Neutrons and Ice Vests

["Cummings, Frederick" <CUMMINFM@inel.gov>]

     Sandy, et. al.,

     The Panasonic UD-802 is a marginal neutron dosimeter for general
     determination of neutron dose equivalent in a wide variety of fields.
     Therefore, the interpreter must rely on field corrections determined
     from measurements using other instruments.  The neutron spectrum
     inside your nuclear power plant is indeed thermalized in most places
     (if I remember, the response of dosimeters irradiated in PWRs
     ***generally*** appears like the response to a ~60 keV neutron beam).
     I have seen sufficiently steep gradients in neutron dose equivalent
     rates and energies inside nuclear power plants to warrant neutron
     dosimetry and field corrections.  Indeed, the old NRC-funded
     construction worker dosimetry and neutron dosimetry at commercial
     nuclear sites studies pointed up the fact that not only was dosimetry
     required, but improved dosimetry was required.  I agree partially that
     wearing the dosimeter under the ice vest can affect the LOE DE in
     beta/gamma fields.w

     However, in spite of that, my experience is that this marginal and
     highly energy dependent dosimeter would not be able to distinguish the
     difference of ***neutron*** dose equivalent determined from a position
     in front of the vest from the neutron DE determined behind the vest.
     Further, as the ice vest refrigerant is pretty tissue-equivalent, it
     will provide sufficient reflection to keep the albedo part of the
     signal relatively in tact.  The important question should be, how did
     you relate dosimeter results to instrument results at your plant in
     order to determine the field corrections.  If your dosimeter was
     unshielded in the neutron field and you apply a correction factor
     (however conservative), then that is what you should continue (i.e.,
     on the outside of the vest.)

     Even if the 802 is sufficient for your application (which it might
     be), neutron dosimetry at best is not sufficiently accurate to warrant
     a lot of effort answering this question.  Your best bet is to conduct
     a small study using your site instruments and dosimeters following the
     protocols used to conduct the neutron dose and spectral surveys and
     obtain the information you need to demonstrate the real effects.

     The bottom line, Sandy, is that I think you'll have to make the
     measurement.  I would not rely on multiple dosimetry (interpretation
     problems), but rather on results you could reference back to your
     original response data.

     Rick Cummings      cumminfm@inel.gov

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     * These are definitely my own personal opinions and don't in any way *
     * reflect anybody else's, whether my employer, sponsor or anybody.  I*
     * should have relied on a computer to generate my answer randomly.   *
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