Radiation Physics Division 49010C, 49011C, 49015C, 49016C RPD-P-11

CALIBRATION IRRADIATIONS OF CUSTOMER SUPPLIED DOSIMETERS

WITH 60Co GAMMA RAYS

Version Date Author Approval Pages Filename

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Purpose

The purpose of this procedure is to describe the setup, measurement, and 

reporting procedures for irradiation of customer supplied dosimeters.

Scope

This procedure covers the irradiation of passive dosimeters in the NIST 60Co 

Gammacell irradiators. The irradiator dose rates are comparable to those used in 

the radiation processing industry. Customer-supplied dosimeters are irradiated at 

prescribed temperatures and returned to the customer with an absorbed-dose 

irradiation certificate.

Definitions

Absorbed dose to water – the energy absorbed from ionizing radiation per unit mass 

of water: 1 J/kg = 1 Gy.

Gammacell User Log Book – for maintaining a log of every irradiation for each 

irradiator.

High-Dose Irradiations Databook – for maintaining a record of irradiations for each 

calibration job.

Single-hole vial geometry – the vial is made up of a polystyrene cylindrical cup 

with a screw cap and has a hole diameter slightly larger than the alanine pellets (5 

mm) and a wall thickness of 3.7 mm. This is mounted on a polystyrene rod with a 

cavity for two quality control alanine dosimeters, which is mounted to a 6 mm 

thick polycarbonate base disk to locate the alanine pellets in the geometrical 

center of the radiation field of each irradiator. This provides a reproducible 

geometry as well as approximate electron equilibrium conditions.

Five-hole cup – A polystyrene cylinder with five equidistant holes, used for 

electronic equilibrium build-up material when irradiating tape tabs, perspex or 

ampoule dosimeters.

Tape tabs - Alanine pellets welded between two sheets of polyethylene 

terephthalate. Pellet remains within barcoded packaging when being measured 

using an EPR spectrometer providing full and constant traceability of the 

dosimeter. 

Quality control (QC) alanine dosimetry – alanine dosimeters that are employed 

routinely to achieve and sustain a predefined level of quality.
Radiation Physics Division 49010C, 49011C, 49015C, 49016C RPD-P-11

CALIBRATION IRRADIATIONS OF CUSTOMER SUPPLIED DOSIMETERS

WITH 60Co GAMMA RAYS

Version Date Author Approval Pages Filename

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Equipment

Essential Equipment Calibration Method Calibration 

Frequency

60Co Vertical Beam Source Water Calorimeter See RPD Procedure 6

MDS Nordion Gammacell 

45

Comparison to Vertical 

Beam Source

Determined by 

Control Charts

MDS Nordion Gammacell 

232

Comparison to 

Gammacell 45 Source

Determined by 

Control Charts

Hopewell Designs, Inc. 

GR420

Comparison to 

Gammacell 45 Source

Determined by

Control Charts

Platinum Thermometer External Service As Needed

Type-T Thermocouple Comparison to Platinum 

Thermometer

As Needed

FTS ThermoJet Temperature 

Forcing System (controls 

sample temperature)

N/A N/A

MPI ThermalAir TA5000A 

Forcing System (controls 

sample temperature) 

N/A N/A

Health and Safety Precautions

Radiation safety

Potential radiation hazards include contamination resulting from leakage of 

radioactive material from any of the 60Co sealed sources and accidental external 

exposure of personnel to gamma radiation from the 60Co irradiators.

The irradiators associated with this procedure are located in a controlled access 

space. Rooms containing 60Co sources have been designated as High Radiation 

Areas. The doors to the facility are posted with cautionary signs to indicate the 

presence of radioactive materials. Whole body dosimetry is required for everyone 

entering the facility. Radiation safety training and assessment services are 

provided by the NIST Radiation Safety Division (RSD). Additional training is 

performed by the Radiation Facility Owner (RFO). Use of the facility must be 

arranged in advance with the RFO.

Authorized users are required to complete three training sessions. Two of these 

trainings are offered by RSD and must be taken annually. One is a general 

radiation training course while the second is specifically oriented to irradiator 

users. The third is a hands-on training session given by the RFO, which shall 

include hands-on demonstrations of the various operating modes of the irradiator. 

RFO-authorized source users are granted use of the facility after completion of all 

three sessions. The list of source users is maintained by RSD and kept up to date 
Radiation Physics Division 49010C, 49011C, 49015C, 49016C RPD-P-11

CALIBRATION IRRADIATIONS OF CUSTOMER SUPPLIED DOSIMETERS

WITH 60Co GAMMA RAYS

Version Date Author Approval Pages Filename

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through submission of the NIST-365 form. Manipulation of the irradiator beyond 

that provided by the control panel shall be restricted to maintenance or other 

operations under the direction and supervision of the RFO.

A logbook shall be kept near each irradiator and shall contain the following 

information: date and time of usage; username, agency, division, and phone 

number; type of sample or purpose of use. All maintenance, testing, and abnormal 

behavior of the irradiator shall be recorded in the logbook.

Hazard Mitigation

Sources showing any evidence of leakage or contamination shall not be used. The 

potential for source leakage in each irradiator is minimal because the source is 

encapsulated in metallic shielding and welded shut. In addition, the source is fixed 

within the heavily shielded housing of the irradiator body. The RSD performs 

routine leak checks semiannually in all irradiators. 

While unoccupied, the doors to the irradiator room are kept closed and locked. 

The Source Custodian trains all authorized users to perform the safety 

interlock/indicator checks and to record the results in the facility logbook. Users 

must inform the Source Custodian if any of the safety interlocks/indicators are not 

functioning as expected. If any of the interlocks/indicators do not function as 

expected, the operator cannot use the facility until the interlock/indicator is 

fixed/replaced.

Loading, unloading, or any repositioning of the source shall not be performed 

without RSD approval. The irradiator manufacturer or other person authorized by 

the Nuclear Regulatory Commission (NRC) or an Agreement State will perform 

non-routine operations such as source loading, unloading and repositioning, 

electrical troubleshooting of the control console, investigating/remediating 

removable contamination/leaking sources, (re)installing source cables, and other 

critical operations requiring special skills or involving the potential for radiation

exposure.

Removal of the access panels shall only be allowed by personnel trained to 

operate and maintain the unit and only under the supervision of the RFO, 

following approval by RSD. If power is on there are electrical and radiation safety 

considerations associated with open panels.

Restrictions on the materials to be irradiated are necessary. Irradiation of the 

following materials is prohibited: explosives, corrosive liquids, radioactive or 

special nuclear materials, or materials that may give off toxic or corrosive fumes.

No flammable materials shall be stored or used in the irradiator area.
Radiation Physics Division 49010C, 49011C, 49015C, 49016C RPD-P-11

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WITH 60Co GAMMA RAYS

Version Date Author Approval Pages Filename

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During irradiation of liquid samples, an appropriate secondary container shall be 

provided in the sample chamber such that none of the liquid sample can spill or 

run out of the chamber. The volume of the secondary container shall be sufficient 

so as to account for expansion of the sample due to thermal heating and/or 

chemical reaction.

Emergency Procedures

REMEMBER: Whenever dealing with an emergency, the SWIM process should 

be used.

• Stop and Think – What should be done and how can it be done safely?

• Warn Others – Notify other workers for safe evacuation. Call for assistance 

immediately.

• Isolate – If appropriate, contain spills, shut down drains and/or ventilation, 

post warning signs and close off the area.

• Minimize – Move to safe buffer zone away from any direct hazards and 

minimize movement to prevent spreading.

Any indication of loss of source integrity shall be reported IMMEDIATELY

to RSD (x5800) and the RFO

If a calibrated survey meter reading indicates that radiation is present inside the 

room: Immediately exit the irradiator area and call RSD (x5800, if no one answers 

call x2222) and the RFO. Wait inside the control area or in the hallway 

immediately outside the facility until help arrives. Prevent all personnel from 

entering the irradiator area.

In case electrical power is lost during drawer movement, the assembly will stop 

immediately at its current position. Verify with a survey meter located in the 

control area that there is no radiation present. If there is, immediately exit the 

irradiator area and call RSD (x5800, if no one answers call x2222). Wait inside 

the control area or in the hallway immediately outside the facility until help 

arrives. Prevent all personnel from entering the irradiator area.

In case an individual is exposed to high voltage, turn off the main breaker located 

in the control area and call x2222. Wait inside the control area or outside the 

facility until help arrives. Visit the NIST Health Unit as soon as possible.

If a fire alarm occurs in the building during operation, no actions are required 

with respect to the irradiator. The source user should exit the room/building as 
Radiation Physics Division 49010C, 49011C, 49015C, 49016C RPD-P-11

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WITH 60Co GAMMA RAYS

Version Date Author Approval Pages Filename

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directed by fire safety personnel.

In case of fire or smoke in the irradiator facility, leave the laboratory immediately 

and call the NIST Fire Department (x2222), RSD (x5800), and the RFO.

In the unlikely event that the room floods or is otherwise invaded by water, no 

actions are required with respect to the irradiator. The source user should exit the 

room and report the incident to RSD (x5800) and the RFO and await further 

instructions. 

If, at any time during an automatic cycle, it is necessary to interrupt the irradiation 

for any reason the user can press the “STOP” button on the irradiator. The 

chamber will immediately move to the upward position. 

If the irradiator assembly were to stop during movement, completion of the stroke 

or emergency movement of the drawer assembly is possible by the use of a hand 

crank. Consult the irradiator manual for details. If this appears to be necessary, the 

RFO and RSD must be immediately notified and all activity shall cease until 

further instructions are given by the RFO and RSD.

If abnormal sounds are heard during drawer assembly movement: 1) Chatter and 

no motion of drawer assembly when the DOWN button is pushed. DO NOT 

PROCEED WITH THE IRRADIATION; INFORM THE RFO IMMEDIATELY; 

2) Chatter and no motion of the drawer assembly when UP button is pushed. IF 

additional time will not ruin the irradiation in progress, leave the unit as is and 

call the RFO. If it is important to end the irradiation for programmatic or safety 

reasons, INFORM THE RFO IMMEDIATELY. THEN, UNDER THEIR

SUPERVISION, REMOVE POWER FROM THE UNIT BY UNPLUGGING 

THE POWER CORD, and raise the drawer assembly with the manual crank; 3) 

Loud clanks or bangs on lowering or raising the drawer. INFORM THE RFO AT 

FIRST OCCURANCE.

Procedures

These are the general customer dosimeter calibration procedures. The Irradiation 

Facilities Record Book has the dose rates for irradiation geometries, laboratory 

instructions, and a record of maintenance of the facility maintenance.

Receive Customer Irradiations Inquiry

Upon customer inquiry, calibration service staff will evaluate whether the 

irradiation can be performed. Calibration service staff will direct customers to 

shop.nist.gov to place their order. Administrative calibration service staff can 

provide assistance in setting up a profile in the system. Quotes are not provided 
Radiation Physics Division 49010C, 49011C, 49015C, 49016C RPD-P-11

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WITH 60Co GAMMA RAYS

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by calibration service staff and calibration fee information is updated on the ecommerce platform. 

Receipt of Customer Order through shop.nist.gov

Upon receipt of a shop.nist.gov order, calibration service staff will evaluate 

whether the calibration service can be completed. If accepted, the calibration 

service staff will change the status to “Accepted” within the e-commerce 

platform. Calibration service staff will log the order in the Electronic Calibration 

Log Book with a unique HD number. An Electronic Test Folder (ETF) is created 

for record maintenance of the calibration order. Relevant documents from the ecommerce platform will be stored in the ETF. After confirmation from the ecommerce platform concerning the payment status, the customer will be notified 

by the calibration service staff to mail customer dosimeters to the NIST 

calibration service staff.

Receive/Store Dosimeters

Upon receipt of dosimeter(s) shipment from the customer, the package and 

contents will be inspected for any damage. If damage has occurred, follow Guide 

RPD-G07 and notify the customer. Dosimeters are kept in the Irradiation Facility 

with accompanying paperwork. Update the Electronic Calibration Log Book with 

dates and dosimeter details.

Establish a Dosimeter Calibration Service Plan

Prior to dosimeter(s) calibration, establish a Dosimeter Calibration Service Plan 

(DCSP) that will outline the specific actions and details for the completion of the 

calibration service. The DCSP includes a review of the previous customer jobs or 

jobs of similar geometry. The DCSP is reviewed by the Dosimetry Group Leader 

or designated staff member within the quality system to ensure that that the 

dosimeters are irradiated according to customer’s specifications. The DCSP 

serves as a guide during the calibration service and is retained in the customer’s 

digital test folder upon completion of the calibration services. Store a copy of 

DCSP in the ETF.

Initiate Irradiation Data Record 

Configure the Excel spreadsheet Customer Calibration Template (see Appendix 

A) in accordance with the DCSP. The worksheet is saved under the HD Customer 

Irradiation folder under the unique HD number (referred to as HD Irradiation

Worksheet). The header information includes the customer and dosimeter details. 

Once the geometry is selected, the corresponding base dose rate is retrieved from 

a master list and the irradiation time is calculated. The Timing Worksheet form 

(see Appendix B) is prepared with customer and dosimeter information. It is a 

written log with identical information as the HD Irradiation Worksheet. 
Radiation Physics Division 49010C, 49011C, 49015C, 49016C RPD-P-11

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WITH 60Co GAMMA RAYS

Version Date Author Approval Pages Filename

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Prepare Dosimeters for Irradiation

Prepare the dosimeters (alanine dosimeters, film dosimeters, or other previously 

calibrated customer supplied or NIST calibration geometry). For example, alanine 

dosimeters are packaged into single hole vial and film dosimeters are sandwiched 

between polystyrene plates. Arrange all labeled dosimeters in irradiation order 

with associated Quality Control (QC) pellets that are unambiguously labeled.

Customer dosimeters will be placed in a labeled envelope or a bag after 

irradiation and the QC pellets will be placed in a separate labeled container.

Except for the sample being irradiated, all customer samples, QC pellets and 

Timing Worksheet will be kept together. The calibration service staff changes the 

order status to “In Process”.

Control Sample Temperature

Samples are normally irradiated at ambient temperature, 22 oC to 25 oC. The 

GC45 does not require cooling to maintain ambient temperature. Compressed air 

is blown into the sample chamber of GC232 or GR420 to maintain ambient

temperature. This is done by opening the valve of the flow meter mounted on the 

side of the appropriate Gammacell. Temperature is monitored with a type-T 

thermocouple placed inside the sample chamber. The type-T thermocouple is 

calibrated against the high-precision platinum thermometer in the Gammacell 

sample chamber (in the “up” position) over a temperature range that corresponds 

to service irradiations. The operational status of the thermocouple is monitored by 

periodic checks and control charts. Thermocouples that do not perform within the 

control limits are replaced. The thermocouple calibration protocol can be found in 

the Irradiation Facilities Record Book.

Start the temperature-recording computer program

Non-ambient temperatures can be achieved using a forced thermally-controlled 

air cycling system for the GC232 and GR420 for sample irradiation temperatures 

approximately between -75 °C to +75 oC. 

Operate Gammacell

Operate the Gammacell(s) as prescribed for the safe operation of GC45, GC232, 

and/or GR420, see Appendix C. Log irradiation into Gammacell User Log Book

for each irradiator.

Record Irradiation Data 

Record all appropriate irradiation data before, during, and after each irradiation as 

needed to ensure accurate completion of a particular dosimeter irradiation on the 

customer’s Timing Worksheet form and the HD Irradiation Worksheet. The 

Timing Worksheet is digitized and stored in the ETF. The HD Irradiation

Worksheet will be logged into the High-Dose Irradiations Databook.
Radiation Physics Division 49010C, 49011C, 49015C, 49016C RPD-P-11

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WITH 60Co GAMMA RAYS

Version Date Author Approval Pages Filename

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Analyze Quality Control 

The QC pellet doses are measured as described in Procedure RPD-P-12. If the 

measured dose is within control limits (±5 %), the quality check is successful. 

If the measured dose is beyond the control limits, halt all irradiations. Notify the 

Dosimetry Group Leader and designated Calibration Service Staff. Start a detailed 

note in the ETF during the investigation into the source of the discrepancy. If the 

discrepancy cannot be resolved, the irradiations must be repeated. Summarize any 

issue and resolution in the summary of the ETF and include the record in the 

Irradiation Facilities Record Book (referencing the HD number and date).

Return Dosimeters

After all irradiations have been completed and QC pellets have been validated to 

be within control limits, the dosimeters are shipped back to the customer. The 

dosimeters are packaged appropriately to avoid any damage during transit. The 

HD Irradiation Worksheet copy is included.

Some dosimeters may have temporal readout requirements. Therefore, upon 

customer request, irradiated customer samples may be released with a partially 

completed HD Irradiation Worksheet. This will be outlined in the DCSP and 

noted in the ETF. 

Issue certificate and close folder

Once the quality check is successful, write a report entitled “Absorbed-Dose 

Irradiation Certificate.” An example is shown in Appendix D. Reference to a 

previous customer report or the use of a template may be used in the preparation.

Include an annotated draft of the certificate in the ETF. A checklist, found in 

Appendix F, for HD irradiation services is filled out and included in the ETF. The 

preparer sends the ETF and the electronic certificate for review. They are

sequentially routed to the reviewer, Group Leader and Division Chief (as 

designated on the certificate) for review and an electronically certified signature.

The certificate with the electronically certified signatures is returned to the 

preparer. The preparer submits the report to the e-Commerce platform and notifies 

the Calibration Administrative Staff of the completion of the work. The order 

status changes to “Completed”. Upon customer request, the preparer may send the 

electronic certificate by email or/and send a printed copy of the electronically 

signed certificate. The Administrative Staff will change the order status to 

“Closed”.

Determination of Uncertainties

The basis for the determination of uncertainties associated with high-dose 

irradiations is the Guidelines for Evaluating and Expressing the Uncertainty of 

NIST Measurement Results [1]. The purpose of this section is to explain the 

derivation of the various components of uncertainty for absorbed-dose certification.

The values for the uncertainty components are listed in Appendix E.
Radiation Physics Division 49010C, 49011C, 49015C, 49016C RPD-P-11

CALIBRATION IRRADIATIONS OF CUSTOMER SUPPLIED DOSIMETERS

WITH 60Co GAMMA RAYS

Version Date Author Approval Pages Filename

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Water Calorimetry: This is the published uncertainty from realization of the gray 

(Gy) [2].

Source Ratio Data: This is the statistical determination of uncertainty from the 

measurement of ratios of electron paramagnetic resonance (EPR) signal response 

for water calorimetry geometry vs. Gammacell geometry.

Geometry Correction Factor: This is the statistical determination of uncertainty 

from the measurement of ratios of EPR signal response for single-hole vial 

geometry vs. film block, Perspex, or ampoule geometry.

Field Uniformity: This is a Type-B estimate of uncertainty for radiation field 

uniformity within a dosimeter volume.

Timer: This is a Type-B estimate of uncertainty for the timer readout relative to the 

shortest irradiation time interval.

Decay Correction: This is a Type-B estimate of uncertainty for the 60Co half-life

value.

Traceability

The SI unit of absorbed dose is the Gy. For this service, the Gy is realized through 

water calorimetry measurements in the Vertical Beam 60Co Gamma-Ray Source [2].

Lower dose measurements are first transferred to GC45 and then higher dose 

measurements are transferred from GC45 to GC232 and GR420 calibration sources

by source-rate ratio measurements using alanine dosimetry. These transfer 

measurement protocols were first described in the NIST SP250-44 and later 

partially revised as described in a NIST Journal of Research manuscript [3, 4]. All 

data and analysis is recorded in the Internal Calibrations Databook.

Upon mutual agreement, dosimetry comparisons are performed with the high-dose 

calibration facility of the National Physical Laboratory of the United Kingdom.

Dosimeters from each facility are exchanged, measured, and the results compared.

Larger (i.e., among more laboratories) international comparisons occur

approximately every 10 years [5]. These data are summarized in the High-Dose 

International Comparisons Databook.
Radiation Physics Division 49010C, 49011C, 49015C, 49016C RPD-P-11

CALIBRATION IRRADIATIONS OF CUSTOMER SUPPLIED DOSIMETERS

WITH 60Co GAMMA RAYS

Version Date Author Approval Pages Filename

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References

1. NIST Technical Note 1297, Guidelines for Evaluating and Expressing the 

Uncertainty of NIST Measurement Results, 1994.

2. Domen, S.R., A sealed water calorimeter for measuring absorbed dose, J. Res. Natl. 

Inst. Stand. Technol., 99, pp. 121 – 141, 1994.

3. Radiation Processing Dosimetry Calibration Services and Measurement Assurance 

Program, Humphreys, J.C., Puhl, J.M., Seltzer, S.M., McLaughlin, W.L., 

Desrosiers, M.F., Bensen, D.L., Walker, M.L. 1998 NIST Special Publication 250-

44.

4. CCRI supplementary comparison of standards for absorbed dose to water in 60Co 

gamma radiation at radiation processing dose levels, D.T. Burns, P.J. AllisyRoberts, M.F. Desrosiers, V. Yu. Nagy, P.H.G. Sharpe, R.F. Laitano, K. Mehta, 

M.K.H. Schneider, Y. Zhang, Radiat. Phys. Chem. 75 (2006) 1087-1092.

5. Discovery of an Absorbed-Dose / Dose-Rate Dependence for the Alanine-EPR 

Dosimetry Systems and Its Implications in High-Dose Ionizing Radiation 

Metrology, M.F. Desrosiers, J.M. Puhl, S.L. Cooper, NIST J. of Res., 113 (2008) 

79-95.

6. Radiation Processing Dosimetry Calibration Services: Manual of Calibration 

Procedures, J. C. Humphreys, M. F. Desrosiers, D. L. Bensen, J. M. Puhl, S. M. 

Seltzer, W. L. McLaughlin, M. L. Walker. 1998 NIST Special Publication 250-45.

Records

Record Contents/Purpose Location

Irradiation Facilities 

Record Book

Records dose rates for irradiation 

geometries, laboratory instructions, and a 

record of maintenance of the facility

245/Irradiation 

facility

Electronic Calibration 

Log Book

A HD number is assigned to all accepted 

orders and logs calibration details. 

In the High 

Dose folder

Gammacell User Log 

Book for each 

irradiator

60Co irradiator logs 245/Irradiation 

facility

High-Dose 

Irradiations Databook

Records all final HD Irradiation

Worksheet

245/B0020

Internal Calibrations

Databook

Source ratio measurements and data 

analysis

245/B0020

High-Dose 

International 

Comparisons 

Databook

Interlaboratory measurement comparisons 

data summaries

245/B0020
Radiation Physics Division 49010C, 49011C, 49015C, 49016C RPD-P-11

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WITH 60Co GAMMA RAYS

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Filing and Retention

All paper copies of customer files are stored in the test folder for that 

service until they can be digitized and stored in ETF at which time it can 

be destroyed. The ETF is stored in OneNote. All customer-related 

electronic files are stored in the “High Dose” folder on the shared network 

drive. The Radiation Physics Division (RPD) Quality Manager shall 

maintain the original and all past versions of this RPD Procedure.
Radiation Physics Division 49010C, 49011C, 49015C, 49016C RPD-P-11

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Appendix A – Example Irradiation Worksheet
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Appendix B – Example Timing Worksheet
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Appendix C – Gammacell Operations

The unit consists of an annular source permanently enclosed within a lead shield, a 

cylindrical drawer, and a drive mechanism to move the drawer up or down along the 

vertical source centerline. The radiation level around the devices is less than 0.05

mSv/hr (5 mR/hr) at 30 cm (12 in) from the surface for all modes of operation.

Definitions

Collar. The collar sits on top of the head and allows access to the sample chamber.

The collar doors must always be closed when the drawer assembly is in motion.

Drawer Assembly. This assembly consists of four parts: the top shielding plug, the 

drawer top, the sample chamber, and the drawer bottom. This entire assembly 

moves vertically through the inner head plug and the head. The overall length of 

travel is 50 cm.

60Co Sources. The source cage contains a cylindrical array of 48 pencil positions.

The drawer assembly passes through the source array and locates the sample 

chamber at the geometrical center of the array during irradiations.

Sample Chamber. The access door of the sample chamber opens to allow items up 

to about 15 cm in diameter and 20 cm high to be inserted.

Drawer Movement. The unit is designed for complete stroke operation only, that is, 

a single stroke down or a single stroke up.

Geometry attenuation factor

All dose measurements are done with alanine-EPR measurements in the single-hole 

geometry. Four alanine pellets are stacked inside a polystyrene vial, see below. This 

vial is elevated to the center field of the chamber using a support rod.

Figure modified from [6]: A polystyrene alanine vial.

Other calibrated geometries include: five-hole cup for tape tab, Perspex, and

ampoule (see below), film sheet, polystyrene cube, and a polystyrene cup for live 

cultures.
Radiation Physics Division 49010C, 49011C, 49015C, 49016C RPD-P-11

CALIBRATION IRRADIATIONS OF CUSTOMER SUPPLIED DOSIMETERS

WITH 60Co GAMMA RAYS

Version Date Author Approval Pages Filename

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Figure modified from [6]: Five-hole cup.

The geometry attenuation factor and the QC geometry measurement factor are 

experimentally determined during geometry calibrations.

The geometry attenuation factor modifies the dose rate to deliver the known dose 

to dosimeters in a given calibrated geometry. These factors are listed in a master 

table that is linked to the Customer Irradiation Worksheet Template. They are 

accessed via a drop-down menu. There is a check box that applies the dewar 

correction factor for non-ambient irradiations. There is a dose-to-silicon factor 

that can also be applied upon customer request.

The QC dosimeters are typically located in a cavity inside the support rod. 

Because the QC dosimeters are not in the same position as the customer 

dosimeter, the QC geometry measurement factor is applied to correct for the 

difference.
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CALIBRATION IRRADIATIONS OF CUSTOMER SUPPLIED DOSIMETERS

WITH 60Co GAMMA RAYS

Version Date Author Approval Pages Filename

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Appendix D – Example Certificate

National Institute of Standards and Technology

ABSORBED-DOSE IRRADIATION 

CERTIFICATE

NIST Service Identification Number 49010C and 49011C

Dosimeter

Alanine Dosimeters Lot 212121

Customer

RAD Sterilizers, Inc.

2100 Gamma Way

Philadelphia, PA 19121

ATTN: K. Gray

Reference: PO# 2121-1234

Irradiation performed by Ileana M. Pazos

Reviewed by Lonnie Cumberland

Report approved by 

Michael G. Mitch, Leader

Dosimetry Group

Approved by

James M. Adams, Chief

Radiation Physics Division

Physical Measurement Laboratory 

For the Director of the National Institute of Standards and Technology

Information on technical aspects of this certificate may be obtained from Ileana M. Pazos, NIST, 100 Bureau 

Drive Stop 8460, Gaithersburg, MD 20899, 301-975-4121, ileana.pazos@nist.gov.

REFERENCE HD2121

682.02/O-00123456789-21

NIST DB 1055/121–122

July 23, 2021

Page 1 of 3 Pages
Radiation Physics Division 49010C, 49011C, 49015C, 49016C RPD-P-11

CALIBRATION IRRADIATIONS OF CUSTOMER SUPPLIED DOSIMETERS

WITH 60Co GAMMA RAYS

Version Date Author Approval Pages Filename

8.00 4/3/2023 IMP AKT 17 of 21 Procedure11v800

RAD Sterilizers supplied alanine dosimeters. The dosimeters were irradiated using gamma 

radiation from a calibrated 60Co irradiator, the NIST Gammacell 220-232. During 

irradiation, the dosimeter pellets were contained in a polystyrene vial. The dates of 

irradiation, values of dose rate, absorbed dose, and mean irradiation temperature were as 

follows:

Dosimeter

Identification Date of Irradiation Dose Rate (kGy/h)

Irradiation

Temp. °C

Absorbed 

Dose

kGy(H2O)

0.300 kGy July 8, 2021 0.424 23 0.300

0.500 kGy July 8, 2021 0.424 23 0.500

1.00 kGy July 8, 2021 0.424 23 1.00

2.00 kGy July 8, 2021 0.424 23 2.00

3.00 kGy July 8, 2021 0.424 23 3.00

REFERENCE HD2121

682.02/O-00123456789-21

NIST DB 1055/121–122

July 23, 2021

Page 2 of 3 Pages
Radiation Physics Division 49010C, 49011C, 49015C, 49016C RPD-P-11

CALIBRATION IRRADIATIONS OF CUSTOMER SUPPLIED DOSIMETERS

WITH 60Co GAMMA RAYS

Version Date Author Approval Pages Filename

8.00 4/3/2023 IMP AKT 18 of 21 Procedure11v800

UNCERTAINTIES AND RELATED FACTORS IN HIGH-DOSE IRRADIATIONS

High-Dose Irradiations in Standard Geometries

using the NIST 60Co Gammacell 220-232

(Expanded uncertainty: 1.2 % at a 95 % confidence level)

The high-dose irradiations at NIST involve the administration of 60Co gamma radiation 

under environmentally controlled conditions. The dose values from Alanine-Electron 

Paramagnetic Resonance (EPR) dosimetry are traceable to the quantity absorbed dose to 

water as directly realized by the NIST primary standard water calorimeter and are corrected 

by certain modifying factors (such as the geometry attenuation factor and source decay 

factor). The irradiated dosimeters, adjusted for dosimeter parameters, may be used to derive 

a calibration curve where dosimeter response is the dependent variable and absorbed dose is 

the independent variable. The absorbed dose value(s) given in this report can be used to 

check the accuracy of customer measurement systems and to verify the capabilities of those 

systems to both transfer and maintain traceability of measurement results. The absorbed 

dose values(s) relate only to the dosimeters in this report.

The uncertainty cited above is pertinent to absorbed dose in water in calibrated geometries.

A detailed list of the various sources of uncertainty and estimates of the magnitude of those 

uncertainties that make up the overall uncertainty given above may be obtained through the 

Internet (https://www.nist.gov/programs-projects/basic-metrology-high-dose-dosimetryuncertainty-tables) or by requesting such information from NIST. The uncertainties are 

divided into two types: A and B. Type A uncertainties are those evaluated by statistical 

methods, often associated with random effects. Type B uncertainties are those evaluated by 

other means, often associated with systematic effects.

Type A Uncertainties

The combined standard uncertainty evaluated by statistical methods is 0.28 % at an 

approximate level of confidence of 68 %.

Type B Uncertainties

The combined standard uncertainty based on scientific judgment is estimated to be 

0.55 % at an approximate level of confidence of 68 %.

Expanded Uncertainty

The Type A and Type B uncertainties have been combined in quadrature (the square root of 

the sum of the squares) and multiplied by a coverage t-factor of 2.0 to yield an expanded 

uncertainty of 1.2 % at an approximate level of confidence of 95 %.

REFERENCE HD2121 

682.02/O-00123456789-21

NIST DB 1055/121–122

July 23, 2021 

Page 3 of 3 Pages
Radiation Physics Division 49010C, 49011C, 49015C, 49016C RPD-P-11

CALIBRATION IRRADIATIONS OF CUSTOMER SUPPLIED DOSIMETERS

WITH 60Co GAMMA RAYS

Version Date Author Approval Pages Filename

8.00 4/3/2023 IMP AKT 19 of 21 Procedure11v800

Appendix E - Sample Table of Uncertainty

GC232 Calibration Geometry Dose Rate 

d.f. Uncertainty Source Type A (%) Type B (%)

6 Water Calorimetry in Vertical Beam 0.16 0.51

7 GC232/GC45 Source Ratio Data 0.08

7 GC45/B036 Source Ratio Data 0.17

3 Geometry Correction Factor (Perspex) 0.10

Field uniformity 0.01

Timer Error ( irradiation time > 8min) 0.20

60Co Decay Correction 0.02

sqrt(sum) 0.27 0.55

effective d.f. combined in quadrature 0.61

19 t-factor for 19 d.f at 95.45 % 2.14

Expanded Uncertainty at 95.45 % conf. 1.3 

Other standard irradiation geometries used in GC232, as well as other geometries in 

GC45 and GR420, will have slightly different values for source ratio uncertainty and 

geometry correction factor uncertainty. In those cases, the expanded uncertainty remains 

unchanged at 1.3 %. For more specialized geometries, such as low-temperature 

irradiations held inside a Dewar, additional components of uncertainty must be included 

and the uncertainty recomputed.
Radiation Physics Division 49010C, 49011C, 49015C, 49016C RPD-P-11

CALIBRATION IRRADIATIONS OF CUSTOMER SUPPLIED DOSIMETERS

WITH 60Co GAMMA RAYS

Version Date Author Approval Pages Filename

8.00 4/3/2023 IMP AKT 20 of 21 Procedure11v800

Appendix F - Checklist for High-Dose Irradiation Services
Radiation Physics Division 49010C, 49011C, 49015C, 49016C RPD-P-11

CALIBRATION IRRADIATIONS OF CUSTOMER SUPPLIED DOSIMETERS

WITH 60Co GAMMA RAYS

Version Date Author Approval Pages Filename

8.00 4/3/2023 IMP AKT 21 of 21 Procedure11v800