Gamma ray production and transport in Mars

Abstract

The elemental composition of the Martian surface can be determined by gamma ray spectroscopy from landers or orbiting spacecraft. We used the well‐tested Los Alamos High Energy Transport (LAHET) Code System (LCS) to numerically simulate the galactic‐cosmic‐ray‐induced processes producing secondary particles and γ rays in Mars. For γ ray lines, LCS was used only for the calculation of the particle fluxes in the Martian soil and atmosphere; these fluxes were then integrated with cross sections to calculate the production rates of γ rays as a function of depth. The fluxes of γ ray lines were then calculated both at the Martian surface and at an altitude of 378 km. The water content of the Martian soil and the atmospheric thickness were varied to establish the dependence of the particle distributions and γ ray fluxes on these parameters. Most attention is devoted to γ rays from neutron‐induced reactions in the Martian soil, but contributions from the atmosphere, natural radioactivity, and from proton interactions are also mentioned. Our results are compared with those from previous studies.

Neutron production in the lunar subsurface from alpha particles in galactic cosmic rays

“…The actual temperature may vary under 333 K, which the LNPE temperature indicators suggested as a maximum, because the LNPE was carried out for 49 h. However, based on the results of our preliminary tests, differences in material temperature primarily affect the shape of the low-energy neutron spectrum but have small effects on the neutron density. Similar results have also been reported by other investigators (Woolum et al, 1975;Dagge et al, 1991;Masarik and Reedy, 1996). Therefore, exact information on the temperature is not important.…”

“…We have therefore focused on the production of neutrons from alpha particles in the GCR. To date, neutron production from alpha particles has been mainly estimated by scaling the calculation of protons (Dagge et al, 1991;Masarik and Reedy, 1996). The primary aim of our study was to compare, in detail, the estimation of neutron production from alpha particles by the proton scaling method with that by alpha particle interaction model.…”

Present denudation rates at selected sections of the South African escarpment and the elevated continental interior based on cosmogenic 3He and 21Ne

“…Minimum exposure ages T 3 and T 21 (ka) and maximum erosion rates ε 3 and ε 21 (m/Ma) of the sampled surfaces. For pyroxenes, data are again reported according to both the production rate calculation methods of (a) Masarik and Reedy (1996) and (b) Kober et al (2005), respectively. Error limits (2) reflect only the analytical uncertainty of the noble gas analysis.…”

“…Since Niedermann et al (2007) have not been able to assess which methods yield the more reliable production rates, we present two values each for the 3 He and 21 Ne production rates in the pyroxene samples (Table 3). They were calculated according to the methods of Masarik and Reedy (1996) and Kober et al (2005), respectively, which are representative for either of the two sets (Niedermann et al, 2007). The major element compositions used for these calculations are given in Table 4. 3 He (pyroxene only) and 21 Ne exposure ages were calculated from the concentrations and production rates given in Table 3 and are shown in Table 5.…”

Identification and measurement of neutron-absorbing elements on Mercury’s surface

“…The effects of gravity and finite neutron lifetime were explicitly taken into account. For a GCR energy-dependent flux spectrum, we used the parameterization for protons and alpha particles given by Masarik and Reedy (1996) that depends on a solar modulation parameter, /, which affects both the shape and absolute normalization of the spectrum. To obtain the solar modulation parameter, we used the procedure of McKinney et al (2006) and Earth-based south-pole neutron monitor data (Bartol Research Institute, 2009) to estimate that / = 300 MV during the time of M1.…”