Simulated Response of a Tissue-equivalent Proportional Counter on the Surface of Mars

Abstract

Uncertainties persist regarding the assessment of the carcinogenic risk associated with galactic cosmic ray (GCR) exposure during a mission to Mars. The GCR spectrum peaks in the range of 300(-1) MeV n to 700 MeV n(-1) and is comprised of elemental ions from H to Ni. While Fe ions represent only 0.03% of the GCR spectrum in terms of particle abundance, they are responsible for nearly 30% of the dose equivalent in free space. Because of this, radiation biology studies focusing on understanding the biological effects of GCR exposure generally use Fe ions. Acting as a thin shield, the Martian atmosphere alters the GCR spectrum in a manner that significantly reduces the importance of Fe ions. Additionally, albedo particles emanating from the regolith complicate the radiation environment. The present study uses the Monte Carlo code FLUKA to simulate the response of a tissue-equivalent proportional counter on the surface of Mars to produce dosimetry quantities and microdosimetry distributions. The dose equivalent rate on the surface of Mars was found to be 0.18 Sv y(-1) with an average quality factor of 2.9 and a dose mean lineal energy of 18.4 keV μm(-1). Additionally, albedo neutrons were found to account for 25% of the dose equivalent. It is anticipated that these data will provide relevant starting points for use in future risk assessment and mission planning studies.

A Practical Approach for Continuous In Situ Characterization of Radiation Quality Factors in Space

“…The resulting predicted E TE and E NTE low-dose metrics for the space environment and for the Mars surface are shown in Table 4. The metrics were somewhat higher for the space environment than for the Mars surface because the space environment spectrum contained a larger contribution of high lineal energies 54 . Of interest is that the low-dose metrics for NTE were 2 to 3 times higher than those for direct TE.…”

“…As an example of potential utility of this approach, we applied the best-t q (y) functions for TE and NTE to calculated 54 microdosimetric lineal energy deposition distributions for the space environment and for the surface of Mars. The resulting predicted E TE and E NTE low-dose metrics for the space environment and for the Mars surface are shown in Table 4.…”

“…Calculations of lineal energy distributions for the space environment and on the Mars surface were obtained from Northum et al, 2015 54 . These spectra were digitized from gures in Northum et al, 2015 54 and tted using polynomial functions. The normalized d(y) functions were combined with the best-t q ε (y) functions using Eq.…”

“…Predicted E TE and E NTE metrics for the space environment and for the Mars surface: Predictions are based on published calculated lineal energy distributions for the space environment and for the Mars surface (from Northum et al, 201554 ), combined with our best-t q (y) functions for TE and NTE. Details of the method are described in the text.…”

A practical approach for continuous in situ characterization of radiation quality factors in space

“…TE and NTE predictions using lineal energy spectra for the space environment and the Mars surface. Calculations of lineal energy distributions for the space environment and on the Mars surface were obtained from Northum et al 55 . These spectra were digitized from figures in Northum et al 55 and fitted using polynomial functions.…”