[ RadSafe ] measurement of Kr-85 using Overhoff 400 portable tritium monitor

JGinniver at aol.com JGinniver at aol.com
Tue Jul 25 17:13:42 CDT 2006

Has anyone on radsafe any experience of calculating Kr-85 concentrations  
from measurements using a gas flow ion chamber?
It would appear that one of the facilities at the site where I work may  have 
discharged some Kr-85.  At the time that the discharge is thought  to have 
occured several measurements were made using a portable tritium  monitor 
(Overhoff Model 400), these indicated measurable amounts of tritium in  the stack 
discharge from a series of shielded caves containing spent nuclear  fuel.  
Subsequent analysis of the tritium bubblers on the vent line  indicate that no 
tritium was present.  As a result it is believed that a  discharge of radioactive 
gas has occurred, and because of the nature of the  facility this is likely to 
have been Kr-85.
While the discharge was within allowable limits, the operators of the  
facility would like a better estimate of the activity discharged and the  only 
available measurements are from the portable tritium monitors.
Having refreshed my memory with my copy of Knoll, it is clear that this is  
not easy to do as the majority of the energy from the beta emissions is likely  
to have been deposited outside of the detection chambers in the  instrument.  
The only reference given in Knoll for further guidance is  T. Torii, Nucl. 
Instrumen. Meth. A356, 255 (1995) a search on google  has turned up the 
T. Torii: Ionization efficiency of a gas-flow ion chamber used for  
measuring radioactive  gases by Monte Carlo  simulation
Nucl.  Instr. Methods A356(1955)255-263.
which I'm assuming is the one mentioned in  Knoll?  Does anyone have an 
electronic copy I could have to look at, or  does anyone have experience of trying 
to do similar calculations?

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