Answer to Question #8558 Submitted to "Ask the Experts"

Category: Instrumentation and Measurements — Surveys and Measurements (SM)

The following question was answered by an expert in the appropriate field:


The 1980 NUREG 1204, "The Design and Construction of a D20-Moderated 252Cf Source for Calibrating Neutron Personnel Dosimeters Used at Nuclear Power Reactors" utilized a 9-inch and 3-inch poly sphere ratio to indicate average neutron energy. Did the 9-inch sphere have an inner cadmium-coated sphere like the neutron rem balls?


The 9-inch sphere that is referred to in NUREG-1204 is, indeed, a 9-inch rem ball, specifically the Eberline rem ball, which was designed with the 9-inch polyethylene moderator and a cadmium shield around the central BF3 detector. The 3-inch ball, so far as I know, was simply a 3-inch polyethylene ball that would accommodate the BF3 tube. The ratio of responses was often used to interpret the energy quality of the neutron field so that appropriate calibration factors could be selected to interpret readings on dosimetric devices, most especially albedo neutron TLD (thermoluminescent dosimeter) devices. The technique had earlier been developed by Dale Hankins, who has made many contributions to the fields of neutron measurements and dosimetry. NUREG-1204 is available on the Web through this National Institute of Standards and Technology link; the specific reference to the 9-inch sphere is on numbered page 4 of the pdf document.

George Chabot, PhD, CHP

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