High-spin states in 218Ra

Fernandez-Niello, J.; Puchta, H.; Riess, F.; Trautmann, W.

doi:10.1016/0375-9474(82)90229-9

Cited by 84 publications

(17 citation statements)

References 17 publications

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“…Our RDM experiment and excitation curve near the barrier (58.5 to 60.0 MeV) yield ordering of the 4 + -2 + and 2 + -0 + transitions opposite to that suggested in Ref. 9.…”

contrasting

confidence: 93%

Molecular Alpha-Particle Clustering inRa218; Dipole Collectivity in the Vicinity of Nuclear Shell Closures

et al. 1983

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Evidence for the presence of alpha-particle clustering in 218 Ra comes from a number of observables: binding energy, S 2n9 Q a , ^(J^), 6 a 2 , and F a . That this clustering is a signature for the new dipole collectivity suggested by Iachello and Jackson follows from observation of simultaneous enhancement of selected El 9 E2, and E3 deexcitation transition matrix elements; of these the El enhancement is most pronounced as would be expected for dipole collectivity.PACS numbers: 21.10. Re, 21.60.Gx, 27.80,+w The existence of alpha clustering in the lowlying states of light nuclei, particularly in the 16 O-20 Ne region, is now well established. 1 Recently published 2 systematics for ground-state alpha-particle widths for heavy nuclei also indicate large reduced alpha-particle widths in the vicinity of the Z= 50 and 82 shell closures. It bears noting that the largest ground-state reduced alpha-particle width for any heavy nucleus yet reported is that 2 for 218 Ra; it exhausts 75% of the Wigner sum-rule limit. These large groundstate reduced widths (0 a 2 ) suggest that configurations such as a +A 2 may indeed exist in the vicinity of shell closures. If the overlap between the alpha cluster and the core nucleus (A 2 ) is small (as suggested by the large 9 a 2 ), it may be appropriate to view these states as physically real molecular alpha-particle cluster states. Such states could then be viewed as the nuclear equivalents of the HBr or HI diatomic molecules which also invoice consitituents of very different sizes.Recently, the possible importance of such alphaparticle clustering in heavy nuclei was emphasized and a phenomenological description was proposed 3 in which the cluster states are associated with a new molecular dipole degree of freedom. 4 The model is developed within the context of a spectrum-generating algebra to emphasize the intrinsic symmetries involved; in this case the cluster is characterized by the length and orientation of the vector separating the a. and A 2 centers of mass and thus is associated with a dipole degree of freedom and with 5 and P (-1 ^ l± ^1) bosons-the generators of U(4).In addition to such molecular states it would be expected, of course, to find the normal quadrupole collective states in the low-energy excitation spectra of these heavy nuclei-and indeed dipole and quadrupole states having the same J 7r would be expected to mix. The result of such mixing of the normal quadrupole ground-state band having a sequence 0 + , 2 + , 4 + , 6 + ,..., and the molecular dipole band 3 having sequence 0 + , 1 ~, 2 + , 3", 4 + ,... then leads to low-lying 1" states, as observed, 5 a sequence 0 + , 2 + , 1", 4 + , 3", again as observed, as well as large ground-state alphaparticle reduced widths and small relative alphaparticle hindrance factors for excited states. In addition, higher-lying states-0 2 + , 2 2 ,-with small hindrance factors are expected. For highspin states it remains possible that the mixing of the ground-state band and the cluster band may not be as important, leaving the i...

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“…Our RDM experiment and excitation curve near the barrier (58.5 to 60.0 MeV) yield ordering of the 4 + -2 + and 2 + -0 + transitions opposite to that suggested in Ref. 9.…”

contrasting

confidence: 93%

Molecular Alpha-Particle Clustering inRa218; Dipole Collectivity in the Vicinity of Nuclear Shell Closures

et al. 1983

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“…The ground state of 218 Ra is expected to be spherical [8], but it has been shown that at high spins, the yrast states form an alternating-parity sequence, with enhanced E1 transitions between the positive-and negative-parity states [9][10][11][12][13]. This high-spin structure is characteristic of strong octupole correlations, and it has been suggested that the octupole shape in this nucleus is stabilised by rotation [12,14].…”

Section: Introductionmentioning

confidence: 99%

Identification of theJπ=1−state inRa218populated viaα
Parr
¹
,
Smith
²
,
Greenlees
³

et al. 2016
Phys. Rev. C
6
0
10
1
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The α decay of 222 Th populating the low-lying J π = 3 − state, and also a proposed 1 − state, in 218 Ra has been observed. The observations suggest an excitation energy of 853 keV for the 1 − state, which is 60 keV above the 3 − state. The hindrance factors of these α decays give a possible boundary to the region of ground-state octupole deformation in the light-actinide nuclei. The relative positions of the J π = 1 − and 3 − states suggest they are produced by an octupole-vibrational mechanism, as opposed to α clustering or rotations of a reflection-asymmetric octupole-deformed shape.

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“…The presence of these E1 transitions from the lowest lying negative parity band to the first excited 0 + and the discoveries in light actinide nuclei [12] of level patterns similar to rotational bands in reflection asymmetric molecules suggest that some nuclei such as 154 Dy at low spin have stable shapes which may incorporate octupole deformation.…”

Section: Resultsmentioning

confidence: 99%

First observation of E1 transitions from the octupole band to the excited 02

Zimba¹,

Bvumbi²,

Masiteng³

et al. 2015

Proceedings of 53rd International Winter Meeting on Nuclear Physics — PoS(Bormio2015)

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The low spin states of 154 Dy were studied with the AFRODITE spectrometer array [1] equipped with 9 clover High Purity Germanium (HPGe) detectors with Compton suppressing Bismuth Germanium (BGO) shielding at iThemba LABS. The Fusion Evaporation reaction 155 Gd ( 3 He, 4n) 154 Dy at 37.5 MeV was used to populate low spin states. A first observation of enhanced E1 transitions in the transitional N = 88 isotones 150 Sm and 152 Gd from the levels in the first excited 0 + band to the lowest negative parity band [2]. The results we report here are on the first observation of enhanced E1 transitions from the low-lying negative parity band to the band built on the first excited 0 + state in 154 Dy. These measurements on 154 Dy extend the systematics on the relationship between the first excited positive parity pairing isomer band and the first excited negative parity band as the nuclear deformation decreases with increasing proton number.

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High-spin states in 218Ra

Cited by 84 publications

References 17 publications

Molecular Alpha-Particle Clustering inRa218; Dipole Collectivity in the Vicinity of Nuclear Shell Closures

Molecular Alpha-Particle Clustering inRa218; Dipole Collectivity in the Vicinity of Nuclear Shell Closures

Identification of theJπ=1−state inRa218populated viaα
Parr
¹
,
Smith
²
,
Greenlees
³

et al. 2016
Phys. Rev. C
6
0
10
1
View full text Add to dashboard Cite

First observation of E1 transitions from the octupole band to the excited 02

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High-spin states in 218Ra

Cited by 84 publications

References 17 publications

Molecular Alpha-Particle Clustering inRa218; Dipole Collectivity in the Vicinity of Nuclear Shell Closures

Molecular Alpha-Particle Clustering inRa218; Dipole Collectivity in the Vicinity of Nuclear Shell Closures

Identification of theJπ=1−state inRa218populated viaαParr1, Smith2, Greenlees3 et al. 2016Phys. Rev. C60101View full textAdd to dashboardCite

First observation of E1 transitions from the octupole band to the excited 02

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Identification of theJπ=1−state inRa218populated viaα
Parr
¹
,
Smith
²
,
Greenlees
³

et al. 2016
Phys. Rev. C
6
0
10
1
View full text Add to dashboard Cite