Ionizing Radiation Measurements
Michael P. Unterweger
Jeffrey T. Cessna
Administrative and Logistics
Please contact the technical staff before shipping instruments or standards to the address listed below.
Fees are subject to change without notice.
NIST offers calibration services on the radioactivity of over 50 radionuclides. Calibrations are provided to meet the requirements of industry, research, environmental monitoring, and the life sciences. Radioactivity calibration services are available for alpha-particle solid sources, beta-particle solutions, and gamma-ray solutions.
In order to offer such a broad range of services, NIST must place stringent limitations on the physical and chemical form and activity range of sources that can be accepted. To ensure that these specifications are understood, it is essential that there be good communication between the technical user and the technical contact at NIST. When planning to have a source calibrated, the user should discuss the following points with the NIST contact:
A. Type of calibration: More than one type of calibration is often available for a given source. A cobalt-60 source, for example, may be calibrated in terms of total activity or gamma-ray-emission rate. (Inquiries regarding the calibration of radioactive sources for exposure rate should be directed to the Dosimetry Group. See Service ID Numbers 47010C to 47040S.) The required uncertainty in the calibration should also be discussed.
B. General packaging and shipping requirements: Two general requirements apply to all sources submitted for calibration: (1) all shipments must conform to applicable Nuclear Regulatory Commission (NRC) and Department of Transportation (DOT) packaging and transport; and (2) source descriptions, including approximate activity, must be provided in advance. The NIST Health Physics Group must approve the receipt of radioactive material, and sources may be refused if the necessary information is not available.
C. Reports of Calibration: A Report of Calibration is sent upon completion of a radioactivity calibration service. If the user has particular requirements for documentation of the calibration, these should be discussed with the technical contact at NIST before the services are performed.
D. Sample Preparation, Packaging, and Shipping: All samples submitted for calibration must be chemically and physically stable. The chemical form of solutions suggested for beta-particle emitters and gamma-ray emitters are described later in this document. A special lot of borosilicate-glass ampoules must be used for gamma-ray emitters. Empty ampoules are provided for this purpose. The volume of material in the ampoule should be (5.0 ± 0.2) mL.
Packaging for all sources must be in compliance with DOT and NRC regulations. Copies of regulations may be obtained from Operations Division, Office of Hazardous Materials, Department of Transportation, Washington, DC 20950. Postal regulations prohibit the mailing of radioactive materials that require a caution label under DOT regulations.
Alpha-particle solid sources must be sent in special source holders designed so that the active area is not touched by any material. For sources to be measured in the 2 π α counter (calibration 43030C), the diameter of the source must be less than 10 cm and that of the active surface less than 9 cm. For the 0.8 π α counter (calibration 43040C), the maximum diameter is 1.6 cm.
All sources arriving at NIST are checked by the Health Physics Group for radiation level and source integrity. Sources should be shipped to the attention of the technical contact at NIST. Do not ship sources to the mailing address. Contact the technical staff for the shipping address.
Tables 1 and 2 list 41 radionuclide solutions that may be calibrated in the NIST "4 π" ϒ ionization chamber. The sources must be submitted flame-sealed in special ampoules provided by NIST. The operation of this type of chamber is described in NCRP Report 58, A Handbook of Radioactivity Measurements Procedures, Section 4.4 "Ionization Chambers", and in NBS SP 250-10, Radioactivity Calibrations with the "4 π" Gamma Ionization Chamber and other Radioactivity Calibration Capabilities (see references).
Table 1. Specifications for Calibration of Solutions of Gamma-Ray Emitting Radionuclides Having Half Lives Greater Than 15 Days
Table 2. Specifications for Calibration of Solutions of Gamma-Ray-Emitting Radionuclides Having Half Lives Less Than 15 Days
Alpha- and beta-particle sources may be calibrated using the National Institute of Standards and Technology 2 π proportional counter. The calibration is in terms of alpha- or beta-particle-emission rate into 2 π steradians (43030C). Alpha-particle-emission rates can be converted to activity upon request. Beta-particle-emission rates can be converted to activity for an increased fee and will result in an uncertified value (43040C) of the activity. Mixed-alpha-emitting sources may be calibrated using the 2 π proportional counter and the percentage per radionuclide is determined using a solid state detector (43050C). Backscattering corrections for a variety of source-mount materials are discussed in NCRP Report 58 (Section 3.7) and in NBS SP 250-5, Alpha-Particle Calibrations. Specifications for these calibration services are given in Table 3.
For alpha-particle sources, emission rates up to 105 counts per second (cps) can be measured utilizing the 2 π proportional and external counters; sources exceeding 104 cps must be part of a set that includes at least one other source that is 104 cps or less. This extra measurement costs an additional 18% of the original fee.
Table 3. Specifications for Calibrations Using the 2 πα/β Proportional Counter and Solid State Detector
Alpha- and beta-particle source blind measurement results can be compared to National Institute of Standards and Technology 2 π proportional counter results. The report is in terms of alpha- or beta-particle-emission rate into 2 π steradians. Backscattering corrections for a variety of source-mount materials are discussed in NCRP Report 58 (Section 3.7) and in NBS SP250-5, Alpha-Particle Calibrations. The source thickness must be such that more than 99.5% of the emitted alpha particles have an energy greater than 400 keV. Further specifications for these calibration services are given in Table 4.
Table 4. Specifications for Calibrations Using the 2 π α/β Proportional Counter
Beta-particle-emitting solutions that conform to the physical, chemical, and activity specifications for measurement are assayed by liquid-scintillation counting as shown in Table 5. The suggested radioactivity concentration range is 20 kBq/g to 2000 kBq/g.
No examination is made for beta-particle-emitting impurities, except in the case of phosphorus-32 for which a half-life determination is made of 33P. The sources are examined for gamma-ray emitting impurities.
Measurement of beta-particle-emitting solutions by techniques other than liquid-scintillation may be made by special arrangement.
Table 5. Specifications for Special Tests of Beta-Particle-Emitting Solution Sources
Special arrangements may be made for measurements of some solid, liquid, and gas alpha-, beta-, or gamma-particle-emitting sources.
NBS Measurement Services: Radioactivity Calibrations with the "4 π" Gamma Ionization Chamber and Other Radioactivity Calibration Capabilities, J. M. Calhoun, Natl. Bur. Stand. (U.S.), Spec. Publ. 250-10 (Oct. 1987).
NBS Measurement Services: Alpha-Particle Calibrations (2004), J. M. R. Hutchinson, Natl. Bur. Stand. (U.S.), Spec. Publ. 250-5a (Jan. 2004).
NCRP Report 58, A Handbook of Radioactivity Measurements Procedures, Section 3.7-Alpha-Particle Counting, W. B. Mann, Ed., Natl. Council Rad. Protect. and Meas., Washington, DC (1985).
Study of the Scattering Correction for Thick Uranium-Oxide and Other-Particle Sources, I: Theoretical, L. L. Lucas and J. M. R. Hutchinson, Int. J. Appl. Radiat. Isotopes 27, 35 (1976).
Study of the Scattering Correction for Thick Uranium-Oxide and Other-Particle Sources, II: Experimental, J. M. R. Hutchinson, L. L. Lucas, and P. A. Mullen, Int. J. Appl. Radiat. Isotopes 27, 43 (1976).
Backscattering of Alpha Particles from Thick Metal Backings as a Function of Atomic Weight, J. M. R. Hutchinson, C. R. Naas, D. H. Walker, and W. B. Mann, Int. J. Appl. Radiat. Isotopes 19, 517 (1968).
An Experimental Study of the Backscattering of 5.3 MeV-Alpha Particles from Platinum and Monel Metal, D. H. Walker, Int. J. Appl. Radiat. Isotopes 16, 183 (1965).