Effective proton-neutron interaction near the drip line from unbound states in ²⁵̛ ²⁶ F
Background: Odd-odd nuclei, around doubly closed shells, have been extensively used to study proton-neutron interactions. However, the evolution of these interactions as a function of the binding energy, ultimately when nuclei become unbound, is poorly known. The ²⁶F nucleus, composed of a deeply bo...
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| Tipo de recurso: | artículo |
| Fecha de publicación: | 2019 |
| País: | España |
| Institución: | Universidad Complutense de Madrid (UCM) |
| Repositorio: | Docta Complutense |
| Idioma: | inglés |
| OAI Identifier: | oai:docta.ucm.es:20.500.14352/5952 |
| Acceso en línea: | https://hdl.handle.net/20.500.14352/5952 |
| Access Level: | acceso abierto |
| Palabra clave: | 539.1 Nuclear-forces Rich nuclei Detector Electricidad Electrónica (Física) Física nuclear 2202.03 Electricidad 2207 Física Atómica y Nuclear |
| Sumario: | Background: Odd-odd nuclei, around doubly closed shells, have been extensively used to study proton-neutron interactions. However, the evolution of these interactions as a function of the binding energy, ultimately when nuclei become unbound, is poorly known. The ²⁶F nucleus, composed of a deeply bound π 0d_(5/2) proton and an unbound ν0d_(3/2) neutron on top of an ²⁴O core, is particularly adapted for this purpose. The coupling of this proton and neutron results in a J^π= 1₁⁺ - 4₁⁺ multiplet, whose energies must be determined to study the influence of the proximity of the continuum on the corresponding proton-neutron interaction. The J^π = 1₁⁺, 2₁⁺, 4₁⁺ bound states have been determined, and only a clear identification of the J^π = 3₁⁺ is missing. Purpose: We wish to complete the study of the J^π = 1₁⁺ - 4₁⁺multiplet in ²⁶F, by studying the energy and width of the J^π = 3₁⁺unbound state. The method was first validated by the study of unbound states in ²⁵, for which resonances were already observed in a previous experiment. Method: Radioactive beams of ²⁶Ne and ²⁷Ne, produced at about 440AMeV by the fragment separator at the GSI facility were used to populate unbound states in ²⁵F and ²⁶F via one-proton knockout reactions on a CH₂ target, located at the object focal point of the R³B/LAND setup. The detection of emitted. γ and neutrons, added to the reconstruction of the momentum vector of the A - 1 nuclei, allowed the determination of the energy of three unbound states in ²⁵F and two in ²⁶F. Results: Based on its width and decay properties, the first unbound state in ²⁵F, at the relative energy of 49(9) keV, is proposed to be a J^π = 1/ 2ˉ arising from a p_(1/2) proton- hole state. In ²⁶F, the first resonance at 323(33) keV is proposed to be the J^π = 3₁⁺ member of the J^π = 1₁⁺- 4₁⁺multiplet. Energies of observed states in ²⁵ʼ²⁶F have been compared to calculations using the independent-particle shell model, a phenomenological shell model, and the ab initio valence-space in-medium similarity renormalization group method. Conclusions: The deduced effective proton- neutron interaction is weakened by about 30-40% in comparison to the models, pointing to the need for implementing the role of the continuum in theoretical descriptions or to a wrong determination of the atomic mass of ²⁶F. |
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