12C(12C,8Be)16O cross-section measurement at sub-barrier energies.

Abstract

Differential cross sections for the /sup 12/C(/sup 12/C, /sup 8/Be..-->..2..cap alpha..)/sup 16/O reaction have been measured at eight incident energies in the 2.43less than or equal toE/sub c.m./less than or equal to5.24-MeV range, detecting ..cap alpha.. particles in 200-..mu..m thick Makrofol polycarbonate foils, which were subsequently carefully etched and scanned under microscope for the /sup 8/Be..-->..2..cap alpha.. group and the ..cap alpha.. groups from the /sup 12/C(/sup 12/C, ..cap alpha..)/sup 20/Ne reaction. The /sup 8/Be channel cross section, ranging between 4 x 10/sup -4/ ..mu..b and 280 ..mu..b, is smaller for E/sub c.m./greater than or equal to3.91 MeV, but larger for E/sub c.m./less than or equal to3.13 MeV than the ..cap alpha../sub 0/+/sup 20/Ne/sub g.s./ channel cross section. The /sup 12/C(/sup 12/C, /sup 8/Be)/sup 16/O cross section is well reproduced by the distorted-wave Born approximation calculation of a direct ..cap alpha..-transfer reaction down to E/sub c.m./ = 3.91 MeV. In the 3.13greater than or equal toE/sub c.m./ greater than or equal to2.43-MeV range, however, the measurements exceed the distorted-wave Born approximation prediction by one to three orders of magnitude. It is suggested that the formation of /sup 12/C-/sup 12/C dinuclear states, favoring an ..cap alpha.. transfer, becomes a predominant processmore » at incident energies E/sub c.m./less than or equal to3.13 MeV.« less