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Re:



As best I can remember, 4pi steradians is the total solid angle surrounding
a point in space. The surface described by 4pi is a sphere. This
nomenclature was used extensively in the days of gas-flow proportional
counters. Those with a hemispherical counting chamber over the source were
referred to as 2pi counters because they had an active volume of 1/2 of a
sphere which is 4pi. There were some 4pi counters where the sample was
suspended in some sort of manner and had active detection volume on both
sides to make an approximation of a sphere. Samples were as thin as
possible, and mounted on very thin backings.

If the sample was actually part of the volume, like C-14 made into CO2 and
introduced into the sealed counting chamber, that was very close to an
absolute 4pi geometry.

Hope this is of some help.

Michael A. Kay, ScD, CHMM
makay@teleport.com

Mike Dupray wrote:

> Does anybody know what a 4pi steridian cross section looks like?
> Michael R. Dupray
> Senior Staff Health Physics Technician
> General Atomics
> 619-455-3561
> FAX 619-455-3465
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