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Ionizing Radiation Measurements

Neutron Sources and Neutron Dosimetry

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Technical Contacts:
M. Scott Dewey
All Services Except 44060C
Tel: 301-975-4843
E-mail: mdewey@nist.gov

Alan K. Thompson
44060C, 44100S
Tel: 301-975-4666
E-mail: alan.thompson@nist.gov

Please contact the technical staff before shipping instruments or standards to the address listed below.

Mailing Address:
National Institute of Standards and Technology
100 Bureau Drive, Stop 8461
Gaithersburg, MD 20899-8461

Service ID
Number
Description of Services Fee ($)
44010C Radioactive Neutron Sources Emission Rates (105 s-1 to 109 s-1) 6441
44020C Radioactive Neutron Sources Emission Rates (108 s-1 to 1010 s-1) 6441
44060C Personnel Protection Instrumentation, Californium Source Bare and Moderated At Cost
44070C Activation Detector Dosimetry, Thermal Neutrons At Cost
44080C Activation Detector Dosimetry, Californium Fission Neutrons At Cost
44090C Activation Detector Dosimetry, 235U Cavity Fission Sources At Cost
44100S Special Tests of Neutron Sources and Dosimeters At Cost
Fees are subject to change without notice.

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Radioactive Neutron Sources (44010C-44020C)

NIST provides calibration services for radioisotope neutron sources with neutron emission rates ranging from 5 x 105 s-1 to 1 x 1010 s-1. Neutron source emission rates are determined by the manganous sulfate bath method, in which the emission-rate of the source to be calibrated is compared to the emission-rate of NBS-1, the national standard Ra-Be photoneutron source. Neutron source calibrations typically have a relative expanded uncertainty of about 3.4%, depending on the details of the source encapsulation.

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Personnel Protection Instrumentations (44060C)

Neutron personnel instruments, both passive (e.g., dosimeters) and active (e.g., remmeters) are calibrated on the basis of a certified free-field dose-equivalent or dose equivalent rate. Two 252Cf source-driven neutron fields are available on a routine basis for this purpose: bare source and heavy-water moderated 252Cf fission neutron sources. Thermal neutron beams are also available for special requirements under Service No. 44100S. For both bare and moderated 252Cf source exposures, maximum dose-equivalent rates are about 5 mSv/h. The relative expanded uncertainty is 10%.

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Activation Detector Dosimetry (44070C-44090C)

Passive neutron detectors, generally activation foils, can be irradiated to a certified neutron fluence (or average fluence-rate) in a fission neutron spectrum or by a Maxwellian thermal neutron field. Typical irradiation parameters are given in Table 5.

Table 5. Irradiation Parameters for Fission Neutron Spectra and Maxwellian Thermal Neutron Fields

Neutron Field Typical
Maximum
Neutron
Fluence
(cm-2)
Typical
Maximum
Neutron
Fluence Rate
(cm-2 s-1)
Relative
Expanded
Uncertainty
(%)
252Cf Fission Source 5 x 1012 2 x 107 2.6(b)
235U Cavity Fission Source(a) 5 x 1015 2 x 1010 4.6(b)
Thermal Neutrons Beam(c) 1 x 1013 8 x 107 5
Isotropic >1 x 1016 2 x 1011 5

(a) Threshold detectors only. Maximum size of the detector disks: 12.7 mm dia. x about 3 mm thick. The radial gradient of the fluence is about 20% center-to-edge.
(b) Uncertainty includes neutron scattering corrections.
(c) Maxwellian distribution corresponding to a temperature of about 40 °C.

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Special Tests of Neutron Sources and Dosimeters (44100S)

Other tests of dosimetry instrumentation and neutron sources may be undertaken by special arrangement with the NIST Ionizing Radiation Division. In particular, for personnel protection instruments, a thermal beam can provide dose equivalent rates of up to approximately 10 mSv/h across a 30 cm diameter circle.

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References-Radioisotope Neutron Sources

NBS Measurement Services: Neutron Source Strength Calibrations at NBS by the Manganese Sulfate Bath Method, E. D. McGarry and E. W. Boswell, Natl. Bur. Stand. (U.S.), Spec. Publ. 250-18 (Mar. 1988).

Neutron Source Calibrations at NBS for Calibration Checks of Neutron Radiation Instruments, V. Spiegel, Jr., Proc. of Symp. on Meas. for the Safe Use of Radiation, Natl. Bur. Stand. (U.S.), Spec. Publ. 456, 87 (Nov. 1976).

Calculation of Thermal Neutron Absorption in Cylindrical and Spherical Neutron Sources, V. Spiedel, Jr., and W. M. Murphey, Metrologia 7, 34 (Jan. 1971).

The Correction Factor for Fast Neutron Reactions on Sulphur and Oxygen in the Manganous-Sulfate-Bath Calibration of Neutron Sources, W. M. Murphey, Nucl. Instrum. Methods 37, 13 (1965).

Absolute Calibration of the National Bureau of Standards Photoneutron Source: III. Absorption in a Heavy Water Solution of Manganous Sulfate, R. H. Noyce, E. R. Mosburg, Jr., S. B. Garfinkel, and R. S. Caswell, J. Nucl. Eng. 17 (7), 313 (1963).

Absolute Calibration of the National Bureau of Standards Photoneutron Standard: I. , J. A. DeJuren, D. W. Padgett, and L. F. Curtiss, J. Res. Natl. Bur. Stand. (U.S.) 55, 63 (Aug. 1955).

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References-Personnel Protection Instrumentation

NBS Measurement Services: Neutron Personnel Dosimetry, R. B. Schwartz, Natl. Bur. Stand. (U.S.), Spec. Publ. 250-12 (July 1987).

Procedures for Calibrating Neutron Personnel Dosimeters, R. B. Schwartz and C. M. Eisenhauer, Natl. Bur. Stand. (U.S.), Spec. Publ. 633 (May 1982).

Calibration Techniques for Neutron Personnel Dosimetry, C. M. Eisenhauer, J. B. Hunt and R. B. Schwartz, Radiat. Prot. Dosim. 10, 43-57.

The Design and Construction of a D2O-Moderated 252Cf Source for Calibrating Neutron Personnel Dosimeters Used at Nuclear Power Reactors, R. B. Schwartz and C. M. Eisenhauer, U.S. Nucl. Reg. Com. Doc. NUREG/CR-1204 (Jan. 1980).

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References-Activation Detector Dosimetry

NBS Measurement Services: Activation Foil Irradiations at NBS by Californium Fission Sources, G. P. Lamaze and J. A. Grundl. Natl. Bur. Stand. (U.S.), Spec. Publ. 250-13 (Mar. 1988).

NBS Measurement Services: Activation Foil Irradiations at NBS by Reactor Cavity Sources, G. P. Lamaze and J. A. Grundl, Natl. Bur. Stand. (U.S.), Spec. Publ. 250-14 (Mar. 1988).

Derivation of Neutron Exposure Parameters from Threshold Detector Measurements, J. A. Grundl, Proc. Sixth ASTM-Euratom Symp. on Reactor Dosimeter, Jackson, WY (June 1987).

Compendium of Benchmark Neutron Fields for Reactor Dosimetry , J. A. Grundl and C. M. Eisenhauer, Natl. Bur. Stand. (U.S.), NBSIR 85-3151 (Apr. 1985).

The U.S. 235U Fission Spectrum Standard Neutron Field Revisited, E. D. McGarry, C. M. Eisenhauer, D. M. Gilliam, J. A. Grundl, G. P. Lamaze, and A. Fabry, Proc. Fifth ASTM-Euratom Symp. on Reactor Dosimetry, Geesthacht, Germany (Sept. 1984).

National Standards for Neutron Measurements, J. A. Grundl, Proc. of a Meeting on Traceability for Ionizing Radiation Measurements, Natl. Bur. Stand. (U.S.), NBS Spec. Publ. 609 (Feb. 1982).

Utilization of Standard and Reference Neutron Fields at NBS, C. M. Eisenhauer, D. M. Gilliam, J. A. Grundl, and V. Spiegel, Proc. Second ASTM-Euratom Symp. on Reactor Dosimetry, Palo Alto, CA (Oct. 1977).

A Californium-252 Fission Spectrum Irradiation Facility for Neutron Reaction Rate Measurements, J. A. Grundl, V. Spiegel, C. M. Eisenhauer, H. T. Heaton II, D. M. Gilliam (NBS), and J. Bigelow (ORNL), Nucl. Tech. 32, 315 (Mar. 1977).

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Program questions: Calibrations
Phone: 301-975-2200, Fax: 301-975-2950
NIST, 100 Bureau Drive, Stop 8363, Gaithersburg, MD 20899-8363