Observation of an<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>E</mml:mi><mml:mn>0</mml:mn><mml:mn /></mml:math>Isomeric Transition from the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi mathvariant="normal">U</mml:mi></mml:mrow><mml:mprescripts /><mml:mrow /><mml:mrow><mml:mn>238</mml:mn></mml:mrow><mml:mrow /><mml:mrow /></mml:mmultiscripts></mml:mrow></mml:math>Shape Isomer

Kantele, J.; Stöffl, W.; Ussery, L.E.; Decman, D.J.; Henry, E. A.; Hoff, R. W.; Mann, L.G.; Struble, G.L.

doi:10.1103/physrevlett.51.91

Cited by 40 publications

(16 citation statements)

References 13 publications

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“…When a secondary minimum is separated from the main minimum by a high barrier, in the extreme case a long-lived isomer, called shape isomer, can be formed [7]. Shape isomerism at spin zero, so far, has clearly been observed only in actinide nuclei -these isomers decay mainly by fission, and in two cases only, 236 U and 238 U, by very retarded γ-ray branches [8][9][10][11].The existence of shape isomers in lighter systems has been a matter of debate for a long time. Already in the 1980s, a study based on microscopic Hartree-Fock plus BCS calculations, in which a large number of nuclei was surveyed, identified ten isotopes in which a deformed 0 þ state is separated from a spherical structure by a significantly high barrier:…”

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Multifaceted Quadruplet of Low-Lying Spin-Zero States in Ni66 : Emergence of Shape Isomerism in Light Nuclei

Leoni¹,

Fornal²,

Mărginean³

et al. 2017

Phys. Rev. Lett.

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þ states, pointing to the oblate, spherical, and prolate nature of the consecutive excitations. In addition, they account for the hindrance of the E2 decay from the prolate 0 þ 4 to the spherical 2 þ 1 state, although overestimating its value. This result makes 66 Ni a unique nuclear system, apart from 236;238 U, in which a retarded γ transition from a 0 þ deformed state to a spherical configuration is observed, resembling a shape-isomerlike behavior. DOI: 10.1103/PhysRevLett.118.162502 The concept of potential energy surface (PES) is central in many areas of physics. Usually, the PES displays the potential energy of the system as a function of its geometry. As an example, the PES of a molecule expressed in such coordinates as bond length, valence angles, etc., can be used for finding the minimum energy shape or calculating chemical reaction rates [1]. The idea of potential energy surface in deformation space has also been widely applied to the nucleus at a given spin. For an even-even nucleus at spin 0, the lowest PES minimum corresponds to the ground state (g.s.), while there may exist additional (secondary) minima in which excited 0 þ states can reside: they can be interpreted as ground states of different shapes [2][3][4][5][6]. When a secondary minimum is separated from the main minimum by a high barrier, in the extreme case a long-lived isomer, called shape isomer, can be formed [7]. Shape isomerism at spin zero, so far, has clearly been observed only in actinide nuclei -these isomers decay mainly by fission, and in two cases only, 236 U and 238 U, by very retarded γ-ray branches [8][9][10][11].The existence of shape isomers in lighter systems has been a matter of debate for a long time. Already in the 1980s, a study based on microscopic Hartree-Fock plus BCS calculations, in which a large number of nuclei was surveyed, identified ten isotopes in which a deformed 0 þ state is separated from a spherical structure by a significantly high barrier:66 Ni and 68 Ni, 190;192 Pt, 206;208;210 Os, and 194;196;214

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confidence: 99%

mentioning

confidence: 99%

Multifaceted Quadruplet of Low-Lying Spin-Zero States in Ni66 : Emergence of Shape Isomerism in Light Nuclei

Leoni¹,

Fornal²,

Mărginean³

et al. 2017

Phys. Rev. Lett.

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“…The overall agreement is reasonably good. Note that the experimental energies were estimated from excitation function measurements [3] except 236,238 U for which γ transitions were observed from the 0 + fission isomers to states in the first well [20,21], allowing accurate determination of excitation energies. Moreover, for 238 U, the E0 conversion-electron transition was observed between the 0 + fission isomer and ground state [21].…”

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On the stability of high-K isomers in the second well of actinide nuclei

et al. 2011

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Abstract. Actinide nuclei are found to be good candidates for the formation of high angular momentum, broken-pair excitations in the second minimum of the potential-energy surface. Configuration-constrained calculations of the energy surfaces, including reflection asymmetry, give predictions of the properties of high-K states in the second well. In addition to excitation energies, spins and parities, the calculations indicate increased barriers towards fission, consistent with the extended half-lives observed experimentally.PACS. 2 1.10. 23.20.Lv Broken-pair excitations can lead to metastable states with an excitation of the quantum degree of freedom, K, that is the angular-momentum projection onto the symmetry axis of a deformed nucleus. A high-K excitation can result in highly forbidden decays to low-K states, due to the K selection rule [1], leading to the formation of longlived high-K isomers, which exist widely in the nuclear chart [2]. From the excitation energies and configurations of the isomers, insight can be gained into the shell structure of nucleon orbits, since quasiparticle excitations are closely related to the orbital fillings of the unpaired nucleons and their intrinsic angular momenta.In atomic nuclei there is another kind of metastable state that owes its existence to a second well of the potentialenergy surface (PES) of the nucleus with a highly elongated shape (where the first well generates the ground state). In the Z > 90 actinide region, the shape-trapping state decays mostly by spontaneous fission (SF), and hence is usually called a 'fission isomer'. The emergence of the second energy minimum is due to the special shell structure of nucleon orbits where clear shell gaps exist at large deformation. Because of very different shapes and a significant barrier between the first and second minima, the decay from the fission isomer to the ground state is inhibited. Indeed, actinide nuclei are well known for fission isomers [3,4] with highly elongated ('superdeformed') shapes, having major-to-minor axis ratios of about 2:1.It is natural to consider the possibility of high-K isomerism in the second well. The superdeformed axiallysymmetric shape is an excellent condition for the conserSend offprint requests to:vation of the K quantum number. In addition, a high-K configuration at the fission shape could increase the stability of an isomer against fission, in a similar manner to the fission inhibition in the first well [5]. This is in accord with experimental observations of longer-lived fission isomers, excited within the second well [3]. We call the state associated with the double isomerism of high K and shape a 'high-K fission isomer'.As early as the 1970s, Limkilde and Sletten explained the observed T 1/2 = 5 ns state in 238 Pu as a K isomer [6], contrasting with the 0.5 ns 0 + fission isomer. The experimental energy relative to the 0 + fission isomer was consistent with twice the pairing gap, as expected for a broken-pair excitation. Recently, high-K fission isomers were investigated the...

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“…The hindered 200 keV transitions represent decay strength arising from mixing between superdeformed and weakly deformed states, with hindrances characteristic of noncollective E2 and Ml transitions, and a mixing amplitude characteristic of observed values [17] for coexisting states in the Pb isotopes. The very hindered 1-2 MeV transitions are assigned strengths similar to those observed [18] in the electromagnetic decay of the fission isomer in 238U.…”

Section: By Internal Pair Formationmentioning

confidence: 62%

The Structure of Nuclei Far from Stability

Zganjar¹

1999

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Observation of anE0Isomeric Transition from theU238Shape Isomer

Cited by 40 publications

References 13 publications

Multifaceted Quadruplet of Low-Lying Spin-Zero States in Ni66 : Emergence of Shape Isomerism in Light Nuclei

Multifaceted Quadruplet of Low-Lying Spin-Zero States in Ni66 : Emergence of Shape Isomerism in Light Nuclei

On the stability of high-K isomers in the second well of actinide nuclei

The Structure of Nuclei Far from Stability

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