Molecular resonance and highly deformed fission fragments in {sup 28}Si+{sup 28}Si

• Published in: Physical review. C, Nuclear physics Nuclear physics, 2001-01, Vol.63 (1)
• Main Authors: Beck, C., Nouicer, R., Disdier, D., Duche {cflx}ne, G., de France, G., Freeman, R. M., Haas, F., Hachem, A., Mahboub, D., Rauch, V.
• Format: Article
• Language: English
• Subjects: ANGULAR CORRELATION; ANGULAR DISTRIBUTION; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; EXCITED STATES; FISSION; FISSION FRAGMENTS; ORBITAL ANGULAR MOMENTUM; RESONANCE; SPIN ORIENTATION
• ISSN: 0556-2813; 1089-490X
• DOI: 10.1103/PhysRevC.63.014607

A high-resolution measurement of fragment-fragment-{gamma} triple coincidence events in the symmetric and near-symmetric mass exit channels from the {sup 28}Si+{sup 28}Si reaction has been undertaken using the EUROGAM Phase II {gamma}-ray spectrometer. The bombarding energy of E{sub lab}({sup 28}Si)=111.6 MeV has been selected to populate the conjectured J{sup {pi}}=38{sup +} quasimolecular resonance in the {sup 56}Ni dinuclear system. In the {sup 28}Si+{sup 28}Si symmetric mass exit channel, the resonance behavior is clearly verified at the chosen energy. The population of highly excited states in the {sup 24}Mg, {sup 28}Si, and {sup 32}S nuclei is discussed within a statistical fusion-fission model. Evidence is presented for selective population of states in the {sup 28}Si fragments arising from the symmetric fission of the {sup 56}Ni compound nucleus. The enhanced population of the K{sup {pi}}=3{sub 1}{sup -} band of the {sup 28}Si nucleus, indicative of an oblate deformed shape, suggests that the oblate configuration plays a significant role in the resonant process. Fragment angular distributions for the elastic and low-lying inelastic channels as well as {gamma}-ray angular correlations for the mutual inelastic channel (2{sup +},2{sup +}) indicate that the spin orientations of the outgoing fragments are perpendicular to the orbital angular momentum. This unexpected result, which is different from the alignment found for the resonance structures in the {sup 24}Mg+{sup 24}Mg and {sup 12}C+{sup 12}C systems, suggests a situation where two oblate {sup 28}Si nuclei interact in an equator-to-equator stable molecular configuration. A discussion concerning the spin alignment and spin disalignment for different reactions such as {sup 12}C+{sup 12}C, {sup 24}Mg+{sup 24}Mg, and {sup 28}Si+{sup 28}Si is presented.