (0.94 s-1cm-2) DU (0.34 s-1cm-2)

No ID

Figure 22: BRD-2 radionuclide identification indication for different fluence rate values without PMMA phantom, source 

speed 1.2 m/s
32

BRD-1 Ba-133 BRD-1 Co-57 BRD-1 DU BRD-2 Ba-133 BRD-2 Co-57 BRD-2 DU BRD-3 Ba-133 BRD-3 Co-57 BRD-3 DU

0

2

4

6

8

10

Level 6

Level 5 Level 5 Level 5

Level 4

Level 4

Level 4 Level 4

Level 4

Level 1

Level 1

Level 1

Level 3

Level 3

Level 3 Trial Number

level 1 level 2 level 3

level 4 level 5 level 6

Level 3

Figure 23: Level indication for the BRD TCS fluence rate values (HEU 0.94 photons/s/cm2, WGPu 2.3 photons/s/cm2and 

DU 0.34 photons/s/cm2) for all the BRDs without PMMA phantom, source speed 1.2 m/s

3.5 Neutron measurement requirements 

The BRD TCS does not include neutron detection as neutron testing is performed in the 

ANSI/IEEE N42.53 standard for BRDs. Discussions took place in the TCS working group 

meetings regarding neutron testing to ensure that the ANSI/IEEE N42.53 requirements are 

sufficient for this type of instruments. The ANSI/IEEE N42.53 requires testing with a 252Cf 

source surrounded by 1 cm steel and 0.5 cm lead that has an emission rate of 20,000 n/s (±20 %, 

1-standard deviation) moving at 1.2 m/s at a distance of 1.5 meters (source to reference point) 

unmoderated and moderated by a 4 cm thick HDPE sphere

The BRD-2 was used to assess the neutron response. The two 252Cf sources listed in Table 1

were used for these measurements. The 2  104neutrons/s 252Cf source was shielded by 1 cm of 

steel, the gamma-ray emission of this source was very low so there was no need to add the lead 

shielding for the neutron tests. While the 4.2  105neutrons/s 252Cf source was considered a bare 

source; it was placed inside a 0.762 mm thick aluminum holder. The sources were placed at the 

same height as the center of the BRD and at 1.5 m from the front face of the BRD. The average 

neutron background at the test location measured using the BRD-2 was 2.7 cps ± 34 %. The 

average neutron background at the same location using the Thermo Eberline ASP 2e neutron 

handheld survey meter was 0.06 cps ± 57 % (integrated over different times ranging from 2 to 6 

min).
33

The large neutron source (4.2  105neutrons/s) was used to determine the BRD-2 neutron count 

rate response as a function of moderator thickness with and without the presence of PMMA 

phantoms, see Figure 24. From this figure it can be observed that the maximum BRD-2 neutron 

response is obtained when the source is moderated by 2 cm or 4 cm thick HDPE spheres when 

the PMMA phantom is located behind the BRD.

The smaller unmoderated neutron source (2  104neutrons/s) was used to determine the BRD-2 

neutron count rate response for different types of phantoms, see Figure 25. From this figure a 

slight increase in response is observed when the PMMA phantom or the water placed in the high 

position (centered in the BRD) is placed behind the BRD-2. The results of these measurements 

are statistically indistinguishable due to the large uncertainties in the measurements. 

Bare 2 cm HDPE 4 cm HDPE 8 cm HDPE 8 cm borated HDPE

0

20

40

60

80

100

120

140

160

 No Phantom With Phantom Neutron Count Rate (cps)

Configuration

Figure 24: Neutron BRD-2 measurements with different moderators with and without the presence of a phantom; 

uncertainties are 1-standard deviation
34

Unmoderated no phantom Unmoderated water low Unmoderated water high Unmoderated PMMA

2.4

2.8

3.2

3.6

4.0

4.4

4.8

5.2 Neutron Count Rate (cps)

Configuration

Figure 25: Unmoderated neutron BRD-2 measurements for different phantoms; uncertainties are 1-standard deviation.

The smaller unmoderated neutron source (2  104neutrons/s) was used to determine the BRD-1, 

BRD-2 and BRD-3 neutron response for different source speeds with different phantoms, results 

are shown in 
35

Table 19 through Table 21 assesses the applicability of the ANSI N42.53 requirements. Ten 

trials were performed for each test condition for each BRD at a distance of 1.5 m from the 

source. The neutron background readings for the different BRDs were as follow:

 For BRD-1 and BRD-2 the neutron background level was equal to 0. For the BRD-1 the 

average neutron background count rate reading was 0.64 cps (±20 %, 1-standard 

deviation).

 For the BRD-3 the neutron background level varied between level 0 and 1. For the BRD3 the average neutron background count rate reading was 3.1 cps (±30 %, 1-standard 

deviation).

The response for the BRD-1 was also obtained for static measurements as this BRD shows a 

gamma-ray response to the neutron source. The static measurements allow the quantification of 

this effect. The results of these measurements are shown inTable 22. From these tables it can be 

observed that the 252Cf source with an emission rate of 2  104neutrons/s is barely detectable by 

all BRDs especially for BRD-2. 
36

Table 19: Neutron dynamic measurement for BRD-1 at 1.5 m for the 2  104neutrons/s source

Speed 

(m/s) Phantom

Number 

of 

gammaray

alarms

Number 

of 

neutron 

alarms

Average 

BRD-1 

gammaray level

Average 

BRD-1 

neutron 

level

Average 

BRD-1 

gamma-ray

net count 

rate (cps)

Unc. (%)

Average 

BRD-1 

neutron 

net count 

rate (cps)

Unc. (%)

1.2 PMMA 3 9 0.6 2.5 37.8 30.5 0.97 22.6

2.2 PMMA 2 9 0.4 2 36.6 31.6 0.87 26.5

1.2 None 2 7 0.2 1.3 28.6 20.1 0.42 20.4

2.2 None 3 8 0 0.9 32.4 21.2 0.41 23.5

Uncertainties are 1-standard deviation.

Table 20: Neutron dynamic measurements for BRD-2 at 1.5 m for the 2  104neutrons/s source

Speed (m/s) Phantom Number of neutron 

alarms BRD-2

1.2 None 1

2.2 None 0

1.2 Water 1

2.2 Water 0

1.2 PMMA 3

2.2 PMMA 3

Table 21: Neutron dynamic measurements for BRD-3 at 1.5 m for the 2  104neutrons/s source

Speed 

(m/s) Phantom

Number of 

gamma-ray

alarms

Number of 

neutron 

alarms

Average 

BRD-3 

gamma-ray

level

Average 

BRD-3 

neutron 

level

Average 

BRD-3

gammaray net 

count 

rate (cps)

Unc.

(%)

Average 

BRD-3

neutron 

net count 

rate (cps)

Unc.

(%)

1.2 PMMA 3 10 0.6 2.2 50.1 4.5 1.2 56

2.2 PMMA 2 10 0.4 1.7 48.0 4.9 1.3 48

1.2 None 0 9 0.0 1.3 56.7 5.0 1.6 34

2.2 None 0 10 0.0 1.3 41.3 5.2 0.7 42

Uncertainties are 1-standard deviation.
37

Table 22: Neutron static measurement for BRD-1 at 1.5 m

Neutron 

emission rate 

(neutrons/s)

Phantom

Average 

BRD-1 

gammaray level

Average 

BRD-1 

neutron 

level

Average 

BRD-1 

gammaray gross 

count rate

(cps)

Unc. (%)

Average 

BRD-1 

neutron 

gross

count rate

(cps)

Unc. (%)

No Source PMMA - - 40 28.67 0.65 10.88

2  104 PMMA 0.5 5.50 53.6 21.17 3.01 23.77

No Source None - - 45.78 23.57 0.8 35.36

2  104 None 1 2.5 60.80 20.05 1.6 22.44

Uncertainties are 1-standard deviation.

4. Conclusions

Summarized below are the conclusions for each of the tests conducted in this study.

 Scaling of source emission with gamma-ray and neutron background measurement at test 

location

From the source scaling measurements it can be observed that the measurements of the gammaray and neutron radiation background have a large uncertainty and the measured value depends 

on the type of instrument used to perform the measurements. This could be an issue if the source 

emission is scaled with the radiation background when testing of BRDs is performed in different 

laboratories.

 BRD response as a function of increasing gamma-ray background level

The background increase measurements show a reduction of the BRD sensitivity with increasing 

gamma-ray dose rate. This issue can be solved by:

a) Reducing the background dose rate range over which testing can occur

b) Having a common instrument to measure background at different test locations allowing 

for scaling of the source emission at different test locations

 Suitability of fluence rate values used for testing BRDs

For the fluence rates specified in the TCS RIIDs Conveyances/Pedestrians Category for HEU 

0.68 photons/s/cm2, WGPu 1.1 photons/s/cm2 and DU 0.22 photons/s/cm2as well as those 

specified in the BRD TCS for HEU 0.94 photons/s/cm2, WGPu 2.3 photons/s/cm2and DU 0.34 

photons/s/cm2 were used to test the BRDs. There seems to be a small variation of the BRD-2 

response when testing with 57Co and 133Ba sources for these different fluence rate values, either 

set of values seem adequate for testing the BRDs. If it is required to be closer to the detection 

limit of the BRDs, the fluence rate values could be further reduced. 
38

The fluence rates specified in the RIIDs Containerized Cargo Category for HEU 0.18 

photons/s/cm2and WGPu 0.3 photons/s/cm2 were also used for testing. These fluence rate values 

are acceptable for use and close to the limit of detection and identification of the BRDs.

The BRDs was able to detect the 90 mg 237Np source bare and shielded by 1 cm of steel at a 2 m 

and a 3 m distance. The radiation detection level was reduced by the presence of the steel 

shielding. For these measurements it was observed that the testing distance for the shielded 237Np 

source can be increased to 3 m or larger if testing requires being closer to the detection limit of 

the BRDs.

 Calculations of emission rates and/or fluence rate for SNM and DU sources

From the SNM and DU measurements and calculations it can be observed that the GADRAS 

1D-model is a useful tool to determine the emission rate of an unknown source with an 

uncertainty of approximately ±12 %. 

 Neutron measurement requirements

From the neutron test results it can be observed that the 252Cf source emission specified in the 

ANSI/IEEE N42.53 standard is close to the limit of detection for the BRDs used in these tests. 

The addition of moderator to the 252Cf source increases the probability of detection for the BRD. 

The use of phantoms increases the probability of detection for the BRD. The presence of a 

phantom is required to mimic the presence of a human body. There seems to be a small variation 

in response depending on the type of phantom used for testing. It is important to define the 

material and dimensions of the phantom used for testing in order to have reproducible results at 

different test locations.

5. Acknowledgments

The authors would like to thank the Department of Homeland Security (DHS) Domestic Nuclear 

Detection Office (DNDO) for funding this work. The authors would also like to thank Mr. Jason 

Combs from Oak Ridge National Laboratory for providing the gamma-ray energy spectra for 

some of their sources. The authors would also like to thank Dr. Ronaldo Minniti from NIST for 

providing the information on the radiation background measurements using several ionization 

chambers. 

6. References

1. ANSI/IEEE N42.53 American National Standard Performance Criteria for Backpack 

Based Radiation Detection Systems Used for Homeland Security

2. Technical Capability Standard for Handheld Instruments Used for the Detection and 

Identification of Radionuclides, Document Number: 500-DNDO-117250v0.00 (2011),

http://www.dhs.gov/xlibrary/assets/dndo/dndo-technical-capability-standard-forhandheld-final.pdf
39

3. Technical Capability Standards, Traceability Memo, September 2012, Document Number 

500-DNDO-119600v1.1

4. ANSI/IEEE N42.43 American National Standard Performance Criteria for Mobile and 

Transportable Radiation Monitors Used for Homeland Security

5. L. Pibida. “Measurements for the Development of a Simulated Naturally Occurring 

Radioactive Material” Journal of Research of the National Institute of Standards and 

Technology, Volume 117 (2012) (http://dx.doi.org/10.6028/jres.117.008)

6. Laboratoire National Henri Becquerel (LNHB), Recommended Data, 

http://www.nucleide.org/DDEP_WG/DDEPdata.htm

7. The physics of radiology, 4th Edition, Publisher Charles C. Thomas. Authors: Harold 

Elford Johns and John Robert Cunningham.