Internal Pair Production in Radium C′

Ra C′ shows a sharp line of 1.4-Mev conversion electrons with no corresponding quanta. The nuclear transition therefore is probably between states of zero angular momentum and like parity. We compute here the ratio of pair production to internal conversion of both $K$ electrons for this process. Various approximations to the complicated exact formula are given for different $Z$ values. For the case of Ra C′ this ratio is about 0.6 percent. This should be observable in a trochoid focusing spectrometer.