Production of 149Tb in deep inelastic transfer reactions: an approach to the angular momentum of fragments

The excitation functions for deep inelastic reactions in which two to six charges are transferred from 40Ar and 63Cu ions to rare earth targets have been measured using activation techniques, the observed radionuclides being 150Dy, 151Dy and 149gTb. From the comparison of the curves relative to 149gTb and those relative to 150Dy, 151Dy, it was deduced that the low spin isomer 149gTb was produced with significant probability for low incident energies. Using data from (heavy ions, xn) reactions, it was possible to attribute this production to the deexcitation of Tb fragments formed in deep inelastic transfers with angular momenta lower than 9n. This result is in good agreement with the angular momentum calculations performed under the hypothesis that the initial angular momentum window leading to deep inelastic reactions is situated between the critical angular momentum for fusion and that corresponding to grazing collisions. As far as Cu induced reactions are concerned, both hypothesis of rolling and sticking are consistent with the experimental data. For Ar induced reactions, the results indicate that the stage of sticking is not reached when the incident energy is lower than 200 MeV