Ep=1.118MeV resonance in theAl27(p,γ)Si28reaction

Abstract

The 12.664-MeV level in $^{28}\mathrm{Si}$ has been populated by resonant proton capture at 1.118 MeV in the $^{27}\mathrm{Al}(p,\ensuremath{\gamma})^{28}\mathrm{Si}$ reaction. $\ensuremath{\gamma}$-ray angular distributions have been measured with a 80-${\mathrm{cm}}^{3}$ Ge(Li) detector. The spin of the 11.432-MeV level is most probably 4 with $T=0$; for the 8.413-MeV level, the assignment ${J}^{\ensuremath{\pi}}={4}^{\ensuremath{-}}$ is in agreement with the present data. Mixing ratios for $\ensuremath{\gamma}$-ray transitions have been extracted from the angular distributions. Lifetime and branching-ratio studies have been made at ${E}_{p}=1.118,1.724, \mathrm{and} 2.876$ MeV. Emphasis was given to measurements on levels at 8.413, 9.702, and 11.577 MeV, as possible candidates for the ${4}^{\ensuremath{-}}$, ${5}^{\ensuremath{-}}$, and ${6}^{\ensuremath{-}}$ states of a ${K}^{\ensuremath{\pi}}={3}^{\ensuremath{-}}$ rotational band based on the 6.879-MeV level. The observed $E2$ transition strengths are not in agreement with the above assumption. A strength of 0.3 Weisskopf units is found for the 12.664\ensuremath{\rightarrow}8.413-MeV $M1$ transition, which is in conformity with a ${J}^{\ensuremath{\pi}}\ensuremath{\rightarrow}{J}^{\ensuremath{\pi}}$, $\ensuremath{\Delta}T=1$ transition in a self-conjugate nucleus; this result may suggest the possibility of another interpretation of these negative-parity states, relied on one-particle - one-hole configurations.[NUCLEAR REACTION $^{27}\mathrm{Al}(p,\ensuremath{\gamma})^{28}\mathrm{Si}$, ${E}_{p}=1.724,2.876$ MeV; measured $\ensuremath{\gamma}$-ray branching ratios, Doppler-shift attenuation. ${E}_{p}=1.118$ MeV; measured resonance strength, $\ensuremath{\gamma}$-ray branching ratios, mixing ratios, Doppler-shift attenuuation; deduced transition strengths. Natural targets, Ge(Li) detectors.]