neutron inst beam correction factor

[Lester Slaback <Lester.Slaback@NIST.GOV>]

As noted previously the typical neutron instrument is a small detector with
a large moderator.  This does not have a uniform areal response like an ion
chamber.  On the other hand if the measurement is done with the beam
centered on the detector then an area ratio correction will be
conservative, albeit a substantial overestimate, because the sensitivity
drops off for the more distal portions of the moderator.  And of course all
of this is neutron energy dependent.  We have some rough data experimental
data if there is an interest.

Of course for neutron instruments like the HPI tissue equivalent
instrument, which are proportional detectors, you can use a volume ratio
(effective detection volume/exposed volume) for a correction factor.

Date: Thu, 26 Aug 1999 11:23:50 -0700
From: "Kathryn M. Brock" <brockkm@engr.orst.edu>
Subject: Beam Correction Factors
When monitoring with a portable neutron remmeter, is it appropriate when
measuring a small collimated beam to correct for the size of the detector
(sphere) volume in the same manner that the dose rate is corrected when
measuring a gamma beam with an ion chamber?  Is there a good reference
available?
Disclaimer:  the above are the personal musings of the author, and do not
represent any past, present, or future position of NIST, the U.S. government,
or anyone else who might think that they are in a position of authority. 
Lester Slaback, Jr.  [Lester.Slaback@NIST.GOV] 
NBSR Health Physics 
Center for Neutron Research 
NIST
100 Bureau Dr.  STOP 3543 
Gaithersburg, MD  20899-3543 
301 975-5810 voice
301 921-9847 fax
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