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RE: Micorshield

Diane Case wrote:

"I compared the exposure rates from a point source at one meter found with (1)
Microshield 5.01 and by the (2) gamma dose constants listed in ORNL "Specific
Gamma-Ray Dose Constants for Nuclides Important to Dosimetry and Radiological
Assesment,"by Unger and Trubey.

These are my results in mR/hr at 1 meter from 1 mCi, in air, no Buildup:"

Tc-94m          MS =1.05                Hand calculation  = 1.15
Fe-59           MS = 0.620              ORNL =  0.662
Ba-133          MS =  0.287             ORNL =  0.455
Sm-153          MS  = 0.055             ORNL =  0.090
Cr-51           MS  = 0.0175            ORNL  = 0.0234"


Diane: Our in-house calculations of exposure rate constants agree most 
closely with the Microshield results you gave above:

Tc-94m  not calculated
Fe-59	6.18 R/hr at 1 cm, per mCi
Ba-133  2.9 R/hr    "        "
Sm-153  0.43 R/hr   
Cr-51   0.18 R/hr

All our calculations use 10 keV as the lower limit for photon energies.  We
used Kocher's Radioactive Decay Data Tables (1981) for photon energies and
intensities, and mass energy absorption coefficients for air from Chilton's
Principles of Radiation Shielding (1984) or from the Rad Health Handbook, 
with either graphical or log interpolation to specific photon energies.  
Without having the ORNL reference, I can't say why their value for Sm-153
is so far off from our calculation, but I'm confident in our value, which
I have hand-calculated more than once.  Hope this helps.


John Laferriere, CHP
DuPont Pharmaceuticals Co.
Medical Imaging Division
john.r.laferriere@dupontpharma.com

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