Gamma Decay ofT=32States inAl25andP29

Abstract

The yield curve of the residual ${\mathrm{Al}}^{25}$ activity from the ${\mathrm{Mg}}^{24}(p, \gamma )$ reaction was used to locate the lowest two $T=\frac{3}{2}$ states in ${\mathrm{Al}}^{25}$ at $E_p=5.864\mathrm{}\pm 0.005$ MeV, $E_x=7.916\mathrm{}\pm 0.006$ MeV and at $E_p=5.936\mathrm{}\pm 0.005$ MeV, $E_x=7.985\mathrm{}\pm 0.006$ MeV. Each of the resonances was narrower than the estimated 3-keV spread in the proton beam. $\gamma$-ray spectra were measured with a Ge(Li) detector at both resonances. The lower resonance shows strong, approximately equal transitions to the ground state and to the third excited state in ${\mathrm{Al}}^{25}$, as well as a weaker branch to the second excited state. The decay of the upper resonance is predominantly that to the ground state, but weaker branches go to the first and second states. The decay schemes support a ${\frac{5}{2}}^{+}$ assignment for the lower $T=\frac{3}{2}$ state and favor ${\frac{3}{2}}^{+}$ for the upper. Rough angular-distribution measurements on the ground-state $\gamma$ ray further support these assignments and indicate that the radiations are close to pure $M1\mathrm{}$. The various $\gamma$-ray transition probabilities are well explained by a rotational picture for the low $T=\frac{3}{2}$ states. $\gamma$ spectra were also taken at the lowest $T=\frac{3}{2}$ resonance in ${\mathrm{P}}^{29}$, which had previously been located at $E_x=8.374\mathrm{}\pm 0.005$ MeV, and it was found to feed the first, second, and third excited states.