Experimental set-up and optimization of a gamma-ray spectrometer for measurement of cosmogenic radionuclides in meteorites

We have developed a highly efficient and selective gamma-ray spectrometer with extremely low background for activity measurement of gamma emitting cosmogenic radionuclides in meteorites. This spectrometer can operate in specific modes to match decay scheme of a particular radionuclide and is specially suited for measurement of positron emitters. The system consists of a hyperpure Ge detector (3 kg, 147% relative efficiency), operating in coincidence with an umbrella of NaI(Tl) scintillator (90 kg) in order to achieve low background. The system is tuned such that strong interference due to naturally occurring uranium daughters, e.g. 214Bi present in the meteorites and in the laboratory environment, is minimized. It enables us to measure 44Ti ( T 1 / 2 = 59.2 y ) which is ideal for studying centennial scale variations of cosmic ray flux in the interplanetary space with good reliability. The specific configuration of the coincidence system and electronics are described here.