Gamma rays from the β decay of ${}_{}{}^{20}{}_{}{}^{}\mathrm{O}$, produced in the ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$(t,p${)}^{20}$O reaction at $E_{\mathrm{t}=3.1\mathrm{}}$ MeV using a Van de Graaff beam and a rabbit target-transfer system, were measured in a Ge-NaI(Tl) Compton-suppression spectrometer. In addition to the principal γ ray, measured as 1056.818(4) keV, a γ ray of 3488.21(10) keV was observed with an intensity corresponding to an ${}_{}{}^{20}{}_{}{}^{}\mathrm{O}$ β-ray branch of 0.027(3)% to the 3488.54(10)-keV $1^{+}$ level of ${}_{}{}^{20}{}_{}{}^{}\mathrm{F}$ with logft=3.65(6). Limits were placed on other β- and γ-ray branches; in particular the β branch to the probable $1^{+}$ level at 3172.6 keV in ${}_{}{}^{20}{}_{}{}^{}\mathrm{F}$ is <0.012% with logft>5.1. The result for the new β branch to the 3488.5-keV level is in excellent agreement with a recent shell-model prediction for the decay to the second $1^{+}$ state of the (2s,1d${)}^4$ model space. The electromagnetic decays of some of the low-lying levels of ${}_{}{}^{20}{}_{}{}^{}\mathrm{F}$ are calculated in this model space and a comparison to experiment reveals a serious discrepancy for level lifetimes in the <50 fs range. An incidental result is an adopted value of 8.2(6)×${10}^{\mathrm{-}3}$% for the β-ray branching of ${}_{}{}^{20}{}_{}{}^{}\mathrm{F}$ to the 4966.5-keV level of ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$.

• Received 18 December 1986

DOI:https://doi.org/10.1103/PhysRevC.35.1479