On gamma-ray spectrometry of rare earth elements on the moon: Reference data from proton accelerator experiment

The laboratory experiment was conducted at Joint Institute for Nuclear Research with a prototype of planetary gamma-ray spectrometer (GRS) based on a High Purity Germanium (HPGe) detector and a proton detector (PD) configured with the GRS in the coincidence mode. The instrument set-up allows to detect gamma rays produced in the target irradiated by protons using integrated gamma-ray spectra (all detected gamma rays) as well as tagged gamma-ray spectra that select only photons synchronized with the proton detection. The latter option improves signal-to-noise ratio by selecting prompt photons produced in the irradiated target. The main objective was to conduct experiment with an irradiation of 11 samples of Rare Earth Elements (REEs) with high energy protons (170 MeV) to find a set of uniquely characterized gamma-ray lines that confidently indicate the presence of the given REE. These measurements are acquired to understand the conditions of a hypothetical space experiment on the lunar surface aimed for the reconnaissance of lunar resources. In this experiment, ambient gamma radiation is produced by charged particles of Galactic Cosmic Rays (GCRs).