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

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 degree excitation functions over the bombarding energy range 6.5 to 17.5 MeV were obtained for gamma 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. The data reveal that the 40Ca(α,γ) reaction proceeds predominantly via the isospin forbidden E1 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 (GQR) below the GDR 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 alpha cluster states in 44Ti. The 48Ca(α, γ) 90 degree differential cross section was investigated over the bombarding energy range 6.0 to 14.0 MeV. The isospin allowed 48Ca(α,γ0) reaction was found to be a factor of 20 smaller in cross section than the isospin forbidden 40Ca(α, γ0) reaction