A Compton Backscatter Densitometer for the RoLand Comet Lander—design concept and Monte Carlo simulations

A Compton Backscatter Densitometer has been proposed for the RoLand probe in order to measure the bulk density of material near the surface of a comet nucleus. RoLand is to be deployed from a spacecraft in orbit around the target comet, as part of the international Rosetta mission. The basis for the use of this technique on RoLand is explained. Densitometers have been used twice before in planetary exploration, however the RoLand design aims to employ a lower energy radioisotope source so that a lightweight detection system can be used. Monte Carlo simulation of scattering and absorption in semi-infinite bulk materials has been used to investigate the design parameters, specifically the variation of backscattered count rate with density and composition. Results indicate that a density measurement can be made provided that the basis elemental composition of the material is known.