Spectroscopic study of multinucleon transfer reactions induced by heavy ions

Abstract

One- and two-nucleon transfer reactions induced by light projectiles have long been established as powerful spectroscopic tools to test one- and two-nucleon configurations of the wave functions describing the excited states of the residual nucleusA comparative to the target nuclei A—! and A—2. As soon as heavy ion beams became available, a further step was made in the experimental study of few-nucleon configurations by increasing the number of transferred particles as well as the variety of reactions leading to the same residual nucleus. It is well known that many theoretical models emphasize the role played by four-nucleon correlations in the microscopic description of deformed states. For nuclei at the beginning of the 2s—ld shell, the ( 6Li, d) and (7Li, t) reactions have largely been used to investigate such many-particle—many-hole configurations. The resuits show that these a-transfer reactions populate very selectively the deformed states such as those of the 4p—-4h rotational band in 160 starting at the 6.06 MeV 0~excited state, the 4p—0h ground state band in 20Ne as well as the negative parity band based on the 1 state at 5.80 MeV. Due to the low cross-sections of the (6Li, d) and (7Li, t) reactions on lf—2p shell nuclei, only very recent experiments were successful in collecting energy spectra on 40Ca, 54Fe and 58Ni targets [1—31. A comparison between (160 12C) and (7Li, t) energy spectra shows that the same levels are generally populated by both reactions but the reaction cross-sections are larger for the former. Furthermore, with the 160 beam at incident energies above the Coulomb barrier, (160 ‘5N) and (160, 14C) reactions having negative Q-values of a few MeV have been observed in addition to the (160 12C) one. The one-proton transfer reactions excite the same states as the (3He, d) reaction. Thus no evidence is seen for two-step processes. The possibility of studying two-proton transfer through (160 ‘4C) is of particular interest due to the experimental difficulties associated with neutron detection in (3He, n) reactions. The experimental study of the reaction mechanism for (160 12C) and (160, ‘4C) has been carried out by measuring angular distributions atseveral incident energies and excitation functions [41 A semi-classical description of the experimental results shows the strong influence of nuclear distortions on multinucleon-transfer reactions which appear with increasing incident energies. It will be seen that spectroscopic information concerning the transferred nucleons can be achieved only through a complete finite range DWBA calculation including a microscopic nuclear structure form factor. The relative influence of the kinematical factors and nuclear structure factors on the DWBA cross-sections has been also investigated. The preliminary results of the DWBA analysis of the 54Fe(160, 12C)58Ni and 48Ca(’60, 14C)50Ti angular distributions are discussed. Finally, (160 ‘4C) and (160 ‘2C) transfer reactions on different lf—2p shell targets [51 are described.