Evaluation of a position sensitive neutron detector based on Li₆Gd(BO₃)₃ scintillator

As a result of the ever increasing demand for higher neutron flux, future neutron scintillator detectors will require faster scintillators with a high light yield and low gamma sensitivity. Initial measurements with single element prototypes demonstrated that the new lithium gadolinium borate (LiGdBO) scintillator, using ⁶Li as the neutron absorber, was a promising candidate. As a result of this work, a full size position sensitive detector module has been made consisting of 120 LiGdBO elements. This module was installed on the High Resolution Powder Diffractometer (HRPD) beam line at ISIS for evaluation. The LiGdBO detector has been constructed with the same geometry and theoretically the same neutron absorption efficiency as the existing HRPD ZnS scintillator detector modules. In this way it was possible to make a more exact comparison of the relative detector performances. Measurements have shown that the neutron energy resolution and detection efficiency of both types of detector are identical. Gamma sensitivity and quiet count rate are somewhat higher for the LiGdBo than the ZnS scintillator detector, but still at an acceptable level for many applications. The short decay time of the LiGdBO scintillator has enhanced the count-rate capability of the detector by an order of magnitude. These measurements show that the realistic large area position sensitive neutron detectors can be fabricated with LiGdBO scintillator using an optical fibre readout. LiGdBO is thus a promising scintillator for future detectors at the new flux facilities currently under construction.