Analysis and interpretation of Carbon ion fragmentation in the Bragg peak energy range

Abstract

Hadrontherapy is the treatment of tumours with Protons (p), or heavier ions like Carbon (C) and Oxygen (O). It is based on the fact that ionising radiation is used to kill tumour cells. One of the advantages of heavy ions compared to conventional radiotherapy is the characteristic behaviour of the energy deposition, which peaks only when the particles are very close to the stopping point, called Bragg peak. The Hadrontherapy is becoming one of the main therapies for the treatment of some malignant neoplasms. Compared to Proton therapy, C therapy has considerable advantages, even though C ions could fragment. In this work the exclusive quasi-elastic fragmentation reaction 12C+x !8 Be+ is studied at the energy of 33MeVu−1 of projectiles, which is the dominant reaction at this energy. The importance of this energy domain relies on the fact that it is the typical value where the fast rise of the energy deposition starts, just before the Bragg peak. Different target materials, namely Carbon, Gold and Niobium, have been used in the present work. In all the cases a contamination of H in the targets has been found. This contamination observed explains the excess of high energy a in the data. The reaction responsible for such an excess, 12C + p !9 B + , has been added to the FLUKA Monte Carlo simulation (MC) code as a pre-equilibrium stage channel of the (p,a) reaction. The identification and the description of the pre-equilibrium reaction in the MC allowed a significant improvement in the comparison between data and MC. This allowed to identify and reduce the background due to the H contamination in the process under investigation and measure its cross section as a function of the fragments’ energy and emission angles.