Long-term Neutron Background Environment Measured by the Dynamic Albedo of Neutrons (DAN) Instrument onboard Mars Science Laboratory (MSL)

Since landing in August 2012, DAN has provided a wealth of scientific data from the successful surface operation in both Active mode and Passive mode. The main scientific objectives of DAN are twofold. The primary objective is... [ view full abstract ]

Since landing in August 2012, DAN has provided a wealth of scientific data from the successful surface operation in both Active mode and Passive mode. The main scientific objectives of DAN are twofold. The primary objective is to measure the bulk hydrogen abundance (in forms of water or hydrated minerals) of the subsurface. The secondary objective is to measure the background neutron environment at the surface. DAN achieves the first objective by using the pulsed neutron generator (PNG) as a pulsed 14 MeV neutron source (active mode). When no neutron pulse is used (passive mode), DAN measures the neutron background environment at the Martian surface. The DAN active data have extensively and successfully used in estimating the near-surface contents of hydrogen (in terms of “water equivalent hydrogen” or WEH) and chlorine (in terms of “absorption equivalent chlorine” or AEC) at multiple locations in Gale crater. In the mean time, DAN has been accumulating the passive mode data in almost all sols since landing, and it is the main topic of this presentation. The main goal of this talk is to present the long-term (through Sol ~1500, covering more than 2 Martian year) behavior of the neutron environment at the Martian surface as measured by DAN and to show possible correlation with variation of the ambient GCR/SEP environment. Extensive Monte Carlo transport simulations using MCNPX have been performed to support the analysis and to aid interpretation of the DAN passive data.