Computer simulation and beam experiment on the identification of elements for planetary exploration

In order to determine the absolute chemical concentration on a planet, highly precise ground-based experiments and computer simulation is needed to drive such information from the mission data. In case of the moon, Apollo data provides ''ground truth'', but those are only for limited point of the entire surface to be observed. For other planets, there would be no such reference data. Therefore, computer simulation will play very important role in determination of concentration, and its consistency has to be verified with the ground-based experiments. The computer simulation has to be able to reproduce variety of interaction from electromagnetic to nuclear interaction when considering from cosmic-rays to induced gamma-rays. Computer code Geant4 has been chosen and tried to optimize the experimental setup. Among the elements that are considered to exist on the lunar surface, iron and aluminium were selected as a realistic simple-material target. In order to reproduce the environmental of planetary surface with no or little atmosphere, proton beam of 210 MeV was bombarded to the target in the computer simulation and measured the gamma-rays leaking from the irradiated surface. Beam experiment was carried out at Riken Ring Cyclotron. The same experimental setups as in the computer simulation were used as much as possible. In order to verify the reliability of computer simulation, the comparison between experimental and numerically calculated result were made. They show a decent match within the error of ∼5% and proved that the Geant4 simulation code is reliable for remote sensing planetary exploration, at least for simple material targets. (M. Suetake)