Answer to Question #2477 Submitted to "Ask the Experts"

Category: Instrumentation and Measurements — Instrument Calibration (IC)

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

What is the "inverse RPG (Radiation Protection Guide) curve" for neutrons? How can I define the curve as a function of neutron energy? The curve defines a conversion factor for a neutron counter in terms of counts/n/cm^2 as a function of neutron energy. The curve is referred to in NCRP Report 38 "Protection against Neutron Radiation".

The dose equivalent per neutron flux, at a given energy, is a derived function, realizing that the radiation weighting factor (or old quality factor) also varies with neutron energy, peaking around 1 MeV. (See page 16 of NCRP No. 38.) Thus, one can plot this neutron flux (needed to cause a given dose equivalent in an occupational work week) vs. energy to obtain an RPG curve.

I believe this "inverse RPG curve for neutrons" you refer to is the engineered balancing of hydrogenous moderator and internal thermal neutron attenuator "filter" (e.g., cadmium perforated metal sleeve), matched with the neutron detector's (i.e., BF₃, He₃, Li glass, etc.) thermal neutron efficiency, such that one has (as best possible) a neutron energy independent rem responding instrument. That is, over a wide range of neutron energies, you'd have a flat response in cps per uSv/hr (or mrem/hr). Also see Q2476.

See specs on a commercial rem ball, noting this phrase, http://www.ludlums.com/product/m12-4.htm.

David J. Allard, CHP

Answer posted on April 9, 2003. The information and material posted on this Web site is intended as general reference information only. Specific facts and circumstances may alter the concepts and applications of materials and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice specific to whatever facts and circumstances are presented in any given situation. Answers are correct at the time they are posted on the Web site. Be advised that over time, some requirements could change, new data could be made available, or Internet links could change. For answers that have been posted for several months or longer, please check the current status of the posted information prior to using the responses for specific applications.