Calibration of the Large Hodoscope ToF-Wall and Preliminary Results of the FIRST Experiment

Hadron therapy is an alternative way of treating cancerous tumors. It consists of irradiating tumors with protons (proton therapy) or light nuclei (alphas, carbon ions). The study of fragmentation processes is relevant for different fields of the physics concerning both basic research and applications. The energy range that is accessible at Heavy Ion Synchrotron SIS is of fundamental importance for shielding in space radiations, hadron-therapy and is interesting for different aspects exploring nuclear physics. The FIRST (Fragmentation of Ions Relevant for Space and Therapy) experiment has been designed to study nuclear fragmentation processes in the energy range between 100 and 1000 MeV/u (Mega Electron Volt per nucleon), measuring double differential cross sections, with respect to kinetic energy and scattering polar angle. This experiment was carried because there is a strong need of high-quality experimental data concerning C-12, O-16 and Fe-56 fragmentation on different targets. The first data taking has been performed at SIS accelerator facility of GSI Laboratory in Darmstadt (Germany) during August 2011 and a set of data has been collected using a 400 MeV/u carbon beam impinging on carbon and gold targets. This experiment helps not only for comparison purposes but also for the evolution of the space IC (Integrated Circuits) radiation damage evaluation. The experimental apparatus is based on both newly designed detectors placed around the target and on an already existing setup made of the ALADiN dipole magnet, the TP-MUSIC IV tracking ionization chamber, the ToF-Wall scintillator array and the LAND neutron detector. The above mentioned instruments have been integrated with new ones specifically designed for interaction region few centimeters around the target: a Start Counter (SC) based on a plastic scintillator, a drift chamber as Beam Monitor (BM), an automated mechanical system as a target holder, a silicon pixel detector Vertex to track charged fragments emerging from the target and a large-angle light fragment detector based on thick scintillators with solid photomultiplier, KENTROS (Kinetic Energy and Time Resolution Optimized on Scintillator). Most of the projectile fragments are produced in the forward direction, within small angles with respect to the beam direction and with velocities very close to those of carbon ions impinging on the target. The trajectories of these charged fragments fall within the ALADiN acceptance and, after magnetic bending, hit the ToF-Wall detector which enables measurements of the impinging point, arrival time and energy released in the scintillator array. In particular, we report performances and preliminary results obtained from ToF-Wall data analysis. This experiment will provide information about the secondary effects of nuclear fragments in healthy biological cells.