Improved scintillator design for thermal neutron detection

Abstract

Neutron detectors are used in various applications in nuclear security and nuclear safety. The most efficient neutron detection systems used in these applications are based on 3He technology. The growing demand for 3He already exceeds production in the next few years leading to an exponential increase of the price. The last decade has been driven by the quest for finding competitive alternative technologies to replace 3He based detectors. Thus, intense research and development continues to explore new phosphor materials as scintillators or the optimization of existing scintillators taking advantage of new technological methods for their preparation. The development of phosphors with rare earth elements such as gadolinium show a high potential for use as efficient and cost-effective inorganic scintillators for neutron detection. The appealing feature of gadolinium, which has one of the highest neutrons capture cross sections, and the production of electrons instead of heavy charged particles, has pushed several research programs to study possible alternatives that use gadolinium. The work presented in this thesis is mainly focussed on the investigation of the development of scintillator layers based on natural gadolinium, mainly Gd2O3:Eu3+, GdBO3:Eu3+, and Li6Gd(BO3)3:Eu3+ for thermal neutron detection. Scintillators were prepared, using the natGd based phosphor prepared using simple urea precipitation method followed by K-bar technique. Hexagonal boron nitride (h-BN) based thin films have also been developed using the RF sputtering technique. Performance of those thin film scintillators were tested for thermal neutrons. The key goals of the presented research work being the identification of improvements in the different parts of neutron detector design based on both experimental measurements and simulation activities. Silicon Photomultipliers (SiPMs) represent a well-consolidated and cost-effective technology for a large range of applications requiring the detection of low light levels. In recent years, research efforts have been devoted to improving the basic performance of this kind of detector. In the presented research, a SiPM based readout system is used. The front-end readout system for the SiPM has been developed and tested. The presented measurement results demonstrate that the implemented circuit has features that are attributable to photon detection. Here the research work mainly focused on reducing the power consumption of the required electronics and reducing the PCB size, to implement a lightweight portable handheld detector for ease of use in field activities.