Imprint of a nuclear bubble in nucleon-nucleus diffraction

Abstract

Background: The density of most nuclei is constant in the central region and is smoothly decreasing at the surface. A depletion in the central part of the nuclear density can have nuclear structure effects leading to the formation of "bubble" nuclei. However, probing the density profile of the nuclear interior is, in general, very challenging. Purpose: The aim of this paper is to investigate the nuclear bubble structure, with nucleon-nucleus scattering, and quantify the effect that has on the nuclear surface profile. Method: We employed high-energy nucleon-nucleus scattering under the aegis of the Glauber model to analyze various reaction observables, which helps in quantifying the nuclear bubble. The effectiveness of this method is tested on $^{28}$Si with harmonic-oscillator (HO) densities, before applying it on even-even $N = 14$ isotones, in the $22 \leq A \leq 34$ mass range, with realistic densities obtained from antisymmetrized molecular dynamics (AMD). Results: Elastic scattering differential cross sections and reaction probability for the proton-$^{28}$Si reaction are calculated using the HO density to design tests for signatures of nuclear bubble structure. We then quantify the degree of bubble structure for $N = 14$ isotones with the AMD densities by analyzing their elastic scattering at 325, 550 and 800 MeV incident energies. The present analyses suggest $^{22}$O as a candidate for a bubble nucleus, among even-even $N = 14$ isotones, in the $22 \leq A \leq 34$ mass range. Conclusion: We have shown that the bubble structure information is imprinted on the nucleon-nucleus elastic scattering differential cross section, especially in the first diffraction peak. Bubble nuclei tend to have a sharper nuclear surface and deformation seems to be a hindrance in their emergence.