Development of low noise scintillator crystals for planetary space missions

The recent development of large volume lanthanum halides (LaBr 3 and LaCI 3 ), has made scintillator based detectors a viable option for use as high resolution γ-ray spectrometers for a large number of space applications. The main drawback of both LaCI 3 and LaBr 3 is the high background noise inherent to the crystal due to the decay of radioactive 138 La, which comprises 0.09% of naturally occurring stable lanthanum ( 139 La). This paper describes the development of a low noise equivalent to LaBr 3 , namely CeBr 3 , Crystal sizes up to 3" have successfully been grown. The energy resolution of CeBr 3 (4.1% FWHM at 662keV) was found to be slightly worse than that observed for LaBr 3 (2.8% FWHM at 662keV) but a measured relative decrease of almost 30 times in internal activity makes it an attractive alternative when low noise operation is required. In parallel to the CeBr 3 development, a Silicon Photo Multiplier(SPM) aimed at having a response matched to both LaBr 3 and CeBr 3 has also been developed. Preliminary results are presented.