Radiation Physics Division 47010C, 47011C RPD-P-07

CALIBRATION OF GAMMA-RAY SOURCE CONTAINING 137Cs or 192Ir

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Procedures for SP250 47010C (Calibration of Gamma-Ray Source containing 137Cs, 

or 192Ir) and 47011C (Each Additional Gamma-Ray Source of Same Radionuclide)

Purpose

This procedure describes the calibration of brachytherapy sources containing the 

radionuclides 137Cs, or 192Ir in terms of air-kerma strength. The national air-kerma 

strength standard for gamma-emitting encapsulated sources resides in calibration 

coefficients of either the spherical-aluminum re-entrant chamber (192Ir) or the sphericalaluminum cavity chamber (137Cs) which were derived from primary standard graphitecavity chamber measurements1-4

.

Scope

Gamma-ray sources submitted for calibration that contain 137Cs must be similar in design 

to the NIST “working standard” sources, and have air-kerma strengths within the range of 

10 Gy m2/h to 1500 Gy m2/h. 192Ir sources must be of the same type used to calibrate 

the NIST spherical aluminum re-entrant chamber, and have air-kerma strengths in the 

range of 0.1 Gy m2/h to 30 Gy m2/h.

Definitions

Air Kerma is the sum of the initial kinetic energies of all electrons liberated by photons in 

a volume element containing a given mass of air. The SI unit of air-kerma is the Gray 

(Gy), where 1 Gy = 1 J / kg.

Air-Kerma Strength is the product of the air-kerma rate, in vacuo, at a distance d and the 

square of this distance. Air-kerma strength is typically expressed in units of Gy m2/h, 

but is also represented by “U”. 

Brachytherapy is a type of radiation therapy in which an encapsulated radioactive source 

is placed in or near a tumor or lesion.

Equipment

• Spherical aluminum re-entrant and cavity chambers, including source-mounting 

tube and trough, respectively.

• NIST-calibrated (using graphite-cavity chambers) “working standard” sources of 

137Cs (R.S.# 67-0385, 67-0386, 67-0387).

•

226Ra source (R.S.# 65-0308) for constancy check on re-entrant chamber 

response.

• High-voltage power supply (Power Designs, Model HV-1565, S/N 702016 or 

equivalent) to bias the ionization chambers.

• Electrometer (Keithley, Model 617, S/N 0661363 or equivalent) and capacitor 

(e.g., General Radio Co., Model 1403-A, S/N 7095, calibrated by the NIST 

Electricity Division) to collect and measure liberated charge.
Radiation Physics Division 47010C, 47011C RPD-P-07

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• Temperature (DigiTec, Model 5810, S/N 63560608 or equivalent) and pressure 

(Wallace & Tiernan, Model FA185260, S/N AE03821 or equivalent) gauges to 

allow correction to reference conditions (22 oC and 760 mm Hg).

Health and Safety Precautions

Radiation Safety – Sources shall always be handled with tongs, with the concrete barrier 

wall in room 245/B145 positioned between the source and the operator, and over a tray to 

contain the source in case it is accidentally dropped. An audible survey meter must be 

kept within reach to ensure that the location of the source is known at all times. A 

radiation dosimetry (TLD or similar) badge must be worn when working in the facility. 

Finger dosimeters shall be worn when manipulating a source. Great care shall be used 

when handling a source, as excessive force could damage the encapsulation and cause 

leakage of radioactive material. When measurements are in progress, a sign designating 

the immediate area around the ionization chambers as a high-radiation area shall be 

displayed, and the door to the laboratory shall be locked. When a source is not in use, it 

shall be placed in its lead pig or stored in the locked, lead-lined safe inside the locked 

laboratory. Radiation safety training and assessment services are provided by the

Gaithersburg Radiation Safety Division (GRSD).

Electrical Safety – Ionization chambers shall remain in their original positions behind the 

concrete barrier at all times, out of the operator’s reach, to avoid possible electric shock 

when high voltage (-1100 V DC) is applied.

Emergency Procedures - If a source is accidentally dropped and can not be immediately 

located visually, the operator shall move away from the last known position of the source 

(but remain in the room) and use the audible survey meter to ensure that the source is not 

attached to them. If the source is somehow attached to the operator, remove the source 

with tongs and call GRSD (x5800) to notify them of the accidental exposure. If not, use 

the survey meter to locate and secure the source. If a source is accidentally damaged, 

escape of radioactive material is possible. The operator shall move away from the source 

(but remain in the room) and call GRSD (x5800) to notify them of the accident. 

Procedures

Acceptance of Sources

1. Calibrations must be scheduled prior to shipment of the sources to NIST. The 

customer must provide the activity and encapsulated radionuclide of each source 

so that a NIST 364 form may be filled out and given to GRSD (electronically 

submitted). 

2. Sources must be shipped directly to GRSD for a contamination check upon 

arrival. GRSD must have a copy of the source manufacturer’s radioactive 

materials license. Sources showing evidence of leakage or shipping containers 

having detectable removable contamination in any manner will not be accepted 

for calibration. 
Radiation Physics Division 47010C, 47011C RPD-P-07

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3. A Report of Calibration Number (DG) shall be obtained from the Dosimetry 

Group office (456/B106-C),and entered into the laboratory notebook prior to 

beginning the calibration of a source. 

Environmental Conditions – Prior to taking any measurements, the temperature in the 

calibration laboratory (245/B145) is recorded. In order to proceed with the calibration, 

the temperature must be within the range (22 ± 4) oC. A lookup table, which explicitly 

shows the conversion of the temperature displayed by the thermometer to the actual 

temperature of the laboratory (taking into account the calibration coefficient for the 

thermometer) located below the thermometer, shall be used to verify that the actual 

temperature falls within the acceptable range for the calibration to proceed.

Calibration Set-up Using Re-Entrant Chamber System

1. With high voltage turned off, “work” the high voltage connections on the power 

supply and chamber to remove any oxidation that may have formed.

2. Turn on high-voltage power supply – the meter should read (-1100 ± 5) V.

3. Measure the background/leakage current.

4. Using long, spring-loaded tongs, remove the 226Ra check source from drawer B10 

in the lead safe, inserting it into the plastic funnel/tube assembly with the black 

end pointing up.

5. Place the tube into the re-entrant chamber and measure ionization current.

6. Re-position the 226Ra check source in the tube with the black end pointing down 

and measure ionization current.

7. Return the 226Ra check source to the lead safe.

8. Measure the background/leakage current. 

Calibration Sequence Using Re-Entrant Chamber System

1. Using long, spring-loaded tongs, remove the 192Ir seed to be calibrated from its 

lead pig and place it flat in the bottom of the glass tube.

2. Insert the thin, black rubber tubing approximately 2 cm into the top of the glass 

tube and place the assembly in the well of the re-entrant chamber.

3. Measure the ionization current two times.

4. Remove the tube assembly from the re-entrant chamber, gently shake to randomly 

re-orient the seed, and replace.

5. Repeat steps 3 and 4 twelve times.

6. Put the 192Ir seed back in its lead pig.

7. Measure the background/leakage current.

8. Repeat the 226Ra check source measurements as described above after all 192Ir 

seeds have been measured. 

Calibration Set-up Using Cavity Chamber System

1. With high voltage turned off, “work” the high voltage connection on the power 

supply to remove any oxidation that may have formed.
Radiation Physics Division 47010C, 47011C RPD-P-07

CALIBRATION OF GAMMA-RAY SOURCE CONTAINING 137Cs or 192Ir

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2. Position the signal-cable connection behind a lead brick.

3. Verify that the cross hairs viewed through the telemicroscope on the concrete 

barrier wall line up with the bottom of the “V” on the plastic trough (source 

holder).

4. Align the cross hairs of the cathetometer at the end of the calibration range with 

the center-line marked on the source holder.

5. Turn on high-voltage power supply – the meter should read (-1100 ± 5) V.

6. Measure the background/leakage current. 

7. Using long, spring-loaded tongs, remove the 137Cs working standard source that is 

closest in activity to the manufacturer’s stated value for the source to be calibrated 

from the lead safe, placing it into the source holder.

8. Note the orientation of the seed using the telemicroscope, and verify using the 

cathetometer that the source is centered on the line on the source holder.

9. Measure the current at least five times.

10. Using tongs, rotate the source by 90 degrees about its long axis and repeat step 9.

11. Flip the source so that the end closest to the telemicroscope is now closest to the 

wall of the room behind the concrete barrier wall and repeat steps 9 and 10.

12. Using tongs, remove the working standard source from the source holder and 

return it to the lead safe.

Calibration Sequence Using Cavity Chamber System

1. Place the lead pig containing the source to be calibrated in a tray behind the 

concrete barrier wall.

2. Open the lead pig and dump the source out onto the tray.

3. Using tongs, place the source into the source holder.

4. Note the orientation of the seed using the telemicroscope, and verify using the 

cathetometer that the source is centered on the line on the source holder.

5. If the radius of the source is large enough such that the top of the source extends 

beyond the top of the “V” trough, use a larger trough.

6. Measure the current at least five times.

7. Using tongs, rotate the source by 90 degrees about its long axis and repeat step 6.

8. Flip the source so that the end closest to the telemicroscope is now closest to the 

wall of the room behind the concrete barrier wall and repeat steps 6 and 7.

9. Using tongs, remove the source from the source holder and return it to the lead 

pig.

Analysis and Reporting of Results

1. All measured currents must be corrected for temperature and pressure deviations 

from reference conditions (22 oC and 760 mmHg), background/leakage, and 

radioactive decay prior to averaging.

2. The quotient of the average corrected current from the customer’s source and the 

average corrected current from the working standard source is multiplied by the 

NIST air-kerma strength value of the working standard source to obtain the NIST 
Radiation Physics Division 47010C, 47011C RPD-P-07

CALIBRATION OF GAMMA-RAY SOURCE CONTAINING 137Cs or 192Ir

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air-kerma strength value of the customer’s source. This value is entered into the 

official calibration report, an example of which is given in Appendix A.

3. After review and approval, the official calibration report is mailed to the 

customer. The lead pigs containing the calibrated sources are re-packaged in their 

original container and shipped either back to the customer or to an Accredited 

Dosimetry Calibration Laboratory (as specified by the customer).

Quality Assurance

1. To verify constancy of the re-entrant chamber’s response over time, the results of 

measurements of the 226Ra source described above are compared to the history of 

such measurements to verify that there are no significant changes. Deviations 

greater than 1 % from the average of previous measurements should be 

investigated by repeating the measurement several times, noting any unusual 

behavior of the measurement system. If after repeated measurements of the 226Ra 

source the > 1 % deviation continues to exist, the electrometer, thermometer, and 

barometer should be re-calibrated using the procedures given below. (Note that 

226Ra check source data exists from December 1977 through December 1987 and 

from February 2001 through the present. The lapse in data occurred due to nonuse of the calibration service, which was subsequently re-established for 192Ir 

source calibrations and internal quality assurance for Model 6711 125I seeds.)

2. To verify constancy of the cavity chamber’s response over time, the results of 

measurements of the 137Cs working standard sources described above are 

compared to the history of such measurements to verify that there are no 

significant changes. Deviations greater than 1 % from the average of previous 

measurements should be investigated by repeating the measurement several times, 

noting any unusual behavior of the measurement system. If after repeated 

measurements of the 137Cs source(s) the > 1 % deviation continues to exist, the 

electrometer, thermometer, and barometer should be re-calibrated using the 

procedures given below.

Calibration of Electrometer – The following procedure should be used to re-calibrate the 

electrometer in the case of out-of-tolerance 226Ra or 137Cs check/working standard source 

measurement results.

1. Connect a capacitor that has been calibrated by the NIST Electromagnetics 

Division (e.g., NBS B-15) between the Fluke Model 343A DC voltage calibrator 

(S/N 2195014 or equivalent) and the electrometer to be calibrated. 

2. Allow both the electrometer and voltage calibrator to warm up for at least 2 hours.

3. Based on which coulomb scales of the electrometer are used when performing 

calibrations, select a series of test voltages to be used to calibrate the electrometer, 

taking into account the capacitance value of the NIST-calibrated capacitor. (A 

minimum of 5 data points per electrometer coulomb scale should be acquired.)

4. Select a voltage on the voltage calibrator and measure the accumulated charge on 

the capacitor with the electrometer.
Radiation Physics Division 47010C, 47011C RPD-P-07

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5. Repeat step 4 until data is acquired for all relevant coulomb scales.

6. Calculate the calibration coefficient for each coulomb scale by taking the average 

of all ratios of the known accumulated charge to the charge indicated by the 

electrometer.

Calibration of Thermometer - The following procedure should be used to re-calibrate the 

thermometer in the case of out-of-tolerance 226Ra or 137Cs check/working standard source 

measurement results.

1. Place the DigiTec Model 5810 thermometer probe and a thermometer that has 

been calibrated by the NIST Measurement Services Division (e.g., Taylor S/N 

3738041) in an insulated box (cardboard/Styrofoam).

2. Record the temperatures obtained from both thermometers over a period of 

several hours until a minimum of 5 data points are acquired.

3. Calculate the calibration coefficient for the DigiTec thermometer by taking the 

average of all ratios of the known temperature to the temperature indicated by the 

DigiTec thermometer.

Calibration of Barometer - The following procedure should be used to re-calibrate the 

barometer in the case of out-of-tolerance 226Ra or 137Cs check/working standard source 

measurement results.

1. Place the Wallace & Tiernan Model FA185260 barometer in close proximity to a 

barometer that has been calibrated by the NIST Measurement Services Division 

(e.g., Wallace & Tiernan S/N XX11242).

2. Record the pressures obtained from both barometers over a period of several 

hours until a minimum of 5 data points are acquired.

3. Calculate the calibration coefficient for the Wallace & Tiernan barometer by 

taking the average of all ratios of the known pressure to the pressure indicated by 

the Wallace & Tiernan barometer.

Evaluation of Measurement Uncertainties

Uncertainties for measurements performed with both the re-entrant and cavity chambers 

are determined based on the Guidelines for Evaluating and Expressing the Uncertainty of 

NIST Measurement Results5. The Type A components of uncertainty are equal to the 

standard deviation of the mean of replicate measurements, and the Type B components 

are evaluated by other means, detailed in Appendices B and C. The combined standard 

uncertainty of the air-kerma strength calibration is equal to the square root of the 

quadratic sum of the Type A and Type B uncertainties, with a final reported expanded 

uncertainty obtained by multiplying the combined standard uncertainty by a coverage 

factor of two (k=2), representing an interval having a level of confidence of 

approximately 95 %.
Radiation Physics Division 47010C, 47011C RPD-P-07

CALIBRATION OF GAMMA-RAY SOURCE CONTAINING 137Cs or 192Ir

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Traceability of Measurements

The SI unit of air kerma (Kair) is the Gray (Gy), which is related to the quantity exposure 

(X) by multiplicative constants, Kair = X (W/e) / (1-g), where W/e is the mean energy per 

unit charge expended in air by electrons, and g is the mean fraction of the energy of the 

secondary electrons that is lost to bremsstrahlung. Exposure is the total charge per unit 

mass liberated in free air by a photon beam (SI units of C/kg), and is directly realized by 

Bragg-Gray graphite cavity chamber measurements1,3. The traceability of spherical 

aluminum re-entrant and spherical aluminum cavity chamber measurements described in 

this procedure to the fundamental Bragg-Gray graphite cavity chamber measurements 

resides in the calibration coefficients of each aluminum chamber for each type of 

brachytherapy source. These calibration coefficients were determined by measuring the 

responses of both Bragg-Gray and spherical-aluminum-type chambers to the same source 

(or multiple sources, in the case of 192Ir). More detailed information concerning 

traceability and uncertainty analyses is summarized in SP250-19, available using the 

following hyperlink: https://dx.doi.org/10.6028/NBS.SP.250-19

Records

All data acquired during measurements is recorded in an official NIST laboratory 

notebook that is stored in a filing cabinet in 245/H115.

References

1. Loftus, T. P., Standardization of Cesium-137 Gamma-Ray Sources in Terms of 

Exposure Units (Roentgens), J. Res. Nat. Bur. Stand. (U.S.) 74A, 1-6 (1969).

2. Loftus, T. P., and Weaver, J. T., Standardization of 60Co and 137Cs Gamma-Ray 

Beams in Terms of Exposure, J. Res. Nat. Bur. Stand. (U.S.) 78A, 465-476 

(1974).

3. Loftus, T. P., Standardization of Iridium-192 Gamma-Ray Sources in Terms of 

Exposure, J. Res. Nat. Bur. Stand. (U.S.) 85, 19-25 (1980).

4. Weaver, James T., Loftus, Thomas P., Loevinger, Robert, NBS Measurement 

Services: Calibration of Gamma-Ray-Emitting Brachytherapy Sources, Nat. Bur. 

Stand. (U.S.) Spec. Publ. 250-19, 60 pages (Dec. 1988).

5. Taylor, Barry N., and Kuyatt, Chris E., Guidelines for Evaluating and Expressing 

the Uncertainty of NIST Measurement Results, National Institute of Standards 

and Technology Technical Note 1297, 24 pages (Sep. 1994).

Filing and Retention

The RPD Quality Manager shall maintain the original and all past versions of this RPD

Procedure. 
Radiation Physics Division 47010C, 47011C RPD-P-07

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Appendix A – Calibration Report

National Institute of Standards and Technology

REPORT OF AIR-KERMA STRENGTH 

MEASUREMENT

FOR

Customer Name

Address

City, State, Country

Seed Identification: Model XXX

Arrival Date: XX Month 20XX

SP250 Service ID # 47010C, 47011C

Measurements performed by Jason Walia

Report reviewed by Ronaldo Minniti

Report approved by Michael G. Mitch, Leader

Dosimetry Group

For the Director

National Institute of Standards and Technology

by:

James M. Adams, Chief

Radiation Physics Division

Physical Measurement Laboratory

Information on technical aspects of this report may be obtained from Jason Walia, 

National Institute of Standards and Technology, 100 Bureau Drive Stop 8460,

Gaithersburg, MD 20899-8460, 301-975-5592. Report format revised 09/18.

 

 DG: XXXXX/XX

Order #: 682.02/O-XXXXXX-XX

 Report Date: XX Month 20XX

 Page 1 of 4
Radiation Physics Division 47010C, 47011C RPD-P-07

CALIBRATION OF GAMMA-RAY SOURCE CONTAINING 137Cs or 192Ir

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National Institute of Standards and Technology

REPORT OF AIR-KERMA STRENGTH

MEASUREMENT

FOR

Customer Name

Address

City, State, Country

Seed Identification: Model XXX

Arrival Date: XX Month 20XX

SP250 Service ID # 47010C, 47011C

Description of seed provided by customer:

Construction:

Diameter (mm):

Length (mm): 

Half-Life (d): 

Radionuclide:

Purity rating:

NIST Reference time and date: 00:00:01 EST, XX Month 20XX

Temperature range during measurements: XX K to XX K

Pressure range during measurements: XXX kPa to XXX kPa

Measurement Results

Source

ID No.

Number of 

Measurements

Air-Kerma Strength

(μGy m2/h)

at 295.15 K (22 oC) and

101.325 kPa (1 Atm)

Reproducibilitya

(%)

Expanded Combined

Relative Uncertaintyb

(%)

a Obtained from the replicate measurements as the standard deviation of the mean.

b See page 3 for note on uncertainty.

DG: XXXXX/XX

Order #: 682.02/O-XXXXXX-XX

Report Date: XX Month 20XX

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Radiation Physics Division 47010C, 47011C RPD-P-07

CALIBRATION OF GAMMA-RAY SOURCE CONTAINING 137Cs or 192Ir

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Explanation of Terms Used in the Calibration Procedures and Tables

Air-Kerma Strength: The realization of the radiation quantity air-kerma strength done 

at NIST establishes the National Standard. This can in turn be transferred to other 

measurement facilities through a suitable measuring instrument, thus enabling traceability 

to the National Standard. The air-kerma strength is the product of the air-kerma rate and 

the square of the distance to the reference point assumed in vacuum, in a direction 

perpendicular to the long axis of the cylindrical encapsulated brachytherapy source. For 

more details see Specification of Brachytherapy Source Strength, Report 21 of the 

American Association of Physicists in Medicine, Am. Inst of Phys., MD, June 1987.

The air-kerma rate of 192Ir and 137Cs brachytherapy sources is directly realized at NIST 

using a variety of spherical, graphite-walled cavity ionization chambers. Measurements

are performed free-in-air at source-to-chamber distances between 0.5 m and 1.0 m with a 

chamber of volume and wall thickness such that Bragg-Gray conditions are satisfied.

The air-kerma rate,

K (Q) air



, is calculated using the equation:

( ) ( , ) ( ) ( )

( / )

( / )

( / )

( / )

1

1 1

( ) K K M K Q K K Q K Q

L

L

e V g

W

K Q d r det stem wall h

air

g r

en g r

en air

air

air

  





 

 

 



















−

































=

 

where: 

W

= the mean energy per ion pair expended when the initial kinetic energy of a charged 

 particle is completely dissipated in air

e = the elementary charge

air = the density of air

V = volume of air in the chamber

g

= is the mean fraction of kinetic energy lost by charged particles in radiative processes

en / 

= the mean photon-energy-fluence-weighted mass energy-absorption coefficient

L/ 

= the mean Spencer-Attix electron-fluence-weighted electron mass stopping 

 power

K (K)

dr



= the recombination correction

M (K,Q)

det



= the net current (corrected for radioactive decay)

Kstem = the stem-scatter correction factor

Kwall(Q) = the wall correction factor

Kh(Q) = the humidity correction factor 

DG: XXXXX/XX

Order #: 682.02/O-XXXXXX-XX

Report Date: XX Month 20XX

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The air-kerma strength is calculated from 

K (Q) air



using the equation: Sk = 

K (Q) air



d

2

.

With d being the source-to-chamber distance. The air-kerma strength(s) given in this 

report can be used to determine a well-chamber calibration coefficient for the identified 

source model.

Uncertainty: The combined standard uncertainty assigned to these results has been 

evaluated as the square root of the quadratic sum of the component standard 

uncertainties, including those evaluated by statistical means (Type A) and those evaluated 

by other means (Type B). The expanded uncertainty has been obtained by multiplying the 

combined standard uncertainty by a coverage factor of two, to represent an interval 

having a level of confidence of approximately 95 %.

DG: XXXXX/XX

Order #: 682.02/O-XXXXXX-XX

Report Date: XX Month 20XX

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Appendix B – Uncertainty analysis for 137Cs and 60Co source calibration by 

substitution. Estimated relative uncertainties (k = 1) are given in percent, and 

include the Type A uncertainty estimated by statistical methods, and the Type B 

uncertainty estimated by other means.

(a) Measurement of secondary working standard A B

using primary graphite standard chambers. (%) (%)

Volume 0.1 0.05

Charge 0.04 0.1

Timing 0.03 0.03

Air density 0.03 0.1

Recombination loss 0.07

Humidity 0.06

Leakage and radiation background 0.02

W / e 0.15

Stopping-power ratio 0.60

Energy-absorption coefficient ratio 0.06

Wall correction 0.17

Stem Scatter 0.02

Effective measurement point 0.05

Radial nonuniformity 0.01

Distance (50 cm) 0.1

Correction to vacuum

Air attenuation 0.05

Room scatter 0.3

Source nonuniformity 0.2

Half-life 0.14

Long-term reproducibility 0.3

Quadratic sum 0.12 0.84

(b) Measurement of source using 2.8-liter

spherical ionization chamber.

Charge 0.05 0.1

Timing 0.03

Air density 0.05 0.05

Recombination loss 0.1

Leakage and radiation background 0.2

Distance 0.1

Difference in scatter 0.2

Source nonuniformity 0.2
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Source size 0.1

Quadratic sum 0.07 0.40

Comparison of user source with

 secondary standard tertiary standard

Combined standard uncertainty 1.03 1.18

Expanded uncertainty (k = 2) 2.05 2.36
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Appendix C – Uncertainty analysis for 192Ir source calibration with the re-entrant 

chamber. Estimated relative uncertainties (k = 1) are given in percent, and include 

the Type A uncertainty estimated by statistical methods, and the Type B uncertainty 

estimated by other means.

(a) Measurement of array of seeds using A B

graphite standard chambers. (%) (%)

Volume 0.01

Charge 0.03 0.05

Timing 0.01

Air density 0.03 0.05

Recombination loss 0.03

Humidity 0.06

Leakage and radiation background 0.02

W / e 0.15

Stopping-power ratio 0.72

Energy-absorption coefficient ratio 0.06

Stem Scatter 0.02

Wall correction 0.17

Effective measurement point 0.05

Radial nonuniformity 0.01

Distance 0.04

Correction to vacuum

Air attenuation 0.1

Room scatter 0.3

Half-life

Platinum encapsulated (2.82 half-lives) 0.5

Stainless steel encapsulated (0.12 half-lives) 0.02

Array cover attenuation 0.1

Reproducibility in exposure measurement 0.2

Quadratic sum for graphite chamber measurement

Platinum encapsulated seeds 0.21 0.97

Stainless steel encapsulated seeds 0.21 0.83

(b) Calibration of aluminum re-entrant

chamber using individual seeds of the array.

Charge 0.03 0.05

Timing 0.01

Air density 0.05 0.05

Recombination loss 0.1
Radiation Physics Division 47010C, 47011C RPD-P-07

CALIBRATION OF GAMMA-RAY SOURCE CONTAINING 137Cs or 192Ir

Version Date Author Approval Pages Filename

4.20 6/22/2021 JSW JMA 15 of 15 Procedure07v420

Humidity 0.06

Leakage and radiation background 0.02

Reproducibility in re-entrant chamber 0.1

Quadratic sum for re-entrant chamber calibration 0.12 0.16

(c) Measurement of single unknown source in

re-entrant chamber

Charge 0.05 0.1

Timing 0.01

Air density 0.05 0.1

Recombination loss 0.1

Leakage and radiation background 0.02

Reproducibility in re-entrant chamber 0.1

Plastic cover 0.3

Quadratic sum for unknown measurement 0.12 0.35

Platinum Stainless steel

Combined standard uncertainty 1.08 0.95

Expanded uncertainty (k = 2) 2.2 1.9