Re: line source calc.

[Joel Baumbaugh <baumbaug@nosc.mil>]

	Radsafers,

	Just to put in - maybe 1 1/2 cents worth - the bremsstrahlung from those
betas could contribute to the dose rate - especially as you approached the
line source...  On a MCA, it shows up as a broad band of photon energies
which (may) mask the backscatter peaks, escape peaks, other photopeaks...
Oh well, NaI(tl) is all I have to work with...(sigh!)

	Joel Baumbaugh (baumbaug@nosc.mil)
	SSC-SD

At 09:46 AM 1/27/98 -0600, you wrote:
>At 06:59 AM 1/27/98 -0600, you wrote:
>>Make sure you have not underestimated the betas from Co60 (96 keV and 626
>>keV average energy) and especially exposure to the skin.
>
>If this thread mentioned anything about encapsulation of the Co-60, I don't
>recall it. If the source is encapsulated, it is probable that none of the
>Co-60 beta radiation will escape the source.
>
>A massless point source (no self absorption) of Co-60 would produce a
>shallow dose rate at 1 foot that is about 5 percent beta, 95 percent
>photon. If the geometry is changed to a line source, the beta contribution
>is smaller because the photon contribution from points away from the
>source's center are reduced by 1/r^2, while the beta contribution is
>reduced by 1/r^2 and attenuation in air. However, even if the source is not
>encapsulated, self-absorption of the rather low energy beta spectrum within
>the source itself will reduce actual emissions to only those betas emitted
>at or extremely close to the surface of the source. After attenuation in
>air (1 foot and more), the beta contribution to the total dose rate will be
>very small, probably well under one percent, and much less than the
>uncertainty in the photon dose rate estimates.
>
>I believe that the beta contribution to skin dose could be neglected in
>this case.
>
>
>
>
Joel T. Baumbaugh, MPH, MHP
baumbaug@nosc.mil / baumbaug@spawar.navy.mil
Radiation Safety Officer
SSC-San Diego, CA. USA

	NOTE:	The contents of this message have not been reviewed, nor approved by
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