NIST Technical Note 1800 

Test Report - Exposure and 

Ambient Dose Equivalent Rate 

Measurements in Support of the 

ITRAP+10 Testing 

L. Pibida 

R. Minniti 

M. O’Brien 

L. Lucas 

 

 
NIST Technical Note 1800 

Test Report - Exposure and 

Ambient Dose Equivalent Rate 

Measurements in Support of the 

ITRAP+10 Testing 

L. Pibida 

R. Minniti 

M. O’Brien 

L. Lucas 

Radiation and Biomolecular Physics Division 

Physical Measurement Laboratory

May 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 1800 

Natl. Inst. Stand. Technol. Tech. Note 1800, 27 pages (May 2013) 

CODEN: NTNOEF 
1

Test Report - Exposure and Ambient Dose Equivalent Rate 

Measurements in Support of the ITRAP+10 Testing

L. Pibida, R. Minniti, M. O’Brien, and L. Lucas 

National Institute of Standards and Technology, 100 Bureau Dr, Gaithersburg, MD 20899-8462 

Abstract 

In this work we studied the response of two different Victoreen® instruments as a 

function of the exposure rate, the instrument orientation and photon energy. The rate 

dependence for both instruments is of the order of 8 % over the range of exposure rates 

tested (0.5 mR/h to 1000 mR/h). Regarding the instrument orientation dependence 

investigation, a significant difference is observed between the two instruments. While the 

Victoreen® 451P shows no significant dependence with instrument orientation, the 

Victoreen® 451P-DE-SI shows a significant dependence of up to 20 % between the three 

different orientations. Finally, the energy dependence measurements of both instruments 

reveal that the instruments measure lower exposure rate values compared to the reference 

values for the low energy x-rays by about 20 %. While, for the 60Co gamma-ray beam 

measurements, both instruments are about 5 % higher than the reference value. 

Key words: 

exposure rate, ambient dose equivalent rate, ITRAP+10 testing, Victoreen 451P, Victoreen 451P-DE-SI

Introduction 

The US Department of Homeland Security (DHS) Domestic Nuclear Detection Office 

(DNDO) requested the National Institute of Standards and Technology (NIST) to perform 

a set of measurements to validate exposure rate and ambient dose equivalent rate 

measurements performed during the Illicit Trafficking Radiation Assessment Program 

(ITRAP+10) testing program. 

The ITRAP+10 is a program initiated by the European Union (EU) that carried out an 

evaluation of commercial available radiation detection equipment against published 

consensus standards. The standards used for testing included those published by the 

American National Standard Institute/ Institute of Electrical and Electronics Engineers 

(ANSI/IEEE) and the International Electrotechnical Commission (IEC). The European 

Commission's (EC) Joint Research Center (JRC), and DNDO agreed to collaborate in 

conducting the ITRAP+10 test campaign and sharing the design of the tests, their 

execution, the data, and the analysis of the data. Testing was carried out at the JRC and 

several DOE National Laboratories. There were nine different categories of instruments 

tested under the ITRAP+10 program, these included: 

 Personal Radiation Detectors (PRDs) 

 Spectroscopic Personal Radiation Detectors (SPRDs) 
2

 Backpack-type Radiation Detectors (BRDs) 

 Radiation Isotope Identification Device (RIIDs) 

 Radiation Portal Monitor (RPMs) 

 Spectroscopic Radiation Portal Monitor (SRPMs) 

 Mobile Systems 

 Neutron Search Devices (NSDs) 

 Gamma Search Devices (GSDs) 

Testing of the PRDs took place at the JRC and at the Savannah River National 

Laboratory (SRNL). Several tests defined in the ITRAP+10 test methods, based on the 

ANSI/IEEE and IEC standards, require determining the ambient dose equivalent rate 

produced by 241Am (or x-rays), 137Cs and 60Co sources. For determining the radiation 

fields, the JRC used a Victoreen®

 451P-DE-SI1 pressurized ionization chamber and 

SRNL used a Victoreen® 451P. The Victoreen® 451P is a pressurized ionization chamber 

instrument calibrated in exposure rate units of roentgens/hour 2

 for gamma-ray and x- ray 

radiation in the energy range of 20 keV to 2 MeV with a case built of high strength 

plastic. The Victoreen® 451P-DE-SI is a similar pressurized ionization chamber 

instrument calibrated in terms of the ambient dose equivalent rate ( ̇

 

 )) in units of 

sieverts/hour for the same energy range of gamma-ray and x- ray radiation. The energy 

and angular response of these two Victoreen® models is different, see instrument manual 

[1]. The Victoreen® 451P used at SRNL was calibrated in a 137Cs beam and the 

Victoreen® 451P-DE-SI used at the JRC was calibrated in an x-ray (L2 beam quality), 

137Cs and 60Co beams.

Due to differences observed in the PRD test results during the ITRAP+10, DNDO 

requested NIST to perform several measurements using a Victoreen® 451P-DE-SI and a 

Victoreen® 451P to assess the differences in the instrument radiation response as a 

function the exposure rate, instrument orientation and gamma-ray and x-ray energy. The 

results of these measurements are summarized here. 

Test facilities and experimental setup 

Four different NIST primary measurement facilities, see Figure 1, were used to perform 

the proposed measurements; two deliver low and high intensity 137Cs gamma-ray 

reference beams while the other two facilities deliver 60Co gamma-ray and x-ray beams 

[3, 4]. 

The NIST primary reference beams provide a well-defined value of air-kerma rate (in 

units of Gy/s) and exposure rate (in units of R/s) at a given point in space. The 

uncertainties of the exposure rate values delivered by these reference beams are well 

 

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

 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. 
3

known and have values of less than 0.5 %. The following exposure rates can be obtained 

in the different measurement facilities: 



137Cs lower intensity reference beams 

- 500 μR/h to 1 mR/h 

- 5 mR/h to 15 mR/h 

- 90 mR/h to 300 mR/h 



137Cs higher intensity reference beam – 500 mR/h to 10 R/h 



60Co reference beam – 52 mR/h to 120 mR/h 

 x-ray reference beam depends on the beam quality 

- NS80 (corresponds to the N80 ISO 4037 beam with a mean energy of 

65 keV) – greater than 127 mR/h 

- WS80 (corresponds to the L2 beam used by the JRC and the W80 ISO 

4037 beam with a mean energy of 57 keV) – greater than 370 mR/h 

Additional measurements using an 241Am source, with a gamma-ray emission rate of 4.11 

× 107 gammas/s (± 5%), were performed by placing the source at a distance of 1 m from 

the reference point of the Victoreen® 451P and the Victoreen® 451P-DE-SI respectively. 

As there is no air-kerma or exposure rate primary standard in the U.S. for 241Am, there is 

no reference exposure rate value available for these measurements. These measurements 

can be used to obtain the relative response of the Victoreen® 451P and the Victoreen®

451P-DE-SI in the three measurement orientations (front, right side, and left side). 

The reference point marked on the instrument was aligned at the point in space where the 

air-kerma rate value is defined. The Victoreen® 451P was placed free in air at the point in 

space where the exposure rate field has the required value, see Figure 2. The Victoreen®

451P was mounted on an aluminum stand in order to reduce scattering. An aligning laser 

system was used to position the Victoreen®451P. 

The Victoreen® 451P was placed in the reference beam in three different orientations 

with the front, right and left side of the instrument facing the source as shown in Figure 2.

For each orientation of the instrument, three independent sets of data were recorded. 

Each set was composed of 30 exposure rate readings. In order to obtain the three 

independent measurement sets, the Victoreen® 451P was removed and placed back at the 

measurement point three times. For each set, the recording of the exposure rate readings 

was started 30 s after the source shutter was opened (source exposed). This 30 s delay 

time between the time the shutter is opened and the recording of data was to allow the 

Victoreen® 451P instruments to reach a stable value (settling time). These measurements 

were repeated for the Victoreen® 451P-DE-SI (serial number 3500). For some of the 

measurements two different Victoreen® 451P units were used (serial number 3796 and 

2396) in order to check for reproducibility in the instrument response. 

The maximum exposure rate that the Victoreen® 451P can measure is 5 R/h and the 

maximum ambient dose equivalent rate that the Victoreen® 451P-DE-SI can measure is 

50 mSv/h [1], so the exposure rates selected for the measurements were kept below 5 

R/h. The cut-off energy of the instruments is 25 keV. 
4

In order to cover several of the instrument exposure rate ranges, NIST performed the 

measurements at the following exposure and air-kerma rate values: 



137Cs – 500 μR/h (4.390 μGy/h), 15 mR/h (131.7 μGy/h), 100 mR/h 

(0.878 mGy/h), 500.3 mR/h (4.391 mGy/h), and 1 R/h (8.784 mGy/h) 



60Co – 100.3 mR/h (0.822 mGy/h) 

 x-ray beam NS80 – 142.9 mR/h (1.253 mGy/h) at 3 m, 129.1 mR/h (1.118 

mGy/h) at 2 m, and 517.8 mR/h (4.538 mGy/h) at 2 m 

 x-ray beam WS80 –approximately 482.4 mR/h (4.248 mGy/h) at 3 m 

The mean energy for the NS80 and the WS80 x-ray beams are 65 keV and 57 keV 

respectively. 

Figure 1: NIST reference beams: (a) 137Cs, (b) 60Co, (c) x-ray measurement facilities 
5

Figure 2: Shown are the reference points of the Victoreen® 451P and orientations 

Data analysis 

The average and standard deviation for the 30 readings for each measurement set was 

calculated. The three independent measurements were combined to obtain the Victoreen®

451P instrument average response for each orientation and beam and/or beam code. The 

Victoreen® 451P instrument response was compared to the actual value of the exposure 

rate delivered by the reference field, then the percent difference to the reference value 

was calculated for each beam and Victoreen® 451P orientation (front, right side and left 

side). This procedure was repeated for the Victoreen®451P-DE-SI. 

The following conversion coefficients obtained from [3] were applied to the Victoreen®

451P-DE-SI readings in order to convert ambient dose equivalent rate to air-kerma rate 

and exposure rate to air-kerma: 

 For 137Cs – 1.20 Sv/Gy and 113.92 R/Gy 

 For 60Co – 1.16 Sv/Gy and 113.74 R/Gy 

 For 241Am – 1.74 Sv/Gy and 114.10 R/Gy

 For NS80 (N80 ISO 4037) x-ray beam – 1.73 Sv/Gy and 114.10 R/Gy 

 For WS80 (W80 ISO 4037) x-ray beam – 1.66 Sv/Gy and 114.10 R/Gy 

For the 241Am measurements of the exposure rate and ambient dose equivalent rate values 

were plotted as a function of the instrument orientation. The ambient dose equivalent rate 

values of the Victoreen® 451P-DE-SI were converted to exposure rate for the comparison 

of instrument response. The exposure rate produced by the 241Am could be calculated 

using exposure rate constants. The problem with this approach is the large discrepancies 

found among the published constants [5, 7, 9, 11, 12 and 13]. The exposure rate constant 

calculated using different methods at 1 m are listed in Table 1. The calculations in 

references [11 and 12] use a cut-off energy of 1 keV, the same value used in the Monte 

Carlo calculation performed using MCNPX by references [7, 9 and 10]. The difference 
6

between the two MCNPX (LNHB) and MCNPX (NBL) exposure rate constant 

calculations are the values used for the gamma-ray emission probabilities for the different 

241Am photon energies. The first one makes use of the values listed in reference [10] and 

the other in reference [9]. 

Table 1: List of calculated exposure rate constants 

Exposure rate constant (R m2/h/Ci)

Point 

source 

estimate 

cut-off 

energy 

1 keV

[5, 9]

Point 

source 

estimate 

cut-off 

energy 

25 keV

[5, 9]

Point 

source 

estimate 

cut-off 

energy 

40 keV

[5, 9]

MCNPX 

(LNHB) 

[7, 10]

MCNPX 

(NBL)

[7, 9]

Smith et 

al.

[11]

Seltzer

[13]

Rad Pro 

calculator

[12]

0.0925 0.01797 0.0155 0.1189 0.097 0.0749 0.0962 0.0166

The calculated exposure rate for the 241Am source using the different exposure rate 

constant values listed in Table 1 at 1 m are shown in Table 2. Based on this large 

variation observed between the different calculated values it is not possible to compare 

the instruments measured with a reference exposure rate value. 

Table 2: Calculate exposure rates for the 241Am source at a 1 m distance 

Exposure rate at 1 m (R/h)

Point 

source 

estimate 

cut-off 

energy 

1 keV

[5, 9]

Point 

source 

estimate 

cut-off 

energy 

25 keV

[5, 9]

Point 

source 

estimate 

cut-off 

energy 

40 keV

[5, 9]

MCNPX 

(LNHB) 

[7, 10]

MCNPX 

(NBL)

[7, 9]

Smith et 

al.

[11]

Seltzer

[13]

Rad Pro 

calculator

[12]

287 55.8 48.1 369 301 233 299 51.6

It is important to note that when setting an ambient dose equivalent rate field (Sv/h) with 

an instrument that measures exposure rate (R/h) the right conversion coefficient shall be 

used in the field determination. The same is true when trying to set up an exposure rate 

field (R/h) with an instrument that measures ambient dose equivalent rate (Sv/h). 

The percent difference between the instrument mean reading and the NIST reference 

exposure rate value was calculated for each beam quality and instrument orientation. A 

calibration factor for the 500 mR/h 137Cs beam for each instrument orientation was 

determined as the ratio between the NIST reference exposure rate value and the 

instrument mean reading. The calibration factor can be applied to the instrument readings 

for the other beam qualities in order to normalize the reading to a reference value. 
7

Measurement results 

The Victoreen® 451P and the Victoreen® 451P-DE-SI readings were monitored 

beginning at the start of the exposure in order to establish the time at which the readings 

became stable. For all beams it took approximately 5 seconds to reach a stable reading. 

The x-ray beam measurements were repeated on two different days and the results for 

both instruments, the Victoreen® 451P and the Victoreen® 451P-DE-SI, are summarized 

in Table 3. For the Victoreen® 451P two different units were used on each day. The 137Cs 

measurements are summarized in Table 4. The 60Co measurements are summarized in 

Table 5. As described previously, each exposure rate shown in the Table corresponds to 

the average of three sets of measurements, where each set was composed of a total of 30 

readings. 

The Victoreen®

451P and the Victoreen®451P-DE-SI are normally used as survey meters 

for health physics applications. These types of instruments are only required to be 

calibrated in a 137Cs reference field at different exposure rates. In this work we calibrated 

the Victoreen®451P and the Victoreen®451P-DE-SI instruments in the x-ray (NS80 and 

WS80 beam qualities) 137Cs and 60Co reference beams. The measured calibration factors 

obtained in each one of these reference fields are listed in Table 6, Table 7 and
8

Table 8 for the 137Cs and 60Co reference beams and in Table 9, Table 10 and Table 11 for 

the x-ray reference beams. 

The paragraphs below summarize the results obtained from studying the response of 

these instruments as a function of exposure rate, instrument orientation and beam energy. 

The measured exposure rate dependence is shown in Figures 3 and 4 for the 137Cs beam 

and Figures 5 and 7 for the x-ray beam. The exposure rate dependence for each radiation 

beam (137Cs and NS80 x-rays) is also presented for each of the three possible instrument 

orientations: front, right and left. For the measurements presented in Figures 3 and 4, the 

calibration factor used for both Victoreen instruments was the one obtained at an 

exposure rate of 500 mR/h in the 137Cs reference beam. From these figures it can be 

observed that there is approximately an 8 % variation in the response of both the 

Victoreen®451P and Victoreen®451P-DE-SI for exposure rates between 500 μR/h and 

1 R/h for 137Cs. For the x-ray measurement results presented in Figure 5 and Figure 6, the 

calibration factor used for both Victoreen instruments was the one obtained in the NS80 

x-ray reference beam at a distance of 2 m using the exposure rate value of approximately 

500 mR/h. This data point is referred to in Figures 5 and 6 as the 2 m High Rate setting. 

From these figures it can be observed that there is approximately a 5 % variation in the 

response of both the Victoreen®

451P (for both serial numbers) and Victoreen®451PDE-SI for exposure rates between 100 mR/h and 500 mR/h for the 2 m and 3 m 

measurement distances for the NS80 beam code. The WS80 beam code was performed 

at a single rate of 500 mR/h at a distance of 3 m; from these figures a difference of 

approximately 7 % can be observed between the NS80 and WS80 beam qualities for the 

Victoreen®

451P (for both serial numbers). For the Victoreen®451P-DE-SI the 

difference in response between the NS80 and WS80 beam codes varies between -10 % 

and 2 % depending on the instrument orientation. 

The dependence of the instrument response as a function of the instrument orientation 

(front, right and left) was also investigated. The results are summarized in Figures 7 and 

8 for the Victoreen 451P and 451P-DE-SI detectors respectively. The orientation 

dependence was obtained in the NS80 and WS80 x-ray, 137Cs and 60Co reference beams. 

The calibration factor for each of the instruments used for the measurement results 

presented in Figures 7 and 8 was the one obtained in the 137Cs reference beam at the 

measured exposure rates of 100 mR/h and 500 mR/h. The 137Cs calibration factor of 

100 mR/h was used for the measurements made in the NS80 x-ray, 137Cs, and 60Co beams 

that delivered rates of 100 mR/h (shown as solid symbols in Figures 7 and 8) on the 

instruments. The 137Cs calibration factor of 500 mR/h was used for the measurements 

made in the 137Cs, WS80 and NS80 x-ray beams that delivered exposure rates of 500 

mR/h (shown as hollow symbols in Figures 7 and 8). The data point for the NS80 x-ray 

shown in Figures 7 and 8 corresponds to the average of the instrument readings over all 

measured distances (2 m and 3 m). Figure 7 indicates that there is a small dependence 

with the instrument orientation for the case of the Victoreen® 451P. The variation 

observed between all three orientations is within 1 %. However the dependence of the 

instrument orientation for the variation observed for the Victoreen® 451P-DE-SI is quite 

significant and it is dependent on the beam quality or beam energy. For example, Figure 
9

8 shows clearly that the readings obtained using the Front orientation are about 20% 

lower than those obtained when the detector faces the source sideways (Right or Left 

orientation). Similarly, the measurements made in the NS80 beam also show a strong 

orientation dependence. The detector readings obtained with the front of the detector 

facing the source are 15 % lower in value than those obtained with the detector facing 

sideways (Right or Left orientations). 

The energy dependence for the Victoreen® 451P (serial number 2396) and the Victoreen®

451P-DE-SI detectors at two different exposure rates of 100 mR/h and 500 mR/h are 

shown in Figure 9. At each exposure rate and orientation the calibration factor used was 

obtained for the 137Cs reference beam. The x-ray beam measurements average over all 

measured distances. From this figure it can be observed that for the Victoreen® 451P-DESI the response drops with energy, and a larger variation is observed when measurements 

are performed from the front. For the Victoreen® 451P there is a similar energy variation 

but the differences between the front and the sides are smaller. 

In order to assess the possible differences in the Victoreen® 451P or Victoreen® 451PDE-SI response due to instrument volume, x-ray measurements were performed at the 

high exposure rate value at 1 m and 2 m from the source, see Figure 10. From this figure 

it can be observed that, as expected, the response from the side at 1 m is much lower (6 % 

to 8 %) than the response measured from the front (2 %). This is due to the large volume 

presented by the instrument when measuring from the side. 

The 241Am measurements are summarized in Figure 11. After applying the conversion 

coefficient (from Sv to R) to the Victoreen® 451P-DE-SI ambient dose equivalent rate 

readings it can be observed that there is no difference in response for the Victoreen®

451P or Victoreen® 451P-DE-SI within the measured uncertainty. Still the difference in 

response for the Victoreen® 451P-DE-SI between the front and side orientations is larger 

than for the Victoreen®

451P. 
10

Front Right Left -5

0

5

10

15

451P

 500 uR/h Cs-137 15 mR/h Cs-137 100 mR/h Cs-137

 500 mR/h Cs-137 1R/h Cs-137 Percent difference from reference value (%) 

Orientation

Figure 3: Rate dependence for the 451P (serial number 2396) detector for the 137Cs reference beams. At each 

exposure rate and orientation the calibration factor used was obtained at the 500 mR/h for the 137Cs reference 

beam. Uncertainties are one standard deviation.
11

Front Right Left -5

0

5

10

15

451P-DE-SI

 500 uR/h Cs-137 15 mR/h Cs-137 100 mR/h Cs-137

 500 mR/h Cs-137 1R/h Cs-137 Percent difference from reference value (%) 

Orientation

Figure 4: Rate dependence for the 451P-DE-SI detector for the 137Cs reference beams. At each exposure rate and 

orientation the calibration factor used was obtained at the 500 mR/h for the 137Cs reference beam. Uncertainties 

are one standard deviation.
12

Front Right side Left side

-10

-5

0

5

10

451P SN 3796 (D1) & 2396 (D2)

 NS80 2m Low D1 NS80 3m Low D1 NS80 2m High D1 WS80 3m High D1

 NS80 2m Low D2 NS80 3m Low D2 NS80 2m High D2 WS80 3m High D2 Percent difference from reference value (%)

Orientation

Figure 5: Rate dependence for the 451P detector for the x-ray reference beams. At each exposure rate and 

orientation the calibration factor used was obtained at the 2 m High (500 mR/h) for the x-ray reference beam. 

The solid symbols represent the unit with serial number 3796 and the open symbols for the serial number 2396. 

Uncertainties are one standard deviation. 
13

Front Right side Left side

-15

-10

-5

0

5

10

451P-DE-SI SN 3500

 NS80 2m High NS80 2m Low NS80 3m Low

 WS80 3m High Percent difference from reference value (%)

Orientation

Figure 6: Rate dependence for the 451P-DE-SI detector for the x-ray reference beams. At each exposure rate 

and orientation the calibration factor used was obtained at the 2 m High (482.4 mR/h) for the x-ray reference 

beam. The values are the average between the two day measurements. Uncertainties are one standard deviation.
14

Front Right side Left side

-20

-15

-10

-5

0

5

451P

 100 mR/h Cs-137 100 mR/h NS80 100 mR/h Co-60

 500 mR/h Cs-137 500 mR/h NS80 500 mR/h WS80 Percent difference from reference value (%) 

Orientation

Figure 7: Orientation dependence for the 451P (serial number 2396) detector at two different exposure rates of 

approximately 100 mR/h and 500 mR/h. At each exposure rate and orientation the calibration factor used was 

obtained for the 137Cs reference beam. The x-ray beam measurements average over all measured distance. 

Uncertainties are one standard deviation. 
15

Front Right side Left side

-25

-20

-15

-10

-5

0

5

10

451P-DE-SI

 100 mR/h Cs-137 100 mR/h NS80 100 mR/h Co-60

 500 mR/h Cs-137 500 mR/h NS80 500 mR/h WS80 Percent difference from reference value (%) 

Orientation

 Figure 8: Orientation dependence for the 451P-DE-SI detector at two different exposure rates of approximately 

100 mR/h and 500 mR/h. At each exposure rate and orientation the calibration factor used was obtained for the 

137Cs reference beam. The x-ray beam measurements averaged over all measured distances. Uncertainties are 

one standard deviation. 
16

-20

-10

0

WS80 NS80 Cs-137 Co-60

-15

-10

-5

0

5

 451P Front 451P Right 451P Left

 451P-DE-SI Front 451P-DE-SI Right 451P-DE-SI Left Percent difference from reference value (%) High rate 500 mR/h

Low rate 100 mR/h Beam code

Figure 9: Beam energy dependence for the 451P (serial number 2396) and the 451P-DE-SI detectors at two 

different exposure rates of approximately 100 mR/h and 500 mR/h. At each exposure rate and orientation the 

calibration factor used was obtained for the 137Cs reference beam. The x-ray beam measurements averaged over 

all measured distances. Uncertainties are one standard deviation.
17

NS80 2m LowNS80 3m LowNS80 2m HighNS80 1m HighWS80 3m High

-15

-10

-5

0

5

10

 451P Front 451P Right 451P Left

 451P-DE-SI Front 451P-DE-S Right 451P-DE-S Left Percent difference from reference value (%)

Beam code

Figure 10: Comparison of the measured percent difference from reference value for the 451P and 451P-DE-SI 

instruments with measurements obtained using a NIST ionization chamber. At each exposure rate and 

orientation the calibration factor used was obtained at the 2 m High (482.4 mR/h) for the x-ray reference beam. 

Uncertainties are one standard deviation. 
18

Front Right side Left side

26

28

30

32

34

36

38

40

42

44

46

48

50

 451P-DE-SI 451P Exposure rate (R/h)

Orientation

Figure 11: Measured exposure rate value for the 451P and 451P-DE-SI instruments as a function of the 

instrument orientation for 241Am source. The red circles represent the results for the 451P and the black squares 

represent the results for the 451P-DE-SI instrument. Uncertainties are one standard deviation. 
19

Table 3: Summary of the 451P and 451P-DE-SI instrument background subtracted readings for the different xray beam configurations without applying the conversion coefficient (Sv/Gy) and the 137Cs calibration factor 

X-ray beam 

configuration

Reference 

beam 

exposure and 

air-kerma 

rates

Victoreen®451P Victoreen®451P-DE-SI

Average 

exposure rate 

readings

(mR/h)

Standard 

deviation

(%)

Average 

ambient dose 

rate readings 

(mSv/h)

Standard 

deviation

(%)

Front - First day Victoreen®451P SN: 3796

NS80 2 m Low 127.6 mR/h or 

1.118 mGy/h 

(± 0.57 %)

99.98 0.05 1.56 0.07

NS80 3 m Low 142.9 mR/h or 

1.253 mGy/h 

(± 0.37 %)

107.88 0.08 1.69 0.02

NS80 2 m High 517.8 mR/h or 

4.538 mGy/h 

(± 0.45 %)

390.33 0.00 6.12 0.41

WS80 3 m High 482.4 mR/h or 

4.248 mGy/h 

(± 0.5 %)

339.99 0.00 4.91 1.24

Right side- First day Victoreen®451P SN: 3796

NS80 2 m Low 127.6 μR/h or 

1.118 mGy/h 

(± 0.57 %)

108.59 0.12 1.86 0.16

NS80 3 m Low 142.9 μR/h or 

1.253 mGy/h 

(± 0.37 %)

117.02 0.40 2.00 0.04

NS80 2 m High 517.8 mR/h or 

4.538 mGy/h 

(± 0.45 %)

421.88 0.33 7.30 0.18

WS80 3 m High 482.4 mR/h or 

4.248 mGy/h 

(± 0.5 %)

370.00 0.00 6.44 0.71

Left side - First day Victoreen®451P SN: 3796

NS80 2 m Low 127.6 μR/h or 

1.118 mGy/h 

(± 0.57 %)

104.41 0.24 1.87 0.22

NS80 3 m Low 142.9 μR/h or 

1.253 mGy/h 

(± 0.37 %)

113.42 0.16 2.00 0.06

NS80 2 m High 517.8 mR/h or 

4.538 mGy/h 

(± 0.45 %)

409.87 0.09 7.14 1.20

WS80 3 m High 482.4 mR/h or 

4.248 mGy/h 

(± 0.5 %)

359.99 0.00 6.41 1.54

Front - Second day Victoreen®451P SN: 2396
20

X-ray beam 

configuration

Reference 

beam 

exposure and 

air-kerma 

rates

Victoreen®451P Victoreen®451P-DE-SI

Average 

exposure rate 

readings

(mR/h)

Standard 

deviation

(%)

Average 

ambient dose 

rate readings 

(mSv/h)

Standard 

deviation

(%)

NS80 2 m Low 129.8 mR/h or

1.138 mGy/h 

(± 1.13 %)

100.13 0.73 1.56 0.58

NS80 3 m Low 138.2 mR/h or

1.211 mGy/h 

(± 0.76 %)

107.79 0.82 1.69 0.67

NS80 2 m High 519.6 mR/h or 

4.553 mGy/h 

(± 0.15 %)

390.00 0.00 6.14 0.81

WS80 3 m High 482.0 mR/h or 

4.225 mGy/h 

(± 0.16 %)

340.00 0.00 4.95 1.38

Right side - Second day Victoreen®451P SN: 2396

NS80 2 m Low 129.8 mR/h or 

1.138 mGy/h 

(± 1.13 %)

106.60 0.84 1.87 0.47

NS80 3 m Low 138.2 mR/h or 

1.211 mGy/h 

(± 0.76 %)

112.86 0.86 2.00 0.15

NS80 2 m High 519.6 mR/h or 

4.553 mGy/h 

(± 0.15 %)

419.33 0.61 6.99 0.62

WS80 3 m High 482.0 mR/h or 

4.225 mGy/h 

(± 0.16 %)

370.00 0.00 6.43 0.75

Left side - Second day Victoreen®451P SN: 2396

NS80 2 m Low 129.8 mR/h or 

1.138 mGy/h 

(± 1.13 %)

104.66 0.81 1.87 1.03

NS80 3 m Low 138.2 mR/h or 

1.211 mGy/h 

(± 0.76 %)

113.86 0.79 2.00 0.09

NS80 2 m High 519.6 mR/h or 

4.553 mGy/h 

(± 0.15 %)

408.66 0.85 7.19 0.35

WS80 3 m High 482.0 mR/h or 

4.225 mGy/h 

(± 0.16 %)

360.30 0.46 6.60 0.00
21

Table 4: Summary of the 451P and 451P-DE-SI instrument background subtracted readings for the different 

137Cs beam configurations without applying the conversion coefficient ((Sv/Gy) and the 137Cs calibration factor

137Cs beam 

configuration

Reference 

beam 

exposure and 

air-kerma 

rates

Victoreen®451P Victoreen®451P-DE-SI

Average 

exposure rate 

readings 

(mR/h)

Standard 

deviation

(%)

Average 

ambient dose 

rate readings 

(mSv/h)

Standard 

deviation 

(%)

Front - Victoreen®451P SN: 2396

500 μR/h 

(230.2 cm)

500 μR/h or 

4.390 μGy/h

(± 0.5 %)

0.43676 1.09 0.00484 1.91

15 mR/h

(210.1 cm)

15 mR/h or 

131.7 μGy/h 

(± 0.5 %)

13.34 0.66 0.14408 0.80

100 mR/h

(344.1 cm)

100 mR/h or 

0.878 mGy/h 

(± 0.5 %)

85.86 0.19 0.95 0.53

500 mR/h

(275.2 m)

500.26 mR/h or 

4.391 mGy/h 

(± 0.5 %)

419.32 0.28 4.60 0.00

1 R/h

(195.2 cm)

1.00 R/h or 

8.784 mGy/h 

(± 0.5 %)

824 2.52 9.08 0.70

Right side- Victoreen®451P SN: 2396

500 μR/h 

(230.2 cm)

500 μR/h or 

4.390 μGy/h

(± 0.5 %)

0.4848 0.95 0.00522 0.48

15 mR/h

(210.1 cm)

15 mR/h or 

131.7 μGy/h 

(± 0.5 %)

14.40 0.58 0.15659 0.59

100 mR/h

(344.1 cm)

100 mR/h or 

0.878 mGy/h 

(± 0.5 %)

92.37 0.40 1.04 0.43

500 mR/h

(275.2 m)

500.26 mR/h or 

4.391 mGy/h 

(± 0.5 %)

446.66 0.34 4.93 0.85

1 R/h

(195.2 cm)

1.00 R/h or 

8.784 mGy/h 

(± 0.5 %)

891 0.19 9.75 0.37

Left side - Victoreen®451P SN: 2396

500 μR/h 

(230.2 cm)

500 μR/h or 

4.390 μGy/h

(± 0.5 %)

0.45911 3.02 0.00519 0.91

15 mR/h

(210.1 cm)

15 mR/h or 

131.7 μGy/h 

(± 0.5 %)

14.29 0.39 0.15466 0.22

100 mR/h

(344.1 cm)

100 mR/h or 

0.878 mGy/h 

(± 0.5 %)

91.65 0.40 1.04 0.42

500 mR/h 500.26 mR/h or 440.10 0.04 4.90 0.42
22

137Cs beam 

configuration

Reference 

beam 

exposure and 

air-kerma 

rates

Victoreen®451P Victoreen®451P-DE-SI

Average 

exposure rate 

readings 

(mR/h)

Standard 

deviation

(%)

Average 

ambient dose 

rate readings 

(mSv/h)

Standard 

deviation 

(%)

(275.2 m) 4.391 mGy/h 

(± 0.5 %)

1 R/h

(195.2 cm)

1.00 R/h or 

8.784 mGy/h 

(± 0.5 %)

869 3.07 9.68 0.33

Front - Victoreen®451P SN: 3796

500 mR/h

(275.2 m)

500.26 mR/h or 

4.391 mGy/h 

(± 0.5 %)

412.44 0.96 NA NA

Right side - Victoreen®451P SN: 3796

500 mR/h

(275.2 m)

500.26 mR/h or 

4.391 mGy/h 

(± 0.5 %)

448.88 0.43 NA NA

Left side - Victoreen®451P SN: 3796

500 mR/h

(275.2 m)

500.26 mR/h or 

4.391 mGy/h 

(± 0.5 %)

440.22 0.09 NA NA

Table 5: Summary of the 451P and 451P-DE-SI instrument background subtracted readings for the different 

60Co beam configurations without applying the conversion coefficient (Sv/Gy) and the 137Cs calibration factor

60Co beam 

configuration

Reference 

beam 

exposure and 

air-kerma 

rates

Victoreen®451P Victoreen®451P-DE-SI

Average 

exposure rate 

readings 

(mR/h)

Standard 

deviation

(%)

Average 

ambient dose 

rate readings 

(mSv/h)

Standard 

deviation 

(%)

Front - Victoreen®451P SN: 2396

100 mR/h

(215 cm)

100.29 mR/h or 

0.882 mGy/h 

(± 0.5 %)

86.39 0.07 0.97 0.24

Right side - Victoreen®451P SN: 2396

100 mR/h

(215 cm)

100.29 mR/h or 

0.882 mGy/h 

(± 0.5 %)

94.23 0.19 1.05 0.10

Left side - Victoreen®451P SN: 2396

100 mR/h

(215 cm)

100.29 mR/h or 

0.882 mGy/h 

(± 0.5 %)

93.39 0.04 1.05 0.15
23

Table 6: Calibration factors determined in the 137Cs and 60Co reference beams for the Victoreen®451P SN: 

2396. The standard deviation of the measurement is shown below each value of the calibration factor. The 

additional underlined digits for the calibration factors are kept to avoid rounding errors when the values are 

used in the calculations, they do not represent the accuracy of the measured calibration factors. 

Co-60 Cs-137 Cs-137 Cs-137 Cs-137 Cs-137 Cs-137

451P, SN 2396 100.00 0.50 15.00 100.00 500.00 1000.00 Combined

mR/h mR/h mR/h mR/h mR/h mR/h

FRONT Average 1.1608 1.1369 1.1239 1.1647 1.1930 1.2143 1.1666

Std. Dev. 0.00 0.01 0.01 0.01 0.01 0.03 0.04

LEFT Average 1.0854 1.0753 1.0495 1.0911 1.1199 1.1520 1.0976

Std. Dev. 0.00 0.03 0.01 0.01 0.01 0.04 0.04

RIGHT Average 1.0642 1.0221 1.0417 1.0826 1.1367 1.1227 1.0812

Std. Dev. 0.00 0.01 0.01 0.01 0.00 0.01 0.05

BOTTOM Average NA NA 1.0640 NA NA NA NA

Std. Dev. 0.01
24

Table 7: Calibration factors determined in the 137Cs reference beams for the Victoreen®451P SN: 3796. The 

standard deviation of the measurement is shown below each value of the calibration factor. The additional 

underlined digits for the calibration factors are kept to avoid rounding errors when the values are used in the 

calculations, they do not represent the accuracy of the measured calibration factors. 

Cs-137

451P, SN 3796 500.00

mR/h

FRONT Average 1.2130

Std. Dev. 0.01

LEFT Average 1.1364

Std. Dev. 0.01

RIGHT Average 1.1145

Std. Dev. 0.01
25

Table 8: Calibration factors determined in the 137Cs and 60Co reference beams for the 451P –DE-SI SN: 3500. 

The standard deviation of the measurement is shown below each value of the calibration factor. The additional 

underlined digits for the calibration factors are kept to avoid rounding errors when the values are used in the 

calculations, they do not represent the accuracy of the measured calibration factors. 

Co-60 Cs-137 Cs-137 Cs-137 Cs-137 Cs-137 Cs-137

451-DE-SI, SN 3500 0.80 4.39 131.70 0.80 4.39 8.78 Combined

mGy/h uGy/h uGy/h mGy/h mGy/h mGy/h

FRONT Average 1.0492 1.0880 1.0970 1.1065 1.1145 1.1613 1.1135

Std. Dev. 0.00 0.02 0.01 0.01 0.03 0.01 0.03

LEFT Average 0.9777 1.0101 1.0219 1.0174 1.0745 1.0889 1.0426

Std. Dev. 0.00 0.01 0.01 0.01 0.04 0.01 0.04

RIGHT Average 0.9744 1.0157 1.0092 1.0123 1.0683 1.0814 1.0374

Std. Dev. 0.00 0.01 0.01 0.01 0.01 0.01 0.04

BOTTOM Average NA NA 1.0300 NA NA NA NA

Std. Dev. 0.01

Table 9: Calibration factors calculated from the x-ray measurements for the Victoreen® 451P SN: 2396. The 

additional underlined digits for the calibration factors are kept to avoid rounding errors when the values are 

used in the calculations, they do not represent the accuracy of the measured calibration factors. 

NS80 

(2 m Low)

NS80 

(3 m Low)

NS80 

(2 m High)

WS80 

(3 m High)

451P, SN 2396 129.81 138.20 519.55 482.04

mR/h mR/h mR/h mR/h

FRONT Average 1.2964 1.2820 1.3322 1.4178

Std. Dev. 0.00 0.00 0.00 0.00

LEFT Average 1.2403 1.2137 1.2713 1.3379

Std. Dev. 0.00 0.00 0.00 0.00

RIGHT Average 1.2178 1.2245 1.2390 1.3028

Std. Dev. 0.00 0.00 0.00 0.00
26

Table 10: Calibration factors calculated from the x-ray measurements for the Victoreen® 451P SN: 3796. The 

additional underlined digits for the calibration factors are kept to avoid rounding errors when the values are 

used in the calculations, they do not represent the accuracy of the measured calibration factors.

NS80 

(2 m Low)

NS80 

(3 m Low)

NS80 

(1 m High)

NS80 

(2 m High)

WS80 

(3 m High)

451P, SN 3796 129.06 142.92 532.80 517.79 482.40

mR/h mR/h mR/h mR/h mR/h

FRONT Average 1.2761 1.3248 1.3502 1.3265 1.4189

Std. Dev. 0.00 0.01 0.02 0.00 0.00

LEFT Average 1.2361 1.2600 1.3658 1.2633 1.3400

Std. Dev. 0.01 0.01 0.01 0.01 0.00

RIGHT Average 1.1886 1.2214 1.2999 1.2273 1.3038

Std. Dev. 0.01 0.01 0.00 0.01 0.00

Table 11: Calibration factors calculated from the x-ray measurements for the Victoreen®

451P-DE-SI SN: 3500. 

The additional underlined digits for the calibration factors are kept to avoid rounding errors when the values 

are used in the calculations, they do not represent the accuracy of the measured calibration factors.

NS80 

(2 m Low)

NS80 

(3 m Low)

NS80 

(2 m High)

WS80 

(3 m High)

451-DE-SI, SN 3500 1.12 1.25 4.54 4.25

mGy/h mGy/h mGy/h mGy/h

FRONT Average 1.2406 1.2848 1.3009 1.2827

Std. Dev. 0.00 0.00 0.02 0.01

LEFT Average 1.0324 1.0839 1.1687 1.0999

Std. Dev. 0.01 0.00 0.02 0.01

RIGHT Average 1.0407 1.0840 1.1367 1.0762

Std. Dev. 0.01 0.00 0.01 0.01

Conclusions

In this work we studied the response of two different Victoreen instruments as a function 

of the exposure rate, the instrument orientation and photon energy. The rate dependence 

for both instruments is of the order of 8 % over the range of exposure rates tested 

(0.5 mR/h to 1000 mR/h). A significant difference is observed between the two 

instruments for the orientation dependence investigation. While the Victoreen® 451P 

shows no significant dependence with instrument orientation, the Victoreen® 451P-DE-SI 

shows a significant dependence of up to 20 % between the three different orientations.

Finally, the measurements of energy dependence of both instruments reveal that the 

instruments measure lower exposure rate values compared to the reference values for the 

low energy x-rays by about 20 %. In comparison, for the 60Co gamma-ray beam, both 

detectors measure 3 % to 5 % higher than the reference value. 
27

Care should be taken in defining the quantity used to determine the field produced by the 

reference radiation beams (e.g., exposure rate, air-kerma, ambient dose equivalent rate, 

personal dose equivalent). Furthermore, when using a radiation detection instrument to 

determine the value of the reference radiation beams, the instrument measurement units 

shall be taken into account in order to obtain the correct radiation filed value. It is 

possible that the reference beam is defined in units of Sv/h while the instrument used to 

perform the measurements displays in R/h. This can introduce a source of error if the 

appropriate conversion coefficients are not used to convert from R/h to Sv/h or vice 

versa. The correction due to the conversion coefficients vary with photon energy. The 

variations are within approximately 2 % and 5 % for 60Co and 137Cs respectively and 

between 45.5 % and 52 % for x-ray beams and 241Am [3]. 

When measuring at close distances from the source (1 m or less), with the instrument in 

the side orientation (Right or Left), corrections should be made to account for the 

instrument volume effect for both the Victoreen® 451P and the Victoreen® 451P-DE-SI 

instruments. 

Based on this large variation in the calculated exposure rate values for 241Am it is not 

possible to compare the instruments measurements with a reference exposure rate value. 

The dependences observed for each instrument in this work as well as the significant 

differences observed between each of the instruments can contribute to the explanation of 

the difference observed between the measurements conducted at the JRC and SRNL 

described in the introduction of this work. 

References 

1. Victoreen®

 451P & 451P-DE-SI Ion Chamber Survey Meter Operators Manual, 

http://www.science.mcmaster.ca/medphys/images/files/courses/3A03/451_Ion_Ch

amber_Survey_Meter.pdf

2. Calibration of x-ray and gamma-ray measuring instruments, P.J. Lamperti and M. 

O’Brien. NIST Special Publication 250-58.

3. ISO 4037-3, X and gamma reference radiation for calibrating dosemeters and 

doserate meters and for determining their response as a function of photon energy 

— Part 3: Calibration of area and personal dosemeters and the measurement of 

their response as a function of energy and angle of incidence 

4. Calibration of a 137Cs Gamma-Ray Beam Irradiator using Large Size Chambers, R. 

Minniti and S. M. Seltzer, Applied Radiations and Isotopes, Vol. 65 (4), pp. 401-

407, 2007. 

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

Harold Elford Johns and John Robert Cunningham. 
28

6. J.H. Hubbell and S.M. Seltzer. Tables of x-ray mass attenuation coefficients and 

mass energy-absorption coefficients 1 keV to 20 MeV for elements Z = 1 to 92 and 

48 additional substances of dosimetric interest. NISTIR 5632. May 2005. 

(http://www.nist.gov/pml/data/xraycoef/index.cfm) 

7. Pelowitz D B, ed., MCNPX User’s Manual, Version 2.5.0, Los Alamos National 

Laboratory report LA-CP-05-0369 (April 2005) 

8. White M C 2002 Photoatomic Data Library MCPLIB04: A New Photoatomic 

Library Based on Data from ENDF/B-VI Release 8, Los Alamos National 

Laboratory Internal Memorandum X-5: MCW-02–111 and LA-UR-03–1019.

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

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

10. Nuclear Data Center, Brookhaven National Laboratory, Evaluated Nuclear Structure 

Data File (ENSDF), http://www.nndc.bnl.gov/

11. D.S. Smith and M.G. Stabin. Exposure Rate Constants and Lead Shielding values 

for over 1,100 Radionuclides, Health Physics The Radiation Safety Journal, Vol. 

102, No. 3, pp. 271–291, March 2012. 

12. Rad Pro Calculator http://www.radprocalculator.com/Gamma.aspx

13. S.M. Seltzer, “Air-kerma-rate coefficients for selected photon-emitting 

radionuclide sources.” NISIP 7092A (2004).