Search

Accurate nuclear data provide an essential foundation for advances in a wide range of fields, including nuclear energy, nuclear safety and security, safeguards, nuclear medicine, and planetary and space exploration. In these and other critical domains, outdated, imprecise, and incomplete nuclear data can hinder progress, limit precision, and compromise safety. Similar nuclear data needs are shared by many applications, thus prioritizing these needs is especially important and urgently needed. Many levels of analysis are required to prepare nuclear measurements for employment in end-user applications. Because research expertise is typically limited to one level, collaboration across organizations and international borders is essential. This perspective piece provides the latest advances in nuclear data for applications and describes an outlook for both near- and long-term progress in the field.

Most accelerator-based space radiation experiments have been performed with single ion beams at fixed energies. However, the space radiation environment consists of a wide variety of ion species with a continuous range of energies. Due to recent developments in beam switching technology implemented at the NASA Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory (BNL), it is now possible to rapidly switch ion species and energies, allowing for the possibility to more realistically simulate the actual radiation environment found in space. The present paper discusses a variety of issues related to implementation of galactic cosmic ray (GCR) simulation at NSRL, especially for experiments in radiobiology. Advantages and disadvantages of different approaches to developing a GCR simulator are presented. In addition, issues common to both GCR simulation and single beam experiments are compared to issues unique to GCR simulation studies. A set of conclusions is presented as well as a discussion of the technical implementation of GCR simulation.

Radiation risk management for human space missions depends on accurate modeling of high-energy heavy ion transport in matter. The process of nuclear fragmentation can play a key role in reducing both the physical dose and the biological effectiveness of the radiation encountered in deep space. Hydrogenous materials and light elements are expected to be more effective shields against the deleterious effects of Galactic Cosmic Rays (GCR) than aluminum, which is used in current spacecraft hulls. NASA has chosen polyethylene, CH2, as the reference material for accelerator-based radiation testing of multi-function composites that are currently being developed. A detailed discussion of the shielding properties of polyethylene under a variety of relevant experimental conditions is presented, along with Monte Carlo simulations of the experiments and other Monte Carlo calculations in which the entire GCR flux is simulated. The Monte Carlo results are compared to the accelerator data and we assess the usefulness of 1 GeV/amu 56Fe as a proxy for GCR heavy ions. We conclude that additional accelerator-based measurements with higher beam energies would be useful.

The design of future spacecraft such as the Crew Exploration Vehicle must take into account the radiation shielding properties of both the structural components as well as dedicated shielding materials. Since modest depths of shielding stop the vast majority of Solar Energetic Particles (SEP), the greater challenge is posed by the need to shield crew from the Galactic Cosmic Rays (GCR), which include highly-charged and highly-energetic particles. Here, we report on results from tests performed with beams of 1 GeV/nuc 56Fe at the Brookhaven National Laboratory. A wide variety of targets, both elemental and composite, were placed in the particle beams, and the spectra of particles emerging from the targets were measured using a stack of silicon detectors. Results are presented primarily in terms of dose reduction per g cm-2 of target material, and support the conclusions of an earlier calculation by Wilson et al. showing that performance improves as the shield's mass number decreases, with hydrogen being by far the most effective. The data also show that, as depth increases, the incremental benefit of adding shielding decreases, particularly for aluminum and other elements with higher atomic mass numbers.

This report describes the highlights and progress made in a program of measurements studying radiation transport through materials of interest to NASA. All measurements were preformed at accelerator facilities, primarily using GCR-like heavy-ion beams incident upon various elemental and composite targets. Both primary and secondary particles exiting the target were measured. The secondary particles include both charged particles and neutrons. These measurements serve as useful benchmarks and input to transport model calculations.

As humanity prepares for extended lunar exploration, understanding the radiation environment on the Moon is important for astronaut safety. This study utilized the Particle and Heavy-Ion Transport code System (PHITS), a stochastic Monte Carlo-based radiation transport code, to simulate the radiation environment inside a habitat, focusing on the impact of galactic cosmic rays (GCRs) interacting with local lunar and habitat material, and to calculate the effective dose equivalent. Placing a lunar base in a crater can provide additional shielding by reducing the GCR flux incident on the base. Furthermore, the secondary radiation field created by GCR interactions may be altered by the local topological features. GCR transport calculations were performed for a hypothetical base on a flat surface and in shallow and deep craters to determine the overall efficacy in dose reduction gained by placing a base in a 100 m diameter crater. Our findings indicate that the depth of lunar habitats significantly influences the effective dose equivalent, with deeper locations offering substantial protection. Specifically, alongside a crater wall at a deep depth (15 m), in solar minimum conditions, the total dose was reduced by approximately 44.9% compared to the dose at the surface. Similarly, at a shallow depth (5 m), a reduction of approximately 10.7% was observed. As the depth of the crater increased, the neutron contribution to the total dose also increased. Comparing the simulated doses to NASA's lifetime exposure limits provides insights into mission planning and astronaut safety, emphasizing the importance of strategic habitat placement and design. [ABSTRACT FROM AUTHOR]

In March 2016 accelerator-based experiments colliding protons (0.4 and 0.8 GeV), helium (0.4 AGeV) and iron (0.4 and 0.8 AGeV) on thick aluminum targets with surface densities of 20, 40, and 60 g/cm2 were performed at the National Aeronautics and Space Administration Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory. Two targets were utilized in each experimental configuration. Hydrogen and helium ions were detected using organic liquid scintillators in conjunction with thin plastic scintillators at 10°, 30°, 45°, 60°, 80°, and 135° from beam axis. Time-of-flight techniques and pulse shape discrimination were used to identify light ion species in order to generate double differential energy spectra of the light ion fragments. Comparisons of these measured yields were compared with Monte Carlo calculations generated by MCNP6. These yields will be used to quantify uncertainty in radiation transport codes utilized in risk assessment for spaceflight missions with prolonged exposures to galactic cosmic rays.

The aim of this research is to produce double differential thick target yields, angular distributions and integrated yields for the inclusive production of neutrons, protons, deuterons, tritons, 3He, and 4He from intermediate heavy-ion interactions on thick targets of aluminium, polyethylene and other targets of interest to the radiation shielding program as specified by the National Aeronautics and Space Administration (NASA). In tandem with the experimental research, transport model calculations of these thick target yields were also performed. The first such experimental run was conducted in May 2015, with the expectation of improved experimental results at a following March 2016 run at the NASA Space Radiation Laboratory (NSRL) on the campus of Brookhaven National Laboratory (BNL). The May 2015 commissioning run served to test the electronics of the experimental setup, as well as the various detectors and other equipment under the conditions in which the following measurements will be run. The series of future accelerator-based experiments will rely on the inclusion of two separate upstream and downstream targets. Analysis of the data from both sets of detectors – liquid scintillator and sodium iodide – using both pulse height and time-of-flight methods will allow NASA to perform uncertainty quantification and sensitivity analysis on their transport codes and future shielding studies.

In March 2016, secondary neutron production from thick-target shielding experiments were conducted at the National Aeronautics and Space Administration’s (NASA) Space Radiation Laboratory at Brookhaven National Laboratory. Ion beams of proton, helium, and iron projectiles were aimed at aluminum targets with areal densities of 20, 40, and 60 g/cm2. The ion beams were extracted at energies of 400 and 800 AMeV and neutron yields were measured with liquid scintillators at 10°, 30°, 45°, 60°, 80°, and 135° off the beam axis. A second 60 g/cm2 aluminum target was placed 3.5 m downstream from the middle of front target to study backscattered neutrons. Double differential thick-target neutron yields for various combinations of projectile, projectile energy, target material, target thickness, and detector location were produced using the time-of-flight technique. These measurements will help NASA perform uncertainty analyses on their transport codes and contribute to shielding design studies for future space applications.

Recently, the Monte Carlo transport code HETC has been extended to include the interactions and transport of energetic heavy ions. Here, for the first time, we compare predictions of fragment production and energy loss with laboratory data measured at Brookhaven National Laboratory and at the National Institute of Radiological Sciences in Japan. Very good agreement is q found for predicted and measured energy loss spectra for a variety of incident laboratory beams and targets. Index Terms--Experimental validation, particle beams, radiation effects, radiation transport codes.

A knockout-ablation-coalescence model capable of making quantitative predictions of neutron spectra produced in high-energy nucleon-nucleus and nucleus-nucleus collisions is presented. A Glauber model is used to describe neutrons produced in the knockout or abrasion stage of the reaction. In the ablation stage, a statistical evaporation model is used to calculate the neutron spectrum produced by the excited prefragment nucleus left over from the abrasion stage. The effects of coalescence in reducing free neutron emission by composite particle formation are included. Typical results for predicted neutron energy and double-differential spectra are presented and compared with recently reported measurements for a variety of projectile and target nuclei of interest in space radiation protection. Except for differences resulting from the neglect of isobar production and decay in the model, predictions are in fairly good agreement with the measured data. Index Terms--Neutrons, nuclear model, space radiator.

We report experimental measurements of neutron production from collisions of neutron beams with polyethylene blocks simulating tissue at the Los Alamos National Laboratory Neutron Science Center and 1 GeV/amu iron nuclei with spacecraft shielding materials at the Brookhaven National Laboratory AGS. Index Terms--High-energy neutrons, neutron moderation, polyethylene.

Stopping target measurements with energetic ion beams are important for building and validating physics models used to predict nuclear fragmentation fields created by interactions between incoming primary ions and target materials. However, the values of the ratio of primary ion range R to target depth d (Rid) are not the same in several of the existing measurements, and as such, this makes the intercomparison between those measurements complicated without corrections for differences in secondary particle transport through differing amounts of target material. Therefore, this work aims to study the influence of the target geometiy on the angular distributions of secondary particles. Cases with 100 and 230 MeV/amu 4He ions bombarding stopping water and iron targets with various dimensions were studied by using the transport model code PHITS (Particle and Heavy Ion Transport code System). With increasing target depth, the impact on the attenuation of secondary particles is more significant for lighter target mass and higher-energy projectiles at forward angles. Also, with deeper targets, more interactions occur between the secondary particles and the target nuclei, which results in more targetlike fragments at large and backward angles. With respect to the cross-sectional area of the stopping targets, the forward angular distributions are similar to the system with smaller cross-sectional area of the targets; however, charged particles are significantly attenuated at large angles, whereas no general rule was found for secondary neutrons at large and backward angles. These results indicate that in order to compare the angular distributions from various stopping target measurements, it will be necessary to utilize a radiation transport code to correct the differences caused by target geometry. [ABSTRACT FROM AUTHOR]