Multipolarities of prompt transitions in 156Dy and spin-parities of the upper band levels

Böer, Philipp; Koldewijn, P.; Beetz, R.; Maarleveld, J.L.; Konijn, J.; Janssens, R. V. F.; Vervier, J.

doi:10.1016/0375-9474(77)90673-x

Cited by 29 publications

(12 citation statements)

References 33 publications

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“…In addition, two new linking transitions (808 and 800 keV) were placed between bands 2 and 1. The DCO ratios for the 755-, 1040-, 971-, and 912-keV linking transitions are consistent with all being pure dipole transitions, and this result coincides with the assignment of negative parity by de Boer et al [14].…”

Section: B Bands 2 3 4 and 4asupporting

confidence: 78%

“…156 Dy assigned this structure as an octupole (Y 30 ) vibrational band [14]; however, as stated above, the possibility of tetrahedral (Y 32 + Y 3−2 ) symmetry in the region near 156 Dy provided the motivation to revisit the character of this band with Gammasphere. As this discussion focuses on two possible types of octupole vibration, we refer the reader to the comprehensive works of Neergärd and Vogel [20], as well as Butler and Nazarewicz [21], concerning this excitation mode.…”

Section: Previous Work Onmentioning

confidence: 99%

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Investigation of negative-parity states in Dy156 : Search for evidence of tetrahedral symmetry

Hartley¹,

Riedinger²,

Janssens³

et al. 2017

Phys. Rev. C

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An experiment populating low/medium-spin states in156 Dy was performed to investigate the possibility of tetrahedral symmetry in this nucleus. In particular, focus was placed on the low-spin, negative-parity states since recent theoretical studies suggest that these may be good candidates for this high-rank symmetry. The states were produced in the 148 Nd( 12 C,4n) reaction and the Gammasphere array was utilized to detect the emitted γ rays. B(E2)/B(E1) ratios of transition probabilities from the low-spin, negative-parity bands were determined and used to interpret whether these structures are best associated with tetrahedral symmetry or, as previously assigned, to octupole vibrations. In addition, several other negative-parity structures were observed to higher spin and two new sequences were established.

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Section: B Bands 2 3 4 and 4asupporting

confidence: 78%

Section: Previous Work Onmentioning

confidence: 99%

Investigation of negative-parity states in Dy156 : Search for evidence of tetrahedral symmetry

Hartley¹,

Riedinger²,

Janssens³

et al. 2017

Phys. Rev. C

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“…To assume complete equality of the shape parameters is a priori physically unlikely. The experimental branching ratios of the NPB levels in 156Dy are found to be in good agreement with the theoretical expressions [16] for B(E1; I-,I+l)/ B(E 1; I--,I-1) and B(E 2)/B(E 1) branching ratios, derived with the use of wave functions for aligned octupole states. Summarizing: it can be shown that the predicted [13] intersection points of the octupole and two-quasiparticle bands in N=88 nuclei can be reproduced by changes in the sign of the slope of A2E with increasing spin (E=level energy).…”

Section: E(r)/6g(r)=osupporting

confidence: 72%

“…In an investigation to determine spins and multipolarities of recently observed upper band levels [15] in 156Dy we have succeeded [16] to establish a NPB up to spin (13). It is interesting to investigate whether Iorit occurs in this N = 90 nucleus with a larger ground state moment of inertia at the same or higher spin value as in the N = 88 nuclei.…”

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confidence: 95%

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Crossing of negative parity bands in even-even nuclei around A?150

Boer

Peker

Koldewijn³

et al. 1978

Z Physik A

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Level energies of negative parity yrast bands (NPB) have been studied with a recently proposed, sensitive method. The irregular behaviour of the NPB's in the N=88 nuclei around spin 9-11 and the smooth behaviour in 156Dy (up to I=13) and in Z38U (up to I = 19) support calculations by Vogel, where NPB's are described as aligned octupole bands up to a critical spin where intersection with two-quasiparticle bands takes place. Considering the NPB levels (I< 13) in 156Dy as members of an aligned octupole band, we obtain a remarkably good reproduction of their decay properties and energies using the VMI model. Considerable interest exists in the structure of negative parity bands (NPB) in doubly even nuclei. These bands have been observed in the deformed nuclei 238U [1] and 16ZEr [2,3] [-11] obtain a set of negative parity levels by coupling quadrupole and octupole bosons of which the lowest sequence is an aligned one starting at U= 3-. The spacing is equal to that of the ground state band apart from an extra term proportional to the (quadrupole) boson quantum number ne. In the deformed region Neerg~rd and Vogel [12] obtain a similar set of negative parity states, now grouped into well defined octupole vibrational bands with K =0-, 1-, 2-and 3-, though these bands are strongly perturbed by Coriolis interaction. If the strength of this interaction reaches its spherical limit and the unperturbed band head energies are degenerate, the lowest octupole band, starting at 3-, becomes an aligned one. An alternative approach to negative parity bands has been applied in the cases of l~[5], 126. tZSBa [6] and 156Er [10], where the NPB's are interpreted as rotational bands built upon two-quasiparticle states. The NPB levels in t52Gd were reproduced by Zolnowski et al. [7] and by Nomura [8], who coupled octupole phonons to the transitional core. Recently, Vogel [13] showed that in deformed nuclei the "yrast" NPB should consist of two branches: an aligned octupole band up to a critical spin value (Iorit) at which band crossing takes place with an aligned two-quasiparticle (2-q.p.) band. The transition to the aligned 2-q.p. situation occurs, according to Vogel, when the octupole correlation energy amounts (according to Vogel R ~ I-Jl), the critcal spins become I = 25-27 and I = 9-11 respectively. Negative parity bands in N = 88 nuclei are known up to high spin values. We have investigated these bands with a new sensitive method [14], by plotting the second differentials of the level energies as a function of I. In this way band irregularities are very clearly demonstrated, as is shown in Figure 1.

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On the nature of the superband in156Dy

Peker

Boer²,

Konijn³

1978

Z Physik A

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Superbands, responsible for the backbending in 156Dy and other N = 90 and N = 88 nuclei, are proposed to be aligned n(i~3/2) 2 bands, whereas it is argued that the recently discovered positive parity band in 156Dy with U = (2 +) up to 10 § members does not constitute the low spin extension of the superband.The backbending phenomenon is considered to be caused by the intersection of the ground state band (GSB) by a second rotational band with an appreciably larger moment of inertia and band head energy around 1.5 MeV. The nature of this band has been explained in several ways: The "twin" backbending phenomena observed in 156Dy [6,7] and in lS~Gd [8] has been explained by Andrews et al. [6] and Szymanski and Krumlinde [7] in terms of a superband that intersects both the GSB and the /Lvibrational band. On basis of the level energies, Broglia et al. [9] concluded that the superband most probably has a K + 0 character and suggested a K ~ ---1 § assignment. Recently, E1-Masri et al. [10,11] reported on a group of six 'upper' levels between 1.8 and 2.8 MeV, which might possibly constitute the low spin extension of the superband. In order to * Present address: Natuurkundig Laboratorium der Vrije Universiteit, De Boelelaan 1081, Amsterdam/The Netherlands establish spins and parities for these levels, we have measured conversion coefficients of depopulating transitions and established [12] that the six levels can be divided into two groups, one with even spins and positive parities, and another one with odd spins and negative parities. By combining results obtained from the 156Ho decay studies [13] and a recent 158Dy(p,t) reaction study [14], energies were obtained of the 4 + and possibly (2 + ) levels belonging to the positive 'upper' band. The levels are shown in Figure l, together with those of the GSB,/3-and superband. In this paper we want to contradict earlier suggestions [10,11] that this band represents the low spin levels of the superband. The parameter A, inversely proportional to the moment of inertia, as a function of the spin, shows (see Fig. 2) a regular behaviour for the upper-, beta-, superand ground state bands. A pronounced discontinuity exists, though, between the 10 + level of the upper band and the 12 + level of the superband indicating no connection and consequently a different structure. The smoother slope of the upper band and the larger moment of inertia show that the nucleus is, in these states considerably more rigid than in the ground stateand beta bands. This can be caused by an increase of the deformation [3, 41, DE J, as well as by a decrease of the pairing force [53, leading to pairing vibrational states. It was shown by Andrews et al. [6] that the curves of the energies of the ~58Er GSB, the 156Dy and 154Gd beta bands, plotted versus I(I + 1), show a clear similarity.

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Multipolarities of prompt transitions in 156Dy and spin-parities of the upper band levels

Cited by 29 publications

References 33 publications

Investigation of negative-parity states in Dy156 : Search for evidence of tetrahedral symmetry

Investigation of negative-parity states in Dy156 : Search for evidence of tetrahedral symmetry

Crossing of negative parity bands in even-even nuclei around A?150

On the nature of the superband in156Dy

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