Development of low noise scintillator crystals for planetary space missions

The recent development of large volume lanthanum halides (LaBr₃ and LaCI₃), 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 LaCI₃ and LaBr₃ is the high background noise inherent to the crystal due to the decay of radioactive ¹³⁸La, which comprises 0.09% of naturally occurring stable lanthanum (¹³⁹La). This paper describes the development of a low noise equivalent to LaBr₃, namely CeBr₃, Crystal sizes up to 3" have successfully been grown. The energy resolution of CeBr₃ (4.1% FWHM at 662keV) was found to be slightly worse than that observed for LaBr₃ (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 CeBr₃ development, a Silicon Photo Multiplier(SPM) aimed at having a response matched to both LaBr₃ and CeBr₃ has also been developed. Preliminary results are presented.