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

Abstract

Galactic cosmic rays enter Earth's atmosphere after interacting with the geomagnetic field. The primary galactic cosmic rays spectrum is fundamentally changed as it interacts with Earth's atmosphere through nuclear and atomic interactions. At points deeper in the atmosphere, such as at airline altitudes, the radiation environment is a combination of the primary galactic cosmic rays and the secondary particles produced through nuclear interactions. The RaD‐X balloon experiment measured the atmospheric radiation environment above 20 km during 2 days in September 2015. These experimental measurements were used to validate and quantify uncertainty in physics‐based models used to calculate exposure levels for commercial aviation. In this paper, the Badhwar‐O'Neill 2014, the International Organization for Standardization 15390, and the German Aerospace Company galactic cosmic ray environment models are used as input into the same radiation transport code to predict and compare dosimetric quantities to RaD‐X measurements. In general, the various model results match the measured tissue equivalent dose well, with results generated by the German Aerospace Center galactic cosmic ray environment model providing the best comparison. For dose equivalent and dose measured in silicon, however, the models were compared less favorably to the measurements.

Cosmic radiation dose measurements from the RaD-X flight campaign

“…It is difficult to determine whether the increase in dose equivalent rate for altitudes greater than 32 km is because the Fourier transform filtering technique extracted from the TEPC flight measurements is a true secular trend in the dose equivalent rate profile, or whether the technique introduced a bias in the altitude structure of the computed average dose equivalent rate. Nevertheless, it is noteworthy to mention that the increase in the dose equivalent rate above 32 km is consistent with the influence of heavy‐ion cosmic ray primaries [ Norman et al , ]. Within the conceptual framework of state‐of‐the‐art cosmic radiation transport models, the differences between the vertical shape of the absorbed dose rate and dose equivalent rate in the region of the conventional Pfotzer maximum is the result of a complex mixture of high‐LET and low‐LET radiations, originating from both cosmic ray primaries and secondaries.…”

“…These two altitude regions, which are above the peak in secondary particle production, enable the dosimetric contributions from cosmic ray primaries to be characterized, which are the ultimate source of radiation exposure at aviation altitudes. Model simulations, based on the deterministic HZETRN transport code, indicate that the contributions from heavy‐ion cosmic ray primaries are discernible in the dosimetric measurements in Region B, while protons comprise the dominant contribution from cosmic ray primaries in Region A [ Norman et al , ].…”

“…To our knowledge, the TEPC spectral dose distribution measurements, which extend to LET > 100 keV/μm, and the Liulin spectral dose measurements, have not been previously published at these altitudes. Consequently, the RaD‐X balloon flight TEPC and Liulin spectral measurements provide an important data set for assessing and validating atmospheric cosmic radiation transport models, since scalar (integrated) dosimetric quantities alone are insufficient to resolve current discrepancies between models and measurements [ Norman et al , ].…”

Overview of the Radiation Dosimetry Experiment (RaD-X) flight mission

“…The initial model comparisons to the RaD‐X balloon flight measurements by Norman et al [] provide the impetus to make a few general remarks concerning the source(s) of aviation radiation model uncertainty. Differences among the widely available GCR models cannot explain the systematic underprediction of aviation radiation models at low latitudes and high‐geomagnetic vertical cutoff rigidities [ Bottollier‐Depois et al , ; Mertens et al , ], as the GCR model differences are largely confined to energies below the vertical cutoff rigidity of the RaD‐X flights [ Norman et al , ]. As a result, high‐latitude and low‐geomagnetic vertical cutoff rigidity balloon flights are needed to select a preferred GCR model for aviation radiation exposure applications.…”

Assessment of the influence of the RaD-X balloon payload on the onboard radiation detectors

“…Figure shows the NAIRAS computed spectral particle fluxes in the B and A Regions [ Norman et al , ]. These fluxes were computed at a geomagnetic cutoff rigidity of 4 GV, which is representative of the cutoff rigidity for the RaD‐X balloon flight near Fort Sumner, New Mexico.…”