Beta decay of 18N to alpha particle emitting states in 18O and a proposed search for parity violation in 18O.

Abstract

The beta-delayed alpha-particle emission from $^{18}\mathrm{N}$ has been studied and the absolute beta decay branching ratios of $^{18}\mathrm{N}$ to the ${1}_{3}^{\mathrm{\ensuremath{-}}}$ and ${1}_{4}^{\mathrm{\ensuremath{-}}}$ states in $^{18}\mathrm{O}$ measured. The $^{18}\mathrm{N}$ nuclei were produced using a 35-MeV/nucleon $^{22}\mathrm{Ne}$ beam and a thick Ta target. Reaction products were separated (from the beam) using a reaction products mass separator. A silicon telescope including five detectors and a two-dimensional, position-sensitive, gas counter was used in the focal plane of the mass separator. We obtain beta decay branching ratios of 6.8\ifmmode\pm\else\textpm\fi{}0.5% and 1.8\ifmmode\pm\else\textpm\fi{}0.2 % to the ${1}_{3}^{\mathrm{\ensuremath{-}}}$ and ${1}_{4}^{\mathrm{\ensuremath{-}}}$ states, respectively, assuming 100% alpha-particle decay branching ratios for these states. Shell-model predictions are compared with these experimental results. The relevance of these data to a new proposed search for parity violation in $^{18}\mathrm{O}$ is discussed.