Passive Detection of Concealed Strontium-90 Radioisotope Thermoelectric Generators in Transport

Abstract

Many radioisotope thermoelectric generators (RTGs) used in civilian and military applications employ ⁹⁰Sr, a high-energy beta emitter. The possibility of indirect or deliberate contamination of the environment with this isotope is not negligible. Detection and identification of a concealed ⁹⁰Sr RTG is possible by monitoring the continuous-energy spectrum of the bremsstrahlung radiation emitted as the source's betaparticles interact with the active material inside the source and with the surrounding container and shielding material. This detection concept is verified by measuring the energy spectrum of the bremsstrahlung radiation emitted from a small-activity shielded ⁹⁰Sr source, using two modest energy-resolution detectors: a NaI(Tl) crystal and a BC-408 plastic scintillator. These measurements were in turn utilised to verify the results obtained from Monte Carlo simulations, to determine the detector response for a realistic RTG source. The minimum detection time was then estimated as a function of the activity of the source and thickness and type of surrounding shielding.