Novel directional detector for radioactive material search and monitoring

A detector which in addition to automatic radiation alarming and gamma-ray spectroscopy enables directional sensing for fixed, relocatable, and vehicle-mounted detection systems, is demonstrated. A robust and reliable directional sensing relies on inter-detector shadowing effect of attached asymmetric NaI(Tl) and CsI(Na) scintillators. The scintillator package is connected to a single photomultiplier tube. Demonstrated directional sensing is based on background-subtracted NaI(Tl) and CsI(Na) total counts. When a Cs-137 source is positioned in front of the NaI(Tl) detector at 0o, the NaI(Tl)/CsI(Na) total count ratio is 1.238(9). At 90o, 180o, and 270o, the ratios are 1.000(7), 0.623(6), and 0.743(6), respectively. Scintillator crystal asymmetry causes the observed difference in ratios between 90o and 270o. The differences can be further increased by enlarging the sizes and/or modifying the shapes of the asymmetric phoswich crystals. This ratio difference, combined with the time behavior of the total counts, forms the basis of directional sensing. Compact single-channel digital nuclear electronics is used for the instrument’s signal processing. Demonstrated technology enables the development of user-friendly and highly integrated detection systems with extended performance.