CdTe survey instruments

[LIPTONW@detroitedison.com]

A recent nuclear power industry event report involved an outgoing radioactive 
material shipment which was surveyed by the shipper using a survey instrument 
with a Cadmium Telluride (CdTe) detector.  The shipper's survey showed the 
highest surface dose rate as 600 mrem/hr.  The receiver of the shipment 
surveyed the package using a survey instrument with an energy compensated GM 
probe, and found the highest surface dose rate to be 950 mrem/hr.  A 
representative of the shipper visited the receiver's facility and was able to 
reproduce the 600 mrem/hr survey.  It was also noted that the contents of the 
package had not shifted. Consultation with the manufacturer of the CdTe 
detector indicated that this underresponse to high energy photons is an 
intrinsic characteristic of CdTe detectors. 
 
Using 20/20 hindsight, it's clear that a CdTe instrument should not be used 
for shipping surveys involving typical power plant radionuclides. There may be 
other "gotchas" out there as well.  I'd be interested in hearing  how other 
facilities assure that the instruments used for shipping surveys provide the 
proper response for the radiation fields being assayed. 
 
Bill Lipton