SHIELDMORC

SHIELDMORC: Detection distances and methods to locate orphan gamma radiation sources in shielded building geometries by mobile gamma spectrometry

SHIELDMORC addresses the problems of mobile detection of shielded gamma-ray sources, which is the most likely scenario when searching for orphan radiation sources. The project in 2020 aims to experimentally determine how the pulse height distribution in mobile gamma spectrometers reflects the scattered radiation from shielded gamma ray sources (primarily Cs-137). The scattered radiation depends on the shielding material, the thickness of the shield and the distance between the radiation source and the detector. In addition, the detector's own absorption and scattering effect distorts the image of the photon fluence in the resulting pulse height distribution. The distribution is also superimposed on the recordings from the natural background radiation. Thus, the composite “signal” in the gamma spectrometer from a shielded radiation source consists of several different components that depend on the radiation shield and the distance to the source superimposed on “interference” from detector effects and background variations. However, through systematic experimental measurements where one parameter is varied at a time (distance, shielding material, shielding thickness, detector type), it should be possible to create a "knowledge library" (as described in the supplemental description) about how these parameters contribute to the result in the pulse height distribution of a mobile spectrometer. In SHIELDMORC 2020, the intention is that each participating team and detector should be able to create such a simple "knowledge library" for a number of well-defined radiation geometries (as many as can be covered during 1½ days of measurements). The intention is for the remaining time (1½ days) to make mobile measurements against similar, but for the teams unknown, variants of source geometries in order to investigate whether it is possible to draw conclusions about source distances, shielding geometries and activities by using the recorded pulse height distributions in combination with the “knowledge library”.

Christopher Rääf: christopher.raaf@med.lu.se

Phone number: +46 40 331145