Alpha particle cluster is an important concept in nuclear physics,
especially for light nuclei. For example, it has been suggested
that the 0+2 state in 12C has
a 3a cluster configuration. Recently,
it has been proposed that the 0+2 state
has a dilute-gas-like structure where three alpha particles
are weakly interacting and are condensed into the lowest s-orbit.
Similar dilute-gas state of alpha clusters have been predicted
in self-conjugate N=4n nuclei. The next natural question addressed
is whether or not such a dilute state of clusters exists in
the other N[\neq]Z nuclei like 11B.
In the present work, the cluster structures of the excited
states in 11B are studied by analyzing the isoscalar
monopole and quadrupole strengths in the deuteron inelastic
scattering at Ed=200 MeV. The excitation strengths
are compared with the theoretical predictions. It is found that
the large monopole strength for the 3/2-3
state is well described by a cluster-model-like wave function
with a dilute 2a + t configuration.
The 5/2-2 state is suggested to have a mixing structure both
with the cluster-model-like and shell-model-like wave functions.
*Note different
day.