Ion charge separation with new generation of nuclear emulsion films

n hadron therapy, the accelerated ions, interacting with the body of the patient, cause the fragmentation of both projectile and target nuclei. The fragments interact with the human tissues depositing energy both in the entrance channel and in the volume surrounding the tumor. The knowledge of the fragments features is crucial to determine the energy amount deposited in the human body, and - hence - the damage to the organs and to the tissues around the tumor target. The FOOT (FragmentatiOn Of Target) experiment aims at studying the fragmentation induced by the interaction of a proton beam (150 -250 MeV/n) inside the human body. The FOOT detector includes an electronic setup for the identification of Z >= 3 fragments integrated with an emulsion spectrometer to measure Z <= 3 fragments. Charge identification by nuclear emulsions is based on the development of techniques of controlled fading of the particle tracks inside the nuclear emulsion, that extend the dynamical range of the films developed for the tracking of minimum ionising particles. The controlled fading strongly depends on temperature, relative humidity and treatment duration. In this study the performances in terms of charge separation of proton, helium and carbon particles, obtained on a batch of new emulsion films produced in Japan are reported.