3α cluster structure and monopole transition in 12C and 14C

3 alpha cluster structures and monopole transitions of 0(+) states in C-12 and C-14 were investigated with 3 alpha and Be-10+alpha cluster models. A gas-like 3 alpha state and a bending chain 3 alpha state were obtained in the 0(2)(+) and 0(3)(+) states of C-12, respectively. In C-14, a linear chain 3 alpha structure was found in the 0(4)(+) state near the Be-10+alpha threshold, but a cluster gas-like state did not appear in low-lying 0(+) states because valence neutrons attract alpha clusters and suppress spatial development of 3 alpha clustering. It was found that the linear chain state in C-14 is stabilized against the bending and alpha escape modes by valence neutrons. The monopole transition strengths in C-12 were enhanced by 3 alpha cluster development, whereas those in C-14 were not enhanced so much because of the tight binding of alpha clusters by valence neutrons.