A study was made of electric monopole transitions from the $0^{+}$ first excited states of certain nuclei. A search for 6.05-Mev ${\mathrm{O}}^{16}$ $E0\mathrm{}$ conversion electrons gave an upper limit of 1×${10}^{-4\mathrm{}}$ for the ratio of the probability for conversion electrons to that of pair emission.

${\mathrm{Ca}}^{40}$ $E0\mathrm{}$ conversion electrons were observed and a ratio of $\frac{W_{\mathrm{conversion}}}{W_{\mathrm{pair}}}=(6.94\mathrm{}\pm 0.20)\times {10}^{-3\mathrm{}}$ was obtained. The momentum distributions of both components of pairs from the first excited state were observed. An upper limit of 6×${10}^{-3\mathrm{}}$ was placed on the ratio of double gamma emission to pair emission. The energy of the first excited state was found to be 3.353±0.003 Mev by measurement of the conversion electron energy.

An excitation function for population of the first excited state of ${\mathrm{Ge}}^{72}$ by inelastic scattering of protons was observed between 2.3 and 6.2-Mev proton bombarding energy. The $K$ and ($L+M+N+O$) $E0\mathrm{}$ conversion electrons were resolved and the ratio $\frac{W_K}{W_{\mathrm{}(L+M+N+O)\mathrm{}}}=8.70\mathrm{}\pm 0.06$ was obtained. The energy of the first excited state was found to be 0.690±0.001 Mev.

An excitation function for population of the first excited state of ${\mathrm{Zr}}^{90}$ by inelastic scattering of protons was obtained between 3.35 and 6.5 Mev proton bombarding energy. The momentum distributions of both components of pairs were observed. The energy of the first excited state was measured as 1.762±0.002 Mev. 2.38±0.08 was obtained for the ratio $\frac{W_{\mathrm{conversion}}}{W_{\mathrm{pair}}}$. The $K$ and ($L+M+N+O$) conversion electrons were resolved and the ratio $\frac{W_K}{W_{\mathrm{}(L+M+N+O)\mathrm{}}}=7.06\mathrm{}\pm 0.08$ was obtained.

All results are consistent within experimental errors with theoretical predictions.

• Received 29 August 1961

DOI:https://doi.org/10.1103/PhysRev.125.639