Buildup Factors-summary

["Karam, Andrew" <Andrew_Karam@URMC.Rochester.edu>]

Following is a summary of the references sent to me.  Many thanks to all who
helped, including Lester Slaback, Bill Lipton, Glenn Carlson, Scottie
Walker, Gerard Falo, Jerry Lahti, and Joe Guido.

Andy
=================
ANSI/ANS-6.4.3-1991, "American National Standard for Gamma-Ray
Attenuation Coefficients and Buildup Factors for Engineering Materials,"
has buildup factors for water for photons down to 15 kev.  The minimum
tabulated mean free paths (mfp) is 0.5.  However for 20 kev photons and
mfp = 0.5, the buildup factor is only 1.29, so, for thinner shields, you
can probably ignore buildup. ("Mean free path" is defined as "The
average distance that photons of a given energy travel before an
interaction in a given medium occurs.  It is equal to the reciprocal of
the attenuation coefficient..."  I think that this is the same as the
"relaxation length."

For air, this standard only goes up to 40 mean free paths.  However, for
200 kev photons and 40 mfp, the buildup factor = 1.05 E4.  Beyond this
point, the buildup factor is probably not a valid approximation, since
the dose rate at the point of interest would probably be heavily
influenced by scattering surfaces.  

I tried out Microshield for long distances.  It seems capable of
providing an answer for any distance you want to input.  
=================
The Engineering Shielding Compendium - This is out of print but may be
available libraries.
Radiation Shielding by Chilton, Shultis, and Faw
Radiation Shielding by Shultis and Faw - I  think this a sucessor to the
above work.
The Photon Shielding Manual by Fodorrero (spelling) - This also may be out
of print.
==================
The best buildup factor data may be found in the ANS standard 6.4.3.  The
draft standard (with all of the data) was published as ORNL/RSIC-49, Sept
1988.  ORNL/RSIC-49 is entitled "New Gamma-Ray Buildup Factor Data for Point
Kernel Calculations:  ANS-6.4.3 Standard Reference Data".  This is the fine
work of David Trubey, now retired from ORNL's Radiation Shielding
Information Center.  Here you will find in Table 5.1, for example, fitting
parameters for water buildup factors for photon energies from 0.015 MeV to
15 MeV.  The data is good to 40 mfp.
===================
An older reference:  "Engineering Compendium on Radiation Shielding"; R.G. 
Jaeger, Editor; Springer-Verlag, 1968; Vol. I, p. 218, Table 4.3-11.  Energy

deposition buildup factors -- point isotropic source, infinite medium -- are

tabulated from 0.015 MeV to 10.0 MeV for water and other materials.
=====================
I have used the publication by Y.Harima Nuclear Science and Engineering
83,299(1983) for 125I with good results. He gives 15 and 20 keV data
directly so you won't have to interpolate as I did.

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