Distinguishing Neutrons and Gammas with MSL's Radiation Assessment Detector (RAD)

The radiation environment on the Martian surface is a complex mixture of charged primary and secondary radiation and of neutral secondary radiation. This neutral component amounts to a significant fraction of the surface radiation field and consists of neutrons and gamma rays. The neutron component is especially important from a radiation protection point of view, but is experimentally difficult to distinguish from the gamma rays. The Radiation Assessment Detector (RAD) on Mars Science Laboratory's (MSL's) rover Curiosity measures both neutrons and gammas. It consists of a compact arrangement of a dense, more gamma-sensitive CsI sctintillator, and a high-proton-content plastic scintillator, which in turn is more sensitive to neutrons. Using sophisticated inversion techniques, the RAD measurements can be inverted to provide reliable estimates for the neutron and gamma spectra on Mars. In this work we will discuss the status of the inversion techniques and calibration data, and relate them with predictions for the neutral component of the Martian surface radiation field.