2021

Reponen, M.; de Groote, R. P.; Al Ayoubi, L.; Beliuskina, O.; Bissell, M. L.; Campbell, P.; Cañete, L.; Cheal, B.; Chrysalidis, K.; Delafosse, C.; de Roubin, A.; Devlin, C. S.; Eronen, T.; Garcia Ruiz, R. F.; Geldhof, S.; Gins, W.; Hukkanen, M.; Imgram, P.; Kankainen, A.; Kortelainen, M.; Koszorús, Á.; Kujanpää, S.; Mathieson, R.; Nesterenko, D. A.; Pohjalainen, I.; Vilén, M.; Zadvornaya, A.; Moore, I. D.

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 100Sn, where the near-equal number of protons (Z) and neutrons (N) lead to enhanced neutron-proton pairing. Here, we present an optical excursion into this region by crossing the N = 50 magic neutron number in the silver isotopic chain with the measurement of the charge radius of 96Ag (N = 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 N = 50. The technical advancements in this work open the N = Z region below 100Sn for further optical studies, which will lead to more comprehensive input for nuclear theory development.