Derived Neutron Data. The GRS Derived Neutron Data (DND) data set is a time series collection of derived neutron data measurements from the Neutron Spectrometer (NS) sub-system of the Mars Odyssey Gamma-Ray Spectrometer. The Derived Neutron Data are an intermediate data product. Raw data are processed, then the neutron data is derived from it. Finally, a set of calculations can be run that will result in thermal, epithermal, and fast neutron fluxes.