Results from NASA's 2001 Mars Odyssey mission have identified
large deposits of water ice near the Martian poles and
hydrogen-rich areas near the planet's equator. Feldman et al.
calculated the energy spectrum from fast neutrons on Mars, which
can be used to make a rough map of the planetary surface and to
estimate a portion of the radiation exposure inside the spacecraft
that would be felt by astronauts of the future. Fast neutrons are
generated by galactic cosmic rays during space flight and can be
used to measure the radiation levels during long-duration space
flight and, above a planetary surface, can also reveal information
about its chemical makeup. While further confirmation of the
water ice findings are necessary, the authors estimate that an
astronaut would receive approximately .40 rem per year from the
neutrons aboard a spacecraft like the Odyssey during its flight to
the red planet. (For comparison, radiation workers can receive a
maximum of 5 rem per year, according to U.S. guidelines).

Title: "Fast neutron flux spectrum aboard Mars Odyssey during
cruise"

Authors:
W. C. Feldman, T. H. Prettyman, R. L. Tokar, R. C. Byrd, K. R. Fuller,
O. Gasnault, J. L. Longmire, R. H. Olsher, S.A. Storms, G.
W. Thornton, Los Alamos National Laboratory, Los Alamos, New
Mexico;
W. V. Boynton, University of Arizona, Tucson, Arizona.

Source: Journal of Geophysical Research-Space Physics (JGR-A)
paper 10.1029/2001JA000295, 2002