Nuclear Electric Monopole Transition inCa42

The $0^{+}$ assignment to the 1.836-Mev, second-excited state in ${\mathrm{Ca}}^{42}$ has been confirmed by the observation of electric monopole electron-positron pairs and internal conversion electrons corresponding to the cross over transition to the ground state. The shape of the continuous positron spectrum from the $E0\mathrm{}$ pairs, as well as the ratio $R=9.0\mathrm{}\pm 1.8$ of pairs to $E0\mathrm{}$ conversion electrons are consistent with theoretical predictions for an $E0\mathrm{}$ transition. 0.305-Mev internal conversion electrons were observed corresponding to the transition between the 1.836-Mev and the $2^{+}$, 1.523-Mev, first excited state. The ratio of 1.836-Mev to 0.305-Mev electron yields is 1.03±0.10. From these and other data the monopole strength parameter $\rho$ was determined to be 0.41.