RE: A Question for Power Reactor Types and others with portal monitors.

["Stabin, Michael" <michael.g.stabin@vanderbilt.edu>]

>We have found that Tc-99 alarms our portals for 1-3 weeks.  I think it

really depends on how much Mo-99 there is as a contaminant.  



I agree with John J - first, I know you meant Tc-99m, but mostly I am

surprised that any place would have enough Moly breakthrough to be so

noticeable. This is supposed to be a major QA point. You are right about

the 10 half-life rule, that just gets you to (1/2^10), not zero, and if

you are set to a sensitive level, this may still be measureable, but

Tc-99m has a 6 hour half-life, a typical administration is perhaps 500

MBq (depends on the compound), so you are down to 1-2 Bq in a week. So I

am also skeptical that Tc-99m would alarm for more than a week, even

with a sensitive detector, and we are back to the Moly hypothesis.



Mike





Michael G. Stabin, PhD, CHP

Assistant Professor of Radiology and Radiological Sciences 

Department of Radiology and Radiological Sciences 

Vanderbilt University 

1161 21st Avenue South

Nashville, TN 37232-2675 

Phone (615) 343-0068

Fax   (615) 322-3764

Pager (615) 835-5153

e-mail     michael.g.stabin@vanderbilt.edu 

internet   www.doseinfo-radar.com



 

************************************************************************

You are currently subscribed to the Radsafe mailing list. To

unsubscribe, send an e-mail to Majordomo@list.vanderbilt.edu  Put the

text "unsubscribe radsafe" (no quote marks) in the body of the e-mail,

with no subject line. You can view the Radsafe archives at

http://www.vanderbilt.edu/radsafe/