Compact LaBr3: Ce Gamma Ray Detector with Si-APD Readout

BrilLanCe 380 (TM) (LaBr(3):Ce) crystal scintillators available from Saint-Gobain Crystals have achieved 2.6% FWHM for 662keV photons (1). This is accomplished with PMT light sensors. Attempts to have similarly good results with PIN photo-diodes and APDs have not been successful. PIN photodiodes do not have any gain and the signal to noise ratio is poor at room temperature. Similarly, even though APDs have sufficient gain, they have poor signal to noise at room temperature. Recently there have been improvements in APDs decreasing the internal noise and increasing their sensitivity, making them an excellent light sensor. With the improved APD, it is now possible to achieve performance with a solid state light sensor comparable to that of PMTs. We have measured 2.8% for 662keV gamma rays at room temperature using an APD for a light sensor on a 20mm long crystal of 1.6cc volume. APDs have advantages of compactness, inherent ruggedness and minimal sensitivity to magnetic fields. Such a device is very practical for hand held and portable field measurement applications(1). ((1)Performance reported in SGC literature.)