Explorando la estructura de halo a través de la dispersion en torno a la barrera en 208Pb : los casos de 15C y 17NeExploring the halo structure via near-barrier scattering on 208Pb : the cases of 15C and 17Ne

Abstract

This thesis intends to reflect the work I’ve performed as a PhD student during the last four years and a half at IEM-CSIC, Madrid, which is the time dedicated to the preparation, development and analysis of the IS619 and E788S experiments. These experiments can be located in a research framework of weaklybound light nuclei whose so-called halo structure manifests on their scattering dynamics at energies near the Coulomb barrier. A series of similar studies began in the early 2000s and extends to the present day, gradually reaching more exotic and heavier nuclei as facilities are able to provide better quality and wider variety of beams. Furthermore, detection systems become more sophisticated and theoretical models gain accuracy. The IS619 experiment, proposed in mid-2016 and carried out in August 2017 at the ISOLDE facility of CERN (Geneva, Switzerland), aims to probe the structure of the neutron-rich nucleus 15C through its differential elastic cross section at 4.37 MeV/u on a 208Pb target. The completion of the HIE post-acceleration line of ISOLDE left a door open to perform this measurement with a 15C beam, being IS619 the first experimental study of this nucleus at energies near the Coulomb barrier. The weakly bound nucleus 15C (Sn = 1218.1(8) keV, S2n = 9394.5(8) keV) has been investigated in several experiments at higher energies. Its total interaction cross section is larger than that of the neighboring 14,16C and its momentum distributions for the one-neutron breakup are iii iv much narrower than for the rest of the isotopes in the carbon chain. These features suggest the presence of a halo configuration that would be unique, according to its spectroscopic factors, due to the almost pure s1/2 single neutron wave function in the ground state, which could partially compensate the relatively large Sn value for a halo structure. The E788S experiment, proposed in late 2019 and carried out in February 2020 at SPIRAL, GANIL (Caen, France), is an analogous study at the proton-rich side of the nuclear chart: with a 17Ne beam at 8 MeV/u on a 208Pb target and a very similar experimental setup. Despite the availability of this beam in the facility for years, it also happens to be the first experimental study of 17Ne dynamics near the barrier ever. The Borromean structure of 17Ne and the difference between its single-proton and its two-proton separation energies (Sp=1469(8) keV, S2p=933.1(6) keV) create a clear similarity with the 11Li two-neutron halo. This fact, together with the large matter radius, which is deduced from high energy measurements of the interaction cross section, and the momentum distributions from the breakup to 15O, have given evidence of a two-proton halo since long ago. However, the effects of such structure at low-energies remained untested. A complete description of how these studies arise, are experimentally planned and carried out, and how results are obtained will be detailed throughout this thesis. Firstly, a general overview about the aspects of nuclear physics related to this research will be given in chapter one. In the second chapter, the most commonly used theories to describe direct nuclear reactions will be introduced. The third chapter will be focused on the experimental technique. Then, in the fourth chapter, the development of the Monte Carlo simulations will be pre- v sented. The analysis methods used to treat IS619 and E788S data will be described in chapters fifth and sixth respectively. The results and their theoretical interpretation will be discussed in chapter seventh. A general summary of the onclusions (in English in chapter eighth and Spanish in chapter ninth) will put an end to the present work