Xenon isotope anomalies in the carbonaceous chondrite murray

Abstract

Isotopic compositions have been measured mass spectrometrically for xenon fractions released from the carbonaceous chondrite Murray in stepwise heating experiments. The isotopic ratios varied quite considerably; for example, the 136Xe/132Xe ratio in the 1000°C fraction was almost identical to the atmospheric ratio (0.330), whereas the ratio in the 1300°C fraction agreed with that in Sucor (0.305). It appears that these variations can best be explained as being due to the fact that reservoirs of two isotopically distinct gases (solar and planetary) exist in the meteorite and that mixtures of these gases in various proportions are being released at different temperatures. The major difference in the isotopic compositions of solar and planetary xenon can be attributed to a mass‐dependent fractionation process, which must have occurred during the early stages of the history of the solar system. The abundance ratios of the xenon isotopes are also altered by the cosmic ray irradiation and neutron capture processes. According to this interpretation, it is unnecessary to assume the existence of the so‐called carbonaceous chondrite fission component. The decay products of extinct radionuclides 129I and 244Pu did not alter the xenon isotopic ratios significantly in the case of the carbonaceous chondrite Murray. The light isotopes 124Xe and 126Xe in the earth's atmosphere appear to be partially of cosmic ray origin.

Abundances and isotopic compositions of rare gases in granites.

“…The experimental procedure employed was essentially the same as that described in previous reports (KURODA et al, 1974KURODA and SHERRILL, 1976), except for the fact that large amounts of rock samples were used for the mass-spectrometric analyses: 7.097 grams of Carney Lake granite; 15.085 grams of Red Rock granite; 15.316 grams of Wausau granite; and 12.374 grams of Westerly granite.…”

Isotopic anomalies in the early solar system.

“…The initial ratio of 26A1 to 27A1 can be cal XENON ISOTOPE ANOMALIES According to KURODA (1971KURODA ( , 1975KURODA ( , 1976KURODA ( , 1979 and KURODA et al (1974KURODA et al ( , 1975, the difference in the isotopic compositions of xenon in the atmosphere and the carbonaceous chon drites can be attributed to a combined effect of (a) mass fractionation, (b) neutron caputre and (c) cosmic-ray irradiation processes which took place in the early solar system. The amount of cosmic-ray-produced 126Xe in car bonaceous chondrites can be calculated from the equations …”

A general solution for the puzzle of the xenon.

“…KURODA et al (1974), on the other hand, have reported that the isotopic composition of the xenon in carbonaceous chondrites can be explained as due to the alterations of the isotopic compositions by a combined effect of a) mass fractionation, b) neutron-capture and c) cosmic-ray. irradiation processes which took place during the early history of the solar system (see also KURODA, 1976).…”