Re: Sr-90 Source Activity/Geometry

[Dave Brown <browndr@nist.gov>]

At 02:08 PM 3/24/99 , 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,

Generally speaking, ......exact details should be obtained from the source provider......the reported Sr-90 activity of X Bq will be in equilibrium with its daughter, Y-90, at X Bq.  Sr-90 average beta energy of 196 keV and Y-90's average energy of 934 keV must be carefully considered in assessing the geometry and emission rates.  Factors such as backscatter and window absorption must be considered in determining these values......again, I'd talk to the supplier.  You should be able to get values for 2 and/or 4 pi emission rates and apply the appropriate value for calibration.

Regards,

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Dave Brown, CHP
National Institute of Standards and Technology
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