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.