DETERMINATION OF PROTON RADII OF NEUTRON-RICH OXYGEN ISOTOPES FROM CHARGE-CHANGING CROSS SECTION MEASUREMENTS

Abstract

The nuclear charge radius is an important bulk property of the nucleus for investigating nuclear structure. The nuclei lying close to the boundaries of the nuclear chart (the drip lines) have revealed new exotic features like the halo and skin. Another new phenomenon that has emerged in the neutron-rich region is the changing or vanishing of magic numbers. The systematic study of the proton radii along an isotopic chain is crucial for understanding the halo and skin formation and also the shell evolution in neutron-rich nuclei near the drip-line. We present the first determination of the proton radii of neutron-rich oxygen isotopes. The proton radii of 16,18-24O were measured using the charge-changing cross sections, σcc, which is the total cross section for the change of the atomic number of the projectile nucleus due to any interaction with the protons in the projectile nucleus. The experiment was performed at the fragment separator (FRS) at GSI, Germany, at a relativistic beam energy of around 900A MeV. The proton radii were extracted from the measured σcc using the finite-range Glauber model analysis. The measured proton radii of stable isotopes of oxygen, 16O and 18O, are consistent with the proton radii derived from the electron scattering experiments. A decrease in proton radii of 22O and 24O was observed, showing signatures of the unconventional shell closures at N = 14 and N = 16. This thesis also reports the first determination of neutron skin thickness (∆R) in neutron-rich oxygen isotopes, determined using the measured proton radii reported in this work and measured matter radii available from the literature. ∆R rapidly increases from 22-24O approaching the neutron drip-line, establishing a thick neutron surface for the neutron-rich oxygen isotopes. We have compared the measured proton radii to the predictions reported using various ab initio approaches with different interactions. The experimental proton radii presented have challenged these predictions.