TheE0-pair decay of the0+second excited states inCa42andCa44

The $E0\mathrm{}$-pair decay branching ratio ($\frac{{\Gamma }_{\pi }}{\Gamma }$) for the 1.84-MeV ($0^{+}$) and 1.88-MeV ($0^{+}$) second excited states of ${}_{}{}^{42}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}$ were measured. The states were excited by proton inelastic scattering. $e^{-}-e^{+}$ pairs from the $E0\mathrm{}$ decay were stopped in a carbon cylinder and the resulting annihilation radiation was detected in two NaI(T1) detectors in triple coincidence with backscattered protons. The observed branching ratios are (0.88±0.14) × ${10}^{-3\mathrm{}}$ and (2.05±0.17) × ${10}^{-2\mathrm{}}$ for ${}_{}{}^{44}{}_{}{}^{}\mathrm{Ca}$ and ${}_{}{}^{42}{}_{}{}^{}\mathrm{Ca}$, respectively, corresponding to monopole strengths of $\rho =0.30\mathrm{}\pm 0.10$ and $\rho =0.34\mathrm{}\pm 0.03$. These results are consistent with a theoretical description of these states which includes large admixtures of deformed state wave functions.