NIST HANDBOOK 150-2D

National

Voluntary

Laboratory

Accreditation

Program

Calibration

Laboratories

Technical Guide

for

Ionizing Radiation

Measurements

C. Douglas Faison and

Carroll S. Brickenkamp, Editors

September 2004

U.S. Department of Commerce

Donald L. Evans, Secretary

Technology Administration

Phillip J. Bond

Under Secretary of Commerce for Technology

National Institute of Standards and Technology

Arden L. Bement, Jr., Director
National Institute of Standards and Technology

NIST Handbook 150-2D

71 pages (September 2004)

CODEN: NIHAE2

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 2004

For sale by the Superintendent of Documents

U.S. Government Printing Office

Internet: bookstore.gpo.gov

Phone: (202) 512-1800

Fax: (202) 512-2250

Mail: Stop SSOP, Washington, DC 20402-0001

NVLAP AND THE NVLAP LOGO

The term NVLAP (represented by the NVLAP logo)

is a federally registered certification mark of the

National Institute of Standards and Technology and

the federal government, who retain exclusive rights

to control the use thereof. Permission to use the term

and/or logo is granted to NVLAP-accredited

laboratories for the limited purposes of announcing

their accredited status, and for use on reports that

describe only testing and calibration within the scope

of accreditation. NIST reserves the right to control

the quality of the use of the term NVLAP and of the

logo itself.
iii

Contents

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii

1 General information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 Purpose . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 Organization of handbook ...............................................1

1.3 Description of Calibration Laboratories Accreditation Program . . . . . . . . . . . . . . . . . 1

1.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.5 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.6 NVLAP documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

1.7 Assessing and evaluating a laboratory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2 Criteria for accreditation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

2.2 General criteria for ionizing radiation calibrations . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

2.3 Alpha-particle calibration of survey instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2.4 Beta-particle calibration of survey instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

2.5 Beta-particle irradiation of personnel dosimeters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

2.6 Gamma-ray calibration of survey instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

2.7 Gamma-ray irradiation of personnel dosimeters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

2.8 Gamma-ray source calibration for air-kerma rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

2.9 Gamma-ray calibration of reference-class instruments . . . . . . . . . . . . . . . . . . . . . . . 37

2.10 X-ray calibration of survey instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

2.11 X-ray irradiation of personnel dosimeters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

2.12 X-ray calibration of instruments for diagnostic radiology levels . . . . . . . . . . . . . . . . 47

2.13 X-ray calibration of reference-class instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

2.14 Neutron calibration of survey instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

2.15 Neutron irradiation of personnel dosimeters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

2.16 Neutron dosimeters and survey instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

2.17 Criteria for a high-dose radiation dosimetry calibration laboratory . . . . . . . . . . . . . . 60

2.18 Criteria for a radionuclide source calibration laboratory . . . . . . . . . . . . . . . . . . . . . . 62

v

Preface

The Calibration Laboratories Accreditation Program was developed by the National Voluntary Laboratory

Accreditation Program (NVLAP) at the National Institute of Standards and Technology (NIST) as a result

of interest from private industry and at the request of the National Conference of Standards Laboratories (now

the NCSL International). The goal of the program is to provide a means by which calibration laboratories

can be assessed for competency. This voluntary program is not designed to serve as a means of imposing

specific calibration procedures or minimum uncertainties on applicant laboratories; instead, the program

allows for all scientifically valid calibration schemes and requires that laboratories derive and document their

measurement uncertainties.

To accomplish this goal, NVLAP employs technical experts on a contract basis, to serve as assessors in each

of the following eight fields of physical metrology calibration:

• electromagnetic dc/low frequency,

• electromagnetic rf/microwave frequency, 

• time and frequency, 

• ionizing radiation, 

• optical radiation, 

• dimensional, 

• mechanical, and 

• thermodynamics. 

NIST Handbooks 150-2A through 150-2H are technical guides for the accreditation of calibration

laboratories, with each handbook corresponding to one of the eight fields of physical metrology calibration.

They are intended for information and use by:

• NVLAP technical experts in assessing laboratories,

• staff of accredited laboratories,

• those laboratories seeking accreditation, 

• other laboratory accreditation systems,

• users of laboratory services, and

• others needing information on the requirements and guidelines for accreditation under the NVLAP

Calibration Laboratories Accreditation Program.

NOTE The Calibration Laboratories Accreditation Program has been expanded to cover chemical calibration for

the providers of proficiency testing and certifiers of spectrophotometric NTRMs. (See NIST Handbooks 150-19 and

150-21.) Other NVLAP handbooks in the chemical calibration area are expected in the future.

The assessor uses NIST Handbook 150, NVLAP Procedures and General Requirements, and the appropriate

guides (NIST Handbooks 150-2A through 150-2H) to validate that a laboratory is capable of performing

calibrations within the laboratory’s stated uncertainties. These technical guides and other relevant technical

information support assessors in their assessments of laboratories. Along with inspecting the facilities,

documentation, equipment, and personnel, the assessor can witness a calibration, have an item recalibrated,

and/or examine the results of measurement assurance programs and round-robins to collect objective

evidence.

NIST Handbooks 150-2A through 150-2H supplement NIST Handbook 150, which contains Title 15 of the

U.S. Code of Federal Regulations (CFR) Part 285 plus all general NVLAP procedures, criteria, and policies.

The criteria in NIST Handbook 150 originally encompassed the requirements of ISO/IEC Guide 25:1990 and

the relevant requirements of ISO 9002 (ANSI/ASQC Q92-1987). These handbook criteria have been updated
vi

to incorporate the requirements of ISO/IEC 17025:1999. The entire series of Handbooks 150-2A through 150-

2H comprises information specific to the Calibration Laboratories Program and neither adds to nor detracts

from requirements contained in NIST Handbook 150.

Any questions or comments on this handbook should be submitted to the National Voluntary Laboratory

Accreditation Program, National Institute of Standards and Technology, 100 Bureau Drive, Stop 2140,

Gaithersburg, MD 20899-2140; phone (301) 975-4016; fax (301) 926-2884; e-mail NVLAP@nist.gov.
vii

Acknowledgments

NIST Handbook 150-2 was first available as a draft covering all eight fields of physical metrology calibration

in one volume. It has been separated into eight handbooks to allow easier updating and electronic

downloading from the NVLAP web site. The preparation of these documents has been a joint effort, with

input from representatives of other government agencies, laboratories, and the private sector.

Acknowledgment of their efforts is in order; however, the listing of individual names is impractical. The

submissions by individuals and companies offering suggestions for improvement to this document were also

very welcome, as were the contributions of those who attended the public workshops.

We thank all the NIST measurement divisions for their work in writing or contributing to the individual

handbooks. Listed below are those from the NIST measurement divisions who deserve special thanks for

input to the first draft of NIST Handbook 150-2D, Technical Guide for Ionizing Radiation Measurements:

• Mr. Jimmy C. Humphreys (High Dose Radiation Dosimetry), 

• Dr. J. M. R. Hutchinson (Radionuclide Sources), and 

• Dr. Robert B. Schwartz (Neutron Dosimeter and Survey Instruments). 

Also, we acknowledge and thank the entire list of contributors to NIST SP 812, Criteria for the Operation

of Federally-Owned Secondary Calibration Laboratories (Ionizing Radiation), October 1991.

On the second draft, we thank:

• Ms. C. Michelle O’Brien and Mr. Stephen M. Seltzer (Alpha-Particle, Beta-Particle, Gamma-Ray, and

X-Ray Measurements),

• Dr. David Gilliam and Dr. Alan Thompson (Neutron Measurements), 

• Dr. Marc F. Desrosiers (High-Dose Radiation Dosimetry), and

• Dr. Michael P. Unterweger (Radionuclides).

Additional thanks go to those who actively participated in the Technical Guide Workshop held November

1993 and to those who served as points of contact within fields of calibration. They include: Ms. Georgia

L. Harris, Mr. Norman B. Belecki, Dr. Theodore D. Doiron, Mr. Robert M. Judish, Mr. Thomas C. Larason,

Ms. Sally S. Bruce, and Dr. Donald B. Sullivan. A special thanks is owed to Mr. James L. Cigler for work

in developing the content and format of this guide, and to Ms. Vanda White for her editorial expertise in

making this a readable document.

Above all, we wish to thank Mr. Jon M. Crickenberger, the editor of the first three drafts of this document,

for literally hundreds of hours of his work in creating this guide. It was he who tasked the contributors to

produce the technical content, assembled the results of their efforts into a consistent format, and provided the

general commentary. Without Jon’s dedicated effort to this monumental task, this guide would never have

been published. 

NVLAP has edited the individual handbooks and made changes resulting from comments by individuals to

earlier draft versions. This editing has been to a different extent for each parameter. Every effort was made

to include all pertinent information relevant to an ISO/IEC 17025-derived technical guide. 

C. Douglas Faison and Carroll S. Brickenkamp, Editors

National Voluntary Laboratory Accreditation Program

National Institute of Standards and Technology

100 Bureau Drive, Stop 2140

Gaithersburg, MD 20899-2140
viii

Summary

This guide presents the general technical requirements (i.e., on-site assessment and proficiency testing) of

the laboratory accreditation program for calibration laboratories along with specific technical criteria and

guidance applicable to ionizing radiation measurements. These technical guidelines are presented to indicate

how the NVLAP criteria may be applied.

Any calibration laboratory (including commercial, manufacturer, university, or federal, state, or local

government laboratory) engaged in calibration in ionizing radiation measurements listed in this handbook

may apply for NVLAP accreditation. Accreditation will be granted to a laboratory that complies with the

criteria for accreditation as defined in NIST Handbook 150. Accreditation does not guarantee laboratory

performance – it is a finding of laboratory competence.

Fields of calibration covered: Specific calibration parameters and related stimulus and measurement devices

in areas of ionizing radiation measurement. 

Scope of accreditation: 

• Calibration parameter(s), range, and uncertainty level 

• Types of measuring and test equipment

• Quality assurance system for measuring and test equipment

Period of accreditation: One year, renewable annually.

On-site assessment: Visit by an assessor(s) to determine compliance with the NVLAP criteria before initial

accreditation, in the first renewal year, and every two years thereafter. Preassessment and monitoring visits

are conducted as required. All calibration parameters or general areas of calibration within the specific scope

of accreditation requested will be assessed.

Assessors: Selected from technical experts with experience in the appropriate areas of calibration and quality

systems assessment.

Proficiency testing (measurement assurance): Each laboratory is required to demonstrate its capability to

successfully perform calibrations as part of on-site assessment or by documented successful completion of

an approved Measurement Assurance Program (MAP) or round-robin intercomparison. Proficiency testing

may be required for initial accreditation, or when other evidence of measurement assurance is not evident,

and may be conducted annually thereafter. Advance notice and instructions are given before proficiency

testing is scheduled.

Fees: Payments are required as listed on the NVLAP fee schedule, including the initial application fee,

administrative/technical support fee, on-site assessment fee, and proficiency testing fee.
NIST Handbook 150-2D 1 September 2004

1 General information

1.1 Purpose

The purpose of this handbook is to amplify the general requirements for accreditation by NVLAP of

calibration laboratories in the area of ionizing radiation measurements covered by the Calibration

Laboratories Program. It complements and supplements the NVLAP programmatic procedures and general

requirements found in NIST Handbook 150, NVLAP Procedures and General Requirements. The interpretive

comments and additional guidelines contained in this handbook make the general NVLAP criteria specifically

applicable to the Calibration Laboratories Program. 

This handbook does not contain the general requirements for accreditation, which are listed in NIST

Handbook 150, but rather provides guidelines for good calibration laboratory practices, which may be useful

in achieving accreditation. 

1.2 Organization of handbook

The handbook is organized in two sections. The first section provides additional explanations to the general

procedures and requirements contained in NIST Handbook 150. The second section provides details and

guidance specifically for ionizing radiation calibration laboratories.

1.3 Description of Calibration Laboratories Accreditation Program

On May 18, 1992, as a result of the petition and public notice process, the Director of the National Institute

of Standards and Technology published in the Federal Register a notice of intent to develop the Calibration

Laboratories Accreditation Program under the procedures of the National Voluntary Laboratory Accreditation

Program . On June 2, 1994, the procedures and general requirements under which NVLAP operates, Title

15, Part 285 of the U.S. Code of Federal Regulations (CFR), were revised to: 

a) expand the procedures beyond testing laboratories to include accreditation of calibration laboratories,

b) update the procedures to ensure compatibility with generally accepted conformity assurance and

conformity assessment concepts,

c) incorporate international changes, especially with relevant International Organization for

Standardization/International Electrotechnical Commission (ISO/IEC) documents (e.g., ISO/IEC Guides

25 (now ISO/IEC 17025:1999), 38, 43, and 58, and the ISO 9000 series), and

d) facilitate and promote acceptance of the calibration and test results between countries to avoid barriers

to trade.

Calibration laboratory accreditation is offered in eight fields of physical metrology calibration covering a

wide variety of parameters and includes accreditation in multifunction measuring and test equipment

calibrations. Specific requirements and criteria have been established for determining laboratory

qualifications for accreditation following prescribed NVLAP procedures. The criteria address the laboratory’s

management organization, quality system, personnel, methods and method validation, equipment, control of

environmental effects, measurement traceability, sampling methods, handling of test and calibration items,

methods to assure the quality of its measurement results, reports, service to its clients, review of requests and
NIST Handbook 150-2D 2 September 2004

contracts, subcontracting, purchasing, control of nonconforming work, handling of complaints, document

and record control, corrective and preventive actions, internal audits, and management reviews.

On September 18, 1992, a public workshop was held at NIST Gaithersburg and attended by a mix of private

sector and government personnel. The workshop reviewed a draft handbook, which included general

requirements, as well as very specific technical requirements for direct current voltage calibrations at all

levels. As a result of the workshop, the draft handbook was revised to take the form of a Calibration

Laboratories Program Handbook, which included the general requirements for laboratories (using ISO/IEC

Guide 25 as a basis), and eight companion Technical Guides covering the specific requirements for each field

of calibration offered for accreditation.

On May 18, 1993, a public workshop on the revised draft program handbook was held at NIST Boulder and

attended by more than 60 industry and government personnel. Comments from this workshop, as well as

responses to a survey/checklist mailing, were used to prepare the final draft of the handbook, now entitled

NVLAP Procedures and General Requirements (NIST Handbook 150), published in March 1994. [NIST

Handbook 150 was revised in 2001 to incorporate ISO/IEC 17025:1999.]

A public workshop for the Calibration Laboratories Technical Guides was held at NIST Gaithersburg, on

November 22 through 24, 1993. More than 60 industry and government personnel attended and provided

comments on the draft version of the Technical Guide for each of eight fields of calibration. As a result, the

eight Technical Guides were incorporated into a draft Handbook 150-2, Calibration Laboratories Technical

Guide, covering the fields being offered for accreditation. [In 2000, Handbook 150-2 (draft) was divided into

eight handbooks, one for each calibration area.]

The need for technical experts to serve as assessors was advertised, and the first group of assessors was

selected and trained during a four-day session held from November 16 through 19, 1993, in Gaithersburg,

using materials developed by NVLAP.

The Calibration Laboratories Accreditation Program officially began accepting applications when notification

was given in the Federal Register dated May 11, 1994. Applications are accepted and processed following

procedures found in NIST Handbook 150.

1.4 References

1.4.1 General

a) White, V. R., Alderman, D. F., and Faison, C. D., editors, NIST Handbook 150: NVLAP Procedures and

General Requirements; available from:

National Voluntary Laboratory Accreditation Program

National Institute of Standards and Technology

100 Bureau Drive, Stop 2140

Gaithersburg, MD 20899-2140

Phone: (301) 975-4016

Fax: (301) 926-2884

E-mail: nvlap@nist.gov

NVLAP Web site: http://www.nist.gov/nvlap

b) Croarkin, M. C., Measurement Assurance Programs, Part II: Development and Implementation, NBS

Special Publication 676-II, U.S. Government Printing Office, Washington, DC, 1985. 
1

NCSL documents available from: NCSL International, 2995 Wilderness Place, Suite 107, Boulder, CO 80301-5404

Phone: (303) 440-3339; Fax: (303) 440-3384; E-mail: info@ncsli.org

NCSLI web site: http://www.ncsli.org

2

ISO and ANSI documents are available from:

Global Engineering Documents (paper copies): Order phone (800) 854-7179

American National Standards Institute (ANSI) (electronic copies): ANSI eStandards Store

ANSI web site: http://www.ansi.org

NIST Handbook 150-2D 3 September 2004

c) NCSL Recommended Practice RP-7: Laboratory Design, 1993.1

d) ISO/IEC/BIPM Guide to the Expression of Uncertainty in Measurement (GUM), 1993.2

e) ISO/IEC/BIPM International Vocabulary of Basic and General Terms in Metrology (VIM), 1993.2

f) Taylor, Barry N., Kuyatt, Chris E., “Guidelines for Evaluating and Expressing the Uncertainty of NIST

Measurement Results,” NIST Technical Note 1297, U.S. Government Printing Office, Washington D.C.,

1994. Available on-line at http://physics.nist.gov/Document/tn1297.pdf.

g) ANSI/NCSL Z540-1-1994, Calibration Laboratories and Measuring and Test Equipment—General

Requirements.1

h) ANSI/NCSL Z540-2-1997, U.S. Guide to the Expression of Uncertainty in Measurement.

1

i) ISO/IEC Guide 43: 1997, Proficiency testing by interlaboratory comparisons, Part 1 and Part 2.

2

j) Ehrlich, C. D., and Raspberry, S. D., “Metrological Timelines in Traceability,” J. Res. NIST, 103, (1),

Jan-Feb, 1998.

k) NCSL International Recommended Practice RP-15: Guide for Interlaboratory Comparisons, 1999.1

l) ISO/IEC 17025: 1999: General requirements for the competence of testing and calibration laboratories.2

m) Taylor, Barry N., ed., “The International System of Units (SI),” NIST Special Publication 330, 2001

Edition, U.S. Government Printing Office, Washington D.C., 2001. Available on-line at

http://physics.nist.gov/Pubs/SP330/sp330.pdf.

1.4.2 Alpha radiation

a) Hutchinson, J. M. R., Naas, C. R., Walker, D. H., and Mann, W. P., “Backscattering of Alpha Particles

from Thick Metal Backings as a Function of Atomic Weight,” Int. J. Appl. Radiat. Isotopes, 19, p. 517,

1968.

b) Mann, W. B., ed., NCRP Report 58, A Handbook of Radioactivity Measurements Procedures, Section

3.7 – Alpha-Particle Counting, Natl. Council Rad. Protect. And Meas., Washington, DC 1985.

c) Hutchinson, J. M. R., “NBS Measurement Services: Alpha-Particle Calibrations,” NBS Special

Publication 250-5, 1987.
NIST Handbook 150-2D 4 September 2004

d) Calhoun, J. M., “NBS Measurement Services: Radioactivity Calibrations with the ‘4π’ Gamma

Ionization Chamber and Other Radioactivity Calibration Capabilities,” NBS Special Publication 250-10,

1987.

1.4.3 Beta radiation

a) ISO 6980-1996, Reference Beta Radiations for Calibrating Dosemeters and Doseratemeters and for

Determining their Response as a Function of Beta Radiation Energy, International Organization for

Standardization, Geneva, 1996.

b) Pruitt, J. S., “Calibration of Beta-Particle Ophthalmic Applications at the National Bureau of Standards,”

J. Res. Natl. Bur. Stand., 91, p. 165, 1986.

c) DOE/EH-0027, Department of Energy Standard for the Performance Testing of Personnel Dosimetry

Systems, U.S. Department of Energy, Washington, DC, 1986.

d) Pruitt, J. S., “NBS Measurement Services: Calibration of Beta-Particle Emitting Ophthalmic

Applications,” NBS Special Publication 250-9, 1987.

e) Pruitt, J. S., Soares, C. G., and Ehrlich, M., “NBS Measurement Services: Calibration of Beta-Particle

Radiation Instrumentation and Sources,” NBS Special Publication 250-21, 1988.

f) Soares, C. G., “Calibration of Ophthalmic applications at NIST – A revised approach,” Med. Phys., 18,

p. 787, 1991.

g) ANSI N13.11-2001, Criteria for Testing Personnel Dosimetry Performance, American National

Standards Institute, New York, NY, 2001.

1.4.4 Gamma radiation

a) DOE/EH-0027, Department of Energy Standard for the Performance Testing of Personnel Dosimetry

Systems, U.S. Department of Energy, Washington, DC, 1986.

b) ISO 4037-1, X and gamma reference radiation for calibrating dosemeters and doserate meters and for

determining their response as a function of photon energy – Part 1: Radiation characteristics and

production methods, International Organization for Standardization, Geneva, 1996.

c) Lamperti, P. J., O’Brien, C. M., “Calibration of X-Ray and Gamma-Ray Measuring Instruments,” NIST

Special Publication 250-58, U.S. Government Printing Office, 2001.

d) ANSI N13.11-2001, Criteria for Testing Personnel Dosimetry Performance, American National

Standards Institute, New York, NY, 2001.

1.4.5 X radiation

a) AAPM (ADCL) Performance Specifications and Acceptance Testing for X-Ray Generators and

Automatic Exposure Control Devices, 1985.

b) DOE/EH-0027, Department of Energy Standard for the Performance Testing of Personnel Dosimetry

Systems, U.S. Department of Energy, Washington, DC, 1986.
NIST Handbook 150-2D 5 September 2004

c) AAPM (ADCL) Equipment Requirements and Quality Control for Mammography, Diagnostic X-Ray

Imaging Committee Task Group #7, 1990.

d) ISO 4037-1, X and gamma reference radiation for calibrating dosemeters and doserate meters and for

determining their response as a function of photon energy – Part 1: Radiation characteristics and

production methods, International Organization for Standardization, Geneva, 1996.

e) Lamperti, P. J., O’Brien, C. M., “Calibration of X-Ray and Gamma-Ray Measuring Instruments,”

National Institute of Standards and Technology Special Publication 250-58, U.S. Government Printing

Office, 2001.

f) ANSI N13.11-2001, Criteria for Testing Personnel Dosimetry Performance, American National

Standards Institute, New York, NY, 2001.

1.4.6 Neutron radiation

a) Lorenz, A., “A Survey of Neutron Sources and Their Applications,” UCRL-51298, TID-4500, UC-34,

Lawrence Livermore Laboratory, 1972.

b) Schwartz, R. B. and Eisenhauer, C. M., “The Design and Construction of a D2O-Moderated 252Cf Source

for Calibrating Neutron Personnel Dosimeters Used at Nuclear Power Reactors,” NUREG/CR-1204,

U.S. Nuclear Regulatory Commission, Washington, DC, 1980.

c) Schwartz, R. B. and Eisenhauer, C. M., “Procedures for Calibrating Neutron Personnel Dosimeters,”

National Bureau of Standards Special Publication 633, U. S. Government Printing Office, Washington,

1982.

d) Prevo, C. T., “Comparison of Calculated Neutron Spectrum and Dose Equivalent from NBS and LLNL

15-cm D2O Spheres,” Hazards Control Department Annual Technology Review, UCRL-50007-83, UC41, Lawrence Livermore National Laboratory, 68, 1983.

e) Eisenhauer, C. M., Hunt, J., and Schwartz, R. B., “Calibration Techniques for Neutron Personnel

Dosimetry,” Radiat. Prot. Dosim. 10, (43), 1985.

f) DOE/EH-0027, Department of Energy Standard for the Performance Testing of Personnel Dosimetry

Systems, U.S. Department of Energy, Washington, DC, 1986.

g) Schwartz, R. B., “NBS Measurement Services: Neutron Personnel Dosimetry,” National Bureau of

Standards Special Publication 250-12, U. S. Government Printing Office, Washington, 1987.

h) Eisenhauer, C. M., Schwartz, R. B., and McCall, R. C., “Effect of Air Scatter on Calibration of

Instruments for Detecting Neutrons,” Radiation Protection Dosimetry, 19, p. 77, 1987.

i) Burger, G. and Schwartz, R. B., “Guidelines on Calibration of Neutron Measuring Devices,” Technical

Reports Series No. 285, IAEA, Vienna, 1988.

j) ISO 8529-1989, Neutron Reference Radiations for Calibrating Neutron-Measuring Devices Used for

Radiation Protection Purposes and for Determining Their Response as a Function of Neutron Energy,

International Organization for Standardization, Geneva, 1989.
NIST Handbook 150-2D 6 September 2004

k) Eisenhauer, C. M. “Review of Scattering Corrections for Calibration of Neutron Instruments,” Radiation

Protection Dosimetry, 28, p. 253, 1989.

l) Kluge, H., Weise, K., and Hunt, J. B. “Calibration of Neutron Sensitive Spherical Devices with Bare and

D2O-Moderated 252Cf Sources in Rooms of Different Sizes,” Radiation Protection Dosimetry, 32, p. 233.

1990.

m) ISO/CD 10647: 1992, Procedures for Calibrating and Determining the Energy Response of Neutron

Measuring Devices used for Radiation Protection, International Organization for Standardization,

Geneva, 1992.

n) ANSI N13.11-2001, Criteria for Testing Personnel Dosimetry Performance, American National

Standards Institute, New York, NY, 2001.

1.4.7 High-dose radiation

a) McLaughlin, W. L., “Standardization of high-dose measurement of electron and gamma-ray absorbed

doses and dose rates,” High-Dose Dosimetry, Proceedings of International Symposium, Vienna, 1984,

IAEA STI/PUB/671, pp. 357-371, International Atomic Energy Agency, Vienna, 1985.

b) DOE/EH-0027, Department of Energy Standard for the Performance Testing of Personnel Dosimetry

Systems, U.S. Department of Energy, Washington, DC, 1986.

c) ASTM E 1250, Standard Test Method for Application of Ionization Chambers to Assess the Low Energy

Gamma Component of Cobalt-60 Irradiators Used in Radiation-Hardness Testing of Silicon Electronic

Devices, 1988.

d) Humphreys, J. C., Hocken, D., and McLaughlin, W. L., “Dosimetry for High Dose Applications,” NBS

Special Publication 250-11, National Bureau of Standards, Gaithersburg, MD, 1988.

e) McLaughlin, W. L., “Reference dosimetry and measurement quality assurance,” Radiation Physics and

Chemistry, 40, pp. 945-951, 1989.

f) McLaughlin, W. L., Boyd, A. W., Chadwick, K. H., McDonald, J. C., and Miller, A., Dosimetry for

Radiation Processing, Taylor and Francis, London, 1989.

g) ASTM E 177-90A, Standard Practice for Use of the Terms Precision and Accuracy in ASTM Test

Methods, 1990.

h) Inn, K. G. W., Coursey, B. M., Eisenhower, E. H., Walker, M. D., Humphreys, J. C., Heaton, H. T.,

Duvall, K. C., “The role of the Office of Radiation Measurement in quality assurance,” The Science of

the Total Environment, 130/131 pp. 497-507, Elsevier Science Publishers B.V., Amsterdam, 1993.

i) ASTM E 1707, Estimating Uncertainties in Dosimetry for Radiation Processing, 1995.

j) IEC 60731 1997-07 Medical electrical equipment - Dosimeters with ionization chambers as used in

radiotherapy. International Electrotechnic Commission, Geneva, 1997.

k) Walker, M. L., Bensen, D. L., Desrosiers, M. F., Humphreys, J. C., McLaughlin, W. L., Puhl, J. M.,

Seltzer, S. M. “Radiation Processing Dosimetry Calibration Services and Measurement Assurance
NIST Handbook 150-2D 7 September 2004

Program,” NIST Special Publication 250-44, National Institute of Standards and Technology,

Gaithersburg, MD, 1998. 

l) ASTM E 170, Standard Terminology Relating to Radiation Measurements and Dosimetry, 1999. 

m) ASTM E 1249, Standard Practice for Minimizing Dosimetry Errors in Radiation Hardness Testing of

Silicon Electronic Devices using Co-60 Sources, 2000.

n) ASTM E 1261, Standard Guide for Selection and Calibration of Dosimetry Systems for Radiation

Processing, 2000.

o) ANSI N13.11-2001, Criteria for Testing Personnel Dosimetry Performance, American National

Standards Institute, New York, NY, 2001.

p) ASTM E 456, Standard Terminology Relating to Quality and Statistics, 2002.

1.4.8 Radionuclide sources

a) Handbook for Analytical Quality Control in Radioanalytical Laboratories, EPA-600/7-77-088, August

1977.

b) Inhorn, Stanley L., ed., Quality Assurance Practices for Health Laboratories, Chapter 17 Radiochemistry,

American Public Health Association, 1015 Eighteenth Street, N.W., Washington, D.C. 20036, 1978.

c) USNRC Regulatory Guide 4.15, Quality Assurance for Radiological Monitoring Programs, February

1979.

d) Hoppes, D. D., and Hutchinson, J. M. R., International Committee for Radionuclide Metrology:

“Guidelines for Acceptance of Radioactivity Calibration Sources,” Applied Radiation Isotopes, 42, (9),

pp. 893-897, 1991.

e) ANSI/IEEE N42.23-1996: Measurement and Associated Instrumentation Quality Assurance for

Radioassay Laboratories, 1996.

f) ANSI/ASME NQA-1-2000, Quality Assurance Program Requirements for Nuclear Facilities, 2000.

g) ANSI N42.22-2002: Traceability of Radioactive Sources to the National Institute of Standards and

Technology (NIST) and Associated Instrument Quality Control, 2002. 

1.5 Definitions

Definitions found in NIST Handbook 150 apply, but may be interpreted differently or stated differently, when

necessary to amplify or clarify the meaning of specific words or phrases as they apply to specific technical

criteria.

1.5.1 Absorbed dose: The quantity of main interest to the clinician for both beta and gamma sources. It

is the quotient of dE by dm, that is, the differential energy absorbed in the differential mass in the medium.

The unit of absorbed dose is the gray (Gy), which is 1 joule per kilogram.
NIST Handbook 150-2D 8 September 2004

1.5.2 Accuracy goals: The maximum acceptable deviation from the accepted reference value of a

measured quantity, where the accepted reference value is defined by the appropriate national standard.

1.5.3 Air kerma: The quotient of dEtr by dm, where dEtr is the sum of the initial kinetic energies of all

electrons liberated by photons in a volume element of air and dm is the mass of air in that volume element.

Kerma is the acronym for Kinetic Energy Released per unit Mass. The SI unit of air kerma is the gray (Gy).

1.5.4 Air kerma strength: The quantity used to specify the strength of a gamma-ray emitting

radionuclide. It is a measure of the energy released in a volume of air at some distance from a radioactive

source. For photon emitting sources used in brachytherapy it has units of Gy s-1m2

.

1.5.5 Attenuator: Absorbing material intentionally placed in the path of a radiation field or beam to

reduce the intensity reaching the detector.

1.5.6 Beam quality: Used to refer to a specific x-ray beam with a characteristic half-value layer and

produced by a constant potential kilovoltage. For example, the beam quality is often given in terms of the

thickness of aluminum or copper required to reduce the air kerma rate to 50 % (half-value layer HVL) and

to 25 % of its original value.

1.5.7 Calibration: The process whereby the response of a dosimeter or measuring instrument is

characterized through comparison with an appropriate standard that is traceable to, and consistent with, a

national standard.

1.5.8 Calibration coefficient: Term used when the calibration or correction has a dimension (such as Gy).

See also calibration factor.

1.5.9 Calibration factor: Term used when the calibration or correction has no dimensions (such as (true

rads)/(calculated rads)). See also calibration coefficient.

1.5.10 Check standard: A standard that is used routinely to calibrate or check material measures,

measuring instruments or reference materials. A check standard is usually calibrated against a reference

standard. A check standard is also known as a working standard.

1.5.11 Collimator: A device used to limit the size, shape, and direction of a radiation beam.

1.5.12 Depth dose: The relationship between the absorbed dose and depth in tissue. For example, one can

define a reference depth in terms of the absorbed dose at 1 cm tissue depth for photons or 2 mm tissue depth

for beta particles.

1.5.13 Dosimetry system: A system used for determining absorbed dose, consisting of dosimeters,*

measurement instruments and their associated reference standards, and operating procedures.

* The types of dosimeters include reference standard dosimeters, transfer standard dosimeters, and routine

dosimeters. See ASTM E 1261 for guidance on the selection and calibration of the various dosimetry

systems for irradiating materials. See ANSI N13.11-2001 for personnel dosimetry systems.

1.5.14 Effective energy, Eeff (of radiation comprised of x rays with a range of energies): Energy of the

monoenergetic x-rays which have the same half-value layer (see 1.5.19 below) as the spectrum in question.

1.5.15 Exposure: The quotient of dQ by dm, where dQ is the sum of the electrical charges on all the ions

of one sign produced in air when all the electrons are completely stopped in air. The SI unit of exposures is
NIST Handbook 150-2D 9 September 2004

the coulomb per kilogram (C/kg); the special unit of exposure, the roentgen (R), is equal to exactly 2.58E-4

C/kg.

1.5.16 Extrapolation chamber: An ionization chamber in which the separation of electrodes is variable,

thereby enabling a series of measurements with decreasing separation so that the measured ion current per

unit volume can be extrapolated to the case of infinitesimal volume. An extrapolation chamber is a primary

standard chamber used at the NIST to establish the surface absorbed dose rate for beta particle emitting

sources. 

1.5.17 Free-air facility: A calibration facility in which the radiation emitted by the source reaches the

instrument under calibration with minimal scatter from nearby structures.

1.5.18 Free-field quantity: A radiation quantity, such as neutron dose equivalent, that has been corrected

to remove contributions from scattered radiation (e.g., air scattering and room return).

1.5.19 Half-value layer (air kerma) (HVL): The thickness of a specified substance which, when

introduced into the path of a given beam of radiation, attenuates the beam of radiation to an extent such that

the air-kerma rate is reduced to half of its original value. 

In this definition, the contribution of all scattered radiation, other than that which might be present initially

in the beam concerned, is deemed to be excluded in determining the HVL.

1.5.20 Homogeneity coefficient (h): The ratio of the first half-value layer to the second half-value layer

(air kerma). 

1.5.21 In-air ionization chamber: A chamber that is open to the atmosphere, therefore requiring humidity,

pressure, and temperature corrections. It is widely used for high activity sources, such as high-dose-rate

iridium-192 sources. 

1.5.22 Ionization chamber: Gas-filled enclosure in which ion pairs created by incident radiation are

collected on electrodes.

1.5.23 Leakage radiation: Radiation other than the useful beam emitted from an x-ray tube housing or a

source container.

1.5.24 Mean energy (mean photon energy), : Ratio defined by the formula:

∫

∫

=

max

0

max

0

E

dE E

E

EdE E

E

φ

φ

where φE is the derivative of the fluence φ of the primary photons of energy E with respect to E, and

defined as 

dE

d E

E

φ( ) φ =
NIST Handbook 150-2D 10 September 2004

1.5.25 Monitor: Instrument used to monitor the stability of the air-kerma rate during irradiation or to

compare values of air kerma after successive irradiations.

1.5.26 Phantom: The material used for the absorbing medium in the experimental dose measurement.

Several different phantom materials are used, including water phantoms and those fabricated from plastics

(e.g., A-150 plastic, tissure-equivalent plastic, and solid water).

1.5.27 Point source: A radiation source whose maximum dimension is small compared with the source-todetector distance used for irradiation of a dosimeter or instrument.

1.5.28 Proficiency testing: Determination of laboratory performance by means of comparing and

evaluating calibrations or tests on the same or similar items or materials by two or more laboratories in

accordance with predetermined conditions. For the NVLAP Calibration Laboratories Accreditation Program,

this entails using a transport standard as a measurement artifact, sending it to applicant laboratories to be

measured, and then comparing the applicant’s results to those of a reference laboratory on the same artifact.

1.5.29 Primary radiation (or beam): Radiation or beam emitted by the x-ray tube.

1.5.30 Primary standard dosimeter: Dosimeter of the highest metrological quality, established and

maintained as an absorbed dose standard by a national or international standards organization.

1.5.31 Quarter-value layer (QVL): The thickness of the specified material added as a beam attenuator

that reduces the air kerma rate to one quarter of the unattenuated beam air kerma rate value.

1.5.32 Radiation processing: The intentional irradiation of products or materials to preserve, modify, or

improve their characteristics.

1.5.33 Radiation quality: The quality of a filtered x radiation is characterized by the following

parameters:

• mean energy, , of a beam, expressed in kiloelectronvolts (keV),

• resolution, RE, expressed in percent (%),

• half-value layer (air kerma), HVL, expressed in mm of Al or Cu, and

• homogeneity coefficient, h.

1.5.34 Radioactivity: The phenomenon of emissions of neutral or charged particles or electromagnetic

radiations from unstable atomic nuclei (radionuclides). Radioactivity is an amount of a radionuclide in a

particular energy state at a given time. Mathematically, it is defined as the quotient of dN by dt, where dN

is the number of spontaneous nuclear transformations from that energy state in the time interval dt.

The unit of activity in SI units is the becquerel (Bq), which is equal to the unit reciprocal second (s-1). In

many fields, the older unit, the curie (Ci), is still in use, where 1 Ci = 3.7 × 1010 Bq (exactly).

The activity of an amount of radionuclide is given by the product of the decay constant, λ, and the number

of nuclei present at time t, thus A = λ N.

The half life, T1/2, is the time necessary for one half of the nuclei to decay. The activity at any time t can be

computed using the initial activity A0 and the decay time t according to A = A0 exp (-(ln 2) t/T1/2).
NIST Handbook 150-2D 11 September 2004

1.5.35 Reference standard dosimeter: A dosimeter, of high metrological quality, used as a standard to

provide measurements traceable to, and consistent with, measurements made using primary standard

dosimeters.

1.5.36 Residual maximum beta energy, Eres: The maximum energy of the beta spectrum from all beta

decay branches of a radionuclide at the calibration distance.

1.5.37 Residual maximum beta range, Rres: The range in an absorbing material of a beta spectrum of

residual maximum energy, Eres.

1.5.38 Resolution (spectral resolution, RE) (full width at half maximum): Ratio, expressed as a

percentage, defined by the formula:

×100 ∆ = E

E RE

where increment ÎE is the spectrum width corresponding to half the maximum ordinate of the spectrum.

In the case where fluorescence radiation is present in the spectrum, the spectrum width measured is based

upon the continuum only. 

1.5.39 Ripple: The periodic variation in the potential difference between the cathode and anode of an x-ray

tube, resulting from rectification of an alternating current. As the ripple is decreased by the use of filtering

circuits, a constant potential is more nearly approached. See also value of peak-to-peak voltage.

1.5.40 Room-scattered radiation: Radiation that is scattered from the walls, floor, ceiling, or other

structural part of the radiation room.

1.5.41 Routine dosimeter: Dosimeter calibrated against a primary-, reference-, or transfer-standard

dosimeter and used for routine absorbed dose measurement.

1.5.42 Scattered radiation: Radiation that, as the result of interaction with matter, has had its direction

changed and, for some interactions, its energy changed.

1.5.43 Second half-value layer: The difference between the quarter value layer and the half-value layer.

1.5.44 Secondary (fluorescence) radiation: Radiation or beam emitted by a medium that is excited by

the primary radiation and subsequently de-excites.

1.5.45 Slab source: A radiation source whose maximum dimension is large compared with the source-todetector distance used for irradiation of a dosimeter or instrument.

1.5.46 Survey instrument: A hand-held instrument used to measure ionizing radiation for purposes of

radiation protection. It does not include instruments designed as area, portal, or personnel monitors, as

monitors of radioactive gases or airborne particulates, or as dose or beam calibrators for medical diagnostic

or therapeutic applications.

1.5.47 Thermoluminescent dosimeter (TLD): Devices based on materials which store a fraction of the

energy deposited by an external source. The stored energy may be released by heating the TLD with a thermal

source or a laser.
NIST Handbook 150-2D 12 September 2004

1.5.48 Thin source: A radiation source consisting of radioactive material uniformly distributed in a thin

layer over the surface of a flat metallic backing plate so as to cause minimal degradation of the energy

spectrum.

1.5.49 Traceability: Property of the result of a measurement or the value of a standard whereby it can be

related to stated references, usually national or international standards, through an unbroken chain of

comparisons all having stated uncertainties. [VIM:1993, 6.10 – reference 1.4.1 e)]

A single measurement intercomparison is sufficient to establish uncertainty relationships only over a limited

time interval (see Ehrlich and Raspberry, 1998); internal measurement assurance (see Croarkin, 1985), using

control (check) standards, is required to fully demonstrate that uncertainties remain within stated levels over

time. For the purposes of demonstrating traceability for NVLAP accreditation, a laboratory must demonstrate

not only that there is an unbroken chain of comparisons to national standards, but also that this chain is

supported by appropriate uncertainties, measurement assurance processes, continuous standard maintenance,

proper calibration procedures, and proper handling of standards. In this way, traceability is related to these

other areas of calibration.

1.5.50 Transfer standard dosimeter: A dosimeter, often a reference standard dosimeter, suitable for

transport between different locations for use as an intermediary to compare absorbed dose measurements.

1.5.51 Transmission chamber: A thin-walled ionization chamber designed to monitor a radiation beam

that is transmitted through the chamber with minimal attenuation or scatter.

1.5.52 Value of peak-to-peak voltage: Ratio, expressed as a percentage, defined for a given current by

the formula:

100

max

max min × −

U

U U

where Umax is the maximum value and Umin the minimum value between which the voltage oscillates. See also

ripple.

1.5.53 Well ionization chamber: A sealed, pressurized ionization chamber (also called a dose calibrator)

intended for use in assaying brachytherapy sources. Its response must be determined for each source type and

will in general depend on the particular source jig and catheter used for the measurement.

1.5.54 Working standard: A standard that is used routinely to calibrate or check material measures,

measuring instruments, or reference materials. A working standard is usually calibrated against a reference

standard. This is also known as a check standard.

1.5.55 X-ray tube: Vacuum tube designed to produce x-rays by bombardment of the anode by a beam of

electrons accelerated through a potential difference.

1.5.56 X-ray tube shielding: Fixed or mobile panel intended to reduce the contribution of scatter xradiation to the primary or fluorescence (secondary) beam.

1.5.57 X-ray unit: Assembly comprising a high-voltage supply, an x-ray tube with its protective hosing

and high-voltage electrical connections, and an x-ray controller.
NIST Handbook 150-2D 13 September 2004

1.6 NVLAP documentation

1.6.1 Accreditation documents

Laboratories granted NVLAP accreditation are provided with two documents: Scope of Accreditation and

Certificate of Accreditation. The Scope of Accreditation lists the “Best Uncertainty” that an accredited

laboratory can provide for a given range or nominal value within a given parameter of measurement. This

“Best Uncertainty” is a statement of the smallest uncertainty that a laboratory has been assessed as capable

of providing for that particular range or nominal value. The actual reported value of uncertainty for any

particular measurement service that the accredited laboratory provides under its scope may vary depending

on such contributors as the statistics of the test and uncertainties associated with the device under test.

1.6.2 Fields of calibration and parameters selection list

The Calibration Laboratories program encompasses eight fields of physical metrology calibration, with

multiple parameters under each field. Each field is covered by a separate handbook (NIST Handbooks 150

-2A through 150-2H). (Fields of accreditation under Chemical Calibration are covered by separate

handbooks.) Depending on the extent of its calibration capabilities, a laboratory may seek accreditation to

all or only selected fields and parameters within the scope of the program. The fields of calibration and their

related parameters are given on the Fields of Calibration and Parameters Selection List, which is provided

to an applicant laboratory as part of the NVLAP application package for the program. Additional fields of

calibration and/or parameters may be added to the Calibration Laboratories program upon requests of

applicant laboratories and/or if decided by NVLAP to be in the best interest of the Calibration Laboratories

Program.

The laboratory is requested to indicate on the Fields of Calibration/Parameters Selection List the parameter(s)

for which accreditation is desired, along with appropriate ranges and uncertainties. There is also provision

for an applicant laboratory to request accreditation for parameters not currently listed on the Selection List,

or for accreditation of the quality system employed for assuring Measurement and Test Equipment (M & TE)

used in support of product certification. Request for accreditation of quality assurance systems for M & TE

will be treated as a separate field of calibration for the purpose of setting appropriate fees. Once a laboratory

meets all the requirements for accreditation for the Fields of Calibration/Parameters Selection List, this

information will become the basis for the Scope of Accreditation document.

1.6.3 Checklists

Checklists enable assessors to document the assessment of the laboratory against the NVLAP requirements

found in NIST Handbook 150. The NVLAP Calibration Laboratories Accreditation Program incorporates

the NVLAP General Operations Checklist. The questions are applicable to evaluating a laboratory’s ability

to operate a calibration program, and address factors such as the laboratory’s organization, management, and

quality system in addition to its calibration competency. 

The NVLAP General Operations Checklist is numbered to correspond to the requirements in NIST Handbook

150. Comment sheets are used by the assessor to explain deficiencies noted on the checklist. Additionally,

the assessor may use the sheets to make comments on aspects of the laboratory’s performance other than

deficiencies.

1.7 Assessing and evaluating a laboratory

1.7.1 On-site assessment
NIST Handbook 150-2D 14 September 2004

1.7.1.1 The NVLAP lead assessor will schedule with the laboratory the date for on-site evaluation, and will

request the quality manual and documented quality and calibration procedures in advance of the visit to

reduce time spent at the laboratory; such materials will be returned by the assessor. NVLAP and the assessor

will protect the confidentiality of the materials and information provided. The laboratory should be prepared

to conduct routine calibrations, have equipment in good working order, and be ready for examination

according to the guidance contained in this handbook, the requirements identified in NIST Handbook 150,

and the laboratory’s quality manual. The assessor will need time and work space to complete assessment

documentation while at the laboratory, and will discuss these needs at the opening meeting of the on-site

assessment.

1.7.1.2 NVLAP technical assessors are provided with the NVLAP General Operations Checklist to help

ensure the completeness, objectivity, and uniformity of the on-site assessment.

1.7.1.3 When accreditation has been requested for a considerable number of fields of calibration and

parameters, the assessment may range from observing calibrations in progress, requiring repeat

measurements on completed calibrations, to listening to laboratory staff describe the calibration process. The

depth into which the assessor performs the assessment depends on the number of fields of calibration and

associated parameters for which accreditation is requested and the time required to perform a given

calibration.

1.7.1.4 The assessor, or the assessment team, does the following during a typical on-site assessment:

a) Conducts an entry briefing with the laboratory manager to explain the purpose of the on-site visit and

to discuss the schedule for the day(s). At the discretion of the laboratory manager, other staff may attend

the briefing.

b) Reviews quality system manual, equipment and maintenance records, record-keeping procedures,

laboratory calibration reports, and personnel competency records. At least one laboratory staff member

must be available to answer questions; however, the assessor may wish to review the documents alone.

The assessor(s) does not usually ask to take any laboratory documents with him/her, and previously

supplied documents will be returned.

c) Physically examines equipment and facilities, observes the demonstration of selected procedures by

appropriate personnel assigned to perform calibrations, and interviews the personnel. The

demonstrations must include preparation for calibration of devices, and the setup and use of measuring

and test equipment, standards and systems.

d) Holds an exit briefing with the laboratory manager and staff to discuss the assessment findings.

Deficiencies are discussed and resolutions may be mutually agreed upon. Items that must be addressed

before accreditation can be granted are emphasized, and outstanding deficiencies require response to

NVLAP within 30 days. Items that have been corrected during the on-site and any recommendations

are specially noted.

e) Completes an On-site Assessment Report, as part of the exit briefing, summarizing the findings. The

assessor(s) attaches copies of the completed checklists to this report during the exit briefing. The report

is signed by the lead assessor and the laboratory’s Authorized Representative to acknowledge the

discussion. This signature does not necessarily indicate agreement; challenge(s) may be made through

NVLAP. A copy is given to the representative for retention. All observations made by the NVLAP

assessor are held in the strictest confidence allowed by applicable laws and regulations.
NIST Handbook 150-2D 15 September 2004

1.7.2 Proficiency testing

1.7.2.1 Background

Once the quality system review and on-site assessment steps have been satisfactorily completed, it is

necessary to gather another set of data points to aid in deciding whether or not the applicant laboratory is

competent to perform calibrations within the fields of interest to the uncertainties claimed. In the eight fields

of calibration covered by Handbooks 150-2A through 150-2H, there are approximately 85 parameters of

interest. Under most parameters there are several subsets, referred to as ranges. For example, in the mass

field, parameters can range from 1 mg (10-6 kg) to 1 x 106

 kg level in value. In view of the many possible

ranges, proficiency testing could be conducted in hundreds of areas. NVLAP reserves the right to test by

sampling in any area; hence, applicant laboratories must be prepared, with reasonable notice, to demonstrate

proficiency in any of a number of parameters.

1.7.2.2 Proficiency testing vs. measurement assurance

There is an important difference between proficiency testing and measurement assurance. The objective of

proficiency testing is to determine through a measurement process that the laboratory’s measurement results

compare favorably with the measurement results of the audit laboratory (NIST or one designated by NVLAP),

taking into account the relative uncertainties assigned by both the applicant and audit laboratories. The

objective of proficiency testing is not to determine and certify the total uncertainty of the applicant laboratory,

as is done in a Measurement Assurance Program (MAP) with NIST, but to verify (through the assessment

process) that the uncertainty claimed by the applicant laboratory is reasonable, and then use the claimed

uncertainty to test that the measurement result obtained through the proficiency test is acceptable.

It is neither the intention nor the mission of NVLAP to conduct MAPs or to otherwise provide traceability

for laboratories. Laboratories obtain these services from the NIST measurement divisions. NVLAP assesses

the implementation, application, and documentation of MAPs by laboratories. NVLAP accreditation

encourages the use of MAPs by the calibration laboratory community, and MAP results produce objective

evidence that NVLAP assessors look for as part of the assessment process.

1.7.2.3 Requirements

NVLAP’s proficiency testing program uses a sampling approach. All applicant laboratories are required to

complete an annual proficiency test in one parameter under each field of calibration for which it has applied

to be accredited. For the purposes of the NVLAP Calibration Laboratories Accreditation Program, the results

of the proficiency test are considered as objective evidence, along with the on-site visit, of a laboratory’s

ability to perform competent calibrations. Proficiency testing is conducted annually using different

parameters in each field; however, those laboratories accredited in only one parameter within a field are

retested in the same parameter.

1.7.2.4 Uncertainty determination

The applicant laboratory is required to perform a measurement or series of measurements on an artifact using

the same calibration method, apparatus, and personnel that it uses to calibrate its customers’ equipment. The

laboratory must be able to identify and quantify all sources of uncertainty that affect the measurement. The

laboratory should attach an overall uncertainty to the measurement by combining all uncertainty

contributions, in their type A and type B components, in the root-sum-squared method as described in NIST

Technical Note 1297 (Taylor, 1994). The confidence limit used should be k = 2, which is equivalent to a 95

% confidence probability.
NIST Handbook 150-2D 16 September 2004

1.7.2.5 Pass/fail criteria

The performance of the proficiency test is judged by calculating the error of the measurement, normalized

with respect to the uncertainty of the measurement, using the following equation:

Enormal =* (Valuelab - Valueref) / ( Uncertaintyref

2

 + Uncertaintylab

2

)

1⁄2 *

where

Enormal = normalized error of the applicant laboratory

Valuelab = the value as measured by the applicant laboratory

Valueref = the value as measured by the reference laboratory

Uncertaintyref = the uncertainty of the reference laboratory

Uncertaintylab = the uncertainty of the applicant laboratory

To pass the proficiency test, the applicant laboratory must have a value for Enormal less than 1 (i.e., Enormal < 1).

The results may be plotted graphically (Enormal vs. laboratory). The anonymity of each applicant laboratory

will always be preserved.

1.7.2.6 Scheduling and handling

Proficiency testing is scheduled by NVLAP-designated reference laboratories. These sites are NIST

laboratories or NVLAP-accredited laboratories that have been found to have the ability to perform the

required proficiency tests to an uncertainty level appropriate for the laboratories they evaluate. The

proficiency test is scheduled independently and not coincident with the on-site visit. Applicant laboratories

are notified in advance of the approximate arrival time of the measurement artifact. Instructions for

performing the test, reporting the results, communicating with the reference laboratory, and shipping are

included along with the artifact as part of the proficiency test package. Applicant laboratories are instructed

to perform all required measurements within a reasonable time and are told where to ship the artifacts once

the testing has been completed.

1.7.2.7 Notification of results

NVLAP notifies each laboratory of its own results in a proficiency test. If a laboratory has received its on-site

assessment prior to the completion of the proficiency test, the status of that laboratory’s accreditation is

contingent upon successful completion of proficiency testing. The laboratory’s accreditation status may be

changed to reflect a partial accreditation, or may be completely suspended pending demonstration of the

laboratory’s ability to successfully complete the proficiency test at a later date.

1.7.3 Traceability

1.7.3.1 Establishing traceability

Laboratories must establish an unbroken chain of comparisons leading to the appropriate international or

national standard, such that the uncertainties of the comparisons support the level of uncertainty that the

laboratory gives to its customers. Generally speaking, the uncertainties of the comparisons increase as they

move from a higher (international or national level) to a lower level standard. This uncertainty chain is the

evidence of traceability and must be documented accordingly. Traceability does not simply mean having

standards calibrated at the national laboratory, but must consider how a measurement, with its corresponding

uncertainty, is transferred from the national level to the calibration laboratory’s customers.
NIST Handbook 150-2D 17 September 2004

1.7.3.2 Considerations in determining traceability

Without some type of measurement assurance process, one cannot be reasonably certain that the measurement

results have been transferred properly to the laboratory’s customers’ standards. The measurement process

itself must be verified to be in control over time. Therefore, traceability is not a static concept that, once

established, may be ignored; it is dynamic. Process control exercised in each calibration provides the

assurance that a valid transfer of the international or national standard has taken place. This assurance may

be accomplished through the use of tools such as check standards and control charts. Also, the laboratory’s

primary standards must be maintained in such a way as to verify their integrity. Examples of this may be

having more than one primary standard to use for intercomparisons, monitoring the primary standard with

a check or working standard (looking for changes), and verifying a primary standard on a well-characterized

measurement/calibration system. Using scientifically sound measurement procedures to transfer the primary

standard value to the working level and the customer’s item is essential to establishing traceability. If the

procedure itself yields the wrong result, there is no way the laboratory can perform a calibration traceable to

the international or national standard. Mishandling the laboratory’s standards affects the measurement

process, and therefore the ability to transfer the standard’s value to the customer. Examples of handling

problems are dirty or improperly cleaned standards, maintaining standards in an improper environment, not

maintaining custody and security, and improper handling of standards during the measurement process.

The above discussion illustrates how traceability is dependent on many aspects of the measurement process

and therefore must be considered in all phases of calibration. It is not just coincidental that the factors

addressed above are main topics of concern in ISO/IEC 17025:1999.

1.7.4 Uncertainty

NVLAP recognizes the methodology for determining uncertainty as described in the Guide to the Expression

of Uncertainty in Measurement, published by ISO [GUM, reference 1.4.1 d)]. To be NVLAP-accredited, a

laboratory must document the derivation of the uncertainties that it reports to its customers. These

uncertainties will appear on the scope issued to each accredited laboratory to an accuracy appropriate to the

standards, procedures, and measuring devices used.
NIST Handbook 150-2D 18 September 2004

2 Criteria for accreditation

2.1 Introduction

2.1.1 Applicant laboratories are assessed using the requirements in NIST Handbook 150, NVLAP

Procedures and General Requirements. This guide, NIST Handbook 150-2D, was developed from a NIST

measurement laboratory perspective and provides examples and guidelines, not requirements, to assessors

and interested calibration laboratories, on good laboratory practices and recommended standards. Therefore,

the guide language reflects this philosophy through the use of “shoulds” instead of “shalls” (along with other

less prescriptive language) when describing criteria. The guidelines presented here are not absolute since

specific requirements depend on the measurement uncertainty for which an applicant laboratory wishes to

be accredited. This is a business decision for each laboratory and beyond the scope of NVLAP. Simply

stated, to be accredited, an applicant laboratory must have a quality system and be able to prove (and

document) that it is capable of doing what it says it does (i.e., correctly calibrate to a stated uncertainty)

within the framework of NIST Handbook 150. Accreditation will be granted, and therefore may be referenced

in calibration reports, etc., only for those specific parameters, ranges and uncertainties using calibration

methods and procedures for which a laboratory has been evaluated. Calibrations performed by a laboratory

using methods and procedures not considered appropriate for the level of measurements being made, and

those that have not been evaluated by the accreditation process, are outside the scope of accreditation and may

not be referenced as “accredited” calibrations on calibration reports and other documents.

2.1.2 The rest of the handbook is divided into two parts. The first part, section 2.2, provides a general

interpretation of NIST Handbook 150 criteria for ionizing radiation calibrations. The second part, sections

2.3 through 2.18, discusses specific calibrations parameters and lists important technical guidelines to satisfy

the requirements of NIST Handbook 150.

2.1.3 Sections 2.3 through 2.18 were patterned after NIST Special Publication 812: Criteria for the

Operation of Federally-Owned Secondary Calibration Laboratories, 1991, with appropriate updating in 2003

to recognize the technical evolution in these fields and to acknowledge the requirements now addressed by

ISO/IEC 17025 that had not been made explicit in earlier requirements.

2.1.4 This document contains the criteria for accreditation of laboratories that calibrate ionizing radiation

instrumentation. Adherence to these criteria will indicate that the laboratory is capable of high standards of

performance in the calibration of instrumentation for use in various radiation environments.

2.2 General criteria for ionizing radiation calibrations

2.2.1 Units

2.2.1.1 Both SI Units and special units in use temporarily, as recognized in NIST Special Publication 330

(Taylor, 2001), are acceptable. Included in those two categories are the following units used in this

handbook. 
3

See 2.2.1.3 and 2.2.1.4.

NIST Handbook 150-2D 19 September 2004

Special Special Conversion

Quantity SI units Unit Name Symbol from SI units

energy joule (J) electronvolt eV 1.602 × 10-19 J = 1 eV

air kerma3

 and gray (Gy) rad (radiation absorbed dose) rad 1 J/kg = 1 Gy = m2 s-2

absorbed dose 10-2 Gy = 1 rad

dose equivalent sievert (Sv) rem (Roentgen equivalent man) rem 10-2 Sv = m2

 s-2 = 1 rem

exposure3 coulomb/kilogram (C/kg) roentgen R 2.58 × 10-4 C/kg = 1 R

activity becquerel (Bq) curie Ci 3.7 × 1010 Bq = s-1 = 1 Ci

2.2.1.2 This document will show the special units in parentheses wherever feasible. The SI units

indicated above will be shown for the quantities of absorbed dose and dose equivalent. 

2.2.1.3 The quantity of exposure is being phased out; therefore, the SI unit coulomb/kilogram will not

be shown in this document. It has no special name and it is inconvenient (especially for exposure rate). The

quantity of exposure has been replaced with the quantity of air kerma, which has the SI unit joule/kilogram

(J/kg) with the special name gray (Gy): 1 Gy = 1 J/kg. 

2.2.1.4 Although the factor used for conversion from exposure in R to air kerma in Gy depends slightly

on photon energy, that variation is insignificant for the purposes of this document and a single value will be

used:

a) air kerma (Gy) = 0.00878 × exposure (R)

b) When a rounded value of the SI value of air kerma is given, the exposure in R will be rounded also

(e.g., 90 FGy/h . 10 mR/h).

2.2.2 Scope

The criteria contained in the General Criteria section of this document should be satisfied by all laboratories

seeking accreditation. In addition, each laboratory should satisfy the specific criteria contained in other parts

of this document for each category (radiation type and energy) for which accreditation is desired.

2.2.3 Personnel

2.2.3.1 The technical director of the laboratory should have a minimum of a bachelor’s degree in physics,

engineering, health physics, or radiological physics, and should have a graduate degree in one of these or a

closely related scientific field. 

2.2.3.2 The individual in charge of day-to-day operation of the laboratory should have at least three years

of practical experience in radiation measurement, including the calibration of radiation instrumentation.

2.2.3.3 All handling, unpacking, and packing of dosimeters, instruments, and reference standards should

be done by trained staff who are familiar with the equipment.
NIST Handbook 150-2D 20 September 2004

2.2.4 Assuring the quality of test and calibration results

2.2.4.1 The laboratory should be capable of providing calibration services with uncertainties as indicated

in the appropriate parts of this document. Each uncertainty should be stated in terms of % deviation from

the national standard.

2.2.4.2 Any new or amended calibration procedure that could have a significant effect on the accuracy

of a calibration should be evaluated by the accrediting body before it is adopted for routine use. A copy of

the latest revision of the laboratory’s protocol should be available for audit at all times.

2.2.5 Accommodation and environmental conditions

2.2.5.1 The effect of external conditions on the internal environment of the laboratory should be

considered in selection of the laboratory site. The laboratory should be located away from, or otherwise

isolated from, 

• sources of mechanical vibration and shock, 

• sources of electrical and electromagnetic interference, and 

• other potential sources of interference with the proper calibration of instrumentation. 

If such potential sources exist, the laboratory should have documentation that demonstrates no adverse effects

on calibration accuracy.

2.2.5.2 Environmental monitoring equipment should be provided for indicating the temperature,

atmospheric pressure, and humidity within the laboratory at all times.

2.2.5.3 In general, strict temperature control is not essential for the calibration work covered by these

criteria. It is, however, desirable that the laboratory be kept at a reasonably uniform temperature so that

calibration accuracy is not adversely affected and to ensure that an adequate level of temperature stability is

reached before the start of calibration measurements. The laboratory temperature should be maintained

nominally within the range of 293.15 K to 297.15 K (20 to 24) EC. When using a vented ionization chamber,

the temperature should not vary more than ± 2 K in any one hour during which a calibration is conducted.

2.2.5.4 The relative humidity should be within the range of 15 % to 65 % for routine laboratory operation.

2.2.5.5 The laboratory should approximate free-air conditions for all radiation beams used for

calibrations.

2.2.5.6 The radiation room (or rooms) should be of sufficient size and design that room-scattered radiation

at the position where instrumentation is normally placed for calibration does not introduce an error

inconsistent with overall accuracy goals. If necessary, proper scatter corrections should be applied.

2.2.5.7 The level of background radiation should be kept as low as practicable and not subject to

variations that could significantly affect the accuracy of calibration work. Radiation sources should not be

stored in the same room in which they are used for calibration. 

2.2.5.8 In uncollimated free-air calibration facilities, the radiation room should be used exclusively for

calibrations to avoid variable scatter conditions. The contribution to absorbed dose by scattered radiation

should be known.
NIST Handbook 150-2D 21 September 2004

2.2.5.9 The electrical power should be appropriate to the equipment used, suitably stable, and free of

switching surges and significant line noise. When necessary, local auxiliary voltage stabilizers and filters

should be provided.

2.2.5.10 The laboratory should be provided with an adequate grounding system. Where there is a

likelihood of interference arising from equipment connected to a single grounding system, separate grounding

systems should be provided and adequate precautions taken against any possible interconnection between

systems.

2.2.5.11 If compressed air is used, a pressure regulator and means for removing moisture, dust, and oil

from the compressed air also should be provided.

2.2.6 Equipment

2.2.6.1 The laboratory should have secondary radiation measurement standards that cover the range of

calibrations performed. The secondary standards should be used only for calibration of instruments and not

for any other purpose. A working standard should be used in lieu of a secondary standard for routine

reference.

2.2.6.2 The laboratory should have a barometer capable of 1 % accuracy and a thermometer capable of

± 1 K accuracy. Each should have been calibrated by comparison with a tertiary or higher-level standard.

A hygrometer capable of monitoring over the range of relative humidity within which the laboratory operates

should be available.

2.2.6.3 The laboratory should have an instrument and radiation source positioning system. The support

should be rigid and enable the reproduction of a desired source/detector geometry. It should produce

minimum scattered radiation.

2.2.7 Test and calibration methods and method validation

The laboratory’s written protocol should include the following:

a) A statement of policy regarding acceptance of instrumentation for calibration. Examples are policy

regarding instruments that are contaminated, in need of repair, or of a particular type not accepted.

Restrictions on type of customer or liability for instrument damage should also be stated.

b) A fully documented procedure for each type of instrumentation calibrated providing the appropriate

operational steps to permit a knowledgeable person to reproduce a particular calibration technique with

a precision consistent with the accuracy goals of the laboratory. Each calibration procedure should

give the following information, as a minimum:

1) a concise but complete account of the procedure,

2) the scope and limitations of the procedure,

3) any environmental constraints that should be met in calibrating the instrumentation, in addition

to those stated in 2.2.5,

4) the sequence of the calibration procedure, drawing attention to special precautions,

5) the equipment and standards to be used in this calibration procedure,
NIST Handbook 150-2D 22 September 2004

6) an example of a completed data sheet (or computer record) for the calibrated instrumentation,

7) the method of data handling and reduction,

8) an assessment of the uncertainty associated with each calibration procedure,

9) an example of a completed calibration report, including a statement of the accuracy to which the

reference value of the radiation field is known,

10) the procedure or reference for auditing calibration data and approving reports,

11) the procedure to ensure the security of calibration records.

2.2.8 Records

2.2.8.1 In addition to specific and implied requirements in ISO/IEC 17025, the laboratory’s record system

should include a bound day-book, or other equivalent record, in which is recorded a description, sufficient

for identification, of every item of instrumentation for which a calibration service was provided and the date

that the calibration was performed.

2.2.8.2 Records for all individual items of instrumentation calibrated should be maintained for a period

of at least five years. Records regarding calibration of standards used should be maintained for a period of

at least 50 years.

2.2.9 Reporting the results

2.2.9.1 A calibration report should be issued for each item of instrumentation calibrated under the scope

of accreditation, including an appropriate statement clearly specifying the conditions (e.g., type of radiation,

the dose rate(s), temperature, the electron energy for electron beams, pulse width, dose rate within the pulse,

repetition rate. orientation of the detector, etc.) under which the calibration was performed. It should also

state limitations to the calibration, i.e., maximum range calibrated if less than the indicated range of an

instrument, scales not calibrated, application of calibration factors, etc.

2.2.9.2 Certificates or reports should state that application of the calibration results to an individual

measurement is the responsibility of the user, and that care must be exercised in interpolation of the

calibration results.

2.2.9.3 If the laboratory discovers a mistake in a calibration report that significantly affects the accuracy

of the calibration, the person or institution that received the report should be notified within 24 h, if possible,

and a written report of the mistake sent to that person or institution within 72 h. The mistake should be

corrected as soon as possible by sending a corrected calibration report or recalibrating the instrumentation.

The laboratory should determine the reason for the mistake and take corrective action to prevent its

recurrence.

2.2.9.4 If the laboratory discovers an apparent generic error in one of its procedures or in the design of

an item of instrumentation that has or could lead to an erroneous calibration, it should notify not only its

clients but also the accrediting body in writing within 10 days. Other accredited laboratories may then be

notified of the problem, along with recommendations for remedial action.

2.3 Alpha-particle calibration of survey instruments
NIST Handbook 150-2D 23 September 2004

2.3.1 Scope

The criteria contained in this part apply to the calibration of survey instruments at radiation protection levels

using alpha radiation sources. These criteria are supplementary to the general criteria contained in 2.2. Both

the general criteria and these specific criteria should be followed if this alpha-particle calibration service is

offered and its inclusion in the Scope of Accreditation is desired.

2.3.2 Equipment

2.3.2.1 Planar or pseudo planar alpha radiation sources should be used for the purpose of calibrating

instruments used for the detection of alpha contamination. A pseudo planar source is one made up of a

closely spaced array of small sources. The combined thickness of the source media and overburden should

be less than one-tenth the range of the least energetic alpha particle in these media. The following thin

sources of alpha radiation are acceptable, provided that their 2π alpha emission rate (per unit area) is known

and traceable to measurements from a source calibrated by the National Institute of Standards and Technology

or to another national measurement institute that has participated in international key comparisons with NIST

in the applicable measurement area:

a) natural or depleted uranium,

b) plutonium-238 or -239, and

c) natural thorium or thorium-230.

2.3.2.2 The radiation fields produced by the sources should cover a range of at least three decades of

alpha emission rates suitable for protection-level calibration. A recommended range is 100 alpha particles

per minute (2π emission rate) to 106

 alpha particles per minute.

2.3.2.3 In addition to radiation sources, the laboratory should have as a minimum the following

equipment:

a) a source and detector support and positioning system that should provide for reproducible and accurate

positioning of a detector with respect to the radiation source;

b) an independent measuring system used as a means of checking the sources for any degradation of their

alpha emission rate.

2.3.3 Test and calibration methods and method validation

2.3.3.1 Emission rate

The source used for calibration should be characterized in terms of the alpha emission rate per unit area. The

boundary of the source should be greater than that of the detector. The relative standard deviation of the

emission rate averaged over every individual segment of the source should be less than ± 6 %. The maximum

area of a segment should be 10 cm2

, and a segment should not exceed 10 % of the total surface area of the

source. The spacing of smaller sources to form a pseudo array should be such that the point-to-point distance

between sources is less than the range of alpha radiation in air.

2.3.3.2 Uncertainty component contributed by reference value
NIST Handbook 150-2D 24 September 2004

The alpha emission rate specified by the laboratory as its reference value for each source of radiation should

be within 10 % of the “true value” as defined by comparison with measurements from an appropriate standard

traceable to measurements from a source calibrated by the National Institute of Standards and Technology

or to another national measurement institute that has participated in international key comparisons with NIST

in the applicable measurement area.

2.3.4 Handling of test and calibration items

Because of the short range of alpha particles in air, calibration measurements using an alpha source should

be made in such a way that the alpha radiation emitted from the source reaches the sensitive volume of the

radiation detector. To assure that this is the case, there should be no shielding materials between the alpha

source and the detector, other than that inherent to the detector or source itself. Additionally, the surface of

the radiation detector should be no further than 3 mm from the surface of the alpha radiation source.

2.3.5 Reporting the results

2.3.5.1 An instrument calibration report should include, as a minimum, the alpha radiation source used

for calibration, the emission rate or rates at which the instrument was calibrated, and the instrument response

at each calibration point.

2.3.5.2 At least one calibration point and a linearity check should be included for each range of the

instrument, where applicable.

2.4 Beta-particle calibration of survey instruments

2.4.1 Scope

The criteria contained in this part apply to the calibration of health physics instruments at radiation protection

levels using a beta particle source. These criteria are limited to the calibration of instruments used to measure

dose rate from external beta sources and are supplementary to the general criteria contained in 2.2. Both the

general criteria and these specific criteria should be followed if this beta-particle calibration service is offered

and its inclusion in the Scope of Accreditation is desired.

2.4.2 Equipment

2.4.2.1 The selection of a source for beta particle calibration of an instrument will depend both on the

nature of the radiation field in which the instrument is to be used and the anticipated energy of the beta

radiation. It is recommended that both point sources and distributed sources be available for instrument

calibration since they represent the extremes of measurement geometry. The radionuclides listed in Table 1

are recommended for use as reference sources for beta calibration; however, other sources may be used if they

more accurately represent the beta energy spectrum in which the calibrated instrument is to be used.

2.4.2.2 The laboratory should have at least the following radionuclide sources of beta particles:

204Tl, and 9OSr/Y.

These sources should comply with ISO 6980.

Table 1. Characteristics of Beta-Particle Sources (ISO 6980: 1996)
NIST Handbook 150-2D 25 September 2004

Radionuclide Emax (MeV) Half-Life (d)

12C 0.156 2 093 000

146Pm 0.225 957

204Tl 0.763 1 381

90Sr/Y (a) 2.274 10 483

106Ru/Rh 3.54 372.6

(a) The source should be sealed with 100 mg/cm2

 (nominal) filtration to remove the 90Sr beta component.

2.4.2.3 In addition to one or more radiation sources and associated control devices, the laboratory should

have as a minimum the following equipment:

a) Thin-window fixed volume ionization chambers or extrapolation chambers. The extrapolation

chamber or thin-window ionization chamber response should have been verified by the NIST or by

comparison to calibrated beta radiation sources whose measurements are traceable to measurements

from a source calibrated by the National Institute of Standards and Technology or to another national

measurement institute that has participated in international key comparisons with NIST in the

applicable measurement area. The chamber response should have an accuracy equivalent to that

described in 2.4.3.7 over the anticipated range of irradiation conditions, i.e., beta energy and depth of

dose measurement point. 

b) An electrometer to measure the charge produced in the ionization chambers.

c) A voltage source suitable for chamber polarizing potential.

d) An independent measuring system for verification of the performance of the secondary standard

ionization chambers and electrometer.

e) An instrument and ionization chamber support and positioning system. The system should provide for

reproducible and accurate positioning of an instrument or chamber with respect to the radiation source.

For beam type irradiation configurations, the positioning system should define the central axis of the

gamma beam.

f) Additional equipment should include a pulse generator, oscilloscope, current source, precision

capacitors and precision resistors.

2.4.3 Test and calibration methods and method validation

2.4.3.1 Dose rate

The beta radiation fields used for calibration should be characterized in terms of absorbed dose rate

(specifying tissue depth and tissue-equivalent material) at a given position or distance from the source. The

dose rate should be known (traceable) at each distance used. Similarly, if calibrations are to be performed

at other tissue depths (for example, simulating exposure of the lens of the eye, rather than exposure of the

skin), then the dose rate at these depths should be known.

2.4.3.2 Attenuation

In order to assure that the energy of the beta radiation that reaches the detector is similar to that originating

from the radionuclide, certain limits on the calibration conditions are recommended. If Eres refers to the
NIST Handbook 150-2D 26 September 2004

residual maximum energy of a beta particle reaching the detector of an instrument and Emax is the energy at

which the beta particle originates, then the conditions shown in Table 2 should be met.

Table 2. Limiting Conditions for Beta Particles

Emax Eres/Emax

<100 keV $ 0.6

100 - 800 keV $ 0.7

>800 keV $ 0.8

These conditions are recommended so that no undue attenuation from the source’s self-absorption,

containment, beam flattening filters, or air attenuation will significantly change the radionuclide’s beta

spectrum. The procedure for determining Eres is given in ISO 6980.

2.4.3.3 Contamination

In addition to the radiation quality considerations addressed in the preceding paragraphs, contamination by

other radionuclides may also significantly change the beta or gamma radiation field from a source. Small

levels of beta contamination are difficult to detect but fortunately are usually accompanied by gamma

contamination. The beta spectral purity is considered adequate if the following hold:

a) the plot used to measure Rres (where Rres is the range in an absorbing material of a beta spectrum of

residual maximum energy, Eres) has a linear section, and

b) the Eres value meets the criteria in Table 2.

The procedure for measurement of Rres is given in ISO 6980.

2.4.3.4 Measurement frequency

Measurement to determine the adequacy of beta spectral purity should be made every 2 years, or more often

if needed.

2.4.3.5 Photon contamination

Photon contamination of the beta field due to sources of gamma, x-ray, and bremsstrahlung radiation should

contribute less than 5 % of the total absorbed dose.

2.4.3.6 Uniformity of beta field

The beta dose rate should be uniform over the area of the detector face. The dose rate across the beam profile

at a depth of 7 mg/cm2

 should not vary more than 5 % from the mean dose rate for Eres greater than or equal

to 300 keV, and not more than 10 % for Eres less than 300 keV. The uniformity of the beta field should be

verified by measurement with a small area detector or film.

2.4.3.7 Uncertainty component contributed by reference value

The dose rate specified by the laboratory as its reference value for each beta-particle beam should be within

10 % of the true value as defined by comparison with a national standard.
NIST Handbook 150-2D 27 September 2004

2.4.4 Handling of test and calibration items

2.4.4.1 Radiation production

The production of a beam (field) of beta radiation for instrument calibration may be achieved by means of

a shutter exposing the source or by moving the source to an exposed position.

2.4.4.2 Beam parameters

The physical size of the beta ray beam (field) should have been predetermined to assure that it is sufficiently

large to accommodate the instrument being calibrated. Provision should be made for identifying the central

axis, and the boundaries of the useful area of the beam should be known. If necessary, beam flattening filters

may be used to meet the requirements of 2.4.3.6. 

2.4.4.3 Timer

If the radiation source is used for the calibration of fluence measuring instruments, the radiation beam should

be controlled by a timer. The timing measurement uncertainty due to the shutter transit times should be

documented, compensated for, and monitored.

2.4.5 Reporting the results

An instrument calibration report should include, as a minimum:

a) the radionuclide and radiation field type (point source or flat field) used for calibration, 

b) the reference dose rate or rates with respect to a specified material or tissue phantom at which the

instrument was calibrated, 

c) the dose rate (or dose) indicated by the instrument at each calibration point,

d) the orientation of the instrument with respect to the radiation beam, and 

e) whether the front face or the effective center of the detector was located at the point where the

reference field was characterized.

2.5 Beta-particle irradiation of personnel dosimeters

2.5.1 Scope

2.5.1.1 The criteria contained in this section of the handbook apply to irradiation of dosimeters at

radiation protection levels using beta-particle sources. These criteria are supplementary to the general criteria

contained in 2.2, and should be followed if this specific irradiation service is offered and its inclusion in the

Scope of Accreditation is desired. In that case, both the general criteria and these specific criteria should be

followed.

2.5.1.2 These criteria apply to irradiation of dosimeters used for personnel monitoring.

2.5.2 Equipment
NIST Handbook 150-2D 28 September 2004

2.5.2.1 One or more sources of beta radiation should be available for irradiation services. They may take

the form of point sources or slab sources. The sources should meet the requirements of national or

international standards (i.e., ANSI N13.11; DOE/EH-0027, ISO 6980). The dose range covered will be a

function of the mission and requirements of the laboratory, but 1.5 mGy to 100 mGy (150 mrad to 10 rad)

should be sufficient for most radiation-protection purposes.

2.5.2.2 In addition to one or more radiation sources and associated control devices, the laboratory should

have as a minimum the following equipment:

a) Extrapolation chamber or thin-window fixed volume ionization chamber that covers the energy and

intensity ranges used for irradiation services.

b) Phantom consisting of a slab of polymethylmethacrylate with a minimum cross section of 30 × 30 cm

and a minimum thickness of 5 cm. The support system for the phantom should be rigid and produce

minimum scattered radiation at the dosimeter position(s).

c) An electrometer to measure the charge produced in the ionization chambers.

d) A voltage source suitable for chamber polarizing potential.

e) An independent measuring system for verification of the performance of the secondary standard

ionization chambers and electrometer.

f) An instrument and ionization chamber support and positioning system. The system should provide for

reproducible and accurate positioning of an instrument or chamber with respect to the radiation source.

For beam type irradiation configurations, the positioning system should define the central axis of the

gamma beam.

g) Pulse generator, oscilloscope, current source, precision capacitors and precision resistors.

2.5.3 Test and calibration methods and method validation

2.5.3.1 Dose rate

The beta radiation field used for irradiation should be characterized in terms of dose rate. 

2.5.3.2 Uncertainty component contributed by reference value

The dose rate specified by the laboratory as its reference value should be within 3 % of the actual value

defined by comparison with measurements from the National Institute of Standards and Technology or

another national measurement institute that has participated in international key comparisons with NIST in

the applicable measurement area. The total uncertainty of the dose delivered to an irradiated dosimeter should

be less than or equal to 5 %. To meet this criterion, the use of a flattening filter and/or position-specific

calibration factors may be required when several dosimeters are irradiated simultaneously.

2.5.3.3 Source containment

Source containment should be sufficiently sturdy to permit its safe and routine use. At the same time, it

should be sufficiently thin to ensure the beta particle energy spectrum of sources specified in ISO 6980.
NIST Handbook 150-2D 29 September 2004

2.5.3.4 Orientation

The dosimeters should be attached to one of the two larger surfaces of the phantom, at least 5 cm from any

edge of the surface, and that surface should face the radiation source. The central axis of the collimated beam

should be perpendicular to that surface, and should pass through its geometric center. The position and

orientation of the phantom should be reproducible and verifiable.

2.5.3.5 Distance

The distance between the radiation source and the phantom surface to which the dosimeters are attached

should comply with requirements in ANSI N13.11 or DOE/EH-0027. It should be reproducible and verifiable.

2.5.3.6 Slab sources

Slab sources may be used when such irradiation geometry is more appropriate than a point source irradiation

geometry.

a) Slab size: The dimensions of the source should exceed the dimensions of the irradiated dosimeter

including all radiation sensitive elements.

b) Source characteristics: The slab should have a protective covering in the range of 3 to 7 mg/cm2

inclusive. For uranium, the dose rate at 100 mg/cm2 divided by the dose rate at 7 mg/cm2 should be

0.58 ± 0.04. The in-phantom dose rate at 1000 mg/cm2

 should be less than 3 % of the dose rate at

7 mg/cm2

. Appropriate dosimeters should be used to confirm these relative dose rates.

c) Dose rate: The beta radiation field on or near (< 1 cm) the surface of the source should be

characterized in terms of absorbed dose rate. An extrapolation ionization chamber or a thin fixedvolume ionization chamber should be used to determine the dose rate.

d) Uncertainty component contributed by reference value: The dose rate specified by the laboratory as

its reference value should be within 3 % of the actual value defined by comparison with measurements

from the National Institute of Standards and Technology or another national measurement institute that

has participated in international key comparisons with NIST in the applicable measurement area. The

total uncertainty of the dose delivered to an irradiated dosimeter should be less than or equal to 5 %.

e) Orientation: Dosimeters should lie flat on the source surface or be suspended parallel to the surface

with a maximum source-to-dosimeter distance of 0.5 cm.

2.5.3.7 Verification of delivered dose

For point sources, a method should be used to verify the delivered dose independent of the timer and known

dose rate. Possible verification methods include an off-axis detector, a small detector embedded in a corner

of the phantom, or a passive detector exposed with each irradiation.

2.5.4 Handling of test and calibration items

2.5.4.1 Shielding

The source storage containers should provide sufficient shielding such that leakage radiation does not

interfere with other uses of the radiation room by raising the background level. Background and leakage
NIST Handbook 150-2D 30 September 2004

radiation from all sources of radiation within the room should not contribute more than 0.1 % of the total dose

to which dosimeters are irradiated.

2.5.4.2 Beam size and uniformity

The beam size should be sufficient to irradiate the entire phantom surface that is facing the source. If several

dosimeters are irradiated simultaneously the beam should be sufficiently uniform and characterized to satisfy

the requirements of 2.5.3.6 d). The use of an appropriate flattening filter might be required to achieve this.

2.5.4.3 Beam emission control

The irradiator should have a built-in device to control emission of the beta radiation. It should be possible

to operate the emission control device with a timer. Any associated random timing uncertainties due to transit

time of the device should be known. Any associated systematic timing uncertainties should be measured,

compensated for, and monitored.

2.5.5 Reporting the results

The laboratory should report to the customer the total depth dose for each dosimeter irradiated.

2.6 Gamma-ray calibration of survey instruments

2.6.1 Scope

The criteria contained in this part apply to the calibration of health physics instruments at radiation protection

levels using one or more gamma-ray sources. These criteria are supplementary to the general criteria

contained in 2.2. Both the general criteria and these specific criteria should be followed if this gamma-ray

calibration service is offered and its inclusion in the Scope of Accreditation is desired.

2.6.2 Equipment

2.6.2.1 One or more of the following radiation sources should be available for use in the calibration of

health physics instruments:

Radionuclide Nominal Energy

241Am 60 kev

137Cs 660 kev

60Co 1.25 Mev

The source(s) should conform to ISO 4037-1.

2.6.2.2 The radiation fields produced by the sources should cover a range of air kerma (exposure) rates

suitable for protection-level calibration. A minimal range is 9 FGy/h to 40 mGy/h (1 mR/h to 5 R/h) and a

more desirable range is 4 FGy/h (0.5 mR/h) to at least 0.9 Gy/h (100 R/h).

2.6.2.3 In addition to one or more radiation sources and associated control devices, the laboratory should

have as a minimum the following equipment:
NIST Handbook 150-2D 31 September 2004

a) Secondary standard ionization chambers suitable for the photon energy and intensity ranges for which

calibration services are offered.

b) An electrometer to measure the charge produced in the ionization chambers.

c) A voltage source suitable for chamber polarizing potential.

d) An independent measuring system for verification of the performance of the secondary standard

ionization chambers and electrometer.

e) Additional equipment including a pulse generator, oscilloscope, current source, precision capacitors

and precision resistors.

f) An instrument and ionization chamber support and positioning system. The instrument and ionization

chamber support and positioning system should provide for reproducible and accurate positioning of

an instrument or chamber with respect to the radiation source. For beam type irradiation

configurations, the positioning system should define the central axis of the gamma beam.

2.6.3 Test and calibration methods and method validation

2.6.3.1 Air-kerma rate (exposure rate)

The gamma radiation field used for calibration should be characterized in terms of air-kerma rate at a given

position or distance from the source. The air-kerma rate should be known and traceable at each distance used.

2.6.3.2 Scattered radiation

The effect of room-scattered radiation (relative to a radiation field with minimal room scatter) on the accuracy

of calibration of each instrument type should be known at each location where a detector is placed for

instrument calibration.

2.6.3.3 Attenuation

If an attenuator is used to reduce the air-kerma rate at any location in the radiation field, the effect of the

altered radiation spectrum (relative to an unattenuated radiation spectrum) on the uncertainty of calibration

of each instrument type should be known. The approximate energy spectrum of the attenuated radiation field

should be known. Secondary electron equilibrium at the calibration position should be documented for

attenuated beams.

2.6.3.4 Uncertainty component contributed by reference value

The air-kerma rate specified by the laboratory as its reference value for each source of radiation should be

within 5 % of the true value as defined by comparison with a national standard above 90 FGy/h (10 mR/h),

and within 7 % of the true value from 4 FGy/h (0.5 mR/h) to 90 FGy/h (10 mR/h).

2.6.4 Handling of test and calibration items

2.6.4.1 Shielding

Radiation barriers and/or storage containers for sources should provide sufficient shielding so that radiation

added to natural background radiation in the calibration area is sufficiently low as to not interfere with
NIST Handbook 150-2D 32 September 2004

ongoing calibration work. Added background radiation and leakage radiation from all sources in the

calibration area should not contribute more than 1 % of the total air-kerma rate at which an instrument is

calibrated or it should be well characterized and accounted for in the calibration.

2.6.4.2 Beam collimation

The gamma radiation beam emitted from a source that has been exposed for calibration should be collimated

so that its size is limited to an area consistent with calibration requirements. An exception to this requirement

is calibration facilities sufficiently large to provide a low room-scatter radiation environment for instrument

calibration, e.g., an uncollimated source in a low scatter room.

2.6.4.3 Source exposure

The source storage container should have a mechanism to control exposure in the gamma beam. If the

radiation source is used for calibration of air-kerma measuring (as contrasted with air kerma-rate measuring)

instruments, the shutter or source transit time and its effect on the total air kerma should be known.

2.6.4.4 Air kerma (exposure) control

If the radiation source is used for the calibration of air-kerma measuring instruments (see 2.6.4.3 above), the

shutter or source transfer should be initiated and terminated by a timer, or the air kerma should be monitored

by use of a transmission chamber. Any associated systematic timing uncertainties should be documented and

compensated for.

2.6.5 Reporting the results

2.6.5.1 An instrument calibration report should include, as a minimum:

a) the radionuclide or photon energy used; 

b) for air kerma rate measurements,

1) the reference air-kerma rate or rates at which the instrument was calibrated, 

2) the air-kerma rate indicated by the instrument, and 

3) the calibration factor at each calibration point;

c) for air kerma measurements, in addition to the radionuclide and air-kerma rate, 

1) the reference air kerma, 

2) instrument reading, and 

3) calibration factor.

2.6.5.2 At least one calibration point should be included for each range of the instrument, where

applicable. 

2.6.5.3 The orientation of the instrument with respect to the radiation beam should be described or

illustrated in the calibration report, and the use of a build-up cap should be noted. 
NIST Handbook 150-2D 33 September 2004

2.6.5.4 For instruments that use a vented ionization chamber, the reported values should be referenced

to a temperature of 295.15 K (22 EC) and a barometric pressure of 1.013 kPa, and the equation needed to

convert to other temperatures and pressures should be provided.

2.7 Gamma-ray irradiation of personnel dosimeters

2.7.1 Scope

2.7.1.1 The criteria contained in this part of the document apply to irradiation of dosimeters at radiation

protection and accident levels (as defined in ANSI N13.11) using gamma-ray sources. These criteria are

supplementary to the general criteria contained in 2.2, and should be followed if this specific irradiation

service is offered and its inclusion in the Scope of Accreditation is desired. In that case, both the general

criteria and these specific criteria should be followed.

2.7.1.2 These criteria apply to irradiation of dosimeters used for personnel monitoring. They do not apply

to dosimeters used for high-level dosimetry in applications such as radiation processing or sterilization.

2.7.2 Equipment

2.7.2.1 One or more 137Cs source(s) of gamma rays should be available for irradiation services. The

radiation fields produced by the sources should cover a range of exposures (air kerma) suitable for protectionlevel irradiations. The range covered will be a function of the mission and requirements of the laboratory,

but 0.3 mGy to 4 Gy (30 mR to 500 R) will suffice for most radiation protection purposes.

2.7.2.2 In addition to radiation source(s) and the associated beam control devices, the laboratory should

have as a minimum the following equipment:

a) Secondary standard ionization chambers that are calibrated for 137Cs gamma rays and that cover the

air-kerma rate ranges used for irradiation services.

b) A phantom consisting of a slab of polymethylmethacrylate with a minimum cross section of 30 cm ×

30 cm and a thickness of 15 cm, with a support system for the phantom that is rigid and produces

minimum scattered radiation at the dosimeter position(s).

c) An electrometer to measure the charge produced in the ionization chambers.

d) A voltage source suitable for chamber polarizing potential.

e) An independent measuring system for verification of the performance of the secondary standard

ionization chambers and electrometer.

f) Additional equipment including a pulse generator, oscilloscope, current source, precision capacitors

and precision resistors.

g) An instrument and ionization chamber support and positioning system. The instrument and ionization

chamber support and positioning system should provide for reproducible and accurate positioning of

an instrument or chamber with respect to the radiation source. For beam type irradiation

configurations, the positioning system should define the central axis of the gamma beam.
NIST Handbook 150-2D 34 September 2004

2.7.3 Test and calibration methods and method validation

2.7.3.1 Air-kerma rate (exposure rate)

The gamma radiation field used for irradiation should be characterized in terms of air-kerma rate in the

absence of a phantom at the location where the center of the front surface of the phantom is placed for

irradiation.

2.7.3.2 Scatter

The contribution from room-scattered radiation should be determined with the phantom removed from the

beam and should not exceed 5 % of the air-kerma rate at any location where a dosimeter is placed for

irradiation. The approximate energy spectrum of room-scattered radiation should be known. The relationship

between shallow dose and deep dose should be measured for each facility because the charged particle surplus

or deficit is highly dependent on local scattering conditions.

2.7.3.3 Uncertainty component contributed by reference value

The air-kerma rate specified by the laboratory as its reference value should be within 3 % of the actual value

defined by comparison with the national standard. The total uncertainty of the dose delivered to an irradiated

dosimeter should be less than or equal to 5 %. To meet this criterion, it might be necessary to use positionspecific calibration factors when several dosimeters are irradiated simultaneously.

2.7.4 Handling of test and calibration items

2.7.4.1 Shielding

Source storage containers should provide sufficient shielding such that leakage radiation does not interfere

with other uses of the radiation room by raising the background level. Background radiation and leakage

radiation from all sources in the radiation room should not contribute more than 0.1 % of the total air kerma

at which dosimeters are irradiated.

2.7.4.2 Beam size and uniformity

The gamma beam emitted from the irradiator should be collimated so that its size is limited to the minimum

area consistent with irradiation requirements. All dosimeters should be irradiated with phantom backing, and

the beam size should be sufficient to irradiate the entire phantom surface that is facing the source. If several

dosimeters are irradiated simultaneously, the beam should be sufficiently uniform and characterized to satisfy

the requirements of 2.7.3.3.

2.7.4.3 Beam emission control

The irradiator should have a built-in device to control emission of the gamma beam. It should be possible

to operate the emission control device with a timer. Any associated random timing uncertainties due to transit

time of the device should be known. Any associated systematic timing uncertainties should be measured,

compensated for, and monitored.

2.7.4.4 Orientation

The dosimeters should be attached to one of the two larger surfaces of the phantom, at least 5 cm from any

edge of the surface, and that surface should face the radiation source. The central axis of the collimated beam
NIST Handbook 150-2D 35 September 2004

should be perpendicular to that surface, and should pass through its geometric center. The position and

orientation of the phantom should be reproducible and verifiable.

2.7.4.5 Distance

The distance between the radiation source and the phantom surface to which the dosimeters are attached

should be one meter or more. The distance should be reproducible and verifiable.

2.7.4.6 Total air kerma

A method should be used to verify the total air kerma independent of the timer and known air-kerma rate.

2.7.5 Reporting the results

The laboratory should report to the customer the total air kerma for each dosimeter irradiated. 

2.8 Gamma-ray source calibration for air-kerma rate

2.8.1 Scope

The criteria contained in this part apply to the calibration of gamma-ray sources in terms of air-kerma rate

in free air. These criteria are supplementary to the general criteria contained in 2.2, and are to be followed

if this specific calibration service is offered and its inclusion in the Scope of Accreditation is desired. In that

case, both the general and these specific criteria should be met.

2.8.2 Equipment

2.8.2.1 The laboratory should have a source of gamma radiation greater than or equal to the activity of

the radiation source to be calibrated. It should have been calibrated in terms of air-kerma rate as a function

of distance, and be subject to periodic quality assurance on at least an annual basis. 

2.8.2.2 In addition, the laboratory should have as a minimum the following equipment:

a) Secondary standard ionization chambers suitable for the photon energy and intensity ranges for which

calibration services are offered.

b) An electrometer to measure the charge produced in the ionization chambers.

c) A voltage source suitable for chamber polarizing potential.

d) An independent measuring system for verification of the performance of the secondary standard

ionization chambers and electrometer.

e) Additional equipment including a pulse generator, oscilloscope, current source, precision capacitors

and precision resistors.

f) An instrument and ionization chamber support and positioning system. The instrument and ionization

chamber support and positioning system should provide for reproducible and accurate positioning of

an instrument or chamber with respect to the radiation source. For beam type irradiation

configurations, the positioning system should define the central axis of the gamma beam.
NIST Handbook 150-2D 36 September 2004

2.8.3 Test and calibration methods and method validation

2.8.3.1 Method

The calibration should be performed by measurement of the source output using secondary standard

ionization chambers or working standard ionization chambers that were calibrated against the secondary

standards. The energy dependence of the standard chamber(s) should be known over the range of photon

energies to be measured.

2.8.3.2 Geometry

The source-detector geometry should be carefully defined. Scattering (excluding that from the source and

collimator) from the surroundings should be minimal and should not exceed 10 % of the air-kerma rate at

any location where a detector is placed for source calibration. The approximate energy spectrum of scattered

radiation should be known.

2.8.3.3 Attenuation

If an attenuator is used by the laboratory to deliberately reduce the air-kerma rate produced by the source, the

effect of the attenuator on the energy spectrum of the gamma radiation should be known and the actual

attenuation factor should be determined by the laboratory. The effect of any secondary electron fluence at the

calibration position should be considered.

2.8.3.4 Uncertainty component contributed by reference value

The laboratory should state the estimated uncertainty of the measured output of the source being calibrated,

and this should not exceed 5 % total. This total uncertainty should be calculated on the basis of a thorough

analysis of possible errors. Accuracy should be maintained through periodic intercomparison with a national

standard as measured by the National Institute of Standards and Technology or another national measurement

institute that has participated in international key comparisons with NIST in the applicable measurement area.

2.8.4 Handling of test and calibration items

These criteria are to allow sealed sources in transportable containers, which can be shipped easily, to be

calibrated and shipped back to the user. The range of air-kerma rates should be from 20 FGy/h to 0.4 Gy/h

(2 mR/h to 50 R/h) measured at the 1 m point in free air. The following sources should be allowed for this

type of calibration: 24lAm, 137Cs, or 60Co.

2.8.5 Reporting the results

The calibration report should include the following information for each source calibration:

a) a complete description of the source-detector geometry used,

b) the measured air-kerma rate at the distance(s) of calibration, with and without specified attenuators,

c) a description of attenuator(s) used, and

d) the estimated uncertainty in the reported air-kerma rate.
NIST Handbook 150-2D 37 September 2004

2.9 Gamma-ray calibration of reference-class instruments

2.9.1 Scope

The criteria contained in this part apply to the calibration of reference-class instruments at radiationprotection levels using one or more gamma-ray sources. The reference-class instruments calibrated according

to these criteria are intended for use by a customer and are not intended for use as working standards in the

laboratory performing the calibration. These criteria are supplementary to the general criteria contained in

2.2. Both the general criteria and these specific criteria should be followed if inclusion of this calibration

service in the Scope of Accreditation is desired.

2.9.2 Equipment

2.9.2.1 One or more of the following radiation sources should be available for use in the calibration of

reference-class instruments:

Radionuclide Nominal Energy

137Cs 660 keV

60Co 1.25 MeV

The radiation fields produced by the sources should cover a range of air-kerma rates suitable for protectionlevel calibration.

2.9.2.2 In addition to one or more radiation sources and associated control devices, the laboratory should

have the same minimum equipment as that required for gamma-ray calibration (see 2.6.2.3).

2.9.3 Test and calibration methods and method validation

2.9.3.1 Air-kerma rate (exposure rate)

The gamma radiation field used for calibration should be characterized in terms of air-kerma rate at a given

position or distance from the source. The air-kerma rate should be known at each distance used.

2.9.3.2 Scattered radiation

The effect of room-scattered radiation (relative to a radiation field with minimal room scatter) on the accuracy

of calibration of each instrument type should be known at each location where a detector is placed for

instrument calibration.

2.9.3.3 Attenuation

If an attenuator is used to reduce the air-kerma rate at any location in the radiation field, the effect of the

altered radiation spectrum (relative to an unattenuated radiation spectrum) on the accuracy of calibration of

each instrument type should be known. The effect of any secondary electron fluence at the calibration

position should be considered. The approximate energy spectrum of the attenuated radiation field should be

known.

2.9.3.4 Uncertainty component contributed by reference value
NIST Handbook 150-2D 38 September 2004

The chamber or instrument calibration coefficient specified by the laboratory for each source of radiation

should be within 3 % of the true value as defined by comparison with a national standard as measured by the

National Institute of Standards and Technology or another national measurement institute that has participated

in international key comparisons with NIST in the applicable measurement area.

2.9.4 Handling of test and calibration items

2.9.4.1 Shielding

Radiation barriers and/or storage containers for sources should provide sufficient shielding so that

background radiation in the calibration area is sufficiently low as to not interfere with ongoing calibration

work.

2.9.4.2 Beam collimation

The gamma radiation beam emitted from a source that is used for calibration should be collimated so that its

size is limited to an area consistent with calibration requirements. An exception to this requirement is a

calibration facility sufficiently large to provide a low room-scatter radiation environment for instrument

calibration, e.g., an uncollimated source in a low-scatter room.

2.9.4.3 Source exposure and exposure control

The source storage container should have a mechanism to control exposure in the gamma beam. If the

radiation source is used for calibration of air-kerma-measuring (as contrasted with air-kerma-rate-measuring)

instruments, the shutter or source transfer should be initiated and terminated by a timer or the air kerma

should be controlled by use of a transmission chamber such that the shutter or source transit time and its

effect on the total radiation air kerma can be determined. Any associated systematic timing uncertainties

should be documented, compensated for, and monitored.

2.9.5 Reporting the results

2.9.5.1 An ionization-chamber calibration report should include, as a minimum, the radionuclide or

photon energy used, the reference air-kerma rate or rates at which the chamber was calibrated, and the

calibration coefficient of the chamber at each calibration point in terms of air kerma per unit charge.

Orientation of the chamber with respect to the radiation beam should be described, the polarity and magnitude

of the polarizing potential should be stated, and the use of a build-up cap should be noted.

2.9.5.2 An instrument calibration report should include, as a minimum, the radionuclide or photon energy

used, the reference air-kerma rate or rates at which the instrument was calibrated, the air-kerma rate indicated

by the instrument, and the calibration factor at each calibration point. In the case of integrating instruments,

in addition to the radionuclide and air-kerma rate, the reference air kerma, instrument reading, and calibration

factor should be included. One calibration point and a linearity check should be included for each range of

the instrument, where applicable. The orientation of the instrument with respect to the radiation beam should

be described or illustrated in the calibration report, and the use of a build-up cap should be noted.

2.9.5.3 For a vented ionization chamber or an instrument that uses such a chamber, the reported values

should be referenced to a temperature of 295.15 K (22 EC) and a barometric pressure of 1.013 kPa, and the

equation needed to convert to other temperatures and pressures should be provided.
NIST Handbook 150-2D 39 September 2004

2.10 X-ray calibration of survey instruments

2.10.1 Scope

The criteria contained in this part apply to the calibration of health physics instruments at radiation protection

levels using an x-ray source. These criteria are supplementary to the general criteria contained in 2.2. Both

the general criteria and these specific criteria should be followed if this x-ray calibration service is offered

and its inclusion in the Scope of Accreditation is desired. Criteria for calibration of instruments for diagnostic

levels using an x-ray source are contained in 2.12.

2.10.2 Equipment

2.10.2.1 A constant potential x-ray generator should be available for use in the calibration of health physics

instruments. Its maximum ripple should not exceed 2 % and it should be operable over a minimum range of

30 kV to 150 kV, 1 mA to 10 mA. 

2.10.2.2 In addition to one or more x-ray machines and associated control devices, the laboratory should

have the same minimum equipment as that required for gamma ray calibration (see 2.6.2) with the following

exception—the secondary standard ionization chambers should be appropriate to the energy and intensity of

x rays for which calibration services are offered.

2.10.2.3 Additionally, the laboratory should be equipped with filters to permit the production of a variety

of x-ray beam qualities, either NIST beams or ISO beams (Tables 3 or 4).

2.10.3 Test and calibration methods and method validation

2.10.3.1 Air-kerma rate (exposure rate)

The x-ray radiation field used for calibration should be characterized in terms of air-kerma rate at a given

position or distance from the anode of the x-ray tube. The air-kerma rate should be known at each distance

used. During calibration of an instrument, the air-kerma rate should not vary by more than 2 % from the

nominal rate when it is 90 FGy/h (10 mR/h) or higher, and should not vary by more than 4 % from the

nominal rate when it is below 90 FGy/h (10 mR/h) .

2.10.3.2 Scattered radiation

The effect of room-scattered radiation (relative to a radiation field with minimal room scatter) on the accuracy

of calibration of each instrument type should be known at each location where a detector is placed for

instrument calibration.

2.10.3.3 Beam quality

The x-ray beam emitted from the tube housing should be filtered before use to provide the appropriate beam

quality meeting either Tables 3 or 4 (see reference 1.4.5 d)). If ISO beams (Table 4) are to be used, then ISO

4037-1 requirements should be met. ISO 4037-1 is also a good guide for developing the beams in general.

If a transmission chamber is used for routine beam monitoring, it should be considered to be added filter

material. Three or more of the beams shown in Tables 3 or 4 should be available.
NIST Handbook 150-2D 40 September 2004

2.10.3.4 Half-value layer and homogeneity coefficients

The first half-value layer and homogeneity coefficients for a given x-ray beam should be within 5 % and 7 %,

respectively, of the values shown in Table 3. If necessary, the indicated tube voltage or added filter, or both,

may be adjusted by 5 % to achieve those values.

2.10.3.5 Air-kerma rate

The air-kerma rate should not vary more than 5 % across the useful area of the beam.

2.10.3.6 Radiation quality

The radiation quality should be checked for stability at least annually. Whenever any part that could affect

the beam quality is repaired or replaced, either Table 3 or ISO 4037-1 requirements for beam quality should

be met.

2.10.3.7 Uncertainty component contributed by reference value

The air-kerma rate specified by the laboratory as its reference value for each x-ray beam should be within 5

% of the true value as defined by comparison with a national standard above 90 FGy/h (10 mR/h) , and within

7 % of the true value from 4 FGy/h (0.5 mR/h) to 90 FGy/h (10 mR/h).

2.10.4 Handling of test and calibration items

2.10.4.1 Radiation production

The production of a useful beam of radiation may be by applying high voltage to the x-ray tube or by opening

a mechanical shutter (which normally acts as a shield to the x-ray beam).

2.10.4.2 Beam collimation

The x-ray beam emitted from the tube housing should be collimated so that its size is limited to an area

consistent with calibration requirements. Provision should be made for identifying the central axis, and the

boundaries of the useful area of the beam should be known.

2.10.4.3 Exposure control

When a radiation source is used for the calibration of air-kerma measuring instruments, the radiation beam

should be controlled by a timer, or the air kerma should be monitored by use of a transmission chamber. The

timing uncertainty due to the shutter transit times or high voltage ramping should be known.

2.10.5 Reporting the results

2.10.5.1 An instrument calibration report should include, as a minimum: 

a) the x-ray beam used for calibration;

b) in the case of air-kerma rate measurements,

1) the reference air-kerma rate or rates at which the instrument was calibrated, 
NIST Handbook 150-2D 41 September 2004

2) the air-kerma rate indicated by the instrument, and 

3) the calibration factor at each calibration point;

c) in the case of integrating instruments, in addition to the x-ray beam and air-kerma rate, 

1) the reference air kerma,

2) the instrument reading, and 

3) the calibration factor.

2.10.5.2 At least one calibration point should be included for each range of the instrument, where possible.

2.10.5.3 The orientation of the instrument with respect to the radiation beam should be described or

illustrated in the calibration report.

2.10.5.4 For instruments that use a vented ionization chamber, the reported values should be referenced

to a temperature of 295.15 K (22 EC) and a barometric pressure of 1.013 kPa, and the equation needed to

convert to other temperatures and pressures should be provided.
NIST Handbook 150-2D 42 September 2004

Table 3. NIST Calibration Conditions for X- and Gamma-Ray Measuring Instruments

(Lamperti and O’Brien, 2001)

Beam

code c Additional Filtrationa Half-value layerb

 (HVL) Homogeneity

coefficient (HC)

Effective

energy

Al

(mm)

Cu

(mm)

Sn

(mm)

Pb

(mm)

Al

(mm)

Cu

(mm)

Al Cu (keV)

X-Ray Beam Qualities

L10 0.037 86

L15 0.059 70

L20 0.070 72

L30 0.30 0.23 60

L40 0.53 0.52 61

L50 0.71 0.79 63

L80 1.45 1.81 56

L100 1.98 2.80 58

M20 0.27 0.15 72

M30 0.5 0.36 65

M40 0.89 0.74 67

M50 1.07 1.04 68

M60 1.81 1.64 0.052 63 60

M80 2.86 2.98 0.10 68 61

M100 5.25 5.00 0.20 74 55

M120 7.12 6.72 0.31 77 53

M150 5.25 0.25 10.1 0.66 88 63

M200 4.35 1.12 14.7 1.64 94 68

M250 5.25 3.2 18.3 3.2 98 85

M300 4.25 6.5 21.7 5.3 100 97

H10 0.105 0.051 77

H15 0.5 0.16 87

H20 1.01 0.36 89

H30 4.50 1.20 86

H40 4.53 0.26 2.93 94

H50 4.0 0.1 4.2 0.14 93 93 38

H60 4.0 0.61 6.0 0.25 94 94 46

H100 4.0 5.2 13.4 1.15 97 92 80

H150 4.0 4.0 1.51 16.9 2.43 100 96 120

H200 4.0 0.6 4.16 0.77 19.7 4.10 99 99 166

H250 4.0 0.6 1.04 2.72 22 5.19 99 98 211

H300 4.1 3.0 5.0 23 6.19 99 98 252

S60 4.35 2.79 0.09 76 66

S75 1.50 1.81 58

Gamma-Ray Beam Qualities

137Cs 10.8 662

60Co 14.9 1250

a

The additional filtration value does not include the inherent filtration. The inherent filtration is approximately 1.0 mm Be for beam codes

L10-L100, M20-M50, H10-H40 and S75; and 3.0 mm Be for beam codes M60-M300, H50-H300 and S60. b

The HVL values were measured directly using the two new x-ray tubes installed in November of 2001 and May of 2002. c

The NIST H group of beam qualities agrees with the ISO narrow spectrum (NS) qualities recommended in ISO 4037-1 (see also Table 4). The

NIST M group of beam qualities agrees with the recommendation for radiation therapy calibration in IEC Publication 60731. H qualities are

usually used for calibration for radiation protection instrumentation since they have the narrowest spectrum at each generating potential and

probably most nearly approximate radiation that has penetrated a protective barrier. M qualities are usually used for calibration radiation

therapy instruments. L qualities are predominately used for calibration of instruments used for measurement of unfiltered or lightly filtered

beams that give high exposure rates, such as in radiation biology and Grenz-ray therapy. For more information, contact the Radiation

Interactions and Dosimetry Group, NIST, 100 Bureau Drive, Stop 8460, Gaithersburg, MD 20899-8460, fax: 301-869-7682.
NIST Handbook 150-2D 43 September 2004

Table 4. ISO X-Ray Beam Quality Parameters Offered at NIST

(Lamperti and O’Brien, 2001)

Beam Additional Filtration (mm)a First HVL Second HVL

Codeb Al Cu Sn Pb mm Al mm Cu mm Al mm Cu

HK10 0.042 0.045

HK20 0.15 0.128 0.170

HK30 0.52 0.408 0.596

HK60 3.19 0.079 0.113

HK100 3.90 0.15 0.298 0.463

HK200 1.15 1.669 2.447

HK250 1.60 2.463 3.37

HK280 3.06 3.493 4.089

HK300 2.51 3.474 4.205

WS60 0.3 0.179 0.206

WS80 0.529 0.337 0.44

WS110 2.029 0.97 1.13

WS150 1.03 1.88 2.13

WS200 2.01 3.09 3.35

WS250 4.01 4.30 4.50

WS300 6.54 5.23 5.38

NS10 0.095 0.049 0.061

NS15 0.49 0.153 0.167

NS20 0.90 0.324 0.351

NS25 2.04 0.691 0.762

NS30 4.02 1.154 1.396

NS40 0.21 0.082 0.094

NS60 0.6 0.241 0.271

NS80 2.0 0.59 0.62

NS100 5.0 1.15 1.19

NS120 4.99 1.04 1.70 1.85

NS150 2.50 2.40 2.52

NS200 2.04 2.98 4.09 4.20

NS250 2.01 2.97 5.26 5.32

NS300 2.99 4.99 6.17 6.30

LK10 0.30 0.061

LK20 2.04 0.441

LK30 3.98 0.18 1.492

LK35 0.25 2.21

LK55 1.19 0.260

LK70 2.64 0.509

LK100 0.52 2.0 1.27

LK125 1.0 4.0 2.107 2.094

LK170 1.0 3.0 1.5 3.565 3.592

LK210 0.5 2.0 3.5 4.726 4.733

LK240 0.5 2.0 5.5 5.515 5.542

a

The additional filtration does not include the inherent filtration. The inherent filtration is a

combination of the filtration due to the monitor chamber plus 1 mm Be for beam codes LK10-LK30,

NS10-NS30, HK10-HK30 and for all other techniques the inherent filtration is adjusted to 4 mm Al. b

LK indicates low air kerma rate; HK high air kerma rate; NS narrow spectrum; WS wide spectrum;

number indicates the constant potential in kilovolts.
NIST Handbook 150-2D 44 September 2004

2.11 X-ray irradiation of personnel dosimeters

2.11.1 Scope

2.11.1.1 The criteria contained in this part of the document apply to the irradiation of dosimeters at

radiation protection levels using x-ray beam sources. These criteria are supplementary to the general criteria

contained in 2.2, and should be followed if this specific irradiation service is offered and its inclusion in the

Scope of Accreditation is desired. In that case, both the general criteria and these specific criteria should be

followed.

2.11.1.2 These criteria apply to the irradiation of dosimeters used for personnel monitoring.

2.11.2 Equipment

2.11.2.1 At least one constant potential x-ray generator should be available to cover a range of exposures

(air kerma) for protection-level irradiations. The range covered will be a function of the mission and

requirements of the laboratory but a minimal range is 0.3 mGy to 4 Gy (30 mR to 500 R). The laboratory

should be able to perform irradiations using three or more of the filtered beams described in ANSI N13.11

and DOE/EH-0027. 

2.11.2.2 In addition to one or more x-ray machines and the associated beam control devices, the laboratory

should have the same minimum equipment as that required for gamma-ray calibration (see 2.6.2.3), plus the

following:

a) a phantom consisting of a slab of polymethylmethacrylate with a minimum cross section of 30 cm ×

30 cm and a thickness of 15 cm, with a support system for the phantom that is rigid and produces

minimum scattered radiation at the dosimeter position(s);

b) secondary standard ionization chambers appropriate to the energy and intensity of x-rays for which

irradiation services are offered.

2.11.3 Test and calibration methods and method validation

2.11.3.1 Air-kerma rate (exposure rate)

The radiation field should be characterized in terms of air-kerma rate in the absence of a phantom at the

location where the center of the front surface of the phantom is placed for irradiation.

2.11.3.2 Scatter

The contribution from room-scattered radiation should be determined with the phantom removed from the

beam and should not exceed 5 % of the air-kerma rate at any location where a dosimeter is placed for

irradiation. The approximate energy spectrum of room-scattered radiation should be known.

2.11.3.3 Beam quality

The x-ray beam emitted from the tube housing should be filtered before use to provide the appropriate beam

quality meeting Tables 3 or 4. The first half-value layer and homogeneity coefficients for a given x-ray beam

should be within 5 % and 7 %, respectively, of the values shown in Tables 3 or 4. If necessary, the indicated

tube voltage or added filter, or both, may be adjusted by 5 % to achieve those values. The intensity of the xray beam should not vary more than 5 % across the useful area of the beam. If a transmission chamber is used

for routine beam monitoring, it should be considered to be added filter material. The radiation quality should
NIST Handbook 150-2D 45 September 2004

be checked for stability at least annually. Whenever any part that could affect the beam quality is repaired

or replaced, the above requirements for radiation quality should be met. Three or more of the beams shown

in Tables 3 or 4 should be available.

2.11.3.4 Uncertainty component contributed by reference value

The air kerma rate specified by the laboratory as its reference value should be within 3 % of the actual value

defined by comparison with the national standard. The total uncertainty of the dose delivered to an irradiated

dosimeter should be less than or equal to 5 %. To meet this criterion, it may be necessary to use positionspecific correction factors when several dosimeters are irradiated simultaneously.

2.11.3.5 Orientation

The dosimeters should be attached to one of the two larger surfaces of the phantom, at least 5 cm from any

edge of the surface, and that surface should face the radiation source. The central axis of the collimated beam

should be perpendicular to the surface, and should pass through its geometric center. The position and

orientation of the phantom should be reproducible and verifiable.

2.11.3.6 Distance

The distance between the radiation source and the phantom surface to which the dosimeters are attached

should be one meter or more. The distance should be reproducible and verifiable.

2.11.3.7 Total air kerma

A method should be used to verify the total air kerma independent of the timer and known air-kerma rate.

2.11.4 Handling of test and calibration items

2.11.4.1 Shielding

Leakage radiation through a closed shutter or x-ray tube head shielding should be less than 0.1 % of the openshutter rates at the position of the dosimeters.

2.11.4.2 Beam size and uniformity

The x-ray beams should be collimated and their size should be limited to an area consistent with the

irradiation requirements. All dosimeters should be irradiated with phantom backing, and the beam size should

be sufficient to irradiate the entire phantom surface that is facing the tube head. If several dosimeters are

being irradiated simultaneously, the beam size and beam uniformity should be sufficiently uniform and

characterized to satisfy the requirements of ANSI N13.11.

2.11.4.3 Exposure control

If a shutter is used to control the beam, the shutter transit time should be known. If a shutter is not used,

radiation produced prior to achieving beam stability should be known in all cases and should be compensated.

The uncertainties associated with stabilization should be known. Any associated systematic timing

uncertainties should be documented, compensated for, and monitored.
NIST Handbook 150-2D 46 September 2004

2.11.5 Reporting the results

The laboratory should report to the customer the total air kerma for each dosimeter irradiated. For conversion

to dose or dose equivalent, the value of the exposure should be multiplied by the factors given in ANSI

N13.11 or DOE/EH-0027. The reference(s) for the factor(s) used should also be given.

2.12 X-ray calibration of instruments for diagnostic radiology levels

2.12.1 Scope

2.12.1.1 The criteria contained in this part of the document apply to calibration of instruments at diagnostic

radiology levels using an x-ray source. These criteria are supplementary to the general criteria contained in

2.2 and should be followed if this specific calibration service is offered and its inclusion in the laboratory’s

Scope of Accreditation is desired. Both the general criteria and these specific criteria should be followed in

that case.

2.12.1.2 Although not part of NVLAP criteria, other requirements for performance of calibration

instruments for diagnostic application may apply. The American Association of Physicists in Medicine

(AAPM) Accredited Dosimetry Calibration Laboratory (ADCL) Program follows regulations under the

Mammography Quality Standards Act published by the Food and Drug Administration and the American

College of Radiology (ACR) standards for professional credentials, equipment specifications, monitoring and

maintenance schedules, record keeping, and data review. Familiarity with these standards and requirements

will assist the NVLAP assessor in his/her review.

2.12.2 Equipment

2.12.2.1 The laboratory should have a constant potential x-ray machine available for calibration of

instruments. It should operate at potentials from 20 kV to 150 kV as a minimum range. The radiation field

produced should cover, as a minimum range, air-kerma rates from 180 mGy/h to 900 mGy/h (20 R/h to

100 R/h), with a stability sufficient to calibrate instruments according to documented laboratory procedures.

During calibration of an instrument, the air-kerma rate should not vary by more than ± 1 %.

2.12.2.2 In addition to one or more x-ray machines and associated control devices, the laboratory should

have the same minimum equipment as that required for gamma ray calibration (see 2.6.2.3).

2.12.2.3 Additionally, the laboratory should be equipped with filters to permit the production of a variety

of x-ray beam qualities (see 2.12.3.4).

2.12.3 Test and calibration methods and method validation

2.12.3.1 Air-kerma rate (exposure rate)

The x-ray field used for calibration should be characterized in terms of air-kerma rate at the location where

the effective center of the instrument’s detector is placed for calibrations.

2.12.3.2 Scatter

The effect of room-scattered radiation (relative to a radiation field with minimal room scatter) on the accuracy

of calibration of each instrument type should be known at each location where a detector is placed for

instrument calibration.
NIST Handbook 150-2D 47 September 2004

2.12.3.3 Uncertainty component contributed by reference value

The air-kerma rate specified by the laboratory as its reference value should be within ± 5 % of the actual value

defined by comparison with the national standard.

2.12.3.4 Beam quality

The first half-value layer and homogeneity coefficients for a given x-ray beam should be within 5 % and 7 %,

respectively, of the values shown in Table 5. If necessary, the indicated tube voltage or added filter, or both,

may be adjusted by as much as 5 % to achieve those values. If a transmission chamber is used for routine

beam monitoring, it should be considered to be added filter material.
NIST Handbook 150-2D 48 September 2004

Table 5. Mammography X-Ray Beam-Quality Parameters at NIST

(Lamperti and O’Brien, 2001)

Beam Code Tube Voltage

(kV)

Added Filter

(mm)

Half-Value Layer

(mm Al)

Homogeneity

Coefficient

(Al)

Mo Anode

Mo/Mo23 23 0.032 Mo 0.271 0.702

Mo/Mo25 25 0.032 Mo 0.296 0.719

Mo/Mo28 28 0.032 Mo 0.332 0.743

Mo/Mo30 30 0.032 Mo 0.351 0.752

Mo/Mo35 35 0.032 Mo 0.392 0.784

Mo/Rh28 28 0.029 Rh 0.408 0.796

Mo/Rh32 32 0.029 Rh 0.445 0.821

Mo/Mo25x 25 0.030 Mo + 2.0 Al 0.566 0.91

Mo/Mo28x 28 0.030 Mo + 2.0 Al 0.626 0.964

Mo/Mo30x 30 0.030 Mo + 2.0 Al 0.660 0.947

Mo/Mo35x 35 0.030 Mo + 2.0 Al 0.748 0.902

Rh Anode

Rh/Rh25 25 0.029 Rh 0.351 0.755

Rh/Rh30 30 0.029 Rh 0.438 0.812

Rh/Rh35 35 0.029 Rh 0.512 0.858

Rh/Rh40 40 0.029 Rh 0.559 0.895

Rh/Rh30x 30 0.029 Rh + 2.0 Al 0.814 0.964

Rh/Rh35x 35 0.029 Rh + 2.0 Al 0.898 0.945

The beam codes are a combination of the chemical symbol of the anode and the filter, respectively, followed by

the constant potential in kilovolts. The letter “x” ends the beam codes which denote “exit” beams. The exit beam

qualities, which are intended to represent the transmission of the x-rays through the breast, are generated by an

additional filtration of 2.0 mm of aluminum.

The inherent filtration is 1 mm Be for all beam qualities. The calibration distance is 1 m. The half-value layers

were determined through direct measurements with the primary standard free-air ionization chamber. The air

kerma rates for the entrance beams are between 0.5 mGy/s, and less than 0.2 mGy/s for the exit beams. 
NIST Handbook 150-2D 49 September 2004

2.12.3.5 Intensity of x-ray beam

The intensity of the x-ray beam should not vary more than 5 % across the useful area of the beam.

2.12.3.6 Radiation quality

The radiation quality should be checked for stability at least annually. Whenever any part that could affect

the beam quality is repaired or replaced, the above requirements for radiation quality should be met.

2.12.4 Handling of test and calibration items

2.12.4.1 Beam collimation

The x-ray beam emitted from the tube housing should be collimated so that its size is limited to the minimum

area consistent with calibration requirements. Provision should be made for identifying the central axis, and

the boundaries of the useful area of the beam should be known.

2.12.4.2 Shutter and exposure control

A shutter should be used to control emission of the x-ray beam from the tube housing. If the beam is used

for calibration of air-kerma-measuring instruments, the shutter should be operated by a timer or a suitable

charge integrating device, so that the shutter transit time can be measured and recorded. Any associated

errors due to shutter transit times should be documented, compensated for, and monitored.

2.12.5 Reporting the results

2.12.5.1 An instrument calibration report should include, as a minimum, 

a) the x-ray beam quality used for calibration;

b) in the case of air-kerma rate measurements,

1) the reference air-kerma rate or rates at which the instrument was calibrated, 

2) the air-kerma rate indicated by the instrument, and 

3) the calibration factor at each calibration point;

c) in the case of integrating instruments, in addition to the x-ray beam and air-kerma rate, 

1) the reference air kerma,

2) the instrument reading, and 

3) the calibration factor.

2.12.5.2 One calibration point and a linearity check should be included for each range of the instrument,

where possible.

2.12.5.3 The orientation of the instrument with respect to the radiation beam should be described or

illustrated in the calibration report.
NIST Handbook 150-2D 50 September 2004

2.12.5.4 For instruments that use a vented ionization chamber, the reported values should be referenced to

a temperature of 295.15 K (22 EC) and a barometric pressure of 1.013 kPa, and the equation needed to

convert to other temperatures and pressures should be provided.

2.13 X-ray calibration of reference-class instruments

2.13.1 Scope

The criteria contained in this part apply to the calibration of reference-class instruments at radiation protection

or diagnostic levels using an x-ray source. The reference-class instruments calibrated according to these

criteria are intended for use by a customer and are not intended for use as working standards in the laboratory

performing the calibration. These criteria are supplementary to the general criteria contained in 2.2. Both

the general criteria and these specific criteria should be followed if inclusion of this calibration service in the

Scope of Accreditation is desired.

2.13.2 Equipment

2.13.2.1 A constant potential x-ray generator should be available for use in the calibration of reference-class

instruments. Its maximum ripple should not exceed 2 % and it should be operable over a minimum range of

30 kV to 150 kV, 1 mA to 10 mA. The radiation fields produced by the x-ray generator should cover a range

of air-kerma rates suitable for protection-level and diagnostic calibration. During calibration of an instrument,

the air-kerma rate should not vary by more than 1 % from the nominal rate.

2.13.2.2 In addition to one or more x-ray machines and associated control devices, the laboratory should

have the same minimum equipment as that required for gamma ray calibration (see 2.6.2.3) with the following

exception: the secondary standard ionization chambers should be appropriate to the energy and intensity of

x-rays for which calibration services are offered.

2.13.2.3 Additionally, the laboratory should be equipped with filters to permit the production of a variety

of x-ray beam qualities (see 2.13.3.3 through 2.13.3.6).

2.13.3 Test and calibration methods and method validation

2.13.3.1 The x-ray radiation field used for calibration should be characterized in terms of air-kerma rate at

a given position or distance from the anode of the x-ray tube. The air-kerma rate should be known at each

distance used.

2.13.3.2 The effect of room-scattered radiation (relative to a radiation field with minimal room scatter) on

the accuracy of calibration of each instrument type should be known at each location where a detector is

placed for instrument calibration.

2.13.3.3 The x-ray beam emitted from the tube housing should be filtered before use to provide the

appropriate radiation quality for calibration purposes. If a transmission chamber is used for routine beam

monitoring, it should be considered to be added filter material. Three or more of the beams shown in Tables

3 or 4 should be available.

2.13.3.4 The first half-value layer and homogeneity coefficients for a given x-ray beam should be within 5

% and 7 %, respectively, of the values shown in Tables 3 or 4. If necessary the indicated tube voltage or

added filter, or both, may be adjusted within 5 % to achieve those values.
NIST Handbook 150-2D 51 September 2004

2.13.3.5 The intensity of the x-ray beam should not vary more than 5 % across the useful area of the beam.

2.13.3.6 The radiation quality should be checked for stability at least annually. Whenever any part that

could affect the beam quality is repaired or replaced, the above requirements for radiation quality should be

met.

2.13.3.7 The chamber or instrument calibration factor specified by the laboratory for each x-ray beam should

be within 3 % of the true value as defined by comparison with a national standard.

2.13.4 Handling of test and calibration items

2.13.4.1 Radiation production

The production of a useful beam of radiation may be by means of the application of high voltage to the x-ray

tube or the opening of a mechanical shutter (which normally acts as a shield to the x-ray beam).

2.13.4.2 Beam collimation

The x-ray beam emitted from the tube housing should be collimated so that its size is limited to an area

consistent with calibration requirements. Provision should be made for identifying the central axis, and the

boundaries of the useful area of the beam should be known.

2.13.4.3 Exposure control

If the radiation source is used for the calibration of air kerma measuring instruments, the radiation beam

should be controlled by a timer or the air kerma should be controlled by use of a transmission chamber. The

timing error due to the shutter transit times or high voltage ramping should be documented, compensated for,

and monitored.

2.13.5 Reporting the results

2.13.5.1 An ionization-chamber calibration report should include, as a minimum, a description of beam

quality in terms of the codes in Tables 3 or 4 or an equivalent method, the reference air-kerma rate or rates

at which the chamber was calibrated, and the calibration coefficient of the chamber at each calibration point

in terms of air kerma per unit charge. Orientation of the chamber with respect to the radiation beam should

be described, and the polarity and magnitude of the polarizing potential should be stated.

2.13.5.2 An instrument calibration report should include, as a minimum, the x-ray beam used for calibration,

the reference air-kerma rate or rates at which the instrument was calibrated, the air-kerma rate indicated by

the instrument, and the calibration factor at each calibration point. In the case of integrating instruments, in

addition to the x-ray beam and air-kerma rate, the reference air kerma, instrument reading, and calibration

factor should be included. One calibration point and a linearity check should be included for each range of

the instrument, where possible. The orientation of the instrument with respect to the radiation beam should

be described or illustrated in the calibration report.

2.13.5.3 For a vented ionization chamber or an instrument that uses such a chamber, the reported values

should be referenced to a temperature of 295.15 K (22 EC) and a barometric pressure of 1.013 kPa, and the

equation needed to convert to other temperatures and pressures should be provided.

2.14 Neutron calibration of survey instruments
NIST Handbook 150-2D 52 September 2004

2.14.1 Scope

The criteria contained in this part apply to the calibration of health physics instruments at radiation protection

levels using neutron radiation. These criteria are supplementary to the general criteria contained in 2.2. Both

the general criteria and these specific criteria should be followed if this neutron radiation calibration service

is offered and its inclusion in the Scope of Accreditation is desired.

2.14.2 Equipment

2.14.2.1 The selection of a source for neutron radiation calibration of an instrument will depend on the

nature of the radiation field in which the instrument is to be used, including the anticipated neutron energy

spectrum. The neutron sources described in Table 6 are frequently used for instrument calibration. As a

minimum, a laboratory should have at least one of the sources shown in Table 6 with appropriate strength for

the dose equivalent or dose-equivalent-rate range of the instruments to be calibrated. A minimum doseequivalent rate range is 0.1 mSv/h to 10 mSv/h (10 mrem/h to 1 rem/h ). The measurements of the neutron

source strength should be known and traceable. If a 252Cf source is used, the laboratory should be capable of

calibrating an instrument using both the bare source and the moderated configuration.

Table 6. Characteristics of Commonly Used Fast Neutron Sources for Calibration of Neutron

Survey Instruments (Lorenz, 1972)

Method of Neutron Energy (MeV)

Source Neutron Production Half-life Max. Average

238Pu (Be) (α,n) 86.4 Y 11.3 5.0

239Pu (Be) (α,n) 24390 Y 10.74 4.5-5 241Am (Be) (α,n) 458 Y 11.5 5.0

252Cf SF 2.654 Y 15 2

252Cf Moderated with SF 2.654 Y 15 0.54

15 cm D2O (e.g., Schwartz,

1980; Prevo, 1983)

The radiation field produced by a neutron source used for calibration should provide an energy spectrum and

dose-equivalent rates appropriate for the instrument undergoing calibration.

2.14.2.2 In addition to a selection of one or more neutron sources appropriate to the radiation field(s) in

which instruments are being calibrated, the laboratory should have the same minimum equipment as that

required for gamma-ray calibration (see 2.6.2.3), with the exception of secondary standard ionization

chambers and that equipment associated with their use.

2.14.3 Test and calibration methods and method validation

2.14.3.1 Dose equivalent rate

The neutron radiation field used for calibration should be characterized in terms of the fluence rate and

spectral composition at the point of calibration. The dose equivalent rate should be calculated on the basis

of these characteristics (see Table 6) as a means of setting calibration points for specific instrument types.

2.14.3.2 Radiation quality
NIST Handbook 150-2D 53 September 2004

In addition to the radiation quality considerations addressed in the preceding paragraphs, contamination of

the neutron field by other types of radiation may also contribute to erroneous instrument response. If this is

the case and the instrument is sensitive to photon and/or beta radiation as well as neutrons, the extent of this

contamination should be known and accounted for when calibrating a given instrument. Photon contamination

of the neutron field should be known and should be less than 20 % of the total dose equivalent rate.

Table 7. Characterization of neutron sources in terms of dose equivalent

Mean neutron fluence Specific Specific neutron

to dose equivalent source dose equivalent

Radionuclide conversion factor(a) (b) strength rate at 1 m(b)

source (Sv @ cm2) (s-1 @ Bq-1) (mSv @ h-1 @ Bq-1)

238Pu(Be) 5.4 × 10-3

239Pu(Be) 4.1 × 10-3

24lAm(Be) 3.9 × 10-10 6.5 × 10-3 7.3 × 10-10

(s-1 @ mg-1) (mSv @ h-1 @ mg-1)

252Cf 3.85 × 10-10 2.4 ×109 2.3 × 10

252Cf moderated 1.05 × 10-10 2.1 × 109 5.4

 Conversion Coefficient hφ

(a) The conversion coefficients were calculated from the equation above, where B is the neutron source strength, BE is

the spectral distribution of neutron source strength, and hφ is the energy averaged neutron-fluence-to-dose equivalent

conversion coefficient, i.e., the quotient of the dose equivalent and the neutron fluence (see ISO 8529-1:2001).

(b) These are typical numbers. BE and hence, the dose equivalent rate from a particular source depends upon variable

factors such as purity, internal absorption, construction details, and encapsulation.

2.14.3.3 Uncertainty component contributed by reference value

The dose-equivalent rate specified by the laboratory as its reference value for each neutron field should be

within 10 % of the true value as defined by comparison with a national standard as measured by the National

Institute of Standards and Technology or another national measurement institute that has participated in

international key comparisons with NIST in the applicable measurement area.

2.14.4 Handling of test and calibration items

2.14.4.1 Radiation production

The production of a field of neutron radiation for instrument calibration should be achieved by moving the

source from a shielded to an exposed position, preferably in a low-scatter environment in an open area or at

the center of a large room (for example, 10 m × 10 m square with the source 4 m from both floor and ceiling).

The neutron radiation field used for calibration should be carefully monitored and controlled. The response

due to room-scattered neutrons at the point of calibration should be less than 25 % of the total instrument

response, and the appropriate corrections should be made.

∫

∞

=

0

( )

1

B h E dE B E φ
NIST Handbook 150-2D 54 September 2004

2.14.4.2 Timer

If the neutron source is used for the calibration of integrated dose equivalent measuring instruments, the

radiation field should be controlled by a timer. Any associated systematic timing uncertainties should be

documented, compensated for, and monitored.

2.14.5 Reporting the results

2.14.5.1 An instrument calibration report should include, as a minimum, the radionuclide and radiation

field type (moderated or unmoderated) used for calibration, the free-field dose equivalent rate or rates at

which the instrument was calibrated, the scatter-corrected instrument reading at each calibration point, and

the basis for any calculation of dose-equivalent rate from source emission rate.

2.14.5.2 At least one calibration point should be included for each decade range of the instrument, where

possible.

2.14.5.3 The orientation of the instrument with respect to the radiation field should be described or

illustrated in the calibration report.

2.14.5.4 The value of the scatter correction should be provided.

2.15 Neutron irradiation of personnel dosimeters

2.15.1 Scope

2.15.1.1 The criteria contained in this part of the document apply to irradiation of dosimeters at radiation

protection levels using neutron sources. These criteria are supplementary to the general criteria contained

in 2.2 and should be followed if this specific irradiation service is offered and its inclusion in the Scope of

Accreditation is desired. In that case, both the general criteria and these specific criteria should be followed.

2.15.1.2 These criteria apply to irradiation of dosimeters used for personnel monitoring. They do not apply

to dosimeters that use neutron activation foils to determine accident level doses.

2.15.2 Equipment

2.15.2.1 These criteria apply to neutrons from radionuclide sources, including sources in a moderator.

They do not apply to accelerator-produced neutrons or neutrons from reactors. Neutron sources specified by

ANSI N13.11 or DOE/EH-0027 should be available. Additional sources may be used if their spectral

distributions, neutron emission rates, and dose equivalent conversion factors are well documented. The range

of dose equivalents covered will be a function of the mission and requirements of the laboratory, but 1.5 to

50 mSv (150 mrem to 5 rem) will suffice for most radiation protection purposes. All irradiations should refer

to free-field quantities and should be performed with phantom backing.

2.15.2.2 In addition to one or more radiation sources and the associated source transport system, the

laboratory should have at least a phantom consisting of a slab of polymethylmethacrylate with a cross section

of 40 × 40 cm and a thickness of 15 cm. The support system for the phantom should be rigid and produce

minimum scattered radiation at the dosimeter position(s). The system should provide for reproducible and

accurate positioning of the phantom with respect to the radiation source.
NIST Handbook 150-2D 55 September 2004

2.15.3 Test and calibration methods and method validation

2.15.3.1 Dose-equivalent rates

The neutron radiation fields used for irradiation should be characterized in terms of the free-field doseequivalent rate at the center of the front surface of the phantom. The neutron emission rate for each source

should be determined by the NIST. Procedures for determining the dose equivalent for dosimeters exposed

to a 252Cf source should follow Eisenhauer, Hunt, and Schwartz, 1985. Procedures for other sources should

be documented. The contribution to the dose equivalent due to photon emission from the neutron source

should be measured and documented. There should be verification of the expected dose-equivalent rate

during irradiation.

2.15.3.2 Scatter

The contribution of air scattering, room return and source scattering should be determined for all irradiation

geometries and distances so that free-field dose equivalents can be determined. To minimize room scatter,

the irradiation room should be as large as is practically possible and irradiations should be conducted near

the center of the room.

2.15.3.3 Uncertainty component contributed by reference value

The dose-equivalent rate specified by the laboratory as its reference value should be within 10 % of the actual

value defined by comparison with the national standard. The total uncertainty in the assigned neutron dose

equivalent for irradiated dosimeters should be less than or equal to 10 %, excluding uncertainties in the dose

equivalent conversion factors and the photon component of the neutron irradiations. To meet this criterion,

it may be necessary to use position-specific calibration factors when several dosimeters are irradiated

simultaneously.

2.15.3.4 Orientation

The dosimeters should be attached to one of the two larger surfaces of the phantom, at least 10 cm from any

edge of the surface, and that surface should face the radiation source. That surface should be perpendicular

to a radial line from the source center to the phantom center. The position and orientation of the phantom

should be reproducible and verifiable.

2.15.3.5 Distance

The distance between the center of the radiation source and the center of the phantom surface to which the

dosimeters are attached should be at least 50 cm. The dose equivalent should be calculated at the location

of each dosimeter. It should be reproducible and verifiable.

2.15.3.6 Delivered dose equivalent

A method should be used to verify the delivered dose equivalent independent of the timer and known dose

equivalent rate. Possible verification methods include an off-axis detector or a passive detector exposed with

each irradiation.

2.15.4 Handling of test and calibration items
NIST Handbook 150-2D 56 September 2004

2.15.4.1 Shielding

The source storage container should provide sufficient shielding such that leakage radiation does not interfere

with other uses of the radiation room by raising the background level. Background radiation and leakage

radiation from all sources in the radiation room should not contribute more than 0.1 % of the total dose

equivalent to which dosimeters are irradiated.

2.15.4.2 Irradiation control

A source transport system should be provided to transport the source from the storage container to the

irradiation position. Both the transit time from storage to irradiation position and the associated doseequivalent contribution to dosimeter irradiation should be known. It should be possible to operate the source

transport system with a timer. Any associated random timing uncertainties due to the transit time of the source

should be known. Any associated systematic timing uncertainties should be measured, compensated for, and

monitored.

2.15.5 Reporting the results

The laboratory should report to the customer the free-field dose equivalent for each dosimeter irradiated. The

ratio of the dose equivalent arising from photon emission by the radiation source to the neutron dose

equivalent should be reported.

2.16 Neutron dosimeters and survey instruments

2.16.1 Scope

The criteria contained in this part of the document apply to laboratories that calibrate neutron measuring

instruments; in particular, neutron radiation protection instrumentation such as neutron dosimeters and

neutron area survey meters. These criteria are supplementary to the general criteria contained in 2.2 and

should be followed if this specific irradiation service is offered and its inclusion in the Scope of Accreditation

is desired. In that case, both the general criteria and these specific criteria should be followed.

2.16.2 Assuring the quality of test and calibration results

2.16.2.1 The laboratory should have one or more radionuclide neutron sources whose emission rate is

traceable to measurements from National Institute of Standards and Technology or to another national

measurement institute that has participated in international key comparisons with NIST in the applicable

measurement area.

2.16.2.2 The laboratory should have a neutron measuring device, calibrated at NIST, to use as a system

check.

2.16.3 Accommodation and environmental conditions

2.16.3.1 The facility should consist of at least one irradiation room and suitable storage, set-up, and office

space, all designed to meet local safety codes and regulations. It should be sufficiently shielded from

extraneous radiation sources so that the neutron-background dose-equivalent rate (H0 ) due to such sources is H0

< 10-3 mSv@h-1. It should be provided with air conditioning and heating adequate to keep the temperature in

the range (295.15 ± 4) K (22 EC ± 4 EC) and the relative humidity between 20 % and 65 %. The laboratory

should be free of undue vibration, shock, and noise.
NIST Handbook 150-2D 57 September 2004

2.16.3.2 The irradiation room may be either “open” or “closed.” An open room is one in which the walls

and ceiling are generally of low-mass, non-hydrogenous material essentially transparent to neutrons.

Radiation protection is provided by means of a sufficiently large exclusion area. A closed room is one in

which the walls and ceiling are sufficiently massive (usually concrete) to provide adequate shielding. A

closed room should be as large as possible to minimize room-scattered neutrons, and, in any case, the inside

linear dimensions should be > 6 m.

2.16.3.3 The source should be used in the center of the room or, in the case of an open facility, as high as

practical above the ground. In use, the source should be supported by a non-hydrogenous structure with as

low a mass as possible.

2.16.3.4 When not in use, the source should be stored in a well-shielded location such that it generates a

background of H0 < 10-3 mSv@h-1 at the position of the test instrument. A method should be provided to move

the source from its shielded position to the “in use” position. The transit time to move the source should be

< 5 s, if practical; otherwise, for times > 5 s, a calibration factor should be applied and any additional

uncertainty accounted for in the uncertainty determination.

2.16.3.5 A support system should be used to position the instrument under test at a known distance and

angle relative to the calibration source. The support should be rigid, but designed to minimize scattered

radiation. It should be possible to move the instrument such that the instrument-to-source separation distance

can be varied, and this distance should be measurable to within an uncertainty of 1 mm.

2.16.3.6 An appropriate phantom should be used for mounting dosimeters for irradiation. At this writing,

ANSI, ISO, and ICRU all recommend slightly different phantoms. Until this situation is resolved, the choice

of phantom should be decided in consultation with NIST.

2.16.4 Equipment

The neutron source(s) should be selected from among those recommended in ISO 8529-1:2001 (252Cf, D2Omoderated 252Cf, 241Am-Be(α,n), 241Am-B(α,n)). More than one type of source may be required. In addition,

sources of different strengths might be required to cover the entire range of required dose equivalents without

the irradiation times becoming either inconveniently long, or so short that the source transit time introduces

a significant uncertainty. The emission rates for the sources should be traceable to the National Institute of

Standards and Technology or to another national measurement institute that has participated in international

key comparisons with NIST in the applicable measurement area.

2.16.5 Test and calibration methods and method validation

2.16.5.1 At this writing, NIST recommends the use of the fluence-to-dose equivalent conversion

coefficients given in ISO 8529:2001. Since this will probably change within the next year or two, it is

recommended that the conversion coefficients be decided upon in consultation with NIST.

2.16.5.2 It is very important that corrections be made for neutron scattering from the surfaces of the

calibration room, and from the air in the room. Various aspects of these corrections are discussed in Schwartz

and Eisenhauer, 1982; ISO/DIS 10646:1992; Eisenhauer, 1989; Kluge, Weise, and Hunt, 1990; and

Eisenhauer, Schwartz, and McCall, 1987. The correction method should be worked out in consultation with

NIST, and should be completely documented.
NIST Handbook 150-2D 58 September 2004

2.16.6 Handling of test and calibration items

All the dosimeters of a particular batch, including controls, should be kept together at all times, except when

the irradiations are actually being performed. During the irradiations, all dosimeters except those actually

being irradiated should be kept in an area well-shielded from any radiation sources.

2.16.7 Reporting the results

2.16.7.1 The calibration report is a permanent archival document. The original should be sent to the

institution for which the calibration was done, and copies kept on file at the laboratory. The calibration report

should contain at least the following information, as appropriate:

a) General information

1) type and serial number(s) of item(s) irradiated,

2) date of irradiation,

3) identification number(s) of source(s) used and their emission rate(s) at time of irradiation,

4) fluence-to-dose equivalent conversion coefficients used (these may be referenced or provided

under separate cover, and

5) average temperature and relative humidity during irradiation.

b) Specific irradiation data

1) source-phantom or source-detector distance,

2) calculated “free field” dose equivalent,

3) length of time of irradiation,

4) total dose equivalent,

5) corrections applied, and

6) estimated uncertainty in the total dose equivalent.

c) Narrative description

All calibration reports should also include a brief narrative description of the physical arrangement for

the irradiations and a brief discussion of the uncertainties. The description may be a drawing or a

combination of text and drawing.

2.16.7.2 Uncertainties

ISO/DIS 10647:1992 contains a complete discussion of the uncertainties involved in these irradiations; this

should be used as the basis for assigning an uncertainty to the calibration.
NIST Handbook 150-2D 59 September 2004

2.17 Criteria for a high-dose radiation dosimetry calibration laboratory

2.17.1 Scope

The criteria contained in this part of the document apply to laboratories that calibrate high- dose dosimeters

at absorbed-dose levels appropriate for radiation processing (gamma rays, electron beams, or x-ray

(bremsstrahlung) beams. These criteria are supplementary to the general criteria contained in 2.2 and should

be followed if this specific irradiation service is offered and its inclusion in the Scope of Accreditation is

desired. In that case, both the general criteria and these specific criteria should be followed.

2.17.2 Definitions

See ASTM E 170 and section 1.5 of this handbook.

2.17.3 Specific criteria for calibrations using photons and electrons

2.17.3.1 Scope

This section sets specific requirements to which a laboratory should adhere if it is to be accredited for

calibrations using gamma rays, electron beams, or x-ray (bremsstrahlung) beams. The criteria contained in

this section apply to high-dose calibration of dosimeters at absorbed-dose levels appropriate for radiation

processing. 

2.17.3.2 Quality system

The absorbed-dose rate of the high dose calibration facility of the laboratory should be within ±5 % of the

value defined by comparison with the appropriate national standard. This level of agreement with the national

standard should be demonstrated through periodic proficiency tests of the laboratory by a national or

international standards laboratory.

2.17.3.3 Facilities and environment

a) If interpretation of the response of a particular type of dosimeter requires a history of the

environmental conditions, the temperature and humidity should be recorded.

b) Fluorescence lamps, sunlight, and other sources of ultraviolet light should be filtered, if the dosimeters

are adversely affected by ultraviolet radiation.

c) Any area used for storage of dosimeters should have its temperature and relative humidity controlled

as required for the specific dosimetry system employed.

2.17.3.4 Equipment

2.17.3.4.1 Radiation source(s) for high-dose calibration facilities

a) The laboratory should have access to a source of gamma radiation, either 60Co or 137Cs, with a fluence

rate sufficient to deliver an absorbed dose within the range of 10 Gy to 105

 Gy (103 rad to 107 rad)

within a reasonable time.

b) In addition, the laboratory may have an electron beam or x-ray beam (bremsstrahlung) radiation

source, or both, that can provide dose rates appropriate to radiation processing conditions.
NIST Handbook 150-2D 60 September 2004

2.17.3.4.2 Characterization of the radiation field

a) Determine the absorbed-dose rate in each location in which dosimeters are irradiated using reference

standard dosimetry systems. Assure that dosimeters are irradiated in the locations where the dose rate

is determined. Dose rates should be traceable to appropriate national standards by direct measurement

intercomparisons.

b) Ensure that the absorbed-dose rate over the volume in which dosimeters are irradiated does not vary

more than ±1 % (at a 95 % level of confidence) from its average value.

c) If the dosimeters are irradiated in open air (for example, with a beam-port or panoramic irradiator),

ensure that the room is of sufficient size and design such that scattered radiation at each position where

dosimeters are placed for irradiation does not compromise the specified overall accuracy goals.

d) Monitor and control the temperature of the irradiation volume during irradiation to the degree required

by the characteristics of the dosimeter. Measure this temperature during a simulated irradiation of

dosimeters or in a manner that will not perturb the radiation field during the irradiation of dosimeters.

e) Maintain information related to the photon or electron energy spectrum at each dosimeter irradiation

location.

f) Minimize low-energy components of the photon source spectrum through the use of a filter box when

dosimeters used for radiation hardness testing are irradiated. For additional information see ASTM

E 1249 and ASTM E 1250.

2.18 Criteria for a radionuclide source calibration laboratory

2.18.1 Scope

The criteria contained in this part of the document apply to laboratories that calibrate or manufacture and

certify radionuclide sources. These criteria are supplementary to the general criteria contained in 2.2 and

should be followed if either of these specific services is offered and its inclusion in the Scope of Accreditation

is desired.

2.18.2 Assuring the quality of test and calibration results

2.18.2.1 Periodic performance tests should be performed to demonstrate the operability and accuracy of

measuring equipment. These tests should be performed daily or prior to use.

2.18.2.2 The laboratory should have control standard sources, traceable to the National Institute of

Standards and Technology or to another national measurement institute that has participated in international

key comparisons with NIST in the applicable measurement area. The laboratory should use these control

standard sources as a system check prior to calibrations.

2.18.2.3 Sources derived from material which are certified to have traceable measurements should be

tested prior to distribution to verify the certificate value. For derived sources made in batches, appropriate

sampling of the batch is acceptable if the process has been demonstrated to produce reproducible sources or

that it is unlikely to have significant differences between sources.
NIST Handbook 150-2D 61 September 2004

2.18.2.4 Appropriate tests should be performed to demonstrate the stability of sources over their expected

lifetimes. Examples of areas of concern include: radiation damage for high-level sources, plateout of

radionuclides from solution, and homogeneity of solid sources.

2.18.3 Accommodation and environmental conditions

2.18.3.1 The laboratory facilities should include space and utilities appropriate for the scope of work

performed. This should include control of environmental factors such as temperature, humidity and other

parameters that could impact the quality of radionuclide sources. If a facility is utilized for the production

of both low-level sources (less than 100 FCi) and high-level sources (greater than 100 FCi), then production

areas should be physically separated to prevent cross contamination of samples.

2.18.3.2 The laboratory areas should include appropriate equipment such as fume hoods, glove boxes,

safety showers, and other appropriate personnel safety gear. Adequate bench space for the number of

employees working in the facility should be provided. Laboratory areas should be maintained to ensure the

work areas are neat, clean, and orderly. Environmental conditions should be maintained as appropriate for

specific operations. For example, analytical balances should be used in areas that are relatively free from

dust, air currents, and excessive vibration. A stable source of electrical power, preferably regulated and

uninterruptible, should be available for radiation detection instrumentation.

2.18.4 Equipment

Equipment for the calibration of radionuclide sources should be maintained and controlled by the laboratory

performing calibrations. Instrumentation should be “state of the art,” with respect to current technology for

calibrating radionuclides. The calibration facility should maintain equipment necessary to measure potential

contaminants or interferences. For example, if gamma-ray emitting radionuclides are calibrated with an

ionization chamber, then high-resolution gamma spectroscopy should be available for assaying gammaemitting impurities. Alpha-particle spectrometry may be necessary to assay impurities in alpha-emitting

sources that are calibrated by liquid-scintillation counting.

2.18.5 Test and calibration methods and method validation

2.18.5.1 The calibration of radionuclides and production of sources should be documented so that each step

of the process can be verified or checked.

2.18.5.2 More than one technique should be utilized for calibrations or a different technique utilized for

verification of the primary technique.

2.18.6 Handling of test and calibration items

2.18.6.1 Contamination levels in laboratory areas should be strictly controlled to prevent contamination

of personnel and samples. This may require more stringent control of radionuclide contamination than

required for personnel safety by applicable regulatory requirements. Appropriate instrumentation and

monitoring procedures should be used to monitor the cleanliness of work areas utilizing radioactive material.

2.18.6.2 Radiation-detection equipment should be physically separated from process areas for radioactive

materials. If common facilities are utilized for both low-level and high-level radionuclide measurements, then

strict contamination-control procedures should be employed before samples are transferred from production

areas to the counting room(s).
NIST Handbook 150-2D 62 September 2004

2.18.6.3 The packing and shipping area should be separate from the production areas. The exteriors of all

packages of radioactive material should be monitored for removable contamination before transfer to the

shipping area.

2.18.7 Reporting the results

2.18.7.1 Minimum information

The calibration laboratory should provide a certificate for each standard that should include at least the

following information:

a) Producer.

b) Radionuclide calibrated.

c) Identification number.

d) Activity or emission rate with associated uncertainties—The certificate should contain a clear and

unambiguous statement of overall uncertainty with the method by which the different components of

error were combined. The stated uncertainty should not be lower than those verified by the national

measurement institute for a given technique.

e) Calibration date and time (if appropriate for the half-life* of the radionuclide)—The certificate should

include decay data and references relevant to the calibration and intended use of the source.

Notes accompanying the sources should provide warnings about any special precautions to be taken in

the use of the source (such as those relating to fragility or sensitivity to moisture). Application notes

dealing with common problems (cascade summing, interference from Compton edge, etc.) affecting

complex applications such as gamma spectrometry should be included.

f) Physical and/or chemical description of the source (see 2.18.7.2 a)).

g) Radiochemical purity (see 2.18.7.2 c)) (identification and assay of contaminants is recommended).

2.18.7.2 Supplemental information

Supplemental information, including preparation and use, may be presented in accompanying notes or

attachments to the certificate. In addition to the information required above, supplemental information should

be provided in the following areas.

a) Physical description of the source

Liquid sources to be dispensed quantitatively by the user should be described in terms of chemical

composition, acidity, carrier concentration, density, and total quantity in grams. Special information needed

for further dilution or deposition should be given in notes. For mixtures of solid particles (soil, dried

biological materials, etc.), the details of homogeneity tests and the limiting sample size for which the standard

may be used should be stated. Gas-mixture certificates should include descriptions of diluting gases when

applicable. Sources to be used directly should address radiation scattering and absorption unless the sources

are exact replicates of samples to be measured by the user. Source dimensions including active area for filters

and radionuclide distribution for charcoal cartridges should be specified as part of the certificate. Blank

samples or construction material (i.e., mylar covering) should be available to a user for evaluating
NIST Handbook 150-2D 63 September 2004

transmission or attenuation when necessary. Resolution tests for alpha-particle or low-energy photon sources

should be described in sufficient detail to permit the user to determine applicability for use. Large-area

sources (greater than 10 cm2

) should be characterized with respect to surface uniformity.

b) Calibration method

The calibration method should be specified. For comparative measurements, both the comparison instrument

and the origin of its calibration should be specified. Literature reference may be given if the method is not

generally used, or if special corrections or calculations are required.

c) Purity

All identified impurities, including progeny, should be listed together with their measured activity and

uncertainty. A limit should be indicated for other possible impurities, as inferred from the known sensitivity

of the stated measurement technique, with special mention of any impurities likely to have been produced

with the primary nuclide.