Secondary Logo

Journal Logo

Institutional members access full text with Ovid®

A COMPARISON BETWEEN GROSS AND NET COUNT MRTHODS WHEN SEARCHING FOR ORPHAN RADIOACTIVE SOURCES

Hjerpe, Thomas; Samuelsson, Christer

PAPERS
Buy

Abstract— Different numerical strategies in searching for orphan radioactive sources in the environment by means of a mobile detector system have been evaluated. A carborne 3- by 3-inch NaI(Tl) spectrometric system was used with an unshielded 2 GBq 137Cs source as a test source. In this paper, a previous method (MB method), based on a moving average algorithm applied on the gross count rate, was extended and compared with three moving average algorithm methods involving different natural background subtraction strategies. For each method the distance from the road that an orphan source can be detected with a probability of 50% (the critical distance, CD) when driving by is determined. The CD for a 2 GBq 137Cs source improved from 105 m to 130 m when the interference from 40K was subtracted from the 137Cs spectral window. However, when the contribution of other natural gamma-emitting nuclides also was subtracted, the ability to find the 137Cs source was reduced.

*Department of Radiation Physics, The Jubileum Institute, Lund University, University Hospital, SE-221 85 Lund, Sweden.

(Manuscript received 13 August 2001;

revised manuscript received 15 April 2002, accepted 22 August 2002)

For correspondence or reprints contact: T. Hjerpe at the above address, or email at thomas.hjerpe@radfys.lu.se.

© 2003 by the Health Physics Society