  It is a well-known fact that a cluster of nucleons can be formed in the
interior of an atomic nucleus, and such clusters may occupy molecular-like
orbitals, showing characteristics similar to normal molecules consisting of
atoms. Chemical molecules having a linear alignment are commonly seen in
nature, such as carbon dioxide. A similar linear alignment of the nuclear
clusters, referred to as linear-chain cluster state (LCCS), has been studied
since the 1950s, however, up to now there is no clear experimental evidence
demonstrating the existence of such a state. Recently, it was proposed that an
excess of neutrons may offer just such a stabilizing mechanism, revitalizing
interest in the nuclear LCCS, specifically with predictions for their emergence
in neutron-rich carbon isotopes. Here we present the experimental observation
of {\alpha}-cluster states in the radioactive 14C nucleus. Using the
10Be+{\alpha} resonant scattering method with a radioactive beam, we observed a
series of levels which completely agree with theoretically predicted levels
having an explicit linear-chain cluster configuration. We regard this as the
first strong indication of the linear-chain clustered nucleus.
