4π Spectrometric Gamma-Ray Scanner with Anti-Collimator

The paper presents the development of a low weight scanning spectrometric system for characterization of the spatial radioactive contamination with a wide scanning field (up to 4π), a wide range of dose rate, and with an angular resolution about 5o. The anti-collimator principle is used to obtain spatial modulation of the signal. When scanning a scene, the system rotates in such a way that anti-collimator blocks the radiation flux to the detector from a certain spatial area. During the scanning of all directions, a primary image is obtained, which is then reconstructed by an iterative procedure using the angular apparatus function of the system. The apparatus function can be measured using point gamma-ray source. The system has the following optimized parameters with CsI(Tl) scintillating detector. A cylindrical lead shutter (anti-collimator), D 3.2 cm x L 4 cm was selected, the distance between the anti-collimator and the detector should be 15 cm. A prototype of the system with spectrometric detector based on a 6 cm3 CsI(Tl) scintillator crystal with silicon photomultipliers (SiPM) was manufactured. The dependence of the detector energy resolution on the number of SiPMs has been studied. When using 4 SiPMs, the energy resolution of Cs-137 was 12.1%. First images of the scenes consisting of different gamma sources were obtained and reconstructed. Results of measurements present angular distribution of partial dose rate of different nuclides at the location of the system.