• Nuclear fragmentation
• FOOT
• Charged particle therapy
• Charge identification
• Time-Of-Flight

Charged Particle Therapy (CPT) is an increasingly used technique in the treatment of deep-seated solid tumors. The rationale for this approach is the favorable depth-dose profile of heavy charged particles with respect to conventional X-rays. This is characterized by low energy deposition in the entrance channel, followed by a high energy release at a certain depth: the Bragg Peak. This behavior makes it possible to spare healthy tissues while delivering high dose to the tumor.
CPT represents a consolidated treatment procedure in clinical practice. Still, research is ongoing to further improve the accuracy of Treatment Planning Systems, by including advanced Monte Carlo models into the dose calculations. One of the many topics discussed in CPT is the contribution of nuclear fragmentation processes to beam dose profiles in both proton and heavy ion therapy. While in proton therapy the short-range recoil nuclei generated in target fragmentation processes could lead to an increased dose in the entrance channel, in ion therapy projectile fragments generate an additional dose tail behind the Bragg Peak. However, it is difficult to exactly evaluate the contribution of fragmentation products to total dose distributions because of the lack of experimental cross section data in the energy range of CPT.
The aim of the FOOT (FragmentatiOn Of Target) experiment is to measure the double differential cross section of nuclear fragmentation processes relevant for CPT. The apparatus will exploit inverse and direct kinematics to accurately characterize both target and projectile fragmentations. To achieve this goal, the system needs to measure the mass, charge, velocity and energy of the nuclear fragments produced by different beams impinging on tissue-like targets.
This thesis focuses on the development and validation of the charge (Z) identification procedure, based on energy deposition (∆E) and Time-Of-Flight (T OF ) measurements performed with the Start Counter (STC) and TOF-Wall (TW) of FOOT. The former is a thin foil of plastic scintillator, while the latter is made of two orthogonal layers of 20 scintillating bars each. These two detectors provide the ∆E (TW) and T OF (TW and STC) values needed to calculate the Z of nuclear fragments traveling through FOOT.
The data analyzed in this work have been acquired during two test beam data takings performed in early 2019. The first one was carried out at CNAO (Centro Nazionale di Adroterapia Oncologica, Pavia) and was dedicated to energy and T OF calibration measurements with protons (60 MeV) and carbon ions (115, 260, 400 MeV/u). The second data taking was performed at GSI Helmoltz Centre for Heavy Ion Research (Darmstadt, Germany). In this case, an oxygen ion beam (400 MeV/u) was used in different acquisitions to both calibrate the detectors and observe the nuclear fragmentations on a 5 mm graphite target.
In this work, data analysis software has been developed to process the raw detector signals. The resulting quantities are then compared to Monte Carlo simulations to calibrate the detectors in terms of both ∆E and T OF . Furthermore, the β of the particles is retrieved from T OF and calibrated data are used to calculate the Z of nuclear fragments through the Bethe-Bloch formula. A direct comparison with Monte Carlo results is also presented as a validation of the procedure. Using the developed reconstruction and analysis framework, the ∆E and TOF measurements have shown energy and time resolution of a few MeV and 50-80 ps respectively. The resulting Z values have been reconstructed with an uncertainty of 2 to 6%, in agreement with the requirements of FOOT.