In this work, we report on systematic Monte Carlo (MC) studies for the FRACAS apparatus, a large acceptance mass spectrometer that will be used to measure the fragmentation cross sections of 12C ions for hadrontherapy. The apparatus, placed in a 100 mbar reaction chamber, will be made of a beam monitor, trackers surrounding a magnet and a Time-Of-Flight (TOF) wall. In order to determine the required performances of the trackers, Geant4 simulations of the whole system and in-house developed algorithms were used. While keeping the beam monitor and TOF-wall positions fixed, the effects of the tracker positions and spatial resolutions on the trajectory reconstruction and mass identification efficiencies have been extracted. An optimal configuration was found where the upstream trackers should be located 6 cm away from the target and spaced 4 cm apart whereas their spatial resolutions should be close to 100 \textmu m. The positions of the downstream trackers will have to be changed according to the beam energy to preserve high identification efficiencies. Their spatial resolutions, even though of a lesser importance compared to the upstream trackers, should be around 1 mm or better. In this optimal configuration, an overall fragment identification efficiency above 90% has been obtained for beam energies ranging from 100 to 400 MeV/nucleon.
A: The FRAgmentation of CArbon and cross Sections large acceptance mass spectrometer will be used to measure the double differential fragmentation cross sections of a 12 C beam in the context of hadrontherapy. The particle identification and the measure of their kinetic energy will be ensured by a time-of-flight appartus. It will be composed of a Parallel Plate Avalanche Counter as the start detector whereas scintillating detectors will ensure the measure of the stop as well as the position and the released energy of the fragments. In this work, we report on the timing performances of this system in terms of Coincidence Resolving Time. The performances evaluated should lead to the identification of all the fragments produced by the interaction of 12 C ions with thin targets of medical interest for energies up to 400 MeV/nucleon.
K: Instrumentation for hadron therapy; Instrumentation and methods for time-of-flight (TOF) spectroscopy; Mass spectrometers; Timing detectors 1Corresponding author.
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