2-NUCLEON TRANSFER-REACTION MECHANISMS

The roles of the one-step (p-t) process in which two particles are transferred simultaneously and the two-step (p-d-t) process in which two particles are transferred sequentially, are quantitatively investigated for two-nucleon transfer (p, t) reactions with realistic triton and deuteron wave functions and realistic finite-range nuclear interactions. A detailed exact finite-range formulation is given, and analyses of both the one-step and the two-step process are carried out. For the intermediate channels in the sequential transfer process, S-1(0) and S-3(1) + D-3(1) unbound deuteron states as well as the ground state are taken into account. A summary of experimental studies of cross sections and analyzing powers for (p,t) reactions is given. It is found that the simultaneous transfer process alone can reproduce neither the experimental absolute cross sections nor the analyzing powers, and that the sequential transfer process is dominant for both the natural and unnatural parity transitions in the Pb-208(p,t)Pb-206 reactions at 22 and 35 MeV. These results are definitely confirmed by comparing the calculated analyzing powers with experimental data. The nuclear shell structure dependence of the analyzing power for the natural and unnatural parity state transitions is investigated.