, p.061302-1 , 2015-06-04 , American Physical Society
Background: Isoscalar monopole transition has been suggested as a key observable to search for exotic cluster states. Recently, excited 0(+) states with strong isoscalar monopole transition strengths were experimentally reported in Mg-24, but their structures were not revealed because of the lack of theoretical analysis. Purpose: We study the structure of the excited 0(+) states of Mg-24 populated by isoscalar monopole transition from the ground state, and identify their cluster configurations. Method: The 0(+) states of Mg-24 and their isoscalar monopole transition strengths from the ground state are calculated with antisymmetrized molecular dynamics combined with the generator coordinate method using the Gogny D1S interaction. Results: The calculated isoscalar monopole strength function shows reasonable agreement with experiment and is consistent with other theoretical calculations. The structures of the excited 0(+) states with pronounced isoscalar monopole transitions are analyzed. It is found that the 0(2)(+), 0(3)(+), and 0(5)(+) states have mixed nature of mean-field and cluster, and that the 0(8)(+) state is dominated by a C-12 + C-12 cluster configuration. In addition, it is predicted that 5 alpha-pentagon + alpha states appear around 23 MeV. Conclusions: The excited 0(+) states which appear as the prominent peaks in the calculated strength function are associated with Ne-20 + alpha, C-12 + C-12, and 5 alpha-pentagon+alpha cluster states.