G. Raciti

Carbon fragmentation measurements and validation of the Geant4 nuclear reaction models for hadrontherapy

Nuclear fragmentation measurements are necessary when using heavy-ion beams in hadrontherapy to predict the effects of the ion nuclear interactions within the human body. Moreover, they are also fundamental to validate and improve the Monte Carlo codes for their use in planning tumor treatments. Nowadays, a very limited set of carbon fragmentation cross sections are being measured, and in particular, to our knowledge, no double-differential fragmentation cross sections at intermediate energies are available in the literature. In this work, we have measured the double-differential cross sections and the angular distributions of the secondary fragments produced in the (12)C fragmentation at 62 A MeV on a thin carbon target. The experimental data have been used to benchmark the prediction capability of the Geant4 Monte Carlo code at intermediate energies, where it was never tested before. In particular, we have compared the experimental data with the predictions of two Geant4 nuclear reaction models: the Binary Light Ions Cascade and the Quantum Molecular Dynamic. From the comparison, it has been observed that the Binary Light Ions Cascade approximates the angular distributions of the fragment production cross sections better than the Quantum Molecular Dynamic model. However, the discrepancies observed between the experimental data and the Monte Carlo simulations lead to the conclusion that the prediction capability of both models needs to be improved at intermediate energies.

Light ions response of silicon carbide detectors

Abstract Silicon carbide (SiC) Schottky diodes 21 μ m thick with small surfaces and high N-dopant concentration have been used to detect alpha particles and low-energy light ions. In particular 12 C and 16 O beams at incident energies between 5 and 18xa0MeV were used. The diode active-region depletion-thickness, the linearity of the response, energy resolution and signal rise-time were measured for different values of the applied reverse bias. Moreover, the radiation damage on SiC diodes irradiated with 53xa0MeV 16 O beam has been explored. The data show that SiC material is radiation harder than silicon but at least one order of magnitude less hard than epitaxial silicon diodes. An inversion in the signal was found at a fluence of 10 15 ions / cm 2 .

Systematic trends of the element distributions in light heavy ion dissipative processes. Charge variance systematics revisited

Abstract Experimental and model dependent correlations between the variance of the element distribution and the total kinetic energy loss (TKEL) or entrance channel impact parameter in light heavy ion dissipative processes at low energy are established. The present results and data for much heavier systems are used to revisit the systematics of the charge variance as a function of the ratio between TKEL and the grazing angular momentum (lgr).

Global features of dissipative processes in light heavy-ion collisions

Abstract The 19 F + 27 Al and 19 F + 12 C collisions at incident energies of 111.4, 125, 136.9 MeV and 111.4, 136.9 MeV respectively, have been studied. Continuous energy and angular distributions for 5≤ Z ≤16 reaction products have been measured. The correlations between different physical observables show similar trends with the case of much heavier interacting systems. Thus, a complete dynamics, from quasielastic to complete dissipation regime, is evidenced also in the reactions between light nuclei. The interaction time, extracted from the experimental angular distributions, increases with increasing total kinetic energy loss from 10 −23 s up to 10 −21 s. Based on simple assumptions about the underlying microscopic reaction mechanisms, semiempirical relationships are suggested and applied to account for the systematic features of the element distributions measured in light-, medium- and heavy-nuclei collisions. Absolute cross sections for reaction and nonfusion processes are deduced from the experimental data. Comparison with microscopic dynamical models is presented.

2He DECAY FROM EXCITED STATES: THE 18Ne CASE

Two-proton radioactivity studies have been performed on excited states of 18Ne produced by 20Ne fragmentation at the FRIBs facility of the Laboratori Nazionali del Sud. The study of the relative-momentum correlations of the two protons allowed to disentangle the diproton, democratic and sequential decay contributions to the 2p emission. In order to extend the study on two-proton decay to other light-masses nuclei, an upgrade of the FRIBs facility is planned. A new configuration of the Fragment Separator would be able to increase the acceptance of the beam line and therefore the yield of the produced radioactive beams. Also the present tagging setup will be modified in view of the gain intensity, in order to sustain the higher foreseen incoming rate. Status and perspectives of the facility will be presented.

Heavy ions fragmentations measurements at intermediate energies in hadrontherapy and spatial vehicles shielding

The study of the nuclear fragmentation process involves many fields of interest, from the hadrontherapy, the new frontier for cancer therapy, to the spatial vehicles shielding design, to work safely in space with acceptable risks from galactic cosmic ray. Indeed, the measure of the fragmentation cross sections is an important information to estimate how this process modifies dose distributions and biological effectiveness. At present, simulations with analytical codes are used to deal with these problems. Such approach presents considerable uncertainty, especially because of a reduced number of experimental data, both on the fragmentation cross sections and on the different radiation biological effectiveness. All these reasons claimed more fragmentation cross section data, in a wide energy range and with different ions and materials.

Nuclear fragmentation measurements for hadrontherapy and space radiation protection

Nuclear fragmentation measurements are necessary in hadrontherapy and space radiation protection, to predict the effects of the ion nuclear interactions within the human body. Nowadays, a very limited set of carbon fragmentation cross sections has been measured and in particular, to our knowledge, no double differential fragmentation cross sections at intermediate energies are available in literature. We have measured the double differential cross sections and the angular distributions of the secondary fragments produced in the 12C fragmentation at 62 AMeV on a thin carbon target. The experimental data have been also used to benchmark the prediction capability of the Geant4 Monte Carlo code at intermediate energies, where it was never tested before.

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.

The FRIBs upgrade at LNS

The FRIBs facility at the Laboratori Nazionali del Sud produces, since 2001, Radioactive Ion Beams (RIBs) at intermediate energies by projectile fragmentation. Using such beams nuclear physics experiments of international relevance have been accomplished so far. The fragments of interest are selected along the extraction line of the superconducting cyclotron, configured as a fragment separator. RIBs rates up to 105 ion/sec on target have been successfully achieved by a cyclotron primary current up to 600 enA. However a possible upgrade of the production and selection system has been studied and it is going to be realized in the next months. Features of the upgrade and the expected improvements in RIBs production yields and transmission are reported.

17F breakup reactions: A touchstone for indirect measurements

Dissociation has become an essential tool in several domains of nuclear physics. It provides useful information about the structure of halo nuclei, and Coulomb breakup can be used as an indirect method to measure radiative-capture cross sections at stellar energies. Though simple it may seem, this indirect technique relies on peculiar assumptions. Recent theoretical analyses of the Coulomb breakup of 8B have shown that these assumptions are not all satisfied. Whereas many experimental investigations on such a phenomenon have been conducted on 8B, the case of 17F has been poorly addressed up to now. An exclusive study of 17F breakup reactions has thus been performed at the FRIBs facility of the Laboratori Nazionali del Sud, Catania (Italy). The experimental setup and the detector systems allowed the measurement, event-by-event, of the X-Y coordinates of the interaction point on the target as well as the momenta and angles of all outgoing decay particles with a geometrical efficiency of 72% and a resolution of approximately 300 keV. The first results and preliminary model comparison are reported.