Speaker
Description
When cosmic rays or energetic solar particles strike the lunar surface, the secondary energetic particles that escape back into space carry information about the surface composition. These “albedo” particles are also a source of additional radiation exposure for astronauts or hardware at or near the lunar surface, which must be understood in order to plan for survivability of space missions there.
Since the 2009 launch of the Lunar Reconnaissance Orbiter (LRO), the science team of its Cosmic Ray Telescope for the Effects of Radiation (CRaTER) sensor has used the Geant4 radiation-transport code to study this process. Using hundreds of processor-years on computer clusters, we have modeled all albedo particle species except neutrinos. We have organized our model results into JSON-formatted files and are making them available to the space science and engineering communities via the Zenodo open archive.
The distributions of albedo particles are calculated for individual energies of ion species from H to Ni arriving isotropically from space. This enables a user to convolve these response functions with any desired incident ion spectra, rather than having to choose from a limited set of spectra hard-coded into the model. We also include with the model some examples of such convolutions, so that users can check their use of the response files.
We will describe the organization of the model files, which allows users to avoid downloading portions not needed for a particular study. To demonstrate usage, we will show the modeled effects of regolith hydrogen on albedo proton and neutron distributions, including the depths probed. We will compare distributions at the surface and at 20 km altitude, to isolate the products of unstable particles that decay on the way up. And we will present the NEWT (Neutron Electron Water Tomography) technique, which can use electrons from neutron decay to probe regolith hydrogenation.
