DIFFERENTIAL CROSS-SECTIONS OF THE C-12,C-13(P,P)C-12,C-13 AND C-12,C-13(P,N)N-12,N-13 REACTIONS NEAR 180-DEGREES

The recoil detection method has been used to measure the differential cross sections at nucleon backward angles, 160 degrees-180 degrees (cm ), for the C-12,C-13(p,p)C-12,C-13 and C-12,C-13(p,n)N-12,N-13 reactio ns at an incident proton energy of 200 MeV. These are the first report ed data in this angular region. The elastic scattering cross sections show a shallow minimum at 180 degrees and are about a factor of 15 lar ger than those predicted by optical model calculations using standard parameters. The (p,n) cross sections are lower than the (p,p), flat wi thin the rather limited statistics, and about a factor of 5 greater th an predicted. The backward-angle elastic scattering cross sections are selectively sensitive to the real central potential and can be brough t into fairly good agreement with experiment without destroying the fi t at more forward angles by greatly reducing both its depth and diffus eness. Adding a Majorana exchange term in the real central and spin or bit potential to a phenomenological potential that fits previously rep orted lower-angle C-12 elastic scattering data does not significantly alter these fits while introducing a peak at 180 degrees.