Ch. Finck

Results concerning understanding and applications of timing GRPCs

Abstract Results of beam tests are reported: the so-called “efficiency puzzle” is investigated using a 0.1 mm gap GRPC operated at different pressures for isobutane gas. The influence of edge effects on the time-response function is studied for a (4×0.3 mm 2 ) -gap GRPC disk of 5 cm diameter and found to have negligible influence on resolution and tails. A design of large-scale array is elaborated for experiments requiring not only good time and position resolution but also good multi-hit capabilities.

Performance of upstream interaction region detectors for the FIRST experiment at GSI

The FIRST (Fragmentation of Ions Relevant for Space and Therapy) experiment at GSI has been designed to study carbon fragmentation, measuring 12C double differential cross sections (∂2σ/∂θ∂E) for different beam energies between 100 and 1000 MeV/u. The experimental setup integrates newly designed detectors in the, so called, Interaction Region around the graphite target. The Interaction Region upstream detectors are a 250 μm thick scintillator and a drift chamber optimized for a precise measurement of the ions interaction time and position on the target. In this article we review the design of the upstream detectors along with the preliminary results of the data taking performed on August 2011 with 400 MeV/u fully stripped carbon ion beam at GSI. Detectors performances will be reviewed and compared to those obtained during preliminary tests, performed with 500 MeV electrons (at the BTF facility in the INFN Frascati Laboratories) and 80 MeV/u protons and carbon ions (at the INFN LNS Laboratories in Catania).

Comparison of two analysis methods for nuclear reaction measurements of 12 C + 12 C interactions at 95 MeV/u for hadrontherapy

During therapeutic treatment with heavier ions like carbon, the beam undergoes nuclear fragmentation and secondary light charged particles, in particular protons and alpha particles, are produced. To estimate the dose deposited into the tumors and the surrounding healthy tissues, the accuracy must be higher than ±3% and±1 mm. Therefore, measurements are performed to determine the double differential cross-section for different reactions. In this paper, the analysis of data from 12C +12C reactions at 95 MeV/u are presented. The emitted particles are detected with ΔEthin−ΔEthick−E telescopes made of a stack of two silicon detectors and a CsI crystal. Two different methods are used to identify the particles. One is based on graphical cuts onto the ΔE−E maps, the second is based on the so-called KaliVeda method using a functional description of ΔE versus E. The results of the two methods will be presented in this paper as well as the comparison between both.

Proton computed tomography from multiple physics processes.

Proton CT (pCT) nowadays aims at improving hadron therapy treatment planning by mapping the relative stopping power (RSP) of materials with respect to water. The RSP depends mainly on the electron density of the materials. The main information used is the energy of the protons. However, during a pCT acquisition, the spatial and angular deviation of each particle is recorded and the information about its transmission is implicitly available. The potential use of those observables in order to get information about the materials is being investigated. Monte Carlo simulations of protons sent into homogeneous materials were performed, and the influence of the chemical composition on the outputs was studied. A pCT acquisition of a head phantom scan was simulated. Brain lesions with the same electron density but different concentrations of oxygen were used to evaluate the different observables. Tomographic images from the different physics processes were reconstructed using a filtered back-projection algorithm. Preliminary results indicate that information is present in the reconstructed images of transmission and angular deviation that may help differentiate tissues. However, the statistical uncertainty on these observables generates further challenge in order to obtain an optimal reconstruction and extract the most pertinent information.

The FIRST experiment for nuclear fragmentation measurements at GSI

Nuclear fragmentation processes are relevant in different fields of physics concerning both basic research and applications. FIRST (Fragmentation of Ions Relevant for Space and Therapy) is an experiment aimed at the measurement of double differential cross sections (DDCS), with respect to kinetic energy and scattering polar angle, of nuclear fragmentation processes relevant for hadron therapy and for space radiation protection applications, in the energy range between 100 and 1000 MeV/u. The experiment was mounted at the GSI laboratories of Darmstadt, in Germany. A first data taking was performed in August 2011, using 400 MeV/u 12C on carbon and gold targets. In this work we present a description of the experimental apparatus and some figures from the data acquisition and from the preliminary work on data analysis.

Search for an optimum time response of spark counters

Abstract A spark counter of the type developed by Pestov has been tested with the aim of searching for an optimum time response function, changing voltage, content of noble and quencher gases, pressure and energy-loss. Replacing the usual argon by neon has brought an improvement of the resolution and a significant reduction of tails in the time response function. It has been proven that a counter as long as 90 cm can deliver, using neon gas mixture, a time resolution σ ps with about 1% absolute tail and an efficiency of about 90%.

Study for online range monitoring with the interaction vertex imaging method

Ion beam therapy enables a highly accurate dose conformation delivery to the tumor due to the finite range of charged ions in matter (i.e. Bragg peak (BP)). Consequently, the dose profile is very sensitive to patients anatomical changes as well as minor mispositioning, and so it requires improved dose control techniques. Proton interaction vertex imaging (IVI) could offer an online range control in carbon ion therapy. In this paper, a statistical method was used to study the sensitivity of the IVI technique on experimental data obtained from the Heidelberg Ion-Beam Therapy Center. The vertices of secondary protons were reconstructed with pixelized silicon detectors. The statistical study used the [Formula: see text] test of the reconstructed vertex distributions for a given displacement of the BP position as a function of the impinging carbon ions. Different phantom configurations were used with or without bone equivalent tissue and air inserts. The inflection points in the fall-off region of the longitudinal vertex distribution were computed using different methods, while the relation with the BP position was established. In the present setup, the resolution of the BP position was about 4-5 mm in the homogeneous phantom under clinical conditions (106 incident carbon ions). Our results show that the IVI method could therefore monitor the BP position with a promising resolution in clinical conditions.

Differential cross sections measurements for hadrontherapy: 50 MeV/n 12C reactions on H, C, Al, O and natTi targets.

In order to keep the benefits of a carbon treatment, the dose and biological effects induced by secondary fragments must be taken into account when simulating the treatment plan. These Monte-Carlo simulations codes are done using nuclear models that are constrained by experimental data. It is hence necessary to have precise measurements of the production rates of these fragments all along the beam path and for its whole energy range. In this context, a series of experiments aiming to measure the double differential fragmentation cross-sections of carbon on thin targets of medical interest has been started by our collaboration. In March 2015, an experiment was performed with a 50 MeV/nucleon 12C beam at GANIL. During this experiment, energy and angular differential cross-section distributions on H, C, O, Al and nat Ti have been measured. In the following, the experimental set-up and analysis process are briefly described and some experimental results are presented. Comparisons between several exit channel models from PHITS and GEANT4 show great discrepancies with the experimental data. Finally, the homemade SLIIPIE model is briefly presented and preliminary results are compared to the data with a promising outcome.

Experiment FIRST: Fragmentation of 12 C beam at 400 MeV/u

The knowledge about fragmentation processes in ion-ion interactions is fundamental in hadrontherapy and radiation protection in space missions. Hadrontherapy, based on 12C, features many advantages with respect to conventional radiation therapy with photons due to the possibility to shape the dose delivery region in tissues but side effects of the projectile fragmentation in healthy tissues are not negligible. NASA recently pointed out that measurements for some light ions and kinetic energies are missing in nuclear fragmentation databases. FIRST experiment aims to measure the fragmentation double differential cross section of 12C in the energy range 1001000 MeV/u on several elements, constituents of organic tissues and electronic devices, in order to fill some of the mentioned lack of information on light ions. A first set of data has been taken in 2011 at GSI (Darmstadt), using 12C beam at 400 MeV/u on C and Au targets. About 3·107 events with C target and 5 · 106 with Au target were recorded. Together with these data other sets of runs have been collected to calibrate the forward part of the whole experimental setup, the ToF-Wall. The calibration procedure and the detector performances, which fit the experiment requirements for what concerns efficiency, resolution and stability, will be illustrated. Moreover, some preliminary results concerning the 12C-12C elastic scattering, in agreement with the Rutherford model, will be presented.

The KENTROS detector for identification and kinetic energy measurements of nuclear fragments at polar angles between 5 and 90 degrees

KENTROS (Kinetic ENergy and Time Resolution Optimized on Scintillator) is a relatively compact detector has been projected and constructed in the framework of the INFN FRAG and TPS experiments. KENTROS has been designed for energy deposition and time of flight measurements of charged particles. The detector ensures an angular coverage from about 5 degrees up to about 90 degrees polar angle in the laboratory frame. Recently KENTROS has been used as part of the FIRST experiment, devoted to measure double differential fragmentation cross sections, with the aim to detect light fragments produced in the nuclear fragmentation process.