Cosmic radiation dose measurements from the RaD-X flight campaign

Abstract

The NASA Radiation Dosimetry Experiment (RaD‐X) stratospheric balloon flight mission obtained measurements for improving the understanding of cosmic radiation transport in the atmosphere and human exposure to this ionizing radiation field in the aircraft environment. The value of dosimetric measurements from the balloon platform is that they can be used to characterize cosmic ray primaries, the ultimate source of aviation radiation exposure. In addition, radiation detectors were flown to assess their potential application to long‐term, continuous monitoring of the aircraft radiation environment. The RaD‐X balloon was successfully launched from Fort Sumner, New Mexico (34.5°N, 104.2°W) on 25 September 2015. Over 18 h of flight data were obtained from each of the four different science instruments at altitudes above 20 km. The RaD‐X balloon flight was supplemented by contemporaneous aircraft measurements. Flight‐averaged dosimetric quantities are reported at seven altitudes to provide benchmark measurements for improving aviation radiation models. The altitude range of the flight data extends from commercial aircraft altitudes to above the Pfotzer maximum where the dosimetric quantities are influenced by cosmic ray primaries. The RaD‐X balloon flight observed an absence of the Pfotzer maximum in the measurements of dose equivalent rate.

The disappearance of the pfotzer-regener maximum in dose equivalent measurements in the stratosphere

“…Therefore, for radiation protection considerations, it should not be assumed that biological dose rates decrease at very high altitudes in the stratosphere. The energy deposition spectrum from RaySure provides direct evidence of this high LET population of particles above the Pfotzer‐Regener maximum. Further evidence can be found in the lineal energy spectra produced by the TEPC instrument [ Mertens et al, ]. We do not, however, find a very significant change in this spectrum in the altitude ranges just above and just below 100,000 feet. The original calibration factors for calculating dose equivalent from RaySure count rates, lead to very good agreement with TEPC data below the Pfotzer‐Regener maximum, and very reasonable agreement at higher altitudes.…”

“…The RaD‐X payload included a HAWK version 3.0 TEPC, manufactured by Far West Technologies. Detailed results from this instrument are presented in an accompanying paper by Mertens et al []. Here we reproduce only the processed dose equivalent rate, as measured by the TEPC, to compare to the same quantity as estimated by RaySure.…”

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

“…For absorbed dose rate measurement comparisons between the RaD‐X instruments and the LLNL Co‐60 gamma ray standard, the dosimeter‐to‐standard measurement ratios were 0.84 ± 0.06, 1.07 ± 0.32, 1.31 ± 0.07, and 0.82 ± 0.24 for the TEPC, TID, Liulin, and RaySure, respectively. These comparisons were used to estimate the systematic uncertainty of the flight‐averaged absorbed dose rate measurements taken during the RaD‐X balloon flight [ Mertens et al , ]. Moreover, the dosimeter‐to‐standard measurement ratios aided the interpretation of the intercomparisons of the RaD‐X instrument flight measurements.…”

“…The paper by Gronoff et al [] derives payload structure correction factors that are applied to the flight measurements [ Mertens et al , ]. The TEPC instrument is housed in a pressurized aluminum container.…”

“…These results were also compared to the NAIRAS and PANDOCA models. The flight‐averaged dosimetric quantities were reported with the other supporting aircraft measurements in the RaD‐X flight paper [ Mertens et al , ].…”