Decay Schemes ofC15,N16, andO19

Abstract

An iron-free intermediate-image spectrometer has been used to measure the beta-ray spectra of 2.25-sec ${\mathrm{C}}^{15}$, 7.4-sec ${\mathrm{N}}^{16}$, and 29-sec ${\mathrm{O}}^{19}$ and to measure the positron-electron internal pair conversion lines occurring in ${\mathrm{C}}^{15}$ and ${\mathrm{N}}^{16}$ decays. ${\mathrm{C}}^{15}$ emits a beta-ray branch of end-point energy 9.82\ifmmode\pm\else\textpm\fi{}0.04 Mev to the \textonehalf{}- ground state of ${\mathrm{N}}^{15}$ and a branch of 4.51\ifmmode\pm\else\textpm\fi{}0.03-Mev end-point energy. Relative intensities are (32\ifmmode\pm\else\textpm\fi{}2)% ($logft=6.0$) and 68% ($logft=4.1$), respectively, and both components have the allowed shape. From pair line measurements at 1.5% resolution the ${\mathrm{C}}^{15}$ gammaray energy is 5.299\ifmmode\pm\else\textpm\fi{}0.006 Mev, and thus the inner beta-ray group leads to the upper member of the (5.276-5.305)-Mev doublet level in ${\mathrm{N}}^{15}$ known from the ${\mathrm{N}}^{14}(d, p){\mathrm{N}}^{15}$ reaction. The internal pair conversion coefficient derived for the 5.299-Mev line agrees best with an $E1$ assignment. Our data require spin and parity \textonehalf{}+ or $\frac{3}{2}+$ for the 5.305-Mev level in ${\mathrm{N}}^{15}$, and spin and parity \textonehalf{}+ or $\frac{3}{2}+$ for ${\mathrm{C}}^{15}$. Taken together with other evidence it seems likely that both states are \textonehalf{}+. No evidence could be found from gamma-ray measurements for the beta decay of ${\mathrm{C}}^{15}$ to other known states of ${\mathrm{N}}^{15}$. Some comments are made on the intermediate-coupling model for $A=15$. In the decay of ${\mathrm{N}}^{16}$ we find that the 3.3-Mev beta-ray branch to the 7.11-Mev level in ${\mathrm{O}}^{16}$ is 11% per decay, based on the Kurie-plot analysis. A value of (4.7\ifmmode\pm\else\textpm\fi{}0.9)% per decay for this branch is derived from the intensity of the 7.11-Mev pair line. ${\mathrm{O}}^{19}$ decays with beta-ray branches of 4.601\ifmmode\pm\else\textpm\fi{}0.015 Mev [(${41.5}_{\ensuremath{-}5}^{+2}$)%, $log ft=5.4$] and 3.25\ifmmode\pm\else\textpm\fi{}0.02 Mev (58.5%, $log ft=4.5$). Other results include a value of 5.416\ifmmode\pm\else\textpm\fi{}0.015 Mev for the beta-ray end-point energy of ${\mathrm{F}}^{20}$ and a value of 6.051\ifmmode\pm\else\textpm\fi{}0.005 Mev for the energy of the pair-emitting state of ${\mathrm{O}}^{16}$.