V. Andersen

Overview of the Martian radiation environment experiment.

Space radiation presents a hazard to astronauts, particularly those journeying outside the protective influence of the geomagnetosphere. Crews on future missions to Mars will be exposed to the harsh radiation environment of deep space during the transit between Earth and Mars. Once on Mars, they will encounter radiation that is only slightly reduced, compared to free space, by the thin Martian atmosphere. NASA is obliged to minimize, where possible, the radiation exposures received by astronauts. Thus, as a precursor to eventual human exploration, it is necessary to measure the Martian radiation environment in detail. The MARIE experiment, aboard the 2001 Mars Odyssey spacecraft, is returning the first data that bear directly on this problem. Here we provide an overview of the experiment, including introductory material on space radiation and radiation dosimetry, a description of the detector, model predictions of the radiation environment at Mars, and preliminary dose-rate data obtained at Mars.

The application of FLUKA to dosimetry and radiation therapy

The FLUKA Monte Carlo code has been evolving over the last several decades and is now widely used for radiation shielding calculations. In order to facilitate the use of FLUKA in dosimetry and therapy applications, supporting software has been developed to allow the direct conversion of the output files from standard CT-scans directly into a voxel geometry for transport within FLUKA. Since the CT-scan information essentially contains only the electron density information over the scanned volume, one needs the specific compositions for each voxel individually. We present here the results of a simple algorithm to assign tissues in the human body to one of four categories: soft-tissue, hard-bone, trabecular-bone and porous-lung. In addition, we explore the problem of the pathlength distributions in porous media such as trabecular bone. A mechanism will be implemented within FLUKA to allow for variable multipal fixed density materials to accommodate the pathlength distributions discovered.

FLUKA status and preliminary results from the July-2005 AGS run

As reported in 2005 Aerospace Conference, the FLUKA Monte Carlo code is being modified as part of NASAs Space Radiation Shielding Program for use in simulating the space radiation environment, in order to evaluate the properties of spacecraft and habitat shielding. Since the last workshop, several notable enhancements have been made to the FLUKA code itself and the ancillary support software. These include improvements to the GUI-based packages for analysis of the results as well as GUI-based tools to ease the setup and running of the programs. Examples of these are presented. From the physics perspective, an accelerator run this July at the AGS was undertaken in collaboration with the groups from LBL and MSFC to measure the fragmentation, neutron and secondary charged particle spectra from Fe, Si and C beams at 3, 5 and 10 GeV/A on a variety of targets including C, Al, Fe, Cu and polyethylene. This energy range is the crossover point in event generator technique and the data help guide the evolution of the event generators in this crucial region. Preliminary results from this run is presented for the angular distribution of the secondary charged particles from scattering angles of 3-45 degrees along with normalized comparisons to RQMD and DPMJET, the event generators that are currently employed within FLUKA

Event generators for simulating heavy ion interactions to evaluate the radiation risks in spaceflight

Simulating the space radiation environment with Monte Carlo codes, such as FLUKA, requires the ability to model the interactions of heavy ions as they penetrate spacecraft and crew members bodies. Monte-Carlo-type transport codes use total interaction cross sections to determine when a particular type of interaction has occurred. Then, at that point, a distinct event generator is employed to determine separately the results of that interaction. The space radiation environment contains a full spectrum of radiation types, including relativistic nuclei, which are the most important component for the evaluation of crew doses. Interactions between incident protons with target nuclei in the spacecraft materials and crew members bodies are well understood. However, the situation is substantially less comfortable for incident heavier nuclei (heavy ions). We have been engaged in developing several related heavy ion interaction models based on a quantum molecular dynamics-type approach for energies up through about 5 GeV per nucleon (GeV/A) as part of a NASA consortium that includes a parallel program of cross section measurements to guide and verify this code development

Progress towards a FLUKA based simulation tool aimed at the evaluation of space radiation environments

Goal of the NASA funded FLEUR project is to develop a simulation tool to predict the impact of radiation environments, in particular to evaluate the effect of shielding in space applications. The heart of this tool is the FLUKA Monte Carlo transport code which is traditionally used in related areas of research such as radio‐protection and dosimetry, cosmic ray physics and modeling of biological effects of radiation on DNA (in connection with further external micro codes). An important aspect in this context are heavy ion nuclear interactions which at this point have been implemented in FLUKA for high and medium energies while work is proceeding to cover the low energy range. Further information is available at http://www.fluka.org and http://fleur.cern.ch