Alpha-Particle Clustering in Nuclei and Four-Alpha-Particle Condensation in 16O

Low density states near the 3 and 4 breakup threshold in 12C and 16O, respectively, are discussed in terms of the -particle condensation. Calculations are performed in OCM(Orthogonality Condition Model) and THSR (Tohsaki- Horiuchi-Schuck-Röpke) approaches. The 0+2 state in 12C and the 0+6 state in 16O are shown to have dilute density structures and give strong enhancement of the occupation of the S-state c.o.m. orbital of the -particles. The 0+6 state in 16O has a large component of +12C(0+2 ) configuration, which is another reliable evidence of the state to be of 4 condensate nature. The possibility of the existence of -particle condensed states in heavier n nuclei is also discussed.