The positron-electron pair coincidence spectrum occurring in the beta decay of 7.4-sec ${\mathrm{N}}^{16}$ has been examined at 1.25% resolution with an intermediate-image pair spectrometer. A line is observed corresponding to internal pair conversion of the 6.14-Mev $E3\mathrm{}$ transition from the 3—second excited state to the 0+ ground state of ${\mathrm{O}}^{16}$. The upper limit on the intensity of a 6.06-Mev nuclear pair line from the 0+ first excited state (electric monopole transition) is 10% relative to the 6.14-Mev line and this corresponds to an upper limit of 1.5×${10}^{-4\mathrm{}}$ for the fractional beta decay to the 6.06-Mev level. A lower limit of 8.2 is derived for the $log\mathrm{ft}$ value of this 2- →0+ beta-ray branch as compared with the known $logft=6.7\mathrm{}$ for the 2- →0+. 10.4-Mev branch to the ground state.

• Received 29 May 1958

DOI:https://doi.org/10.1103/PhysRev.111.1586