Re: MicroShield Exposure Estimates

["Drew Thatcher" <Thatcher.Drew@home.com>]

To add a bit further to the thread that Dr. Falo ended on - if you are
comparing soil exposure values in terms of He, then there are some
differences between the computations provided between the sources (from a
soil exposure).  Eckerman (FR 12) goes into some detail about the
differences between MS (using ICRP 51 which uses the GSF model) and the
hermaphrodite phantom model used by Eckerman.  As I recall, the differences
are at most 10% to 20%.  The gender specific phantom will calculate higher
dose coefficients for internal organs of the female due to less shielding
that is not considered in the hermaphrodite phantom.

Perhaps another area to consider when comparing results in addition to the
conversion from exposure to effective dose (equivalent) (as Falo mentioned)
is uniformity of exposure - the rad health handbook would would not consider
the orientation of the body, FR 12 is in terms of rotational exposure.  MS
provides answers for a number of orientations, including PA, AP, isotropic,
and rotational.

Further information on comparisons of the various orientations can be found
in ICRP 74.

Hope this helps,
Drew Thatcher, MSHP, CHP
Washington Department of Health
thatcher.drew@home.com
360.236.3255

-----Original Message-----
From: Falo Gerald A <Gerald.Falo@APG.AMEDD.ARMY.MIL>
To: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
Date: Thursday, April 15, 1999 6:38 AM
Subject: RE: MicroShield Exposure Estimates


>Dr. Lowe,
>
>Off the top of my head, I can think of 2 possible causes of the
>discrepancies. With respect to the point source calculation, you do not
>mention if your MS run included build up which is not explicitly included
in
>the gamma constant calculation.  Furthermore, and I am not very sure about
>this point, I think that the gamma constants do not include contributions
>from x-rays.  According to the revised edition of the Radiological Health
>Handbook (1992) only gamma rays with energies greater than 0.01 MeV are
>considered in the gamma constant.
>
>You don't mention your source for the Ra-226 in soil numbers, but the
values
>in FGR 12 are calculated using Monte Carlo and transport methods and
>estimate the effective dose equivalent to a person - not the external
>exposure rate.  For a surface source, the numerical value for the exposure
>rate is about 45% greater than the calculated effective dose equivalent
>rate; that is, 1.45 R corresponds to about 1 rem (EDE). In fact, the actual
>difference is likely even greater than that.
>
>I suspect that the difference on the order of 10 to 20% that you see is not
>unusual.
>
>I hope this helps and that I have not misled you, but in the words of me
>thesis advisor, "I reserve the right to be wrong."
>
>Take care,
>
>Jerry
>
>Jerry Falo, Ph.D., CHP
>HMJ Professional Associate
>USACHPPM
>Medical Health Physics Program
>gerald.falo@apg.amedd.army.mil
>
>
>-----Original Message-----
>
><snip>
>
>We often do calculations involving NORM radionuclides and have found that
>MS appears to give  exposure estimates that are larger (by 20% or more)
>than one would obtain from other references e.g.. for Ra-226 in soil.  In
>fact,  the MS estimate for a point Ra-226 source (and decay products) is
>about 10% larger than the 0.825 R/h per Ci at 1 m given in the
>Radiological Health Handbook.
>
>
>Is this the "latest" value for a point Ra-226 source?  Has anybody else
>found similar discrepancies with MS?
>
>
>
>Leo M. Lowe, Ph.D.
>
>Senior Health and Environmental Physicist
>
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