Near the doubly-magic nucleus 78Ni ( <math altimg='si1.svg'><mi>Z</mi><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mn>28</mn></math>, <math altimg='si2.svg'><mi>N</mi><mo linebreak='goodbreak' linebreakstyle='after'>=</mo><mn>50</mn></math>), there has been a decades-long debate on the existence of a long-lived isomer in 76Cu. A recent mass measurement claimed to have settled the debate, by measuring the energy of the isomer and shedding light on the structure of the nucleus. In this work, we present new, more accurate, and precise values of the half-lives of the isomeric and ground states in 76Cu. Our findings suggest that both states have very similar half-lives, in the 600&#8211;700 ms range, in disagreement with the literature values, implying that they cannot be differentiated by their decay curves. These results raise more questions than they answer, reopening the debate and showing that the structures in 76Cu are still not fully understood.

Spain

Canada

Switzerland

B. Olaizola

Italy

Finland

A. Illana

J. Benito

D.P. Suárez-Bustamante

G. Del Piccolo

A. Algora

Slovakia

B. Andel

United Kingdom

A.N. Andreyev

Poland

M. Araszkiewicz

Y. Ayyad

South Africa

R.A. Bark

T. Berry

M.J.G. Borge

K. Chrysalidis

Belgium

T.E. Cocolios

Romania

C. Costache

J.G. Cubiss

P. Van Duppen

Z. Favier

L.M. Fraile

Denmark

H.O.U. Fynbo

F. Galtarossa

France

G. Georgiev

P.T. Greenless

United States

R. Grzywacz

L.J. Harkness-Brennan

R. Heinke

M. Huyse

P. Ibañez

K. Johnston

P.M. Jones

D.S. Judson

J. Konki

A. Korgul

U. Köster

J. Kurcewicz

M. Labiche

I. Lazarus

R. Lică

M. Llanos-Expósito

M. Madurga

N. Marginean

R. Marginean

B.A. Marsh

C. Mihai

Czechia

R.E. Mihai

J.R. Murias

E. Nácher

C. Neacsu

A. Negret

V.M. Nouvilas

J. Ojala

J.N. Orce

C.A.A. Page

R.D. Page

J. Pakarinen

J. Papadakis

S. Pascu

A. Perea

M. Piersa-Siłkowska

A.M. Plaza

Zs. Podolyák

W. Poklepa

V. Pucknell

P. Rahkila

C. Raison

E. Rapisarda

K. Rezynkina

F. Rotaru

Germany

K. Schomacker

M. Siciliano

C. Sotty

M. Stryjczyk

O. Tengblad

J.M. Udías

V. Vedia

S. Viñals

R. Wadsworth

N. Warr

H. De Witte

D. Yates

Z. Yue

The 76Cu conundrum remains unsolved

The magnetic dipole moments (μ) of $^{209}$Tl$^{g}$ (<math><mi>N</mi><mo>=</mo><mn>128</mn></math>) and $^{207}$Tl$^{m}$ (<math><mi>N</mi><mo>=</mo><mn>126</mn></math>) have been measured for the first time using the in-source laser resonance-ionization spectroscopy technique with the Laser Ion Source and Trap (LIST) at ISOLDE (CERN). The application of the LIST suppresses the usually overwhelming background of the isobaric francium isotopes and allows access to heavy thallium isotopes with <math><mi>A</mi><mo>⩾</mo><mn>207</mn></math>. The self-consistent theory of finite Fermi systems based on the energy density functional by Fayans et al. well describes the N dependence of μ for <math><mn>1</mn><mo>/</mo><msup><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msup></math> thallium ground states, as well as μ for the <math><mn>11</mn><mo>/</mo><msup><mrow><mn>2</mn></mrow><mrow><mo>−</mo></mrow></msup></math> isomeric states in europium, gold and thallium isotopes. The inclusion of particle-vibration coupling leads to a better agreement between the theory and experiment for μ(Tl$^{g}$, <math><msup><mrow><mi>I</mi></mrow><mrow><mi>π</mi></mrow></msup><mo>=</mo><mn>1</mn><mo>/</mo><msup><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msup></math>). It is shown that beyond mean-field contributions to μ cannot be neglected at least for thallium isotopes with <math><msup><mrow><mi>I</mi></mrow><mrow><mi>π</mi></mrow></msup><mo>=</mo><mn>1</mn><mo>/</mo><msup><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msup></math>.

CERN

A.E. Barzakh

I.N. Borzov

M. Au

M. Balogh

S. Bara

C. Bernerd

D. Brugnara

A. Gottardo

L. Le

R. Lica

B. Marsh

C. Nita

P. Papadakis

G. Penyazkov

S.D. Prosnyak

E. Reis

S. Rothe

M. Sedlak

L.V. Skripnikov

S. Stegemann

S.V. Tolokonnikov

W. Wojtaczka

Magnetic moments of thallium isotopes in the vicinity of magic = 126

Prompt and delayed γ-ray spectroscopy of the neutron-deficient, semi-magic isotope $^{187}$Pb has been performed using the recoil-decay and isomer-decay tagging techniques at the Argonne Gas-Filled Analyzer. A new 5.15(15)-μs isomeric state at only 308 keV above the spherical 3/2$^{−}$ ground state is identified and classified as a shape isomer. A strongly-coupled band is observed on top of the isomer, which is nearly identical to the one built on the prolate 7/2$^{−}$[514] Nilsson state in the isotone $^{185}$Hg. Based on this similarity and on the result of the potential-energy surface calculations, the new isomer in $^{187}$Pb is proposed to originate from the same configuration. The retarded character of the 308-keV (7/2$^{−}$)→3/2<math><msubsup><mrow></mrow><mrow><mi>g</mi><mi>s</mi></mrow><mrow><mo>−</mo></mrow></msubsup></math> transition with a deduced <math><mi>B</mi><mo>(</mo><mi>E</mi><mn>2</mn><mo>)</mo><mo>=</mo><mn>5.6</mn><mo>(</mo><mn>2</mn><mo>)</mo><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>4</mn></mrow></msup></math> W.u. can be well explained by the significant difference between the prolate parent and spherical daughter configurations, leading to the shape isomerism. The excitation energy of the isomer is surprisingly low, being roughly half of the excitation energies of the known 0$^{+}$ intruder bandheads in the neighboring $^{186,188}$Pb isotopes. The combined results of the present work and the previous α-decay and laser spectroscopy studies present evidence for triple shape coexistence at low energy in the negative-parity configurations of $^{187}$Pb, which is well reproduced by the potential-energy surface calculations.

China

W.Q. Zhang

Japan

Z. Liu

D. Seweryniak

H. Huang

Z.H. Li

J.G. Li

C.Y. Guo

D.T. Doherty

Russia

S. Antalic

M. Block

A. Bronis

M.P. Carpenter

P. Copp

B. Ding

F. Giacoppo

T.H. Huang

X.H. Yu

B. Kindler

F.G. Kondev

T. Lauritsen

G.S. Li

B. Lommel

H.Y. Lu

M. Al Monthery

P. Mošať

Y.F. Niu

W. Reviol

G. Savard

S. Stolze

G.L. Wilson

H.Y. Wu

Z.H. Wang

F.R. Xu

Q.B. Zeng

X.H. Zhou

First observation of a shape isomer and a low-lying strongly-coupled prolate band in neutron-deficient semi-magic Pb

The decay of the 13/2$^{+}$ isomeric state in $^{183}$Hg was observed for the first time following the α decay of the 13/2$^{+}$ isomer in $^{187}$Pb produced in the $^{142}$Nd($^{50}$Cr, 2p3n) reaction. Using <math><mi>α</mi><mo>−</mo><mi>γ</mi></math> delayed coincidence measurements, the half-life of this isomer was measured to be 290(30) μs. This isomer is proposed to deexcite by an unobserved low-energy M2 transition to the known 9/2$^{−}$ member of a strongly prolate-deformed 7/2$^{−}$[514] band, followed by a 105-keV M1 transition to the bandhead. A lower limit of B(M2) ≥ 0.018 W.u. was deduced for the unobserved transition. The presumed retardation is proposed to be due to the notable shape change between the initial, nearly spherical, and the final, strongly deformed, states. A similar scenario is also considered for the 13/2$^{+}$ isomer in $^{181}$Hg, suggesting both are cases of shape isomers. The <math><mi>B</mi><mo>(</mo><mi>M</mi><mn>2</mn><mo>)</mo></math> systematics of neutron transitions across the nuclear chart is discussed.

F.F. Zeng

First observation of the decay of the 13/2 Isomer in Hg and ( 2) Systematics of Neutron Transitions Across the Nuclear Chart

The β decay of <math><msubsup><mrow></mrow><mrow><mspace width="0.25em"></mspace><mn>75</mn></mrow><mrow><mn>192</mn></mrow></msubsup></math>Re$_{117}$, which lies near the boundary between the regions of predicted prolate and oblate deformations, has been investigated using the KEK Isotope Separation System (KISS) in RIKEN Nishina Center. This is the first case in which a low-energy beam of rhenium isotope has been successfully extracted from an argon gas-stopping cell using a laser-ionization technique, following production via multi-nucleon transfer between heavy ions. The ground state of $^{192}$Re has been assigned <math><msup><mrow><mi>J</mi></mrow><mrow><mi>π</mi></mrow></msup><mo>=</mo><mo>(</mo><msup><mrow><mn>0</mn></mrow><mrow><mo>−</mo></mrow></msup><mo>)</mo></math> based on the observed β feedings and deduced logft values towards the <math><msup><mrow><mn>0</mn></mrow><mrow><mo>+</mo></mrow></msup></math> and <math><msup><mrow><mn>2</mn></mrow><mrow><mo>+</mo></mrow></msup></math> states in $^{192}$Os, which is known as a typical γ-soft nucleus. The shape transition from axial symmetry to axial asymmetry in the Re isotopes is discussed from the viewpoint of single-particle structure using the nuclear Skyrme-Hartree-Fock model.

H. Watanabe

Y.X. Watanabe

Y. Hirayama

South Korea

T. Hashimoto

Australia

G.J. Lane

Yu.A. Litvinov

Hong Kong

J.J. Liu

H. Miyatake

J.Y. Moon

A.I. Morales

M. Mukai

S. Nishimura

T. Niwase

M. Rosenbusch

P. Schury

Y. Shi

M. Wada

P.M. Walker

Beta decay of the axially asymmetric ground state of Re

The extremely neutron-deficient isotopes $^{177,179}$Au were studied by means of in-beam γ-ray spectroscopy. Specific tagging techniques, α-decay tagging in $^{177}$Au and isomer tagging in $^{179}$Au, were used for these studies. Feeding of positive-parity, nearly spherical states, which are associated with 2<math><msub><mrow><mi>d</mi></mrow><mrow><mn>3</mn><mo>/</mo><mn>2</mn></mrow></msub></math> and 3<math><msub><mrow><mi>s</mi></mrow><mrow><mn>1</mn><mo>/</mo><mn>2</mn></mrow></msub></math> proton-hole configurations, from the 1<math><msub><mrow><mi>i</mi></mrow><mrow><mn>13</mn><mo>/</mo><mn>2</mn></mrow></msub></math> proton-intruder configuration was observed in $^{177}$Au. Such a decay path has no precedent in odd-Au isotopes and it is explained by the effect of mixing of wave functions of the initial state.

M. Venhart

A. Herzáň

J.L. Wood

Iraq

F.A. Ali

D.T. Joss

K. Auranen

R.J. Carroll

M.C. Drummond

Population of a low-spin positive-parity band from high-spin intruder states in Au: The two-state mixing effect