Shape coexistence in the light Po isotopes

Oros, A. M.; Heyde, K.; Coster, C. De; Decroix, B.; Wyss, R.; Barrett, B. R.; Navrátil, Petr

doi:10.1063/1.57348

“…With Eq. (1) we investigate shape and blocking effects using the deformed Woods-Saxon (WS) model [12,13]. According to the Strutinsky energy theorem [14], the total energy of a nucleus can be decomposed into a macroscopic and microscopic part.…”

mentioning

confidence: 99%

Mean-field and blocking effects on odd-even mass differences and rotational motion of nuclei

Fang

¹

,

Wyss

²

,

Walker

³

1999

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The odd-even differences of nuclear masses are strongly influenced by mean-field and odd-nucleon blocking effects. When such effects are taken into account, the determination of the pairing interaction strength needs to be modified, resulting in larger pairing gaps. This method leads to an improved description for both moments of inertia and backbending frequencies of rotational bands, with no additional parameters. ͓S0556-2813͑99͒50111-8͔PACS number͑s͒: 21.60. Cs, 21.10.Dr, 27.70.ϩq Since the Bardeen-Cooper-Schrieffer ͑BCS͒ theory was applied to atomic nuclei ͓1,2͔, pairing correlations have been crucial to the understanding of many properties, such as binding energies, collective rotational motion, and quasiparticle excitation energies. The interaction strength, G, of the pairing force is the key parameter that governs the properties of the short-range correlations.The G value is usually determined by fitting the BCS pairing gaps (⌬ϭG ͚ i U i V i ͓2͔͒ of even-even nuclei to experimental odd-even mass differences. However, if one then calculates the corresponding theoretical mass differences ͑i.e., in the same manner as calculating the experimental value, but with theoretical masses͒, it turns out that they are systematically smaller than the experimental mass differences and also smaller than the BCS pairing gaps, at least for the deformed rare-earth nuclei described below. The experimental mass difference should, in principle, be identical to the corresponding theoretical value, but not to the pairing gap, though the gap plays the dominant role in determining the mass difference.The above systematic discrepancies suggest that other significant effects exist. It has been pointed out, in a recent work by Satuła, Dobaczewski, and Nazarewicz ͓3͔, that one of the important effects stems from the deformed mean field. Due to the twofold Kramers degeneracy of single-particle levels, odd-and even-nucleon systems in the deformed field have different energies, which contribute to odd-even mass differences. For light-and medium-mass nuclei, the Kramers effect can be comparable with the pairing contribution ͓3͔. Furthermore, when neighboring nuclei have different deformations, the shape-changing effect also plays a role. These two factors originate from the deformed mean field and, therefore, we will refer to them in the following as the meanfield effect.Moreover, the pairing gaps of even-even nuclei cannot include the odd-nucleon blocking effects of adjacent odd nuclei, while experimental odd-even mass differences of course contain such blocking effects ͓2,4͔. This can become significant when the density of single-particle levels around the Fermi surface is not very high. Simple BCS calculations typically show that the odd-nucleon blockings can reduce pairing gaps by more than 10% for the rare-earth nuclei. Hence, it should be expected that the mean-field and blocking effects influence the determination of pairing strengths.Two very sensitive probes of pairing correlations and, therefore, of the pairing strengths, are...

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“…On the other hand, the great uncertainty of theoretical prediction in the excited energy levels force us to consider extended version of IBM. As have expressed in different lectures such [20][21][22][23][24][25][26][27][28][29][30], we expect 2p-2h configuration in the Hg isotopic chain and in such conditions, the IBM-2 version are usual method which we would consider in the next studies.…”

Section: Theoretical Results For Energy Levels and Transition Probabilities Of 190 Hgmentioning

confidence: 84%

“…When the numbers of protons (or neutrons) are modified, the energy levels and electromagnetic transition rates of atomic nuclei change too and suggest a transition from one kind of the collective behavior to another [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34]. The transitional Hamiltonians are especially interesting cases occur when they describe critical points in the transitions from a given shape to another.…”

Section: Introductionmentioning

confidence: 99%

Enerji Spektrumları ve Quadrupole Geçiş olasılıklarının 190 Hg'nin Teorik Tanımı

tazekand¹,

Sabri²,

Mohammadi³

2018

Cumhuriyet Science Journal

0

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In this paper, we have considered the coexistence of two quite different structures, the deformed and spherical shapes in 190 Hg nucleus. To this aim, we have determined the energy spectra and quadrupole transition probabilities of this nucleus. A transitional Interacting Boson Model Hamiltonian which are based on affine(1,1) SU lie algebra have been used to provide a new general technique for description of shape coexistence.Parameter free (up to overall scale factors) predictions for theoretical predictions are found to be in good agreement with experimental counterparts. Also, our results offer a combination of O(6) and U(5) dynamical symmetries for description of regular and intruder configurations, respectively.

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“…Finally, there is no firm experimental evidence regarding the shape of the ground state in 190 Po and the existing theoretical predictions are conflicting. Beyond mean-field calculations present the ground state as predominantly oblate 29 , whereas particlecore model calculations suggest predominantly prolate shape 47,48 . While the ground state is a mixture of spherical, oblate and prolate configurations with unknown admixtures, reduced α-decay widths cannot be unambiguously used as a tool to assign the configuration of the 0 þ 2 state in 186 Pb.…”

Section: An Intensity Value Ofmentioning

confidence: 92%

Reassigning the shapes of the 0+ states in the 186Pb nucleus

Ojala

¹

,

Pakarinen

²

,

Papadakis

³

et al. 2022

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Across the physics disciplines, the 186Pb nucleus is the only known system, where the two first excited states, together with the ground state, form a triplet of zero-spin states assigned with prolate, oblate and spherical shapes. Here we report on a precision measurement where the properties of collective transitions in 186Pb were determined in a simultaneous in-beam γ-ray and electron spectroscopy experiment employing the recoil-decay tagging technique. The feeding of the $${0}_{2}^{+}$$ 0 2 + state and the interband $${2}_{2}^{+}\to {2}_{1}^{+}$$ 2 2 + → 2 1 + transition have been observed. We also present direct measurement of the energies of the electric monopole transitions from the excited 0+ states to the 0+ ground state. In contrast to the earlier understanding, the obtained reduced transition probability $$B(E2;{2}_{1}^{+}\to {0}_{2}^{+})$$ B ( E 2 ; 2 1 + → 0 2 + ) value of 190(80) W.u., the transitional quadrupole moment $$| {Q}_{t}({2}_{1}^{+}\to {0}_{2}^{+})| =7.7$$ ∣ Q t ( 2 1 + → 0 2 + ) ∣ = 7.7 (33) eb and intensity balance arguments provide evidence to reassign the $${0}_{2}^{+}$$ 0 2 + and $${0}_{3}^{+}$$ 0 3 + states with predominantly prolate and oblate shape, respectively. Our work demonstrates a step-up in experimental sensitivity and paves the way for systematic studies of electric monopole transitions in this region. These electric monopole transitions probe the nuclear volume in a unique manner and provide unexploited input for development of the next-generation energy density functional models.

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Shape coexistence in the light Po isotopes

Cited by 4 publications

References 31 publications

Mean-field and blocking effects on odd-even mass differences and rotational motion of nuclei

Mean-field and blocking effects on odd-even mass differences and rotational motion of nuclei

Enerji Spektrumları ve Quadrupole Geçiş olasılıklarının 190 Hg'nin Teorik Tanımı

Reassigning the shapes of the 0+ states in the 186Pb nucleus

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