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NKS Programme Area:NKS-B
Research Area:Emergency preparedness
Report Number:NKS-433
Report Title:SHIELDMORC– Detection distances and methods to locate orphan gamma radiation sources in shielded building geometries by mobile gamma spectrometry
Activity Acronym:SHIELDMORC
Authors:Christopher L. Rääf (chair), Robert R. Finck (co-chair), Vikas C. Baranwal, Antanas Bukartas, Marie-Andrée Dumais, Kjartan Guðnason, Yvonne Hinrichsen, Gísli Jónsson, Mattias Jönsson, Peder Kock, Sune Juul Krogh, Simon Karlsson, Frode Ofstad, Jan Steinar Rønning, Petri Smolander, Kasra Tazmani, Mikael Westin,
Abstract:Mobile gamma spectrometry is a key method when searching for gamma-emitting radioactive sources that have come out of regulatory control through accidents or deliberate events. Such sources can be more or less shielded, which reduces and distorts the gamma spectrometric signal. It makes detection more difficult as the signal from the primary radiation decreases. An estimate of the shielding is needed to assess the potential hazard before approaching to handle the source. The NKS/SHIELDMORC activity is a step on the way to gain experiences in mobile gamma spectrometry for detection of shielded sources. It is carried out in collaboration between mobile detection teams from Denmark, Finland, Iceland, Norway and Sweden. The aim is to develop and test practical methods to detect lost or hidden gamma emitting sources and estimate their locations and activities. This report describes results from preparatory theoretical calculations and some experimental acquirements on situations with shielded Cs-137 and Co-60 sources, using a 4 litre NaI(Tl)-spectrometer. A method of applying a ratio of count rates in three regions of interest (ROI) representing selected parts of the Compton scattered registrations together with one ROI for primary registrations seems to be useful for determination of the amount of scattered radiation from a possible shield around the source. The method may also roughly indicate the physical properties of the shield in terms of thickness and whether the material has high or low atomic number. However, further experiments are needed to verify this. The intention is to make the verification in a joint Nordic field experiment in 2020. The report describes a proposed design for such an experiment.
Keywords:Mobile gamma spectrometry, MORC, orphan hidden gamma sources, radiation accidents, shielding, Compton scattering
Publication date:09 Mar 2020
ISBN:ISBN 978-87-7893-523-6
Number of downloads:174
Download:pdf NKS-433.pdf

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