The $\beta$-ray branching of ${\mathrm{N}}^{16}$ to the 6.05-MeV $0^{+}$ first excited state of ${\mathrm{O}}^{16}$ has been detected by observing the subsequent positron-electron nuclear pair emission from the 6.05-MeV level with a magnetic pair spectrometer. A previously developed spiral baffle system was used in the spectrometer to enhance the sensitivity for detecting the 6.05-MeV $E0\mathrm{}$ pair line relative to the 6.13-MeV $E3\mathrm{}$ pair line, the latter following the principal ${\mathrm{N}}^{16}$ $\beta$-ray branch. The branch to the 6.05-MeV state was found to be (1.2±0.4)×${10}^{-4\mathrm{}}$ per decay. Based on the measured branching ratios, the $log{f}_{1}t$ values for the unique first-forbidden decays to the ground and 6.05-MeV states are calculated to be 9.12±0.04 and 9.98±0.15, respectively. The results are consistent with recent descriptions of the ground and first excited states of ${\mathrm{O}}^{16}$.

• Received 14 June 1968

DOI:https://doi.org/10.1103/PhysRev.175.1275