Evidence of a sudden increase in the nuclear size of proton-rich silver-96

Abstract

<jats:title>Abstract</jats:title><jats:p>Understanding the evolution of the nuclear charge radius is one of the long-standing challenges for nuclear theory. Recently, density functional theory calculations utilizing Fayans functionals have successfully reproduced the charge radii of a variety of exotic isotopes. However, difficulties in the isotope production have hindered testing these models in the immediate region of the nuclear chart below the heaviest self-conjugate doubly-magic nucleus <jats:sup>100</jats:sup>Sn, where the near-equal number of protons (<jats:italic>Z</jats:italic>) and neutrons (<jats:italic>N</jats:italic>) lead to enhanced neutron-proton pairing. Here, we present an optical excursion into this region by crossing the <jats:italic>N</jats:italic> = 50 magic neutron number in the silver isotopic chain with the measurement of the charge radius of <jats:sup>96</jats:sup>Ag (<jats:italic>N</jats:italic> = 49). The results provide a challenge for nuclear theory: calculations are unable to reproduce the pronounced discontinuity in the charge radii as one moves below <jats:italic>N</jats:italic> = 50. The technical advancements in this work open the <jats:italic>N</jats:italic> = <jats:italic>Z</jats:italic> region below <jats:sup>100</jats:sup>Sn for further optical studies, which will lead to more comprehensive input for nuclear theory development.</jats:p>