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Lapoux, V.

Publications and source records attributed to Lapoux, V..

12 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Evolution of the two-neutron configuration from 11 Li to 13 Li

In this work we investigate the two-neutron decay of 13 Li and of the excited states of 11 Li populated via one-proton removal from 14 Be and 12 Be, respectively. A phenomenological model is used to describe the decay of 11 Li and 13 Li. While the first one displays important sequential components, the second one appears dominated by the direct two-neutron decay. A microscopic three-body model is used to extract information on the spatial configuration of the emitted neutrons before the decay and shows that the average distance between the neutrons increases going from 11 Li to 13 Li.

Dineutron decay↗
DOE OSTI2023

First observation of 28 O

Subjecting a physical system to extreme conditions is one of the means often used to obtain a better understanding and deeper insight into its organization and structure. In the case of the atomic nucleus, one such approach is to investigate isotopes that have very different neutron-to-proton ($N/Z$) ratios than in stable nuclei. Light, neutron-rich isotopes exhibit the most asymmetric $N/Z$ ratios and those lying beyond the limits of binding, which undergo spontaneous neutron emission and exist only as very short-lived resonances (about 10 -21 s), provide the most stringent tests of modern nuclear-structure theories. Here we report on the first observation of 28 O and 27 O through their decay into 24 O and four and three neutrons, respectively. The 28 O nucleus is of particular interest as, with the $Z$ = 8 and $N$ = 20 magic numbers, it is expected in the standard shell-model picture of nuclear structure to be one of a relatively small number of so-called ‘doubly magic’ nuclei. Furthermore, both 27 O and 28 O were found to exist as narrow, low-lying resonances and their decay energies are compared here to the results of sophisticated theoretical modelling, including a large-scale shell-model calculation and a newly developed statistical approach. In both cases, the underlying nuclear interactions were derived from effective field theories of quantum chromodynamics. Finally, it is shown that the cross-section for the production of 28 O from a 29 F beam is consistent with it not exhibiting a closed $N$ = 20 shell structure.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Level structures of 56,58 Ca cast doubt on a doubly magic 60 Ca

Gamma decays were observed in 56 Ca and 58 Ca following quasi-free one-proton knockout reactions from 57,59 Sc beams at ≈200 MeV/nucleon. For 56 Ca, a γ ray transition was measured to be 1456(12) keV, while for 58 Ca an indication for a transition was observed at 1115(34) keV. Both transitions were tentatively assigned as the $2^{+}_{1}\rightarrow0^{+}_{gs}$ decays, and were compared to results from ab initio and conventional shell-model approaches. A shell-model calculation in a wide model space with a marginally modified effective nucleon-nucleon interaction depicts excellent agreement with experiment for $2^{+}_{1}$ level energies, two-neutron separation energies, and reaction cross sections, corroborating the formation of a new nuclear shell above the N = 34 shell. Its constituents, the 0$f$ 5/2 and 0$g$ 9/2 orbitals, are almost degenerate. This degeneracy precludes the possibility for a doubly magic 60 Ca and potentially drives the dripline of Ca isotopes to 70 Ca or even beyond.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Intruder configurations in 29 Ne at the transition into the island of inversion: Detailed structure study of 28 Ne

Detailed γ-ray spectroscopy of the exotic neon isotope 28 Ne has been performed for the first time using the one-neutron removal reaction from 29 Ne on a liquid hydrogen target at 240 MeV/nucleon. Based on an analysis of parallel momentum distributions, a level scheme with spin-parity assignments has been constructed for 28 Ne and the negative-parity states are identified for the first time. The measured partial cross sections and momentum distributions reveal a significant intruder p-wave strength providing evidence of the breakdown of the N=20 and N=28 shell gaps. Only a weak, possible f-wave strength was observed to bound final states. Large-scale shell-model calculations with different effective interactions do not reproduce the large p-wave and small f-wave strength observed experimentally, indicating an ongoing challenge for a complete theoretical description of the transition into the island of inversion along the Ne isotopic chain.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

New narrow resonances observed in the unbound nucleus F 15

The structure of the unbound 15 F nucleus is investigated using the inverse kinematics resonant scattering of a radioactive 14 O beam impinging on a CH 2 target. The analysis of 1 H( 14 O,p) 14 O and 1 H( 14 O,2p) 13 N reactions allowed the confirmation of the previously observed narrow 1/2 - resonance, near the two-proton decay threshold, and the identification of two new narrow 5/2 - and 3/2 - resonances. The newly observed levels decay by 1p emission to the ground of 14 O, and by sequential 2p emission to the ground state (g.s.) of 13 N via the 1 - resonance of 14 O. Gamow shell model (GSM) analysis of the experimental data suggests that the wave functions of the 5/2 - and 3/2 - resonances may be collectivized by the continuum coupling to nearby 2p- and 1p- decay channels. Finally, the observed excitation function 1 H( 14 O, p) 14 O and resonance spectrum in 15 F are well reproduced in the unified framework of the GSM.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Investigation of the ground-state spin inversion in the neutron-rich Cl 47 , 49 isotopes

A first γ -ray study of Cl 47 , 49 spectroscopy was performed at the Radioactive Isotope Beam Factory with Ar 50 projectiles at 217 MeV/nucleon, impinging on the liquid hydrogen target of the MINOS device. Prompt deexcitation γ rays were measured with the NaI(Tl) array DALI2 + . Through the one-proton knockout reaction Ar 50 ( p , 2 p ) , a spin assignment could be determined for the low-lying states of Cl 49 from the momentum distribution obtained with the SAMURAI spectrometer. A spin-parity J π = 3 / 2 + is deduced for the ground state of Cl 49 , similar to the recently studied N = 32 isotope K 51 . The evolution of the energy difference E ( 1 / 2 1 + ) - E ( 3 / 2 1 + ) is compared to state-of-the-art theoretical predictions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Extending the Southern Shore of the Island of Inversion to F 28

Detailed spectroscopy of the neutron-unbound nucleus 28 F has been performed for the first time following proton/neutron removal from 29 Ne/ 29 F beams at energies around 230 MeV / nucleon . The invariant-mass spectra were reconstructed for both the 27 F(*) + n and 26 F(*) + 2n coincidences and revealed a series of well-defined resonances. A near-threshold state was observed in both reactions and is identified as the 28 F ground state, with S n ( 28 F) = -199(6) keV, while analysis of the 2n decay channel allowed a considerably improved S n ( 27 F) = 162(60) keV to be deduced. Comparison with shell-model predictions and eikonal-model reaction calculations have allowed spin-parity assignments to be proposed for some of the lower-lying levels of 28 F. Importantly, in the case of the ground state, the reconstructed 27 F + n momentum distribution following neutron removal from 29 F indicates that it arises mainly from the 1p 3/2 neutron intruder configuration. Finally, this demonstrates that the island of inversion around N = 20 includes 28 F, and most probably 29 F, and suggests that 28 O is not doubly magic.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗