The radiation hardness of ⁶LiI:Ag for lunar surface neutron measurement from the LVRAD experiment

Lunar vehicle radiation dosimeter (LVRAD) is an experiment for lunar surface radiation measurement through Artemis missions. The LVRAD instrument will evaluate biological effects from radiation effects, search lunar surface water by neutron measurement, and investigate lunar surface radioactive substances by gamma-ray spectroscopy. The LVRAD instrument consists of the lunar radiation dosimeter and spectrometer, and the neutron spectrometer. The (LiI)-Li-6:Ag scintillators are used for the thermal and epithermal neutron spectrometer from the LVRAD instrument. (LiI)-Li-6:Ag measures neutron energy from Li-6(n, ?)H-3 reaction and it can separate neutron signals from gamma rays using pulse shape discrimination. Because of the radiation environment on a lunar surface, such as cosmic rays, and albedo neutrons, the radiation damage effects of (LiI)-Li-6:Ag should be investigated for the LVRAD experiment. 45 MeV proton beam in the Korea Institute of Radiological and Medical Sciences is used for the radiation hardness test. The pulse height spectra from 511 keV gamma rays decrease by 13.2%, and the figure of merit values of pulse shape discrimination decrease by 8% when the absorbed dose is 3508 rad. The emission peak intensity at 495 nm decreases by similar to 30% when the absorbed dose is 1300 x 10(3) rad. The results show that (LiI)-Li-6:Ag has high radiation hardness and can be used in high-radiation environments.