Speaker
Description
Selene’s Explorer for Roughness, Regolith, Resources, Neutrons and Elements (SER3NE) is a small lunar orbiter mission led by UiO, aiming on mapping the global composition of solids and volatiles and thus the elemental abundance of the lunar surface in unprecedented spatial resolution. One of the instruments onboard is the Gamma-Ray-including-Neutrons Spectrometer GRiNS, a hybrid radiation detection instrument sensitive to gamma-rays, neutrons, and charged particles. The main objective for the GRiNS on SER3NE is elemental abundance mapping from gamma-ray spectroscopy, as well as neutron detection. Besides the abundance mapping, GRiNS also targets the space-based estimation of the neutron lifetime. To do so, GRiNS will host two detector units, one pointing nadir for mapping, one pointing zenith for detecting gravitationally bound thermal neutrons at a different time of flight in their trajectories back to the moon. Although not part of the official SER3NE mission objectives, the zenith module also allows for detecting Gamma-ray bursts in the pointing direction of the spacecraft.
The detector units consist of hybrid gamma-ray and neutron sensitive crystal scintillators packaged in a plastic scintillator based anti-coincidence shield (ACS). The crystal scintillators, a combination of LaBr3 and CLLBC, are partially wrapped in Gd foil and allow for gamma-ray detection in the range of 100keV – 8MeV with a spectral resolution of about 4% at 662keV, as well as thermal and epithermal neutrons. The ACS vetoes events caused by high energetic charged particles, improving the signal-to-noise ratio of the spectrum. However, the number of events rejected within a given integration time will indicate solar activity.
The scintillators are read out by Silicon Photomultipliers (SiPMs) attached to application specific read-out ICs, the IDEAS IDE3380, and data handling electronics, providing a histogram of gamma-equivalent energies and count rates.
The SER3NE mission just concluded MDR with the mission and instrument requirements defined and the GRiNS instrument design proposed. A laboratory demonstrator of the GRiNS instrument with an CLLBC scintillator, SiPM arrays and IDE3380 based readout delivers promising results: demonstrating neutron and gamma-ray separation capabilities and spectral resolutions of better than 4.5% at 662keV. The details of the GRiNS instrument design, as well as an engineering model, is in planning.
Acknowledgement: The SER3NE pre-Phase-A study was financed by the ESA within the Terra Novae E3P programme.
