I-125 standards for cartridges

[MARKT@HARV-EHS.mhs.harvard.edu]

I was forwarded your message about developing I-125 standards for carbon 
cartridges. I have done research in this area and may have useful 
information. I started by sealing 7-8 spiked filter papers in laminated 
plastic; the filters were spiked with NIST-traceable I-125 solution. Next 
I opened several cartridges, and placed the sealed-moist filters at a 
different depth for each of them. This provided me with a series of 
cartridges containing known I-125 activities at known depths. The 
cartridges were then resealed and analyzed using a front/back counting 
technique (Montgomery; in Radioactivity & Radiochemistry, Vol.1, pages 
4-9, 1990). The front/back technique is quite useful and allowed me to 
establish relationships between the front/back count ratio, depth of 
burial, and counting efficiency, i.e., calibration curves.

These curves can be used in operational sample analysis to determine the 
cartridge counting efficiency based on the observed front/back count 
ratio. If you have many samples, you may wish to determine an average 
efficiency for all samples based on a determination of average depth of 
burial. 

Good Luck Wes,

Mark A. Tries 
Harvard University, Radiation Protection Office
46 Oxford Street
Cambridge, MA  02138-1995