Optimizing the Sensitivity of a GAGG:Ce-Based Thermal Neutron Detector

The neutron sensitivity of the cerium-doped gadolinium aluminum gallium garnet (GAGG:Ce) has been determined for five different scintillator volumes. The good gamma ray detection performance of GAGG:Ce potentially results in a background signal that hides the low-lying neutron-capture gamma rays from de-excitation of Gd-156 and Gd-158 when the detector volume, and therefore the total gamma ray absorption, is large. We have investigated the competition between the detection of the neutron signature and discrimination of the background gamma rays. A significant improvement in the neutron response has been demonstrated with a reduction in the scintillator volume. The peak-to-background ratio of the key neutron signature increased with decreasing scintillator thickness to a maximum value of 14 +/- 3 for 50 mu m. The limit of this correlation was not determined since the thinnest scintillator available (50 mu m) is greater than the mean free path of a neutron in Gd-157 (15.54 +/- 0.09 mu m).