Some radiation-chemical aspects of chemistry in cometary nuclei

The radiation-chemical approach to chemistry in the cometary nucleus is examined. The inventory of absorbed doses in the core and icy surface layers is made after considering the contribution of cosmic rays and some radionuclides imbedded in the cometary material during accretion. The amount of radiation-induced alterations of pristine cometary material is estimated in the light of achievments in radiation chemistry and appears to be more important than generally admitted. Radiation-chemical consequences of the possible existence of a liquid core produced by the radio-genic heat of 26Al are also considered. Experimental approaches at low temperatures are examined, as well as the contribution of room temperature experiments on systems relevant to cometary nuclei. It has been pointed out that more systematic experimental work is need which should concern not only the icy surface layers but the entire cometary nucleus, including a possible liquid core. It is concluded that the radiation-chemical approach merits more attention than it has been given until now in multidisciplinary studies of cometary nuclei.