Novel neutron detectors

Abstract

A new set of thermal neutron detectors has been developed as a near term 3He tube replacement. The zinc oxide scintillator is an ultrafast scintillator which can be doped to have performance equal to or superior to 3He tubes. Originally investigated in the early 1950s, this room temperature semiconductor has been evaluated as a thermal neutron scintillator. Zinc oxide can be doped with different nuclei to tune the band gap, improve optical clarity, and improve the thermal neutron detection efficiency. The effects of various dopant effects on the scintillation properties, materials properties, and crystal growth parameters have been analyzed. Two different growth modalities were investigated: bulk melt grown materials as well as thin film scintillators grown by metalorganic chemical vapor deposition (MOCVD). MOCVD has shown significant advantages including precise thickness control, high dopant incorporation, and epitaxial coatings of neutron target nuclei. Detector designs were modeled and simulated to design an improved thermal neutron detector using doped ZnO layers, conformal coatings and light collection improvements including Bragg reflectors and photonic crystal structures. The detectors have been tested for crystalline quality by XRD and FTIR spectroscopy, for scintillation efficiency by photo-luminescence spectroscopy, and for neutron detection efficiency by alpha and neutron radiation tests. Lastly, a novel method for improving light collection efficiency has been investigated, the creation of a photonic crystal scintillator. Here, the flow of optical light photons is controlled through an engineered structure created with the scintillator materials. This work has resulted in a novel radiation detection material for the near term replacement of 3He tubes with performance characteristics equal to or superior to that of 3He.