Angular-Correlation Studies of the ReactionsO16(He3,pγ)F18andO16(He3,αγ)O15

Abstract

The properties of some bound and nearly bound states of ${\mathrm{F}}^{18}$, excited in the reaction ${\mathrm{O}}^{16}({\mathrm{He}}^{3},p\ensuremath{\gamma}){\mathrm{F}}^{18}$, have been studied by particle-gamma coincidence experiments. Angular correlations of the decay gamma rays, in coincidence with protons detected at angles close to 180\ifmmode^\circ\else\textdegree\fi{} in an annular counter, were measured for three bombarding energies: 4.69, 4.84, and 5.26 MeV. Strong correlations associated with the 2.10-MeV level were observed for 5.26-MeV ${\mathrm{He}}^{3}$ energy, enabling it to be shown that the 2.10 MeV\ensuremath{\rightarrow}0 transition is almost pure dipole, and to be confirmed that the 1.08-MeV level has spin zero. Results have been obtained for 12 levels of ${\mathrm{F}}^{18}$, from 3.72- to 5.29-MeV excitation energy, which had previously been little studied. Gamma-ray decay schemes have been given for all these levels, and in many cases limits have been placed on their spins from the angular-correlation results. The 3.72- and 4.84-MeV levels have been assigned $J=1$. Further experimental support was found for the suggestion that the 4.65- 4.74-, and 4.96-MeV levels are the analog states of the 3.55-, 3.63-, and 3.92-MeV levels of ${\mathrm{O}}^{18}$. Among the unbound levels, no evidence was found for alpha-particle emission competing with the gamma-ray decay, except for the 5.29-MeV level, the highest level studied. Some additional results are also given for the 5.19-5.24-MeV doublet of ${\mathrm{O}}^{15}$ excited in the reaction ${\mathrm{O}}^{16}({\mathrm{He}}^{3},\ensuremath{\alpha}\ensuremath{\gamma}){\mathrm{O}}^{15}$.