Abstract
Background: The neutron-rich calcium isotopes have gained particular interest as evidence of closed-shell structures has recently been found in two exotic nuclei, at and . Additionally, the study of such neutron-rich systems has revealed new aspects of nuclear forces, in particular regarding the role of three-nucleon forces.
Purpose: We study the electromagnetic properties of Ca isotopes around the neutron number .
Methods: High-resolution bunched-beam collinear laser spectroscopy was used to measure the optical hyperfine spectra of the isotopes.
Results: The ground-state magnetic moments of and quadrupole moments of were measured for the first time, and the ground-state spin /2 was determined in a model-independent way. Our experimental results are compared with state-of-the-art shell-model calculations using both phenomenological interactions and microscopic interactions derived from chiral effective field theory.
Conclusions: The results for the ground-state moments of neutron-rich isotopes are in excellent agreement with predictions of interactions derived from chiral effective field theory including three-nucleon forces. Lighter isotopes illustrate the presence of particle-hole excitations of the core in their ground state. Our results provide a critical test of modern nuclear theories, and give direct answer to the evolution of ground-state electromagnetic properties in the Ca isotopic chain across three doubly closed-shell configurations at , 28, 32 of this unique system.
- Received 10 November 2014
- Revised 8 April 2015
DOI:https://doi.org/10.1103/PhysRevC.91.041304
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Published by the American Physical Society