Heavy-ion Coulomb excitation of 72Ge

doi:10.1016/0375-9474(90)90451-Q

Nuclear Physics A

Volume 519, Issue 3, 10 December 1990, Pages 646-658

https://doi.org/10.1016/0375-9474(90)90451-Q Get rights and content

Abstract

The nucleus ⁷²Ge has been Coulomb excited using ¹⁶O, ⁵⁸Ni and ²⁰⁸Pb. Seventeen E2 matrix elements coupling the low-lying states have been determined. Based on these data, an interpretation of the structure of ⁷²Ge has been proposed that includes an “intruder” 0⁺ state perturbing what the present work shows to be a triaxial quadrupole-deformed collective rotational structure.

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Cited by (55)

Axial and triaxial degrees of freedom in 72Zn
2023, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
The unstable $N = 42$ nucleus ⁷²Zn has been studied using multiple safe Coulomb excitation in inverse kinematics. The experiment was performed at the REX-ISOLDE facility at CERN making first use of the silicon detector array C-REX in combination with the γ-ray spectrometer Miniball. The high angular coverage of C-REX allowed to determine the reduced transition strengths for the decay of the yrast $0_{1}^{+}$ , $2_{1}^{+}$ and $4_{1}^{+}$ as well as of the $0_{2}^{+}$ and $2_{2}^{+}$ states in ⁷²Zn. The quadrupole moments of the $2_{1}^{+}$ , $4_{1}^{+}$ and $2_{2}^{+}$ states were extracted. Using model independent quadrupole invariants, the ground state of ⁷²Zn was found to have an average deformation in the γ degree of freedom close to maximum triaxiality. In comparison to experimental data in zinc isotopes with $N < 40$ , the collectivity of the $4_{1}^{+}$ state in neutron-rich ⁷²Zn is significantly larger, indicating a collective yrast band based on the ground state of ⁷²Zn. In contrast, a low experimental $B (E 2; 0_{2}^{+} \to 2_{1}^{+})$ strength was determined, indicating a different structure for the $0_{2}^{+}$ state. Shell-model calculations propose a $0_{2}^{+}$ state featuring a larger fraction of the (spherical) $N = 40$ closed-shell configuration in its wave function than for the $0_{1}^{+}$ ground state.
The results were also compared with beyond mean field calculations which corroborate the large deformation in the γ degree of freedom, while pointing to a more deformed $0_{2}^{+}$ state. These experimental and theoretical findings establish the importance of the γ degree of freedom in the ground state of ⁷²Zn, located between the ^68,70Ni nuclei that have spherical ground states, and ⁷⁶Ge, which has a rigid triaxial shape.
An experimental view on shape coexistence in nuclei
2022, Progress in Particle and Nuclear Physics
Nuclear shape coexistence is the phenomenon in which distinct shapes occur within the same nucleus and at a similar energy. In this work, we provide an overview of the experimental investigations of shape coexistence, focusing on those regions of the nuclear chart that have been the most actively investigated within the past decade. In particular, we focus on coexistence phenomena at low angular momentum and on the new experimental information, placed within the context of previous results. We first give a summary of the experimental signatures that can be used for assessing shape coexistence, and then discuss the evidence for shape coexistence from experimental results, with particular attention paid to regions where its presence has been suggested along isotopic or isotonic chains, and in regions where “islands” of such structures have been proposed. We conclude with an overview, with an emphasis on the emerging regions where indications for multiple shape coexistence exist.
Shape coexistence and the role of axial asymmetry in 72Ge
2016, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
The quadrupole collectivity of low-lying states and the anomalous behavior of the $0_{2}^{+}$ and $2_{3}^{+}$ levels in ⁷²Ge are investigated via projectile multi-step Coulomb excitation with GRETINA and CHICO-2. A total of forty six E2 and M1 matrix elements connecting fourteen low-lying levels were determined using the least-squares search code, gosia. Evidence for triaxiality and shape coexistence, based on the model-independent shape invariants deduced from the Kumar–Cline sum rule, is presented. These are interpreted using a simple two-state mixing model as well as multi-state mixing calculations carried out within the framework of the triaxial rotor model. The results represent a significant milestone towards the understanding of the unusual structure of this nucleus.
Spectroscopy of 74Ge: From soft to rigid triaxiality
2014, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics
The first heavy ion fusion–evaporation reaction study for ⁷⁴Ge has been performed through the reaction channel ${}^{70}{Zn} ({}^{7}{Li}, 2 n p) {}^{74}{Ge}$ at beam energies of 30 and 35 MeV. Previously known yrast band is extended to higher spins and five new collective bands are established. Based on comparison with the neighboring ^72,76Ge isotopes, an intermediate pattern of energy staggering $S (I)$ is observed in the γ band of ⁷⁴Ge. The collective structure of ⁷⁴Ge, including the excitation energies and transition probabilities of ground-state band and γ band, is reproduced by the state-of-the-art five-dimensional collective Hamiltonian (5DCH) model constructed from the covariant density functional. By including the ^72,76,78Ge isotopes, systematical investigation of the structure evolution in Ge isotopes is performed. Based on the systematic comparisons and analysis, the triaxial evolution with spin in ⁷⁴Ge is revealed and ⁷⁴Ge is found to be the crucial nucleus marking the triaxial evolution from soft to rigid in Ge isotopes.
Model independent determination of quadrupole deformation parameters from coulomb excitation measurements
2011, International Journal of Modern Physics E
Open problems in the microscopic theory of large-amplitude collective motion
2010, Journal of Physics G: Nuclear and Particle Physics

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¹: Permanent address: SLCJ, University of Warsaw, Warsaw PL-02097, Poland.

²: Permanent address: Institute of Experimental Physics, University of Warsaw, Warsaw PL-00681, Poland.

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Nuclear Physics A

Abstract

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Cited by (55)

Axial and triaxial degrees of freedom in <sup>72</sup>Zn

An experimental view on shape coexistence in nuclei

Shape coexistence and the role of axial asymmetry in <sup>72</sup>Ge

Spectroscopy of <sup>74</sup>Ge: From soft to rigid triaxiality

Model independent determination of quadrupole deformation parameters from coulomb excitation measurements

Open problems in the microscopic theory of large-amplitude collective motion