We report on the single neutron and proton removal reactions from unstable nuclei with large asymmetry ΔS = S(n)-S(p) at incident energies below 80 MeV/nucleon. Strong nonsudden effects are observed ...in the case of deeply-bound-nucleon removal. The corresponding parallel momentum distributions exhibit an abrupt cutoff at high momentum that corresponds to an energy threshold occurring when the incident energy per particle is of comparable magnitude to the nucleon separation energy. A large low-momentum tail is related to both dissipative processes and the dynamics of the nucleon removal process. New limits for the applicability of the sudden and eikonal approximations in nucleon knockout are given.
The structure of low-lying states in the light krypton isotopes 72Kr, 74Kr, and 76Kr has been studied with the finite-range Gogny D1S effective interaction via Hartree–Fock–Bogolyubov based ...calculations within a configuration-mixing formalism treating axial and triaxial quadrupole deformations. The good overall agreement with the experimental low-lying excitation spectra and matrix elements supports the shape coexistence scenario and a transition of the ground-state shape from oblate in 72Kr to prolate in 76Kr. The triaxial degree of freedom is shown to be crucial to reproduce the experimental data in general and the inversion of the oblate and prolate configurations in particular.
Breakup reactions and their ambiguities Gómez-Ramos, M.; Obertelli, A.; Sun, Y. L.
European physical journal. A, Hadrons and nuclei,
2021/4, Letnik:
57, Številka:
4
Journal Article
Recenzirano
Odprti dostop
We review the ambiguities in the nuclear information extracted from breakup reactions, focusing on those originating from the description of the reaction mechanism and the overall ambiguity inherent ...to their interpretation in terms of shell occupancies. We present the current discussion about nucleon knockout reactions and how the understanding of the reaction mechanism would help reducing uncertainties. For the former, we consider the case of
11
Li, due to the existing large data set. For the latter, we recall the paradigmatic example of the electro-dissociation of the deuteron to address the question of the scale and scheme dependence from the theoretical framework used for the interpretation.
Single nucleon pickup reactions were performed with a 18.1 MeV/nucleon (14)O beam on a deuterium target. Within the coupled reaction channel framework, the measured cross sections were compared to ...theoretical predictions and analyzed using both phenomenological and microscopic overlap functions. The missing strength due to correlations does not show significant dependence on the nucleon separation energy asymmetry over a wide range of 37 MeV, in contrast with nucleon removal data analyzed within the sudden-eikonal formalism.
The proton-rich isotope 68Br was discovered in secondary fragmentation reactions of fast radioactive beams. Proton-rich secondary beams of 70,71,72Kr and 70Br, produced at the RIKEN Nishina Center ...and identified by the BigRIPS fragment separator, impinged on a secondary 9Be target. Unambiguous particle identification behind the secondary target was achieved with the ZeroDegree spectrometer. Based on the expected direct production cross sections from neighboring isotopes, the lifetime of the ground or long-lived isomeric state of 68Br was estimated. The results suggest that secondary fragmentation reactions, where relatively few nucleons are removed from the projectile, offer an alternative way to search for new isotopes, as these reactions populate preferentially low-lying states.
Direct reactions have been a unique tool to address the nuclear many-body problem from the experimental side. They are now routinely used in inverse kinematics with radioactive ion beams (RIB). ...However, weakly bound nuclei have recently raised questions on the applicability of reaction formalisms benchmarked on stable nuclei to the study of single-particle properties and correlations in these unstable systems. The study of the most exotic species produced at low intensity have triggered new technical developments to increase the sensitivity of the setup, with a focused attention to direct reactions such as transfer at low incident energy or knockout at intermediate energies.
MINOS is a new apparatus dedicated to in-beam nuclear structure experiments with low-intensity exotic beams in inverse kinematics at intermediate energies above 150MeV/nucleon. The device is composed ...of a thick liquid-hydrogen target coupled to a compact time projection chamber (TPC) serving as a vertex tracker. Either used for in-beam gamma spectroscopy of bound excited states or invariant-mass spectroscopy of unbound states, MINOS aims at improving the luminosity by a very significant factor compared to standard solid-target material experiments while improving experimental resolutions.
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