Nuclear linear-chain structure arises in carbon-14

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 12 C while evidenced its appearance in 16 C. It is then necessary to investigate the linear-chain molecular structures in 14 C 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 14 C 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 14 C. The present results encourage further studies on even longer chain configurations in heavier neutron-rich nuclei.