In the dehydrogenation during Po-210 alpha (LET = 200 eV nm(-1)) and Co-60 gamma (0.2 eV nm(-1)) radiolysis of C-5-C-10 cycloalkanes and their iodine solutions bicycloalkyls (in radical combination reactions), cross-bridged bicycloalkanes (from greater than or equal to C-7 rings, in unimolecular H-2 elimination) and cycloalkenes (in both reactions) are produced. The yields of all of these are lower at higher LET irradiation. While the ring sizes do not influence the competition between the dimerization and the scavenging of the cycloalkyl radicals the yields of the unimolecular decompositions are in positive correlation with the strain energy of the ring.