Dr Marco Toppi (infn)
The study of the nuclear fragmentation processes occuring in the interaction of highly energetic ions in matter is of great interest both in basic research (e.g. to improve the understanding of hadronic showers development in the atmosphere) and in applied physics, in particular in cancer therapy and space radiation protection fields. Accurate measurements of fragmentation cross sections of light ions interacting with elemental and composite targets are crucials to benchmark and improve the nuclear interaction models implemented in Monte Carlo (MC) simulation codes. In order to provide the necessary experimental input to MC simulations, a small set of measurements can be used: the interpolation of cross sections for different energies and target materials composition allows, starting from a selected number of target/energy combinations, to build a model covering all the application needs. The current agreement between predictions of nuclear interaction models implemented in MC codes and experimental data is encouraging but there is still room for improvement, mainly due to the lack of available data and to their limited precision. So far, only yields or total and partial charge-changing fragmentation cross sections have been measured with high precision and in a variety of target and beam energy configurations. However the most valuable results, the double differential cross section measurements, that would allow a stringent test of the nuclear model predictions, are still missing. In particular, while the fluences and the total cross sections are currently well described, the production of light fragments and their angular distribution is affected by large uncertainties and different algorithms are predicting yields that can differ up to an order of magnitude. The NASA recently completed a survey of a large data base  of measured nuclear fragmentation cross sections including approximately 50000 datasets, and concluded that several experimental data are missing, including double differential cross sections for carbon ions at energies below 400 MeV/nucleon. The FIRST (Fragmentation of Ions Relevant for Space and Therapy) experiment at the Helmholtz Center for Heavy Ion research (GSI) was designed and built by an international collaboration from France, Germany and Italy in order to perform precise measurements of the fragmentation cross sections of a 12C ion beam with different thin targets. The experiment main purpose was to measure the fragmentation double differential cross sections at different angles and energies between 100 and 1000 MeV/nucleon, of interest for applications in particle therapy and radio-protection in space. In this contribution we present the analysis of data collected with the FIRST apparatus using a 12C beam of 400 MeV/nucleon impinging on a 0.5 mm Au target. The experimental setup was optimized to study two distinct angular regions: the small angle region (subject of this contribution), where fragments are produced with a polar angle (theta) with respect to the impinging beam direction (z axis) smaller than 5◦ and a large angle region with theta between 5◦ and 40◦. The analysis techniques used for the fragments reconstruction in the forward angular region and the results of the elemental and isotopic single differental cross sections with respect to fragment angle and energy will be discussed. The obtained results will be compared with the available experimental results. The comparison with a detailed FLUKA MC simulation will be reported as well.  J. W. Norbury, J. Miller et al., Review f Nuclear Physics Experiments for Space Radiation, NASA/TP2011- 217179, (2011).
Dr Marco Toppi (infn)