Nuclear isomers formed in various nuclear reactions.

In 1917 Soddy in discussing his ideas about atomic nuclei conceived the possibility of nuclei having the same charge and mass but being different in their radioactive behaviour. Hahn first discovered this phenomenon of nuclear isomerism in 1921. He found two beta activities of half-lives 1.15 minutes and 6.7 hours in the decay of thorium extracted from natural uranium, both of which activities reverted to uranium. We now know the decay chain to be as follows