L. Pinsky

Overview of the Martian radiation environment experiment.

Space radiation presents a hazard to astronauts, particularly those journeying outside the protective influence of the geomagnetosphere. Crews on future missions to Mars will be exposed to the harsh radiation environment of deep space during the transit between Earth and Mars. Once on Mars, they will encounter radiation that is only slightly reduced, compared to free space, by the thin Martian atmosphere. NASA is obliged to minimize, where possible, the radiation exposures received by astronauts. Thus, as a precursor to eventual human exploration, it is necessary to measure the Martian radiation environment in detail. The MARIE experiment, aboard the 2001 Mars Odyssey spacecraft, is returning the first data that bear directly on this problem. Here we provide an overview of the experiment, including introductory material on space radiation and radiation dosimetry, a description of the detector, model predictions of the radiation environment at Mars, and preliminary dose-rate data obtained at Mars.

The application of FLUKA to dosimetry and radiation therapy

The FLUKA Monte Carlo code has been evolving over the last several decades and is now widely used for radiation shielding calculations. In order to facilitate the use of FLUKA in dosimetry and therapy applications, supporting software has been developed to allow the direct conversion of the output files from standard CT-scans directly into a voxel geometry for transport within FLUKA. Since the CT-scan information essentially contains only the electron density information over the scanned volume, one needs the specific compositions for each voxel individually. We present here the results of a simple algorithm to assign tissues in the human body to one of four categories: soft-tissue, hard-bone, trabecular-bone and porous-lung. In addition, we explore the problem of the pathlength distributions in porous media such as trabecular bone. A mechanism will be implemented within FLUKA to allow for variable multipal fixed density materials to accommodate the pathlength distributions discovered.

Simulation of Space Shuttle neutron measurements with FLUKA

FLUKA is an integrated particle transport code that has enhanced multigroup low-energy neutron transport capability similar to the well-known MORSE transport code. Gammas are produced in groups but many important individual lines are specifically included, and subsequently transported by the main FLUKA routines which use a modified version of EGS4 for electromagnetic (EM) transport. Recoil protons are also transported by the primary FLUKA transport simulation. The neutron cross-section libraries employed within FLUKA were supplied by Giancarlo Panini (ENEA, Italy) based upon the most recent data from JEF-1, JEF-2.2, ENDF/B-VI, JENDL-3, etc. More than 60 different materials are included in the FLUKA databases with temperature ranges including down to cryogenic temperatures. This code has been used extensively to model the neutron environments near high-energy physics experiment shielding. A simulation of the Space Shuttle based upon a spherical aluminum equivalent shielding distribution has been performed with reasonable results. There are good prospects for extending this calculation to a more realistic 3-D geometrical representation of the Shuttle including an accurate representation of its composition, which is an essential ingredient for the improvement of the predictions. A proposed project to develop a combined analysis and simulation package based upon FLUKA and the analysis infrastructure provided by the ROOT software is under active consideration. The code to be developed for this project will be of direct application to the problem of simulating the neutron environment in space, including the albedo effects.

Modelling human exposure to space radiation with different shielding: The FLUKA code coupled with anthropomorphic phantoms

Astronauts exposure to the various components of the space radiation field is of great concern for long-term missions, especially for those in deep space such as a possible travel to Mars. Simulations based on radiation transport/interaction codes coupled with anthropomorphic model phantoms can be of great help in view of risk evaluation and shielding optimisation, which is therefore a crucial issue. The FLUKA Monte Carlo code can be coupled with two types of anthropomorphic phantom (a mathematical model and a voxel model) to calculate organ-averaged absorbed dose, dose equivalent and biological dose under different shielding conditions. Herein the biological dose is represented by the average number of Complex Lesions (CLs) per cell in a given organ. CLs are clustered DNA breaks previously calculated by means of event-by-event track structure simulations at the nm level and integrated on-line into FLUKA, which adopts a condensed-history approach; such lesions have been shown to play a fundamental role in chromosome aberration induction, which in turn can be correlated with carcinogenesis. Examples of calculation results will be presented relative to Galactic Cosmic Rays, as well as to the August 1972 Solar Particle Event. The contributions from primary ions and secondary particles will be shown separately, thus allowing quantification of the role played by nuclear reactions occurring in the shield and in the human body itself. As expected, the SPE doses decrease dramatically with increasing the Al shielding thickness; nuclear reaction products, essentially due to target fragmentation, are of minor importance. A 10 g/cm2 Al shelter resulted to be sufficient to respect the 30-day limits for deterministic effects recommended for missions in Low Earth Orbit. In contrast with the results obtained for SPEs, the calculated GCR doses are almost independent of the Al shield thickness, and the GCR doses to internal organs are not significantly lower than the skin doses. Furthermore, nuclear interactions play a much larger role for GCR than for SPE doses.

The hadronic models for cosmic ray physics: the FLUKA code solutions

FLUKA is a general purpose Monte Carlo transport and interaction code used for fundamental physics and for a wide range of applications. These include Cosmic Ray Physics (muons, neutrinos, EAS, underground physics), both for basic research and applied studies in space and atmospheric flight dosimetry and radiation damage. A review of the hadronic models available in FLUKA and relevant for the description of cosmic ray air showers is presented in this paper. Recent updates concerning these models are discussed. The FLUKA capabilities in the simulation of the formation and propagation of EM and hadronic showers in the Earth’s atmosphere are shown.

A very high momentum particle identification detector

Abstract.A new detector concept has been investigated to extend the capabilities of heavy-ion collider experiments, represented here through the ALICE detector, in the high transverse momentum (pT region. The resulting Very High Momentum Particle Identification Detector (VHMPID) performs charged hadron identification on a track-by-track basis in the 5 GeV/c < p < 25 GeV/c momentum range and provides heavy-ion experiments with new opportunities to study parton-medium interactions at RHIC and LHC energies, where the creation of deconfined quark-gluon matter has been established. The detector is based on novel advances to the pressurized gaseous ring imaging Cherenkov (RICH) concept, which yield a very compact, high resolution addition to existing heavy-ion experiments. We conclude that in order for the device to yield statistically significant results not only for single particle measurements, but also for di-hadron and jet-tagged correlation studies, it has to cover contiguously up to 30% of a central barrel detector in radial direction. This will allow, for the first time, identified charged hadron measurements in jets. In this paper we summarize the physics motivations for such a device, as well as its conceptual design, layout, and integration into ALICE.

Heavy-ion collisions: preliminary results of a new QMD model coupled with FLUKA

Quantum Molecular Dynamics (QMD) models are considered viable tools to simulate the initial hot stages of heavy-ion collisions and investigate the properties of the nuclear matter equation of state. A new QMD model has been developed by scratch by our group during the last few years and recently coupled to the FLUKA fission/Fermi breakup/ evaporation module which describes the latest stage of the reactions, when slower processes leading nuclei to the equilibrium occur. Comparisons with experimental data collected both in symmetric and in asymmetric collisions are shown, covering a wide range of projectile and target masses. Reproduction of the experimental light particle (Z < 3) yields is one of the most difficult challenges to be met by QMD models, traditionally prone to underestimate a particle emission while dramatically overestimating proton and neutron emission. Our results seem to be quite satisfactory with respect to this issue, thanks to the form of the potential terms involved in the nucleon-nucleon interaction and to many refinements applied in the fragment definition scheme, based on the potential which each particle experiences because of its neighbors. Nucleon isospin is taken into account all over the simulation, as well as the experimental binding energy constraints on nuclear states. The introduction of further refinements to describe pre-equilibrium processes is under development.

Carbon induced reactions at low incident energies

Accurate knowledge of the reactions which occur when two heavy ions interact is of importance in many trans-disciplinary fields, particularly in cancer therapy and space radiation protection. In these cases one needs to know what happens in a natural process to which all possible reaction mechanisms contribute and thus a theoretical calculation, to be really usable, must indeed be able to reproduce large sets of data in wide energy and mass ranges. We show here the results of an analysis of the spectra of intermediate mass fragments produced in the C + Al interaction at 13 MeV/n, both in direct and inverse kinematics, which supplies a very reasonable reproduction of a great number of data providing useful information on the leading reaction mechanisms.

A Monte Carlo approach to study neutron and fragment emission in heavy-ion reactions

Abstract Quantum Molecular Dynamics models (QMD) are Monte Carlo approaches targeted at the description of nucleon–ion and ion–ion collisions. We have developed a QMD code, which has been used for the simulation of the fast stage of ion–ion collisions, considering a wide range of system masses and system mass asymmetries. The slow stage of the collisions has been described by statistical methods. The combination of both stages leads to final distributions of particles and fragments, which have been compared to experimental data available in the literature. A few results of these comparisons, concerning neutron double-differential production cross-sections for C, Ne and Ar ions impinging on C, Cu and Pb targets at 290–400xa0MeV/A bombarding energies and fragment isotopic distributions from Xexa0+xa0Al at 790xa0MeV/A, are shown in this paper.

FLUKA status and preliminary results from the July-2005 AGS run

As reported in 2005 Aerospace Conference, the FLUKA Monte Carlo code is being modified as part of NASAs Space Radiation Shielding Program for use in simulating the space radiation environment, in order to evaluate the properties of spacecraft and habitat shielding. Since the last workshop, several notable enhancements have been made to the FLUKA code itself and the ancillary support software. These include improvements to the GUI-based packages for analysis of the results as well as GUI-based tools to ease the setup and running of the programs. Examples of these are presented. From the physics perspective, an accelerator run this July at the AGS was undertaken in collaboration with the groups from LBL and MSFC to measure the fragmentation, neutron and secondary charged particle spectra from Fe, Si and C beams at 3, 5 and 10 GeV/A on a variety of targets including C, Al, Fe, Cu and polyethylene. This energy range is the crossover point in event generator technique and the data help guide the evolution of the event generators in this crucial region. Preliminary results from this run is presented for the angular distribution of the secondary charged particles from scattering angles of 3-45 degrees along with normalized comparisons to RQMD and DPMJET, the event generators that are currently employed within FLUKA