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

Results are reported for cumulative thick-target yields of Xe-126,Xe-128,Xe-130 upon irradiating metallic tellurium of natural isotopic composition with protons of similar to 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(0) = 100 MV), a spectrum-averaged yield <(eta)over bar> (Xe-126)(Te) = 4.2 x 10(-4 126)Xe atoms per incident proton and yield ratios <(eta)over bar> (Xe-128)/<(eta)over bar>(Xe-126) = 1.42 and <(eta)over bar>(Xe-130)/<(<eta)over bar>)(Xe-126) = 0.33. In order to account for the excesses of Xe-126 occasionally observed, up to 3.0 x 10(-11) cm(3) 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 x 10(18) cm(-2) and 8 x 10(15) cm(-2), respectively. If the irradiated matter was a surface layer of a regolith, the Xe-126 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 Xe-126 that are occasionally observed in lunar samples and gas-rich meteorites.