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CIRMS Presentation on the Comparison of Moderated AmBe and Cf for Neutron Instrument Calibrations
Posted on April 16th, 2018

Frederick Straccia, CHP, of RSCS will present on “Comparison of Moderated AmBe and Cf for Neutron Instrument Calibrations” this week at the Council on Ionizing Radiation Measurements and Standards (CIRMS) meeting. 

The requirements for calibration of neutron dose and dose rate instruments are described in various national and international standards, including ANSI N323A 1997, ANSI/NCSL Z540.1-1994 and IAEA Safety reports series, ISSN 1020–6450; no. 16. Neutron sources described in these standards include neutrons produced via α/n reactions (AmBe, PuBe) as well as spontaneous fission sources (bare and moderated Cf).  The average neutron energies of these sources differ significantly, varying from 4 – 5 MeV for the α/n sources, 2 MeV for bare Cf, and 0.55 MeV for moderated Cf.  While the lower energy neutrons from Cf sources are often better suited for calibration due to their closer match to fission spectrum neutrons, the costs associated with maintaining these sources are very expensive.  This is due to the high cost of the Cf sources as well as the relatively short half-life of the radionuclide. 

RSCS will provide technical information on the use of moderated α/n sources as an alternative to Cf.  The presentation will provide details on the energy reduction from moderation with high density polyethylene (HDPE) and other moderators which provides better alignment with fission spectrum neutrons.   A review of recent literature as well as data from HDPE-moderated AmBe will be discussed. 

For over 25 years, CIRMS has hosted public meetings to provide an exchange of technical information on methods for measuring radiation.  Their 26th annual meeting this year is focused on topics related to medical uses of radioactive materials, measurements for safety and homeland security applications and industrial applications and materials. The meeting will be hosted on the NIST campus in Gaithersburg, MD on April 16, 2018.

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