Abstract
We perform the first direct mass measurements of neutron-rich calcium isotopes beyond neutron number 34 at the RIKEN Radioactive Isotope Beam Factory by using the time-of-flight magnetic-rigidity technique. The atomic mass excesses of are determined for the first time to be , , and , respectively. We examine the emergence of neutron magicity at based on the new atomic masses. The new masses provide experimental evidence for the appearance of a sizable energy gap between the neutron and orbitals in , comparable to the gap between the neutron and orbitals in . For the nucleus, an open-shell property in neutrons is suggested.
- Received 5 January 2018
- Revised 21 April 2018
DOI:https://doi.org/10.1103/PhysRevLett.121.022506
© 2018 American Physical Society