On the production by solar protons of ¹²⁶Xe via Te (p,xn) reactions

Results are reported for cumulative thick-target yields of ^126,128,130Xe upon irradiating metallic tellurium of natural isotopic composition with protons of ∼3,7 MeV, 10 MeV, 14 MeV, and 17 MeV, respectively. Combined with existing data we find, for a spectrum of solar protons as derived from lunar studies (R_o = 100 MV), a spectrum-averaged yield η̄ (¹²⁶Xe)_Te = 4.2 × 10^{-4 126}Xe atoms per incident proton and yield ratios η̄ (¹²⁸Xe)/η̄ (¹²⁶Xe) = 1.42 and η̄ (¹³⁰Xe)/η̄ (¹²⁶Xe) = 0.33. In order to account for the excesses of ¹²⁶Xe occasionally observed, up to 3.0 × 10^-11 cm³ STP/g in bulk lunar samples and 250 times smaller ones in stone meteorites, the product of tellurium concentration, in ppm, times the proton dose must have been 2 × 10¹⁸ cm^-2 and 8 × 10¹⁵ cm^-2, respectively. If the irradiated matter was a surface layer of a regolith, the ¹²⁶Xe thus produced will be diluted, by mixing with deeper layers, to an extent that depends on time of exposure and rate of "gardening." It remains to be shown, by analysing suitable samples for both xenon and tellurium, whether this production mode can quantitatively account for the excesses of ¹²⁶Xe that are occasionally observed in lunar samples and gas-rich meteorites.