S35 DIS Surveys

[10525kfb@ibm.cl.msu.edu (Kristin Erickson)]

In response to Sue Dupre's questions on S35 waste monitoring, I would be
extremely leery of surveying for any low energy betas inside a bag or any
other container.  The isotope would definitely be attenuated.  In fact,
even poly-backed lab paper will block the signal if measured from the other
side of the contamination.  Add to that the fact that S35's range is but a
few inches in air, much less in solid or liquid materials.

I monitored a bunch of S35 waste a few years ago.  None of the bags gave
readings from the outside; so, I went inside the bags, ended up picking
apart the waste and found plenty of S35.  Micro tubes gave very little or
no signal if closed, but high readings when opened.

An indicator of attenuation is to calibrate a meter with cap off, then put
some Saran wrap on; check attenuation..  Next, try plastic (like the bags),
check attenuation, then other materials, such as the common ones used,
e.g., microtubes, 12 X 75 glass, etc.  I think it will show you why a
survey "in a bag" will not work, and, in fact, the waste should be spread
out.

We run into this issue when workers in the labs try to do their
contamination surveys with the cap on the meter, or covered with parafilm
or Saran wrap.  When they don't understand our explanation of the
attenuation, or don't believe us, we calibrate both ways.  The numbers are
clear and convincing.

I don't believe most regulators would accept this method of monitoring for
low betas, but perhaps some licensees will correct me.  Good luck!

Regards,


Kristin

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Kristin Erickson, Radiation Safety Officer
Office of Radiation, Chemical and Biological Safety
C124 Research Complex-Eng.
Michigan State University
East Lansing, Michigan 48824
Telephone: (517) 355-5008   Fax: (517)353-4871   Email: 10525kfb@msu.edu
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