RE: Gamma Attenuation and Build-up

[Fred_Haywood@radian.com]

Michael,

Many years back, I conducted an experiment at the Nevada Test Site that
bears on your question. In this case, we had a Co-60 source of several
thousand curies mounted in an elevator on a 1500 ft tall tower (the BREN
Tower, still standing in Area 25 of the NTS). This source was raised from
its shield at six heights on the tower and measurements were made in open
air as a function of slant range from the source and as a function of height
of the source above the ground as well as the height of measurement above
the ground. The source was positioned at 30', 100', 300', 500' 1125', and
1500' above the ground. measurements were made at distances ranging from 100
ft to 3000 ft from the base of the tower and at heights of 0 ft to 100 ft
above the ground. The two most important factors for gamma-ray attenuation
is the height of the source above the ground and the attenuation in air. At
the distances and heights involved in this work, the gamma-ray distribution
had reached equilibrium in air. It would be fairly simple to extrapolate to
larger distances. This work was published in Health Physics, but in 1963 or
1964. It was also published as an AEC Report. I have both somewhere. If you
have any interest I will try to find this info and share it. 

Fred Haywood

> -----Original Message-----
> From:	mborisky@mail.arl.mil [SMTP:mborisky@mail.arl.mil]
> Sent:	February 03, 2000 1:27 PM
> To:	Multiple recipients of list
> Subject:	Gamma Attenuation and Build-up
> 
> Radsafers,
> 
> Can someone direct me to a code that can be used to calculate the dose
> rate at 
> kilometer distances from an unshielded gamma source, considering
> attenuation 
> and build-up in air.  Something I could down-load from the internet would 
> really be nice.  Thanks
> 
> Michael Borisky
> Health Physicist
> Army Research Laboratory
> mborisky@arl.army.mil
> 301-394-6310
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