EXPERIMENTAL STUDY AND DISTORTED-WAVE PREDICTIONS FOR THE (He$sup 3$,$alpha$) REACTION ON Fe ISOTOPES

Angular distributions of some alpha-particle groups from the (He/sup 3/, alpha ) reaction on Fe/sup 54/, Fe/sup 56/, Fe/sup 57/, and Fe/sup 5 8 /have been obtained experimentally. The He/sup 3/ beam energy was about 14.3 Mev except that data were also obtained for the Fe/sup 57/ target with a beam energy of 24.9 Mev. Angular distributions were also obtained for He/sup 3/ and alpha particles elastically scattered from Fe/sup 56/. For the (He/sup 3/, alpha ) reaction, groups corresponding to 1 = 3 neutron transfers were peaked strongly forward, while groups corresponding to 1 = 1 neutron transfers were not but showed much more diffraction structure. The cross sections for the strong 1 = 3 groups were very much larger than those for the strongest of the 1 = 1 groups. This ratio is in distinct contrast to the results of (d,t) and (p,d) experiments on the same isotopes. In addition, the Fe/sup 57/(He/sup 3/, alpha ) reaction to the ground and firstexcited states of Fe/sup 56/ proceeded with a cross section lower by more than an order of magnitude than that expected on the basis more » of data from the (d,t) and (p,d) reactions. The (He/sup 3/, alpha ) reaction cannot be satisfactorily analyzed with the plane-wave Butler-Born calculation. In contrast, the distorted-wave Born-approximation calculation predicts curves which are usually in good agreement with the experimental angular distributions, and yields ratios of spectroscopic factors which are in fair to good agreement with the results of a plane-wave analysis of the (d,t) data and in fair agreement with the results of a distorted-wave analysis of the (p,d) data. The parameter values used in the distorted-wave calculation for the (He/sup 3/, alpha ) reaction on Fe/ sup 54/, Fe/sup 56/, and Fe/sup 58 /were very nearly those which yielded the best optical-model fits to the Fe/sup 54/ elastic scattering data. The distorted-wave calculation for the Fe/sup 57/(He/sup 3/, alpha )Fe/sup 56/ reaction required somewhat different parameter values. (auth) « less