[ RadSafe ] Sr-90 Question

Cindy Bloom radbloom at comcast.net
Wed Oct 17 07:07:48 CDT 2007


The rule of thumb you cite is for point source beta emitters and has units 
of rad per hour in air per Ci at 1 ft (which is close to per mCi at 1 ft 
(30.48^2/1000=0.929).  Also you have to consider the Y-90 (T1/2 = 64 h) 
that would likely be in equilibrium with the Sr-90.  Consideration of 
geometry, bremsstrahlung production (significant in high energy beta 
emitters), and detector composition are a few of the variables that could 
effect your readings.  Sometimes manufacturers report actual source 
readings in their manuals or literature.  Determining what instrument 
response you would expect for a given source and geometry and does not seem 
to me to be a trivial task;  it would likely be different for an air 
ionization chamber, a GM detector and a tissue equivalent dose meter.

Good luck.


At 10:11 AM 10/16/2007 -0400, MCCORMICK, LUKE I wrote:
>Can anyone tell me about how much Sr-90 I would need to get a reading of
>0.5 mR/hr at 1 meter? I know that if you go by the rule of thumb (300
>R/hr at 1 cm per mCi) you should need around 330 micro-Curies. Can
>anyone tell me how close this estimate is?
>Luke McCormick
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