RE: help on point source calculations

["Langenegger, Armin" <alang@allsaintshealthcare.org>]

The Answer to the first calculation is simple. For a point source the
Exposure rate is given by

E = (Gamma*Activity)/(square of distance)

Therefore a simple ratio of distances works. Ie. E2/E1=(D1/D2)^2 or
D2=D1*SQRT(E1/E2) = 2*SQRT(4.2/.1) = 12.96'

The answer to question 2 is a little more complex. It involves breaking the
source mathematically up into small segments and integrating the Sievert
integral over the length of the source. An excellent reference can be found
in any medical physics text book under the brachytherapy section. Try Johns
and Cunningham or Khans the "Physics of Radiation Therapy"

Armin


		-----Original Message-----
		From:	Lzjk@aol.com [mailto:Lzjk@aol.com]
		Sent:	Monday, May 29, 2000 3:25 PM
		To:	Multiple recipients of list
		Subject:	help on point source calculations

		Can anyone show me how to do the following problems? or send
me some good 
		examples with equations. 

		If the Co-60 point source had a radiation intensity of 4.2
R/hr at two feet, 
		the distance at which the exposure rate would be 100 mR/hr
is ? 

		What equation do I use and please give a example on how to
do it.


		next question

		Calculate exopsure rate at 3' from a 11' long line source.
The line source is 
		reading an exposure rate of 600 mR/hr at 1 inch from the
line.

		Thanks for any help I can get.
	
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