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NKS Programme Area:NKS-B
Research Area:Emergency Preparedness
Report Number:NKS-474
Report Title:COMBMORC - Combined analysis of primary and scattered components in mobile gamma spectrometric data for detection of materials out of regulatory control, NKS-B COMBMORC Report 2021
Activity Acronym:COMBMORC
Authors:Christopher L. Rääf (chair), Robert R. Finck (co-chair), Einar Améen, Vikas C. Baranwal, Marco Brønner, Antanas Bukartas, Jon Drefvelin, Johannes Eriksson, Kjartan Guðnason, Gísli Jónsson, Mattias Jönsson, Simon Karlsson, Peder Kock, Marie Lundgaard Davidsdóttir, Bredo Møller, Petri Smolander, Mikael Westin,
Abstract:Radioactive material that has come out of authorities control (MORC) poses a danger. If such a threat is suspected, authorities must localise and secure the radioactive source. One method of searching for gamma-emitting radionuclides is mobile gamma spectrometry, where the primary gamma energy identifies the source. The primary gamma fluence becomes reduced if a shielding material is located between the source and the detector, leading to the distance at which gamma detectors can detect a source becoming shorter. At the same time, the scattered radiation increases, having lower energy than the primary radiation due to the Compton interaction in the radiation shield. A gamma spectrometer also registers the scattered radiation. The ratio of scattered to primary radiation provides information about the thickness of a radiation shield. The Nordic countries' radiation safety authorities have experimented with mobile gamma spectrometry to explore a combined analysis of primary and scattered radiation components. Mobile gamma spectrometry teams made measurements in eighteen setups with shielded and unshielded Cs-137 sources at varying distances from a road. Teams used one-second acquisition time intervals, passing the sources at 50 km/h. The experiments show that combined analysis of primary and scattered components could identify the shielding of sources, provided that the detector revealed a signal from primary photons. The results indicate that combined analysis may slightly increase the detection distance for shielded sources. The detection distance does not increase with combined analysis for unshielded radiation sources, but such an analysis can provide information that the source is unshielded.
Keywords:Mobile gamma spectrometry, orphan sources, shielding
Publication date:21 Jun 2023
Number of downloads:487
Download:pdf NKS-474.pdf
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