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The shape and internal structure of an atomic nucleus can change significantly with increasing excitation energy, angular momentum, or isospin asymmetry. As an example of this structural evolution, linear-chain configurations in carbon or heavier isotopes have been predicted for decades. Recent studies have found non-stability of this structure in 12C while evidenced its appearance in 16C. It is then necessary to investigate the linear-chain molecular structures in 14C to clarify the exact location on the nuclear chart where this structure begins to emerge, and thus to benchmark theoretical models. Here we show a cluster-decay experiment for 14C with all final particles coincidentally detected, allowing a high Q-value resolution, and thus a clear decay-path selection. Unambiguous spin-parity analyses are conducted, strongly evidencing the emergence of the π-bond linear-chain molecular rotational band in 14C. The present results encourage further studies on even longer chain configurations in heavier neutron-rich nuclei. The existence of linear-chain configurations in light nuclei has been predicted for decades, but the finding of the exact location on the nuclear chart where this exotic structure emerges has proven to be challenging experimentally. Here, the authors performed an inelastic excitation and cluster-decay experiment followed by unambiguous spin-parity analyses and provide evidence for the emergence of the nuclear chain structure starting from 14C. [ABSTRACT FROM AUTHOR]

The surface of neutron-rich heavy nuclei, with a neutron skin created by excess neutrons, provides an important terrestrial model system to study dilute neutron-rich matter. By using quasi-free a cluster– knockout reactions, we obtained direct experimental evidence for the formation of a clusters at the surface of neutron-rich tin isotopes. The observed monotonous decrease of the reaction cross sections with increasing mass number, in excellent agreement with the theoretical prediction, implies a tight interplay between a-cluster formation and the neutron skin. This result, in turn, calls for a revision of the correlation between the neutron-skin thickness and the density dependence of the symmetry energy, which is essential for understanding neutron stars. Our result also provides a natural explanation for the origin of a particles in a decay. [ABSTRACT FROM AUTHOR]