Computer Science
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30q.484b&link_type=abstract
Meteoritics, vol. 30, no. 5, page 484
Computer Science
Anomalies, Isotopic, Gases, Solar Rare, Regolith, Samples, Lunar, Xenon
Scientific paper
Lunar regolith samples exposed to solar radiation have been extensively studied to obtain the isotopic composition of the solar noble gases implanted into them [1, 2]. Regolithic Xe in these samples has been shown to be a mixture of a primary solar wind component with components produced in situ by cosmic ray spallation, by neutron capture reactions on I, and also by decay of extinct radionuclides (cf. e.g. [3]). In addition an essentially monoisotopic contribution at 126Xe has been observed to be present in at least some samples, its relative proportion varying from sample to sample [3]. A possible origin of this excess from the reaction 127I(n,2n)126I, followed by beta- -decay to 126Xe was suggested [3] but after considering the required iodine abundances this mechanism of production was argued against. We propose that the low energy proton reaction with Te, viz. 126Te(p,n)126I(beta-,gamma)126Xe could explain this anomaly. Since the threshold for this reaction is low (< 3 MeV) the abundant low energy protons on the lunar surface might be able to account for this anomaly. Moreover, because the same reaction on 128Te will produce 128Xe this might also account for the "rough correlation between excess 126Xe and excess 128Xe" [3]. According to available cross section data for proton energies between 10 MeV and 20 MeV the production ratio 126Xe/128Xe from (p,n)-reactions acting on natural Te is 0.8 which translates into a ratio delta 126Xe/ delta 128Xe of about 16. In order to look into the feasibility of this reaction to explain the size of the 126Xe anomaly we have irradiated Te targets with 4, 10, 14, and 17 MeV protons. Data will be presented for the cross sections that will allow to estimate whether the product (proton dose x tellurium content x cross section) yields the observed excesses. References: [1] Wieler R. et al. (1986) GCA, 50, 1997-2017. [2] Benkert J.-P. et al. (1993) JGR Planets, 98, 13147-13162. [3] Pepin R. O. et al. (1995) GCA, submitted.
Begemann Friedrich
Mathew K. J.
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