Isoscalar transitions and $$\alpha $$ cluster structures in heavy nuclei

Abstract

Isoscalar monopole and dipole transitions are investigated in the medium and heavier systems, such as $$^{44}\hbox {Ti}$$ and even $$^{104-110}\hbox {Te}$$ nuclei by employing the macroscopic $$\alpha $$ cluster model of $$\alpha + {}^{40}\hbox {Ca}$$ and $$\alpha + {}^{100-106}\hbox {Sn}$$ , respectively. Theoretical calculations predict that the strengths of the monopole and dipole transitions are strongly enhanced in the excitation energy below 10 MeV. These low-lying enhancements are induced by the excitation in the relative motion of the $$\alpha $$ cluster and the residual nucleus, and the magnitudes of the transition matrix element are comparable to the single nucleon excitation, which requires much higher excitation energy than the energy for the $$\alpha $$ excitation. The electric dipole strength is also calcluated for $$^{135}\hbox {Cs}$$ with the cluster model of $$\alpha + {}^{131}\hbox {I}$$ , which is a kind of nuclear waste. The application of the monopole and dipole transitions involving the $$\alpha $$ emission to the nuclear transmutation of the nuclear wastes is also discussed.