Re: half value thickness of water for I-125

[Chris Alston <alstonc@odrge.odr.georgetown.edu>]

If, when you say "I-125", you mean the Model 3711 seeds as the sources, then
the effective E (from the manufacturer's data sheet) is (to the best of my
recollection) ~28 keV. The Rad Health Handbook (1970) gives an HVL, for a
narrow beam of that E, of about 1.75 cm, in water. Caveat emptor. There was
recently a paper in Medical Physics (Vol 23, No 4, April 1996) by Chengwei
Sun et alia, entitled "Measurement of the Effective Attenuation Coefficients
with Model 6711 Seeds". They measured the attenuation coefficients of Au,
Pb, Cu, and the transmission by varying thicknesses of polystyrene. For a
single seed, the transmission at a tissue thickness of 2.0 cm was 0.786; for
four strands of five seeds, in a planar array on one (1) cm centers, the
transmission was 0.750.

chris alston
alstonc@odrge.odr.georgetown.edu
As a final rule, my employer takes no responsiblity for my pronouncements here.

At 11:25  03/23/98 -0600, you wrote:
>the subject says it all...
>
>What is the half value thickness of water for I-125?
>
>Thanks
>
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