High Brilliance Fast Scintillator for Neutron Detection and Imaging

Abstract

High data rate detectors are needed for neutron reflectometer instruments and diffractometers require high spatial resolution detectors. Scintillators are the predominant material for the neutron converters in single crystal detector instruments, with GS20 being the most common choice. Here we report on the development and properties of Ce3+ activated 6LiI crystal scintillator grown with the aim of minimizing the decay time to support the high data rate applications while providing high brightness and high efficiency compared to GS20. The LiI crystals doped with Ce3+ were grown by the vertical Bridgman technique using 95%-enriched 6Li. It demonstrates two decay components with the primary decay of 43- 50 ns (93%) and the secondary decay of ~300 ns (7%), significantly faster than the Eu2+ doped 6LiI decay (~1 µs). Light yield for thermal neutron interactions was measured to be ~18,500 photons/interaction, which is a factor of 3 higher than the GS20. The X-ray excited radioluminescence spectrum of Ce3+ activator in LiI at room temperature shows three well-defined emission bands in the range of 400 to 700 nm, peaking at 430, 474, and 590 nm, which are due to 4f-5d transitions of Ce, The crystals also demonstrate high gamma equivalent energy (GEE) of nearly 3 MeV, thereby permitting effective pulse height neutron/gamma discrimination