Anomalous xenon isotopes in carbonaceous chondrites.

Origin of xenon-124 and -126 in carbonaceous chondrites.

“…The average number (Q) of neutrons gen erated. per.. square, centimeter of the earth's surface per second by the incidence of cosmic radiation was calculated by Libby (1964) to be about 2 and hence we have a value of Fn = Q • T = (2) (3.16 X 10') (1.03 X 1014) 7 X 1021 (n/cm2) which is in essential agreement with the value of Fn = 6 X 1021 (n/cm2) calculated earlier from the difference between the isotopic composi tions of the xenon in the carbonaceous chon drites and in the earth's atmosphere (Saebo and Kuroda, 1985). In high energy spallation reac tions the flux of secondary neutrons should be at least equal to or several times the proton flux.…”

“…2, the line C has a slope of 1/0.59 = 1.7, which corresponds to the cosmic-ray production ratio of 126Xe and 124Xe. The line P has a slope of about 113, which corresponds to the ratio of the primordial abundance ratios of 126Xe/132Xe = 0.0076 and 124Xe/132Xe = 0.0024, respectively (Saebo and Kuroda, 1985). Here ( Fig.…”

“…where the 1V's are the relative abundances of the xenon found in the meteorites and in the atmo sphere; i is the mass-number: the P's are the relative abundances of the xenon isotopes in a primordial (or cosmic-ray-corrected atmospheric xenon): ni is the changes of the abundance caused by the neutron-capture processes at mass number i; and si is the contribution from the high-energy spallation processes at mass number i (see also Saebo and Kuroda, 1985).…”

“…According to Saebo and Kuroda (1985), the 126Xe/136Xe ratio for the primordial xenon (or the cosmic-ray-corrected atmospheric xenon) is 0.0024 (= 126P) and the observed values of 126Xe/136Xe ratio for the meteorites Murray and Murchison are 0.0131 and 0.0130, respectively and -126 in carbonaceous chondrites 109 (Kuroda et al, 1974;1975 (Anders and Ebihara, 1982). It follows then that the 136Xe content of a meteorite parent body whose chemical composition represented that of the solar nebula must have been initially as high as 2.88 X 10-s cc STP 136Xe per gram and the spallogenic 126Xe content was 0.0107 times of this value or 3.08 X 10-'cc STP per gram.…”

“…The surviving theories are those based on supernovae injection of dust grains or survival of primary condensates formed in the expanding shell of a supernova (Clayton, 1975;Cameron and Truran, 1977;Lattimer et al, 1978;. Saebo and Kuroda (1985) have pointed out, however, that recent observational and experi mental evidence supports the idea that the young sun went through a high activity or T Tauri phase (Worden et al, 1981;Feigelson, 1982;Strazzula, 1985). This rejuvenates the early proposal of Kuroda (1971) and Kuroda et al (1974Kuroda et al ( , 1975 that such a flux, along with mass fractionation and the accompanying neu tron-capture processes, could be responsible for the observed anomalies.…”