GCR environmental models III: GCR model validation and propagated uncertainties in effective dose

Abstract

This is the last of three papers focused on quantifying the uncertainty associated with galactic cosmic rays (GCR) models used for space radiation shielding applications. In the first paper, it was found that GCR ions with Z > 2 and boundary energy below 500 MeV/nucleon induce less than 5% of the total effective dose behind shielding. This is an important finding since GCR model development and validation have been heavily biased toward Advanced Composition Explorer/Cosmic Ray Isotope Spectrometer measurements below 500 MeV/nucleon. Weights were also developed that quantify the relative contribution of defined GCR energy and charge groups to effective dose behind shielding. In the second paper, it was shown that these weights could be used to efficiently propagate GCR model uncertainties into effective dose behind shielding. In this work, uncertainties are quantified for a few commonly used GCR models. A validation metric is developed that accounts for measurements uncertainty, and the metric is coupled to the fast uncertainty propagation method. For this work, the Badhwar-O'Neill (BON) 2010 and 2011 and the Matthia GCR models are compared to an extensive measurement database. It is shown that BON2011 systematically overestimates heavy ion fluxes in the range 0.5-4 GeV/nucleon. The BON2010 and BON2011 also show moderate and large errors in reproducing past solar activity near the 2000 solar maximum and 2010 solar minimum. It is found that all three models induce relative errors in effective dose in the interval [À20%, 20%] at a 68% confidence level. The BON2010 and Matthia models are found to have similar overall uncertainty estimates and are preferred for space radiation shielding applications.

Atmospheric radiation modeling of galactic cosmic rays using LRO/CRaTER and the EMMREM model with comparisons to balloon and airline based measurements

“…One source contributing to the uncertainty is the transport of GCRs through the heliosphere. A series of papers in 2014 showed that different transport models can lead to differences of up to 50% in the resulting effective dose [ Slaba and Blattnig , , ; Slaba et al , ]. We leave a detailed analysis of how these different models affect the model's output to a future study.…”

Evaluating galactic cosmic ray environment models using RaD-X flight data

“…The limited measurements were shown to lead to a calibration bias, in which the models are found to be reasonably accurate (less than 15% model error) [ NCRP , ] when compared to the available data, but larger differences (>50%) in radiation exposure calculations behind shielding using the GCR models were found [ Mrigakshi et al , ; Slaba and Blattnig , ]. The discovery of the calibration bias has led to more rigorous sensitivity analysis and validation [ Slaba and Blattnig , ; Slaba et al , ]. The validation work will be aided by future improved measurements with the Alpha Magnetic Spectrometer instrument on the International Space Station [ Aguilar et al , ].…”

“…radiation exposure calculations behind shielding using the GCR models were found Slaba and Blattnig, 2014a]. The discovery of the calibration bias has led to more rigorous sensitivity analysis and validation [Slaba and Blattnig, 2014b;Slaba et al, 2014]. The validation work will be aided by future improved measurements with the Alpha Magnetic Spectrometer instrument on the International Space Station [Aguilar et al, 2015].…”

Light Ion Yields from Bombardment of Thick Targets by Protons, Helium-4 and Iron-56

“…These estimates of risk are based on particle fluences simulated by deterministic radiation transport codes, which are verified and validated by fits to measurements of GCR ion fluences from probes in Earth's atmosphere. The available database for comparison is limited, as the majority of data were collected at energies below 500 AMeV [2]. However, GCR at these energies are limited contributors to effective dose [3].…”

“…H-1, He-4, and Fe-56 beams were extracted at 0.4 AGeV, while H-1 and Fe-56 were extracted at 0.8 AGeV,. These projectiles were incident on the the center of the primary upstream target, composed of either aluminum with thicknesses of 20, 40, and 60 g/cm 2 and area 30 x 100 cm 2 . A second downstream target was placed 3.5 m from the center of the upstream target.…”