Excited states have been observed for the first time in the very neutron-deficient odd-odd nucleus 57120La63. The observed γ rays have been assigned based on coincidences with lanthanum X rays ...measured with the JUROGAM 3 array and with A=120 fusion-evaporation residues measured with the MARA separator. The observed γ rays form a rotational band which decays to the ground state via a cascade of four low-energy transitions. Based on the systematic comparisons with the heavier odd-odd La isotopes we assign spin-parity 4+ to the ground state and a πh11/2⊗νh11/2 configuration to the rotational band. The nuclear shape has been investigated by the cranked Nilsson-Strutinsky model. Two quasiparticle plus triaxial rotor model calculations including the np interaction nicely reproduce the spin of the inversion between the even- and odd-spin cascades of E2 transitions, giving credit to the np interaction as an important parameter responsible for the mechanism inducing the inversion. The position of the Fermi levels, in particular for neutrons, also has a strong impact on the observed inversion in the chain of lanthanum nuclei.
The electromagnetic character of the ΔI=1 transitions connecting the 1- to 0-phonon and the 2- to 1-phonon wobbling bands should be dominated by an E2 component, due to the collective motion of the ...entire nuclear charge. In the present work it is shown, based on combined angular correlation and linear polarization measurements, that the mixing ratios of all analyzed connecting transitions between low-lying bands in 135Pr interpreted as 0-, 1-, and 2-phonon wobbling bands, have absolute values smaller than one. This indicates predominant M1 magnetic character, which is incompatible with the proposed wobbling nature. All experimental observables are instead in good agreement with quasiparticle-plus-triaxial-rotor model calculations, which describe the bands as resulting from a rapid re-alignment of the total angular momentum from the short to the intermediate nuclear axis.
Lifetimes of low-lying excited states in the νi13/2+ bands of the neutron-deficient osmium isotopes 169,171,173Os have been measured for the first time using the recoil-distance Doppler shift and ...recoil-isomer tagging techniques. An unusually low value is observed for the ratio B(E2;21/2+→17/2+)/B(E2;17/2+→13/2+) in 169Os, similar to the “anomalously” low values of the ratio B(E2;41+→21+)/B(E2;21+→0gs+) previously observed in several transitional rare-earth nuclides with even numbers of neutrons and protons, including the neighbouring 168,170Os. Furthermore, the evolution of B(E2;21/2+→17/2+)/B(E2;17/2+→13/2+) with increasing neutron number in the odd-mass isotopic chain 169,171,173Os is observed to follow the same trend as observed previously in the even-even Os isotopes. These findings indicate that the possible quantum phase transition from a seniority conserving structure to a collective regime as a function of neutron number suggested for the even-even systems is maintained in these odd-mass osmium nuclei, with the odd valence neutron merely acting as a “spectator”. As for the even-even nuclei, the phenomenon is highly unexpected for nuclei that are not situated near closed shells.
Prolate-oblate shape coexistence close to the ground state in the strongly-deformed proton-rich A≈120 nuclei is reported for the first time. One of the four reported bands in 119Cs, built on a 11/2− ...state at 670 keV, consists of nearly degenerate signature partners, and has properties which unequivocally indicate the strongly-coupled πh11/250511/2− configuration associated with oblate shape. Together with the decoupled πh11/25413/2− band built on the 11/2− prolate state at 110 keV, for which a half-life of T1/2=55(5)μs has been measured, the new bands bring evidence of shape coexistence at low spin in the proton-rich strongly deformed A≈120 nuclei, a phenomenon predicted since long time, but not yet observed. Calculations using the particle-number conserving cranked shell model and two dimensional tilted axis cranking covariant density functional theory support and well reproduce the observed oblate and prolate coexisting low-energy states in 119Cs.
Candidate revolving chiral doublet bands in 119Cs Zheng, K. K.; Petrache, C. M.; Zhang, Z. H. ...
The European physical journal. A, Hadrons and nuclei,
2022/3, Letnik:
58, Številka:
3
Journal Article
Recenzirano
Two rotational bands are identified in
119
Cs, one of which having very similar pattern to that of the strongly-coupled
π
g
9
/
2
404
9
/
2
+
band. The properties of the bands with similar patterns ...extracted from the experimental data are in agreement with a chiral interpretation. Tilted axis cranking covariant density functional theory with pairing correlations and particle-number conserving cranked shell model calculations are employed to determine the deformation and to investigate the band configurations, respectively. It results that the backbending is induced by the rotational alignment of two
h
11
/
2
protons, whose angular momenta reorient from the short to the intermediate axis, in a plane orthogonal to the angular momentum of the strongly-coupled
g
9
/
2
proton which keeps aligned along the long axis. The total spin points in 3D, inducing the breaking of the chiral symmetry. This is the first observation of candidate chiral bands built on a configuration with three protons, one in the strongly coupled
404
9
/
2
+
orbital which does not change orientation with increasing rotational frequency, and two in the
h
11
/
2
orbital which reorients to the rotation axis. The bands are observed in the transient backbending regime, showing that the chirality in nuclei is a general phenomenon, being robust and present not only in nuclei with nearly maximal triaxiality and pure configurations, but also in nuclei with moderate triaxiality and mixed configurations which gradually evolve from one to three-quasiparticle configurations, like in the backbending region.
Multiple chiral bands in 137Nd Petrache, C. M.; Lv, B. F.; Chen, Q. B. ...
The European physical journal. A, Hadrons and nuclei,
2020/8, Letnik:
56, Številka:
8
Journal Article
Recenzirano
Two new bands have been identified in
137
Nd from a high-statistics JUROGAM II gamma-ray spectroscopy experiment. Constrained density functional theory and particle rotor model calculations are used ...to assign configurations and investigate the band properties, which are well described and understood. It is demonstrated that these two new bands can be interpreted as chiral partners of previously known three-quasiparticle positive- and negative-parity bands. The newly observed chiral doublet bands in
137
Nd represent an important support to the existence of multiple chiral bands in nuclei. The present results constitute the missing stone in the series of Nd nuclei showing multiple chiral bands, which becomes the most extended sequence of odd–even and even-even nuclei presenting multiple chiral bands in the Segré chart.
Abstract
Excited states in the extremely neutron-deficient nucleus
$$^{172}{\mathrm {Pt}}$$
172
Pt
were populated via
$$^{96}\mathrm {Ru}(^{78}\mathrm {Kr},2p)$$
96
Ru
(
78
Kr
,
2
p
)
and
...$$^{92}\mathrm {Mo}(^{83}\mathrm {Kr},3n)$$
92
Mo
(
83
Kr
,
3
n
)
reactions. The level scheme has been extended up to an excitation energy of
$$\approx 5~\hbox {MeV}$$
≈
5
MeV
and tentative spin-parity assignments up to
$$I^\pi = 18^+$$
I
π
=
18
+
. Linear polarization and angular distribution measurements were used to determine the electromagnetic E1 character of the dipole transitions connecting the positive-parity ground-state band with an excited side-band, firmly establishing it as a negative-parity band. The lowest member of this negative-parity structure was firmly assigned spin-parity
$$3^-$$
3
-
. In addition, we observed an E3 transition from this
$$3^-$$
3
-
state to the ground state, providing direct evidence for octupole collectivity in
$$^{172}{\mathrm {Pt}}$$
172
Pt
. Large-scale shell model (LSSM) and total Routhian surface (TRS) calculations have been performed, supporting the interpretation of the
$$3^-$$
3
-
state as a collective octupole-vibrational state.
.
Lifetimes of high-spin states have been measured in the semi-magic
(
N
=
50
)
nucleus
94
Ru. Excited states in
94
Ru were populated in the
58
Ni(
40
Ca, 4
p
)
94
Ru
*
fusion-evaporation reaction at ...the Grand Accélérateur National d’Ions Lourds (GANIL) accelerator complex. DSAM lifetime analysis was performed on the Doppler broadened line shapes in energy spectra obtained from
γ
-rays emitted while the residual nuclei were slowing down in a thick 6mg/cm^2 metallic
58
Ni target. In total eight excited-state lifetimes in the angular momentum range
I
=
(
13
-
20
)
ℏ
have been measured, five of which were determined for the first time. The corresponding
B
(
M
1) and
B
(
E
2) reduced transition strengths are discussed within the framework of large-scale shell model calculations to study the contribution of different particle-hole configurations, in particular for analyzing contributions from core-excited configurations.
Lifetimes of the first excited 2^{+} and 4^{+} states in the extremely neutron-deficient nuclide ^{172}Pt have been measured for the first time using the recoil-distance Doppler shift and ...recoil-decay tagging techniques. An unusually low value of the ratio B(E2:4_{1}^{+}→2_{1}^{+})/B(E2:2_{1}^{+}→0_{gs}^{+})=0.55(19) was found, similar to a handful of other such anomalous cases observed in the entire Segré chart. The observation adds to a cluster of a few extremely neutron-deficient nuclides of the heavy transition metals with neutron numbers N≈90-94 featuring the effect. No theoretical model calculations reported to date have been able to explain the anomalously low B(E2:4_{1}^{+}→2_{1}^{+})/B(E2:2_{1}^{+}→0_{gs}^{+}) ratios observed in these cases. Such low values cannot, e.g., be explained within the framework of the geometrical collective model or by algebraic approaches within the interacting boson model framework. It is proposed that the group of B(E2:4_{1}^{+}→2_{1}^{+})/B(E2:2_{1}^{+}→0_{gs}^{+}) ratios in the extremely neutron-deficient even-even W, Os, and Pt nuclei around neutron numbers N≈90-94 reveal a quantum phase transition from a seniority-conserving structure to a collective regime as a function of neutron number. Although a system governed by seniority symmetry is the only theoretical framework for which such an effect may naturally occur, the phenomenon is highly unexpected for these nuclei that are not situated near closed shells.
One new pair of positive-parity chiral doublet bands have been identified in the odd-A nucleus Nd-135 which together with the previously reported negative-parity chiral doublet bands constitute a ...third case of multiple chiral doublet (M chi D) bands in the A approximate to 130 mass region. The properties of the M chi D bands are well reproduced by constrained covariant density functional theory and particle rotor model calculations. The newly observed M chi D bands in Nd-135 represents an important milestone in supporting the existence of M chi D in nuclei.
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