Determining Charged Particle Flux Direction in MSL/RAD

Monday, 15 December 2014
Jan Kristoffer Appel1, Jan Kohler1, Jingnan Guo1, Bent Ehresmann2, Cary J Zeitlin3, R F Wimmer-Schweingruber1, Don Hassler4, Scot CR Rafkin2, Eckhard Boehm1, Stephan I Böttcher1, Cesar Martin-Garcia1, David E Brinza5, Eddie Weigle6, Henning Lohf1, Sönke Burmeister7, Guenther Reitz8, Daniel Matthiae8, Arik Posner9, Javier Martín-Torres10 and Maria-Paz Zorzano10, (1)University of Kiel, Kiel, Germany, (2)Southwest Research Institute Boulder, Boulder, CO, United States, (3)Southwest Research Institute, Durham, NH, United States, (4)Southwest Research Inst, Boulder, CO, United States, (5)Jet Propulsion Laboratory, Pasadena, CA, United States, (6)Big Head Endian, Burden, KS, United States, (7)Christian-Albrechts-Universität zu Kiel, Institute for Experimental and Applied Physics, Extraterrestrial Physics, Kiel, Germany, (8)German Aerospace Center DLR Cologne, Cologne, Germany, (9)NASA Headquarters, Washington, DC, United States, (10)Centro de Astrobiologia, Madrid, Spain
The Radiation Assessment Detector (RAD) is an instrument onboard the Mars Science Laboratory (MSL) rover Curiosity, currently characterizing the radiation environment on the surface of Mars. The radiation entering the instrument from above consists mostly of Galactic Cosmic Rays (GCRs) modulated by the Martian atmosphere. From below, the instrument is exposed to secondary radiation produced by the interactions of the GCR with the soil. This secondary radiation gets further modulated going through the rover body before entering RAD.

We developed a method of determining the direction of the charged particles measured by RAD. This method also extends the energy range possible for measurements with RAD beyond the intruments design limit. Using a combination of GEANT4 and Planetocosmics simulations, we reconstructed the expected charged particle spectra and intensities for upward and downward directed radiation which can be compared with observations. With the developed method, we are able to, for the first time, measure the upward charged particle flux with RAD both during the cruise phase and the surface science phase. Comparing the results of the simulations with the instrument data sets enables us to evaluate the simulation tools used to predict the Martian radiation envronment.