Light ion fragmentation

Over the last decade, we have accumulated much fragmentation data at HIMAC, using ion beams at energies from 230 to 800 MeV/u, for species from He to Fe. The primary goal of the measurements is to improve the database of fragmentation cross sections used in transport calculations by NASA; these calculations are important for determining dose and dose equivalent received by astronauts on space missions, both current and planned. A significant dose from heavy ions in the Galactic Cosmic Rays (GCR) is unavoidable for astronauts on long-duration missions, especially in Mars exploration missions that could last up to 3 years. The many results of this long-term study are being compiled and will soon be available to other researchers through a new website that is being constructed at LBNL. The fragmentation data are taken with a stack of silicon detectors placed in the forward direction (that is, at 0deg) with respect to the incident beam. In recent runs, we have expanded our measurement team to include members from NASA-Marshall Spaceflight Center (MSFC), who have provided the 'ZDDS' to measure fragments produced at small angles with respect to the incident beam, and a group from the University of Houston. The ZDDS consists of large-area segmented silicon detectors with coverage from about 3deg to 10deg in θ and 2π in φ. The University of Houston group has provided an array of silicon strip detectors, used to count the multiplicity of charged particles in the angular range from 3deg to 45deg. The ZDDS and UH systems both have their own data acquisition systems, and integration with the LBNL system will allow us to extract differential (in angle) cross sections and to make correlations of multiplicity with the fragments measured at 0deg. In Table 1, we show a comprehensive list of data obtained at HIMAC in all our experiments to date. The cross sections measured in these data sets fill in a significant part of the fragmentation database that is needed for further development of NASA's space radiation transport codes. Cross sections are measured behind targets made of polyethylene, carbon, aluminum, copper, tin, and lead. Subtracting the carbon-target cross sections from those obtained with polyethylene (CH2) yields hydrogen-target cross sections, which are of interest in shielding and astrophysics. Analysis of cross sections has been performed on many of the data sets obtained at HIMAC, including earlier runs in the time period from 1997-2000 with 12C, 14N, and 16O beams. An article containing the Ne beam cross sections and a detailed description of the analysis method has been published. Cross sections for silicon fragmentation will also soon by published. Additional publications will be forthcoming, but in the interests of rapid dissemination of the results, it has been decided to create a web site, hosted by the LBNL group, through which all results will be available. (author)