The radiative capture reactions 40Ca(α, γ)44Ti and 48Ca(α, γ)52Ti in the region of the giant dipole resonance

Abstract

Abstract An investigation of the reactions 40Ca(α,γ)44Ti and 48Ca(α,γ)52Ti in the region of the giant dipole resonance (GDR) has been completed. For the 40Ca(α,γ) reaction, 90° excitation functions over the bombarding energy range 6.5–17.5 MeV were obtained for γ- transitions to the ground state and first excited state in 44Ti and for a sum of the unresolved transitions to the third and fourth excited states in 44Ti. Angular distributions were measured at the extrema of the excitation functions. These data suggest that the 40Ca(α,γ) reaction proceeds predominantly via an isospin forbidden El transition and populates the T = 1, GDR states of 44Ti via T = 0 isospin impurities. The results provide an estimate of the isospin mixing in the GDR as well as support for a possible giant quadrupole resonance somewhat lower in excitation energy in 44Ti. The excitation functions exhibit a gross structure which reflects the isospin mixing in the GDR of 44Ti, and a structure of intermediate width which may reflect T = 0 α- cluster states in 44Ti. The 48 Ca (α,γ o ) differential cross section was investigated at 90° over the bombarding energy range 6.0–14.0 MeV. The cross section for the isospin allowed 48 Ca (α γ 0 ) reaction was found to be a factor of 20 smaller than that for the isospin forbidden 40 Ca (α,γ 0 ) reaction.