An alternative calibration method for counting P-32 reactor monitors

Conference · Fri Jul 01 04:00:00 EDT 2011

OSTI ID:22086998

Quirk, T J ^[1]; Vehar, D W ^[2]

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1. Applied Nuclear Technologies, Sandia National Laboratories, MS 1143, PO Box 5800, Albuquerque, NM 87185-1143 (United States)
2. Sandia National Laboratories, Albuquerque, NM 87185-1143 (United States)

Radioactivation of sulfur is a common technique used to measure fast neutron fluences in test and research reactors. Elemental sulfur can be pressed into pellets and used as monitors. The {sup 32}S(n, p) {sup 32}P reaction has a practical threshold of about 3 MeV and its cross section and associated uncertainties are well characterized [1]. The product {sup 32P} emits a beta particle with a maximum energy of 1710 keV [2]. This energetic beta particle allows pellets to be counted intact. ASTM Standard Test Method for Measuring Reaction Rates and Fast-Neutron Fluences by Radioactivation of Sulfur-32 (E265) [3] details a method of calibration for counting systems and subsequent analysis of results. This method requires irradiation of sulfur monitors in a fast-neutron field whose spectrum and intensity are well known. The resultant decay-corrected count rate is then correlated to the known fast neutron fluence. The Radiation Metrology Laboratory (RML) at Sandia has traditionally performed calibration irradiations of sulfur pellets using the {sup 252}Cf spontaneous fission neutron source at the National Inst. of Standards and Technology (NIST) [4] as a transfer standard. However, decay has reduced the intensity of NIST's source; thus lowering the practical upper limits of available fluence. As of May 2010, neutron emission rates have decayed to approximately 3 e8 n/s. In practice, this degradation of capabilities precludes calibrations at the highest fluence levels produced at test reactors and limits the useful range of count rates that can be measured. Furthermore, the reduced availability of replacement {sup 252}Cf threatens the long-term viability of the NIST {sup 252}Cf facility for sulfur pellet calibrations. In lieu of correlating count rate to neutron fluence in a reference field the total quantity of {sup 32}P produced in a pellet can be determined by absolute counting methods. This offers an attractive alternative to extended {sup 252}Cf exposures because it can be performed regardless of the characterization of the exposure environment. Count rates produced by sulfur pellets are correlated to the measured quantity of separated {sup 32}P. A posteriori spectral and cross section determination can be used to correlate the quantity of phosphorus back to a neutron fluence in a reference field. This paper outlines a method for the setup, calibration, and use of the detector systems, {sup 32}P sample preparation, and analysis of the beta spectrum. An uncertainty analysis and comparison to ASTM E265 is also included. (authors)

• Research Organization: American Society for Testing and Materials - ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA, 19428-2959 (United States); European Working Group on Reactor Dosimetry - EWGRD, SCK.CEN, Mol (Belgium)
• OSTI ID: 22086998
• Report Number(s): INIS-US--13-ISRD-14-P2-7
• Country of Publication: United States
• Language: English

Related Subjects

07 ISOTOPE AND RADIATION SOURCES
BETA PARTICLES
BETA SPECTRA
CALIBRATION
CALIFORNIUM 252
COUNTING RATES
CROSS SECTIONS
FAST NEUTRONS
IRRADIATION
MONITORS
NEUTRON EMISSION
NEUTRON SOURCES
PELLETS
PHOSPHORUS 32
REACTION KINETICS
RESEARCH REACTORS
SPONTANEOUS FISSION
SULFUR
SULFUR 32
TEST REACTORS