EFFECTS OF D+HE-5 CLUSTER CONFIGURATION IN THE 7-NUCLEON SYSTEM

The d + He-5 configuration is adopted to expand the model space of a previous resonating-group study in the seven-nucleon system which employs t + alpha, n + Li-6, and n + Li-6* cluster configurations. The results show that the addition of this particular configuration has only moderate effects on the phase-shift values and the level positions. On the other hand, it is also found that, with this configuration, the calculated total reaction cross sections are substantially modified. In the t + alpha-channel at 15.95 MeV and the n + Li-6 channel at 12.8 MeV, the calculated results of the total reaction cross sections are equal to about 70% and 80% of the experimental values, respectively. In addition, we obtain from this investigation also several pieces of useful information concerning reaction mechanisms. These are: (i) at relatively low energies, sequential-decay processes are considerably more important than direct-breakup processes, (ii) one-nucleon transfer processes make large contributions and must always be taken into consideration, and (iii) two-step processes have moderate, but not dominant, influence. Defects of this study are also discussed. The finding that the calculated total reaction cross sections are still too small is a clear indication that the model space needs to be further expanded. Based on theoretical considerations and experimental information, we are quite certain that the most important missing configuration is the d' + He-5 cluster configuration, with d' representing the singlet S-state of the deuteron.