Angular-Correlation Measurements and theSi30(p, γ)P31Reaction

Abstract

Gamma-ray angular-distribution and triple-correlation measurements have been performed at the $E_p=1095-, 1204-, \mathrm{and} 1322$-keV resonances in the ${\mathrm{Si}}^{30}(p, \gamma ){\mathrm{P}}^{31}$ reaction which provide new information on properties of the $E_x=3.29-, 3.51-, 4.26-, \mathrm{and} 4.63$-MeV levels of ${\mathrm{P}}^{31}$. The angular-correlation data have been analyzed with newly developed search programs which utilize the substate population representation and a recently introduced factored form of the correlation functions which is applicable to multiple cascades. The previous assignments 3.29 ($\frac{5}{2}$), 3.51 ($\frac{3}{2}$), and 4.26 ($\frac{3}{2}$) are confirmed, and $J=\frac{3}{2}$ is assigned to the 4.63-MeV level. The 3.29-MeV level decays in the ratio 77:23 to the 1.27- and 2.23-MeV levels. No evidence is found for the previously reported 3.29 → 0 transition. The quadrupole-dipole amplitude ratios ($\delta$) for the 3.29 → 1.27 and 3.29 → 2.23 transitions are -0.44±0.02 and -0.41±0.06, respectively. The value of $\delta$ for the 3.51 → 0 transition is -0.41±0.03 or 7.1±1.0. The 3.51-MeV level was also found to decay to both the first-and second-excited states and unambiguous values for the mixing ratios were obtained. The 4.26-MeV level was found to decay in the ratio 76:20:4 to the ground, first-excited, and second-excited states. The 4.63-MeV level was found to decay in the ratio 27:52:21 to the same states. A new decay scheme is proposed for the $E_p=1095\mathrm{}$-keV resonance which proved to be more complex than had been previously reported. The values of $\delta$ obtained for the 4.26→0, 4.26→1.27, 4.63→0, and 4.63→1.27 transitions are -0.32±0.04 or 4.7±0.9, -0.25±0.05, 0.07±0.04 or 1.48±0.12, and -0.02±0.05 or -3.9±1.0, respectively. All the ambiguities in $\delta$, except for the last one, are due to inherent limitations in the intensity-direction correlation method. The extended version of the triple-correlation formulation for multiple cascades was found to be very useful in some of the more complex situations encountered in this work. A brief review of recent model calculations which relate to properties of states in ${\mathrm{P}}^{31}$ is given. On the basis of comparison of results of available calculations, it appears that the weak-coupling unified models receive the most support from the existing data.