Re: Sr-90 Source Activity/Geometry

[LIPTONW@dteenergy.com]

Two factors you have to consider are: (1) the Y-90 activity, which would be
in 
secular equilibrium, and (2) the backscatter factor.  The vendor should be 
able to help.  Usually, both the absolute Sr-90 activity and the 2 pi beta 
emission rate are supplied in the calibration documentation.  The value to
use 
for calibration depends on the counter being calibrated and the expected 
samples.  If the samples will be on a backing similar to that of the 
calibration source, no correction would be needed for backscatter.  If the 
samples are different from the calibration source, however - eg., the cal 
source is on a metal disk, but the samples will be on filter paper, then you 
must account for the difference in backscatter factors.  Here, knowing the 2 
pi emission rate would be helpful. 
 
The opinions expresed are strictly mine. 
It's not about dose, it's about trust. 
 
Bill Lipton 
liptonw@dteenergy.com 
 
You wrote: 
 
>We recently purchased a Sr-90 source from Amersham. 
>The certificate of calibration lists the activity as 802 Bq, which is for 
>the Sr-90 only. 
>Our crew is having a discussion about what the activity, in dpm, would be 
>for 2 pi and 4 pi geometry. 
>Also, if you are calibrating a CAM with this source, would you use the 2 pi 
>or 4 pi dpm to determine efficiency? 
>Anyone care to comment? 
 
>Bill Miller 
>INEEL 

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