6{alpha}-cluster resonance structures in {sup 12}C+{sup 12}C system and their decay in {alpha} and {sup 8}Be channels

The excitation functions have been measured for the {sup 12}C ({sup 12}C,{alpha}){sup 20}Ne and {sup 12}C({sup 12}C,{sup 8}Be){sup 16}O reactions leading to the excited states up to 25 MeV in {sup 20}Ne and 20 MeV in {sup 16}O, respectively, in the beam energy range E({sup 12}C)=48{endash}72 MeV. The region of excitation investigated was E{sub x}=38{endash}50 MeV in {sup 24}Mg which is well above the threshold for breakup into six alpha particles. In the {sup 8}Be channel leading to the 6{endash}7 MeV region of {sup 16}O, excitation functions were also measured for {sup 8}Be- {gamma} coincidences in {sup 12}C ({sup 12}C,{sup 8}Be){sup 16}O{sup *}{r_arrow}{gamma}+{sup 16}O{sub g.s.} particularly to distinguish between the otherwise unresolved 6.05 MeV, 0{sup +} and 6.13 MeV, 3{sup {minus}} states in {sup 16}O. It is observed that a cluster of resonances in the excitation region 39{endash}43 MeV in {sup 24}Mg decays via {alpha} and {sup 8}Be channels predominantly to the particle-hole states in {sup 20}Ne and {sup 16}O which are members of deformed bands. Another cluster of resonances in the region 44{endash}49 MeV (centered at E{sub c.m.}=32.5 MeV) decays predominantly to the 20.48 MeV state in {sup 20}Ne (which is above the 5{alpha} breakup threshold) and to amore » possible 4{alpha} linear chain band in {sup 16}O around 18 MeV, indicating their highly deformed nature. This latter cluster structure coincides in energy with the possible 6{alpha} linear chain resonance identified in the literature at E{sub c.m.}=32.5 MeV in the inelastic scattering channels {sup 12}C{sub 7.65,0{sup +}}+{sup 12}C{sub 7.65,0{sup +}} and {sup 12}C{sub 7.65,0{sup +}}+{sup 12}C{sub 9.64,3{sup {minus}}}. In this excitation energy region intermediate structures in the {sup 8}Be channel are found at E{sub c.m.}=31.5 and 33.5 MeV decaying to the 6.13 MeV, 3{sup {minus}} state and at E{sub c.m.}=32.5 MeV decaying to the 6.92/7.13 MeV states of {sup 16}O. (Abstract Truncated)« less