Proton-neutron configurations in atomic nuclei can manifest in a variety of different structures, and exotic nuclei provide fruitful ground for exploring their relation to fundamental symmetries. Here, we report on in-beam <italic>&#947;</italic>-ray spectroscopy of the very neutron-deficient 184Pb nucleus using the <small-caps>jurogam II</small-caps> spectrometer at the <small-caps>ritu</small-caps> separator in a recoil-decay tagging experiment. For the first time, transitions from the non-yrast states have been observed in a Pb nucleus beyond the neutron <math altimg='si1.svg'><mi>N</mi><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mn>104</mn></math> midshell. In comparison to neighboring Pb isotopes and theoretical models, de-excitation patterns from these states are similar to those associated with predominantly oblate shapes in heavier Pb isotopes. Together with the known predominantly prolate yrast band and the spherical ground state, this suggests that triple-shape coexistence prevails in the 184Pb nucleus.

Finland

J. Ojala

J. Pakarinen

United Kingdom

R. Wadsworth

H. Badran

D.M. Cox

A.D. Briscoe

A. Brown

T. Calverley

T. Grahn

P.T. Greenlees

J. Hilton

R. Julin

J. Konki

R. Llewellyn

S. Juutinen

M. Leino

P. Papadakis

J. Partanen

P. Rahkila

M. Sandzelius

J. Sarén

C. Scholey

S. Stoltze

J. Uusitalo

B. Wallis

Competing structures in the beyond neutron N=104 midshell nucleus 184Pb

Competing configurations, assigned with three different shapes, are mixed at low angular momentum in the neutron-deficient $^{188}$Pb nucleus. Here, we present a simultaneous conversion electron and γ-ray in-beam spectroscopic precision measurement employing the sage spectrometer. The level energy of the first excited state, <math><msubsup><mrow><mn>0</mn></mrow><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msubsup></math>, has been determined at 591(1)keV through direct measurement of conversion electrons. By using the intensity of the observed <math><msubsup><mrow><mn>0</mn></mrow><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msubsup><mo>→</mo><msubsup><mrow><mn>0</mn></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup></math> transition to the ground state, the feeding of the <math><msubsup><mrow><mn>0</mn></mrow><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msubsup></math> state has been determined for the first time, which suggests the <math><msubsup><mrow><mn>0</mn></mrow><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msubsup></math> state is the head of the predominantly prolate band. The compositions of the <math><msubsup><mrow><mn>4</mn></mrow><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msubsup><mo>→</mo><msubsup><mrow><mn>4</mn></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup></math> and <math><msubsup><mrow><mn>2</mn></mrow><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msubsup><mo>→</mo><msubsup><mrow><mn>2</mn></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup></math> inter-band transitions have been determined, indicating configuration mixing between the bands.

K. Auranen

Poland

K. Hadyńska-Klek

Slovakia

A. Herzáň

R.D. Herzberg

U. Jakobsson

A. Mistry

D. O'Donnell

P. Peura

P. Ruotsalainen

J. Sorri

Belgium

K. Wrzosek-Lipska

Direct observation of 0 Transitions in Pb through in-beam spectroscopy

We present the first experimental evidence of the scissors mode in the superheavy nucleus 254No produced in the 208Pb( 48Ca, <math altimg='si1.svg'><mn>2</mn><mi>n</mi><mi>&#947;</mi></math>)) 254No reaction. The spectrum of <italic>&#947;</italic> rays emitted by the excited 254No nuclei shows an enhanced <italic>&#947;</italic>-ray yield for transition energies of &#8776;2.5 MeV. By measuring the linear polarization properties of the emitted <italic>&#947;</italic> rays, we confirm that the transitions in the enhancement region are predominantly of magnetic-dipole character, characteristic for the scissors mode. To further characterize the enhanced <italic>&#947;</italic>-ray yield, simulations of the electromagnetic decay of 254No were performed. The observed enhancement is reproduced by including an <italic>M</italic>1 component in the <italic>&#947;</italic> strength function with total strength <math altimg='si2.svg'><mi>B</mi><mo stretchy='false'>(</mo><mi>M</mi><mn>1</mn><mo stretchy='false'>&#8593;</mo><mo stretchy='false'>)</mo><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mn>11.8</mn><mo stretchy='false'>(</mo><mn>19</mn><mo stretchy='false'>)</mo><mspace width='0.25em' /><msubsup><mrow><mi>&#956;</mi></mrow><mrow><mi>N</mi></mrow><mrow><mn>2</mn></mrow></msubsup></math>. This is in good agreement with the integrated <italic>M</italic>1 strength from sum-rule estimates and new calculations within the quasi-particle random-phase approximation presented here. Our results provide a stringent test of phenomenological formulae for the scissors mode currently used in stellar nucleosynthesis calculations. We find that those formulae are not satisfactory, and we recommend using sum-rule estimates assuming a rigid-body moment of inertia instead for describing the scissors mode in superheavy nuclei.

Norway

F.L. Bello Garrote

France

A. Lopez-Martens

A.C. Larsen

I. Deloncle

S. Péru

F. Zeiser

B.V. Kheswa

United States

D.L. Bleuel

L. Crespo Campo

Germany

F. Giacoppo

A. Görgen

M. Guttormsen

T.W. Hagen

L. Harkness-Brennan

K. Hauschild

G. Henning

T.A. Laplace

J.E. Midtbø

V. Modamio

T. Renstrøm

K. Rezynkina

S. Siem

S. Stolze

Experimental observation of the <italic>M</italic>1 scissors mode in 254No

The spectroscopic quadrupole moment of the first <math><msup><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msup></math> state of $^{12}$C has been measured employing the Coulomb-excitation re-orientation technique. Our result of <math><msub><mrow><mi>Q</mi></mrow><mrow><mi>s</mi></mrow></msub><mo>(</mo><msubsup><mrow><mn>2</mn></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup><mo>)</mo><mo>=</mo><mo>+</mo><msubsup><mrow><mn>9.3</mn></mrow><mrow><mo>−</mo><mn>3.8</mn></mrow><mrow><mo>+</mo><mn>3.5</mn></mrow></msubsup><mspace width="0.25em"></mspace><msup><mrow><mtext>efm</mtext></mrow><mrow><mn>2</mn></mrow></msup></math> suggests a larger oblate deformation than previously reported. Combining this with the consistently re-analyzed adopted value, we present the most precise value to date of <math><msub><mrow><mi>Q</mi></mrow><mrow><mi>s</mi></mrow></msub><mo>(</mo><msubsup><mrow><mn>2</mn></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup><mo>)</mo><mo>=</mo><mo>+</mo><mn>9.5</mn><mo>(</mo><mn>18</mn><mo>)</mo><mspace width="0.2em"></mspace><msup><mrow><mtext>efm</mtext></mrow><mrow><mn>2</mn></mrow></msup></math>, which is consistent with a geometrical rotor description. This simple outcome is compared to state-of-the-art shell-model, mean-field, ab initio calculations, cluster-based and geometrical-like theories, which show varying degrees of emergent quadrupole collectivity.

J. Saiz-Lomas

M. Petri

I.Y. Lee

I. Syndikus

S. Heil

J.M. Allmond

L.P. Gaffney

U. Forsberg

P. Greenlees

K. Hadyńska-Klȩk

M. Jenkinson

A.O. Macchiavelli

M. Mathy

The spectroscopic quadrupole moment of the State of C: A benchmark of theoretical models

Proton-emission branches of the <math><msup><mrow><mn>10</mn></mrow><mrow><mo>+</mo></mrow></msup></math> isomer in the <math><msub><mrow><mi>T</mi></mrow><mrow><mi>z</mi></mrow></msub><mo>=</mo><mo>−</mo><mn>1</mn></math> nucleus $^{54}$Ni have been imaged with the active target and time projection chamber (ACTAR TPC) in an experiment conducted at the Grand Accélérateur National d'Ions Lourds (GANIL). The completed decay scheme allows derivation of the reduced transition strengths, <math><mi>B</mi><mo>(</mo><mi>E</mi><mn>2</mn><mo>;</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>+</mo></mrow></msup><mo>→</mo><mspace width="0.2em"></mspace><msup><mrow><mn>8</mn></mrow><mrow><mo>+</mo></mrow></msup><mo>)</mo></math> and <math><mi>B</mi><mo>(</mo><mi>E</mi><mn>4</mn><mo>;</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>+</mo></mrow></msup><mo>→</mo><mspace width="0.2em"></mspace><msup><mrow><mn>6</mn></mrow><mrow><mo>+</mo></mrow></msup><mo>)</mo></math>, for the two competing γ-ray transitions. By means of a comparison with their well-known ‘mirror transitions’ in <math><msub><mrow><mi>T</mi></mrow><mrow><mi>z</mi></mrow></msub><mo>=</mo><mo>+</mo><mn>1</mn></math> $^{54}$Fe, and aided by a variety of shell-model calculations in the fp model space, effective charges for E4 transitions near <math><mi>N</mi><mo>=</mo><mi>Z</mi></math> $^{56}$Ni can be deduced: <math><msub><mrow><mi>ε</mi></mrow><mrow><mi>π</mi></mrow></msub><mo>≈</mo><mn>1.40</mn></math> and <math><msub><mrow><mi>ε</mi></mrow><mrow><mi>ν</mi></mrow></msub><mo>≈</mo><mn>0.30</mn></math>. Mirror-energy differences are explored with various shell-model interactions and isospin-symmetry breaking terms.

Sweden

D. Rudolph

B. Blank

J. Giovinazzo

T. Roger

Spain

H. Alvarez-Pol

A. Arokia Raj

P. Ascher

M. Caamaño-Fresco

L. Caceres

B. Fernández-Domínguez

J. Lois-Fuentes

M. Gerbaux

S. Grévy

Canada

G.F. Grinyer

O. Kamalou

Japan

B. Mauss

A. Mentana

J. Pancin

J. Pibernat

J. Piot

O. Sorlin

C. Stodel

J.C. Thomas

M. Versteegen

Mirror symmetry at mass = 54: 4 Effective Charges Near Doubly Magic Ni

The electromagnetic character of the <math><mi>Δ</mi><mi>I</mi><mo>=</mo><mn>1</mn></math> 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 $^{135}$Pr 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.

China

B.F. Lv

C.M. Petrache

South Africa

E.A. Lawrie

S. Guo

A. Astier

K.K. Zheng

H.J. Ong

J.G. Wang

X.H. Zhou

Z.Y. Sun

CERN

B. Cederwall

A. Ertoprak

H. Liu

Hungary

I. Kuti

J. Timár

A. Tucholski

J. Srebrny

C. Andreoiu

Evidence against the wobbling nature of low-spin bands in Pr

Lifetimes of low-lying excited states in the <math><mi>ν</mi><msub><mrow><mi>i</mi></mrow><mrow><mn>13</mn><mo>/</mo><msup><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msup></mrow></msub></math> bands of the neutron-deficient osmium isotopes $^{169,171,173}$Os 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 <math><mi>B</mi><mo>(</mo><mi>E</mi><mn>2</mn><mo>;</mo><mn>21</mn><mo>/</mo><msup><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msup><mo>→</mo><mn>17</mn><mo>/</mo><msup><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msup><mo>)</mo><mo>/</mo><mi>B</mi><mo>(</mo><mi>E</mi><mn>2</mn><mo>;</mo><mn>17</mn><mo>/</mo><msup><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msup><mo>→</mo><mn>13</mn><mo>/</mo><msup><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msup><mo>)</mo></math> in $^{169}$Os, similar to the “anomalously” low values of the ratio <math><mi>B</mi><mo>(</mo><mi>E</mi><mn>2</mn><mo>;</mo><msubsup><mrow><mn>4</mn></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup><mo>→</mo><msubsup><mrow><mn>2</mn></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup><mo>)</mo><mo>/</mo><mi>B</mi><mo>(</mo><mi>E</mi><mn>2</mn><mo>;</mo><msubsup><mrow><mn>2</mn></mrow><mrow><mn>1</mn></mrow><mrow><mo>+</mo></mrow></msubsup><mo>→</mo><msubsup><mrow><mn>0</mn></mrow><mrow><mi>gs</mi></mrow><mrow><mo>+</mo></mrow></msubsup><mo>)</mo></math> previously observed in several transitional rare-earth nuclides with even numbers of neutrons and protons, including the neighbouring $^{168,170}$Os. Furthermore, the evolution of <math><mi>B</mi><mo>(</mo><mi>E</mi><mn>2</mn><mo>;</mo><mn>21</mn><mo>/</mo><msup><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msup><mo>→</mo><mn>17</mn><mo>/</mo><msup><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msup><mo>)</mo><mo>/</mo><mi>B</mi><mo>(</mo><mi>E</mi><mn>2</mn><mo>;</mo><mn>17</mn><mo>/</mo><msup><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msup><mo>→</mo><mn>13</mn><mo>/</mo><msup><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msup><mo>)</mo></math> with increasing neutron number in the odd-mass isotopic chain $^{169,171,173}$Os 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.

W. Zhang

M. Doncel

Ö. Aktas

Türkiye

R. Liotta

C. Qi

B.S. Nara Singh

D.M. Cullen

D. Hodge

M. Giles

T. Braunroth

Y.D. Fang

E. Ideguchi

M. Kumar Raju

H. Li

S. Matta

P. Subramaniam

M.J. Taylor

Italy

J.J. Valiente-Dobón

Lifetime measurements of excited states in Os: Persistence of anomalous ( 2) Ratios in Transitional Rare Earth Nuclei in the Presence of a Decoupled Valence Neutron

The isotopic distribution of nuclei produced in the 50Ti + 249Cf reaction has been studied at the gas-filled recoil separator TASCA at GSI Darmstadt, which separates ions according to differences in magnetic rigidity. The bombardment was performed at an energy around the Bass barrier and with the TASCA magnetic fields set for collecting fusion-evaporation reaction products. Fifty-three isotopes located “north-east” of 208Pb were identified as recoiling products formed in non-fusion channels of the reaction. These recoils were implanted with energies in two distinct ranges; besides one with higher energy, a significant low-energy contribution was identified. The latter observation was not expected to occur according to kinematics of the known types of reactions, namely quasi-elastic, multi-nucleon transfer, deep-inelastic collisions or quasifission. The present observations are discussed within the framework of two-body kinematics passing through the formation of a composite system.