Alpha-Alpha Angular Correlations inB11(p, αα)He4

Abstract

The angular correlation in the reaction ${\mathrm{B}}^{11}(p, \alpha \alpha ){\mathrm{He}}^4$ has been measured between the alpha particle emitted from ${\mathrm{C}}^{12}$ and one of the break-up alpha particles from ${\mathrm{Be}}^8$. The measurement was made in a plane at 90 degrees to the proton beam with bombarding energies of 163 and 290 kev. Thin targets of natural boron were used, and the alpha particles detected with thin scintillation counters. The theoretical correlation functions in the laboratory system were obtained by a numerical integration of the center-of-mass angular correlation functions over the 2.9-Mev level in ${\mathrm{Be}}^8$. The probability for decay of the ${\mathrm{C}}^{12}$ state was assumed to have the same energy dependence for different angular momenta of the emitted alpha particle. This energy variation was obtained from the energy spectrum of the alpha particles. Using the two lowest values of angular momentum for the first alpha particle, the 163-kev data were found to be consistent with a 2+ state in ${\mathrm{C}}^{12}$, and 2+ but not 0+ or 4+ in ${\mathrm{Be}}^8$. The data at 290 kev are not consistent with a pure state of spin 1- or 2- or 3+ in ${\mathrm{C}}^{12}$. They are in agreement with a pure state of 2+ or with a superposition of states at this energy.