The effect of gamma-irradiation of anthracite coal and oil bitumen

Anthracite coal and oil bitumen were submitted to γ-radiation at a total dose of 1 MGy and the radiation-processed samples were studied by FT-IR spectroscopy, thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The coal samples were studied also by TGA coupled with FT-IR spectroscopy of the evolved gases. Thermal analysis has revealed a completely different behavior of the radiolyzed samples in comparison to the unirradiated samples. Both for coal and bitumen significantly less volatile fraction was released during the TGA and in both cases a significant increase in the amount of carbon coke produced at 800-900 °C was observed. The radiation processed bitumen increased significantly its ethyl acetate insolubles content. These results were interpreted in terms of extensive crosslinking and coalification of the samples under the action of γ-radiation. The results of this study have been applied to the carbonization process of terrestrial sedimentary organic matter which is commonly attributed to the action of heat flux from the depth of the Earth but which may be also due to the action of natural radiation. Other application of the results of the present study is to the complex organic matter present on the surfaces of comets and meteorites. This complex matter was formed by exposure of simple precursors to a field of high energy radiation for millions or billions of years and is consequently transformed into coal-like and bitumen-like matter. The same arguments apply to the carbon grains present in the interstellar and circumstellar medium.