``Southwestern'' boundary of the $N=40$ island of inversion: First study of low-lying bound excited states in $^{59}\mathrm{V}$ and $^{61}\mathrm{V}$

“Southwestern” boundary of the $N = 40$ island of inversion: First study of low-lying bound excited states in ${}^{59}V$ and ${}^{61}V$

Z. Elekes et al. (Sunflower Collaboration)

Phys. Rev. C 106, 064321 – Published 19 December 2022

Abstract

The low-lying level structure of ${}^{59}V$ and ${}^{61}V$ was investigated for the first time. The neutron knockout reaction and inelastic proton scattering were applied for ${}^{61}V$ while the neutron knock-out reaction provided the data for ${}^{59}V$ . Four and five new transitions were determined for ${}^{59}V$ and ${}^{61}V$ , respectively. Based on the comparison to our shell-model calculations using the Lenzi-Nowacki-Poves-Sieja (LNPS) interaction, three of the observed $γ$ rays for each isotope could be placed in the level scheme and assigned to the decay of the first $11 / 2^{-}$ and $9 / 2^{-}$ levels. The $(p, p^{'})$ excitation cross sections for ${}^{61}V$ were analyzed by the coupled-channels formalism assuming quadrupole plus hexadecapole deformations. Due to the role of the hexadecapole deformation, ${}^{61}V$ could not be unambiguously placed on the island of inversion.

Received 26 August 2022
Accepted 9 December 2022

DOI:https://doi.org/10.1103/PhysRevC.106.064321

Physics Subject Headings (PhySH)

Electromagnetic transitions Energy levels Nuclear reactions Nuclear structure & decays

Nuclear Physics

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Vol. 106, Iss. 6 — December 2022

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Figure 1
Doppler corrected singles $γ$ -ray spectra for ${}^{61}V$ using vertex reconstruction and add-back procedure [upper panel: Mainly ${}^{62}V (p, p n) {}^{61}V$ reaction including ${}^{62}V (p, p^{'}) {{}^{62}V}^{*} \to {{}^{61}V}^{*} + n$ decay channel; lower panel: Inelastic scattering]. The data with error bars and shaded area represent the experimental spectrum, the red line is the simulation plus a free-parameter double-exponential background, and the latter function (exponential background) is also plotted separately as a blue line. The magenta lines illustrate the individual response functions for the transitions.
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Figure 2
Doppler corrected coincidence $γ$ -ray spectra for ${}^{61}V$ using all the reaction channels. The data with error bars and shaded area represent the experimental spectrum, the red line is the simulation plus a free-parameter double-exponential background, and the latter function (exponential background) is also plotted separately as a blue line. The magenta lines illustrate the individual response functions for the transitions. Upper panel: Events coincident with the 643-keV transition (gate: 590–690 keV) with the subtraction of background events using a side gate between 1300 and 1400 keV; lower panel: Events coincident with the 238-keV transition (gate: 190–290 keV) with the subtraction of background events using a side gate between 690 and 790 keV.
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Figure 3
Doppler-corrected singles $γ$ -ray spectra for ${}^{59}V$ originating from the $(p, p 2 n)$ reaction channel using vertex reconstruction and add-back procedure. The data with error bars and shaded area represent the experimental spectrum, the red line is the simulation plus a free-parameter double-exponential background, and the latter function (exponential background) is also plotted separately as a blue line. The magenta lines illustrate the individual response functions for the transitions.
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Figure 4
Partial level and decay scheme of ${}^{61}V$ . Three of the five observed $γ$ rays could be placed in two slightly different ways (Experiments A and B). $X$ is the energy of a transition (<200 keV) not detected in the present experiment. The origin of the remaining two $γ$ rays (978, 1106) could not be unambiguously determined; they probably belong to the decay of states above the $11 / 2_{1}^{-}$ level. The intensity of the two $γ$ rays relative to the 1106-keV transition found in the singles spectrum of the $(p, p n)$ channel is also indicated next to the downward arrows. The experimental data were compared with our shell-model calculations on the left-hand side where the calculated $γ$ -ray branching ratios are also written next to the downward arrows.
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Figure 5
Partial level and decay scheme of ${}^{59}V$ . Three of the four observed $γ$ rays could be placed in the level scheme (Experiment) using the analogy to ${}^{59}V$ and ${}^{61}V$ as well as our shell-model calculations on the left-hand side. $X$ is the energy of a transition (<200 keV) not detected in the present experiment. The origin of the remaining $γ$ ray (1611) could not be unambiguously determined; it probably belongs to the decay of states above the $11 / 2_{1}^{-}$ level. The relative intensity of the three $γ$ rays found in the singles spectrum of the $(p, p 2 n)$ channel is also indicated next to the downward arrows while the calculated $γ$ -ray branching ratios are also written next to the downward arrows for the shell model.
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Physical Review C

covering nuclear physics

“Southwestern” boundary of the $N = 40$ island of inversion: First study of low-lying bound excited states in ${}^{59}V$ and ${}^{61}V$

Z. Elekes et al. (Sunflower Collaboration)

Phys. Rev. C 106, 064321 – Published 19 December 2022

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Physical Review C

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“Southwestern” boundary of the N=40 island of inversion: First study of low-lying bound excited states in V59 and V61

Z. Elekes et al. (Sunflower Collaboration)

Phys. Rev. C 106, 064321 – Published 19 December 2022

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“Southwestern” boundary of the $N = 40$ island of inversion: First study of low-lying bound excited states in ${}^{59}V$ and ${}^{61}V$