Electric Monopole Transitions In Ca-40

The $E0$ pair decay branching ratio ($\frac{{\ensuremath{\Gamma}}_{\ensuremath{\pi}}}{\ensuremath{\Gamma}}$) for the 5.21-MeV ${0}^{+}$ fifth excited state of $^{40}\mathrm{Ca}$ was measured. The state was excited by inelastic proton scattering. The ${e}^{\ensuremath{-}}\ensuremath{-}{e}^{+}$ pairs were detected in two $\ensuremath{\Delta}E\ensuremath{-}E$ scintillation telescopes in coincidence with backscattered protons. A branching ratio limit of 1.4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ was determined which corresponds to a monopole strength $\ensuremath{\rho}l0.06$. This result is consistent with theoretical descriptions which contain multiparticle excitations and core deformations. In addition, the branching ratio $R(\frac{({2}_{2}^{+}\ensuremath{\rightarrow}{0}_{2}^{+})}{({2}_{2}^{+}\ensuremath{\rightarrow}{0}_{1}^{+})})=(2.1\ifmmode\pm\else\textpm\fi{}0.1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ for the decay of 5.25-MeV ${2}^{+}$ state was measured and corresponds to a $B(E2)=(3.5\ifmmode\pm\else\textpm\fi{}0.6) {e}^{2}$${\mathrm{fm}}^{4}$.NUCLEAR REACTIONS $^{40}\mathrm{Ca}(p, {p}^{\ensuremath{'}})$, $E=7\ensuremath{-}10$ MeV; $^{40}\mathrm{Ca}$, measured $E0$ branching ratios. Deduced $E0$ matrix elements. Natural targets.