Radiation-matter interaction in the disc

The presence of certain short-period isotopes in meteorites (7Be, 10Be, 36Cl, 41Ca) cannot be the result of a nucleosynthetic remnant from other stars and indicates, to the contrary, the occurrence of spallation reactions in the disc caused by the interaction between matter and radiation. The young Sun was a source of accelerated protons and alpha particles with energy sufficient to produce nuclear reactions in the gases and solids within the disc. The irradiation of gases by the photons emitted by the young Sun, or by nearby massive stars, could, in turn, be responsible for the fact that certain light elements were elementarily and isotopically fractionated. Therefore, the results of the Genesis mission have led to a better understanding of the nature of the isotopic variations of O and N (the major components of the original gas, as CO and N2, respectively) by determining the initial isotopic composition of the nebula. It appears that H, N, and O (and probably C, to a lesser extent) are enriched in heavy and rare isotopes (D, 15N, and 17,18O). Noble gases trapped in meteorites are concentrated in an organic phase and are also isotopically fractionated.

Covariation of the isotopic compositions of hydrogen and nitrogen in the solar system. The composition of the Sun is that of a proto-solar nebula. All of the solar system bodies are largely enriched in D and 15N, and the gas-radiation interactions in the nascent solar system may have played a role in the generation of these heterogeneities. Understanding the nature and role of these interactions will be one of the key elements of this study. (Adapted from Marty et al., Science, 2011)

Isotopic exchange alone during "classical" chemical reactions cannot account for all of the isotopic fractionation of volatile elements ; the interaction of photons and matter must also have played an important role. We propose to study these interactions using a low-pressure experimental approach that consists of ionising gas mixtures at low pressure (H2-CO-N2-noble gases) and analysing the resultant solid products. In parallel, the coupled analysis of N, O, and possibly C, by ion probe, and of the noble gases by laser ablation, in primitive matter will be used to explore the role of radiation- induced spallation in the origin of the isotopic variations of stable isotopes. The possible relationship between the aforementioned extinct, short-lived radioactivities and certain isotopic variations, mentioned above, will be investigated in selected components of primitive meteorites. We hope, through a multi-elementary/isotopic approach, to better identify and, if possible, quantify the irradiation processes of gases and the first solids by the young Sun.