Study Of ~8b Breakup Reaction

Halo structure is one of the hot topics in nuclear physics accessible with the development of radioactive beam facility, particle detection technique and theory in the past 30 years. This thesis focuses on the halo structure of the proton drip line nuclei 8B. There are two experiemtnal evidences to confirm8 B as a halo nucleus, theabrupt enhanced total reaction cross section and the narrow momentum distribution. Previous experiment preformed at GSI showed the narrow longitudinal momentum distribution of 7Be to illustrate the existence of halo structure in 8B.And the experiment at MSU with the incident energy of 41 AMe V gave a very narrow momentum distribution and they found it can be explained by theoretical model without halo structure in 8B. So it is still an open question whether the narrow momentum distribution is an evidence of halo structure for 8B.The erecent experiment at MSU with the incident energy of 86.7 Me V/u showed a new technology to distinguish the diffraction and stripping mechanism in the breakup of 8B. In this thesis, the same technology is used to study thestripping and diffraction mechnisms in8 B breakup reactionsand the longitudinal momentum distributions of 7Be are presented for the first time at 36.7 Me V/u 8B breakup reaction.The experiment is performed at Radioactive Ion Beam Line in Lanzhou(RIBLL). The secondary 8B beams at 36.7Me V/u bombardthe Carbon target.Two position-sensitive Parallel-Plate Avalanche Counters(PPACs) are settled before the target to provid the position of the incoming beams with a position resolution better than 1 mm. A ΔE-E telescope array is used todetect the reaction products with completely kinematic measurement. The first part of the telescope array is a double-sided silicon strip detector(DSSD) with a thickness of 1000μm and a sensitive area of 40×40 mm2 which is divided into 40 strips in each side. The second part is a Cs I(Tl) crystal array which is composed of 64(8×8) Cs I(Tl) crystals. With the coincidence fragments7 Be and proton, the sum energy spectrum of 8Bare reconstructed and the stripping and diffraction events are clearly distinguished.The FWHMs of 7Be longitudinal momentum distribution for diffraction and stripping mechanismsin the lab frame are 92±7Me V/c and 124±17Me V/crespectively. Additionally, the angular distribution of fragmental 7Be; the one proton removal cross section of 8B; the one and two proton removal cross section of 9C are also measured in this experiment.With CDCC calculation for diffraction mechanism and eikonal model with KDe and KDp potential for stripping mechanism, the theoretical results show the same tendency with experimental data. For part of energy exciting the target nucleus, the longitudinal momentum distribution from the stripping part is wider than that from the diffractive part. The stripping width of the unmodified Serber model agreement with our data, it means that after distinguishing the reaction mechanisms the localization effect and opaque limit are unnecessary to be employed. Based on the core of 7Be and a valence proton Serber model, the 7Be longitudinal momentum distribution in diffraction mechanism is very well agreement with our data.It illustrate that, after considering the reaction mechanisms, the distribution in diffraction is still an evidence to support the 8B halo structure.