Positron Decay in Halogen Compounds

The decay of positrons has been investigated in the halogen derivatives of benzene, both at room temperature and at - 100^∘{}C, and in a number of halogen compounds. A lifetime of the order of 4×{}10^-10 sec is found in all the investigated compounds but fluorobenzene, and suggests the presence of a positron-halogen bound state; a search for the excited levels of such a bound state, whose decay features were predicted by Goldansky and co-workers, was inconclusive.