The Badhwar-O'Neill 2020 Model

The Badhwar-O'Neill (BON) model has been used for some time to describe the galactic cosmic ray (GCR) environment encountered in deep space by astronauts and sensitive electronics. The most recent version of the model, BON2014, was calibrated to available measurements to reduce model errors for particles and energies of significance to astronaut exposure. Although subsequent studies showed the model to be reasonably accurate for such applications, modifications to the sunspot number (SSN) classification system and a large number of new high precision measurements suggested the need to develop an improved and more capable model. In this work, the BON2020 model is described. The new model relies on daily integral flux from the Advanced Composition Explorer Cosmic Ray Isotope Spectrometer (ACE/CRIS) to describe solar activity. For time periods not covered by ACE/CRIS, the updated international SSN database is used. Parameters in the new model are calibrated to available data, which includes the new Alpha Magnetic Spectrometer (AMS-02) and Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) high-precision measurements. It is found that the BON2020 model is a significant improvement over BON2014. Systematic errors associated with BON2014 have been removed. The average relative error of the BON2020 model compared to all available measurements is found to be <1%, and BON2020 is found to be within 15% of a large fraction of the available measurements (26,269 of 27,646 95%)

Three Methods for Solving the Low Energy Neutron Boltzmann Equation

The solution to the neutron Boltzmann equation is separated into a straightahead component dominating at high energies and an isotropic component dominating at low energies. The high-energy solution is calculated using HZETRN-05, and the low-energy isotropic component is modeled by two non-coupled integro-differential equations describing both forward and backward neutron propagation. Three different solution methods are then used to solve the equations. The collocation method employs linear I3-splines to transform each equation into a system of ODES; the resulting system is then solved exactly and evaluated using numerical integration techniques. Wilson\u27s method uses a perturbational approach in which a fundamental solution is obtained by solving a simple ODE, a new source term is generated by the fundamental solution, and the collocation method is then used to solve the remaining equation. The fixed-point series method extends Wilson\u27s method by continuing the perturbational procedure until desired convergence criteria are met. In all three cases, the total neutron flux is found by adding the forward and backward components. Comparisons are made between the three methods in one, two and three layer configurations in various space environments and compared to Monte Carlo data where available

Faster Heavy Ion Transport for HZETRN

The deterministic particle transport code HZETRN was developed to enable fast and accurate space radiation transport through materials. As more complex transport solutions are implemented for neutrons, light ions (Z 2) transport algorithm in HZETRN is reviewed, and a simple modification is shown to provide an approximate 5x decrease in execution time for galactic cosmic ray transport. Convergence tests and other comparisons are carried out to verify that numerical accuracy is maintained in the new algorithm

A Bi-Exponential Repair Algorithm for Radiation-Induced Double-Strand Breaks: Application to Chromosome Aberrations

Chromosome aberrations (CAs) are one of the effects of radiation exposure and are used as a biomarker. A new simulation program, named RITCARD (Radiation induced tracks, chromosome aberrations, repair, and damage) was developed to simulate radiation-induced CA. RITCARD is used with the program RITRACKS (Relativistic Ion Tracks), which simulates the radiation tracks. The restitution kinetics algorithm presented here is a significant improvement over the one used in the first version. Simulations of radiation-induced CA were performed for several ion types and mixed irradiation fields. These simulations will be useful to help interpreting experiments of galactic cosmic rays (GCR) simulator

Evaluation of HZETRN on the Martian Surface: Sensitivity Tests and Model Results

The Mars Science Laboratory Radiation Assessment Detector (MSLRAD) is providing continuous measurements of dose, dose equivalent, and particle flux on the surface of Mars. These measurements have been highly useful in validating environmental and radiation transport models that will be heavily relied upon for future deep space missions. In this work, the HZETRN code is utilized to estimate radiation quantities of interest on the Martian surface. A description of the modeling approach used with HZETRN is given along with the various input models and parameters used to define the galactic cosmic ray (GCR) environment and Martian geometry. Sensitivity tests are performed to gauge the impact of varying several input factors on quantities being compared to MSLRAD data. Results from these tests provide context for inter-code comparisons presented in a companion paper within this issue. It is found that details of the regolith and atmospheric composition have a minimal impact on surface flux, dose, and dose equivalent. Details of the density variation within the atmosphere and uncertainties associated with specifying the vertical atmospheric thickness are also found to have minimal impact. Two widely used GCR models are used as input into HZETRN and it is found that the associated surface quantities are within several percent of each other

Radiation Transport Methods for Space Applications

No abstract availabl

Galactic Cosmic Ray Simulator Design at NSRL

No abstract availabl

Galactic Cosmic Ray Simulation at the NASA Space Radiation Laboratory

The external Galactic Cosmic Ray (GCR) spectrum is significantly modified when it passes through spacecraft shielding and astronauts. One approach for simulating the GCR space radiation environment at ground based accelerators would use the modified spectrum, rather than the external spectrum, in the accelerator beams impinging on biological targets. Two recent workshops have studied such GCR simulation. The first workshop was held at NASA Langley Research Center in October 2014. The second workshop was held at the NASA Space Radiation Investigators' workshop in Galveston, Texas in January 2015. The results of these workshops will be discussed in this paper

Galactic Cosmic Ray Simulator at the NASA Space Radiation Laboratory

The external Galactic Cosmic Ray (GCR) spectrum is significantly modified when it passes through spacecraft shielding and astronauts. One approach for simulating the GCR space radiation environment is to attempt to reproduce the unmodified, external GCR spectrum at a ground based accelerator. A possibly better approach would use the modified, shielded tissue spectrum, to select accelerator beams impinging on biological targets. NASA plans for implementation of a GCR simulator at the NASA Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory will be discussed

Radiation Shielding Optimization on Mars

Future space missions to Mars will require radiation shielding to be optimized for deep space transit and an extended stay on the surface. In deep space, increased shielding levels and material optimization will reduce the exposure from most solar particle events (SPE) but are less effective at shielding against galactic cosmic rays (GCR). On the surface, the shielding provided by the Martian atmosphere greatly reduces the exposure from most SPE, and long-term GCR exposure is a primary concern. Previous work has shown that in deep space, additional shielding of common materials such as aluminum or polyethylene does not significantly reduce the GCR exposure. In this work, it is shown that on the Martian surface, almost any amount of aluminum shielding increases exposure levels for humans. The increased exposure levels are attributed to neutron production in the shield and Martian regolith as well as the electromagnetic cascade induced in the Martian atmosphere. This result is significant for optimization of vehicle and shield designs intended for the surface of Mars