Beta Decay ofN17to Bound States inO17

Abstract

The beta decay of ${\mathrm{N}}^{17}$ to bound states of ${\mathrm{O}}^{17}$ has been investigated by observation of the beta-ray and gamma-ray spectra with scintillation spectrometers. A gas target of ${\mathrm{N}}_2^{15}$ was bombarded with 2-MeV tritons from an electrostatic generator to yield 4.2-sec ${\mathrm{N}}^{17}$ by the reaction ${\mathrm{N}}^{15}(t, p){\mathrm{N}}^{17}$. Gamma rays of 0.87 and 2.19 MeV were observed, corresponding to beta transitions to the 0.87- and 3.06-MeV levels in ${\mathrm{O}}^{17}$. Analysis of the beta-ray spectrum indicated the presence of a beta-decay branch to the ground state of ${\mathrm{O}}^{17}$. The branching fractions and $log\mathrm{ft}$ values for these three beta transitions are: ${\mathrm{O}}^{17}$ g.s.—1.6%, $logft=7.3\mathrm{}$; 0.87-MeV level—2.6%, $logft=6.8\mathrm{}$; and 3.06-MeV level—0.5%, $logft=6.9\mathrm{}$. Uncertainties in these $log\mathrm{ft}$ values are about ±0.1. The large $log\mathrm{ft}$ value for the allowed transition to the 3.06-MeV state lends support to previous theoretical calculations which indicate that this low-lying negative parity state in ${\mathrm{O}}^{17}$ consists of a three-particle excitation of the ${\mathrm{O}}^{16}$ core.