Catherine Olmer

In order to investigate whether new nuclear structure information can be obtained from studying the direct transfer of more than two nucleons using heavy-ion projectiles, we have investigated the ²⁸Si(¹⁶O, ¹²C) ³²S and ¹²C (¹⁴N, d) ²⁴Mg reactions as candidates for the direct transfer of four- and twelve-nucleons, respectively.

Using a new experimental technique developed in this work–the counter telescope-position sensitive detector kinematic coincidence method–both angular distributions (22^˚ < θ_L < 95^˚ , E_L = 55.54 MeV) and excitation functions (θ_L = 26˚, 50 < E_L < 63 MeV) were obtained for strongly excited states below 10 MeV in excitation in the first reaction. For the ¹²C + ¹⁴N interaction, a measurement of the angular distri­butions (25° < 0L < 14o⁰,    = 20,25 MeV) for proton, deuteron and alpha-particle emission to many low lying states suf­ficed for the present purposes.

Comparison of Hauser-Feshbach statistical model cal­culations with these data indicated that the light-particle production from the ¹²C + ¹⁴N interaction as investigated here is predominantly compound nuclear in nature. On the other hand, the selectively strong population of a few states in 3²S by the ²⁸Si(¹⁶O,¹²C)³²S reaction is primarily direct. The structure of these states was deduced from available light-ion-induced transfer reaction studies and shell model calculations: the importance,of shell model con­ figurations is indicated, and an alpha-particle transfer model can not account for the observed selectivity.

Calculations of the ²⁸Si(¹⁶O,¹²C)3²S reaction with a microscopic multinucleon transfer code indicate selectivities consistent with the present results. Moreover, the calcu­ lations suggest the presence of other, unexpected selecti­vities, all of which may be understood on a physical basis, and some of which appear as an extension of a similar effect seen in two-nucleon transfer reactions.