Brunet, M.*; Podolyk, Zs.*; Berry, T. A.*; Brown, B. A.*; Carroll, R. J.*; Lica, R.*; Sotty, Ch.*; Andreyev, A. N.; Borge, M. J. G.*; Cubiss, J. G.*; et al.
Physical Review C, 103(5), p.054327_1 - 054327_13, 2021/05
The structure of Po populated through the EC/ decay of At is investigated using -ray spectroscopy at the ISOLDE Decay Station. The presented level scheme contains 27 new excited states and 43 new transitions, as well as a further 50 previously observed rays which have been (re)assigned a position. Through the analysis using the shell model calculations approximately half of the -decay strength of At is found to proceed via allowed decay and half via first-forbidden decay. The first-forbidden transitions predominantly populate core excited states at high excitation energies, which is qualitatively understood using shell model considerations.
Gillespie, S. A.*; Stott, A.*; Andreyev, A. N.; 他30名*
Physical Review C, 103(4), p.044307_1 - 044307_9, 2021/04
Proton-rich Au isotopes are an excellent laboratory to study shape coexistence and isomerism at low excitation energies. In this work, two new isomeric states were found in the odd-odd nuclide Au in an experiment at RITU in JYFL, Jyvaskyla. These two isomers significantly extend the current knowledge of this nucleus and pave the way to future in beam studies where they will be used to tag new gamma rays. Possible spin assignments for the new isomeric states are proposed. Finally, the new data will help clarify the poorly known -decay scheme of two long-lived states in the Tl to Au decay chain.
Schmitt, C.*; Lemasson, A.*; Schmidt, K.-H.*; Jhingan, A.*; Biswas, S.*; Kim, Y. H.*; Ramos, D.*; Andreyev, A. N.; Curien, D.*; Ciemala, M.*; et al.
Physical Review Letters, 126(13), p.132502_1 - 132502_6, 2021/04
Isotopic distributions of fragments from fission of the neutron-deficient Hg nuclide are reported. This experimental observable is obtained for the first time in the region around lead using an innovative approach based on inverse kinematics and the coincidence between the large acceptance magnetic spectrometer VAMOS++ and a new detection arm close to the target. The average fragment ratio and prompt neutron multiplicity are derived and compared with current knowledge from actinide fission. A striking consistency emerges, revealing the unexpected dominant role of the proton subsystem with atomic number between the = 28 and 50 magic numbers. The origin of nuclear charge polarization in fission and fragment deformation at scission are discussed.
Zhang, Z. Y.*; Yang, H. B.*; Andreyev, A. N.; Liu, M. L.*; Ma, L.*; 他37名*
Physical Review Letters, 126(15), p.152502_1 - 152502_6, 2021/04
A new -emitting isotope U, produced by the fusion-evaporation reaction W(Ar,4n)U, was identified by employing the gas-filled recoil separator SHANS and the recoil- correlation technique. More precise -decay properties of even-even nuclei U were also measured in the reactions of Ar, Ca beams with W targets. By combining the experimental data, improved -decay reduced widths for the even-even Po-Pu nuclei in the vicinity of the magic neutron number = 126 are deduced. Their systematic trends are discussed in terms of the scheme in order to study the influence of proton-neutron interaction on decay in this region of nuclei. It is strikingly found that the reduced widths of U are significantly enhanced by a factor of two as compared with the systematics for the 84 90 and 126 even-even nuclei. The abnormal enhancement is interpreted by the strong monopole interaction between the valence protons and neutrons occupying the 1 and 1 spin-orbit partner orbits, which is supported by the large-scale shell model calculation.
渡邉 寛*; 渡辺 裕*; 平山 賀一*; Andreyev, A. N.; 橋本 尚志*; Kondev, F. G.*; Lane, G. J.*; Litvinov, Yu. A.*; Liu, J. J.*; 宮武 宇也*; et al.
Physics Letters B, 814, p.136088_1 - 136088_6, 2021/03
The decay of Re, 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. The ground state of Re has been assigned = based on the observed feedings and deduced log values towards the and states in Os, which is known as a typical -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.
Day Goodacre, T.*; Afanasjev, A. V.*; Barzakh, A. E.*; Marsh, B. A.*; Sels, S.*; Ring, P.*; 中田 仁*; Andreyev, A. N.; 他36名*
Physical Review Letters, 126(3), p.032502_1 - 032502_7, 2021/01
The charge radii of Hg have been studied for the first time and those of Hg remeasured by laser spectroscopy at ISOLDE (CERN). The characteristic kink in the charge radii at the = 126 shell closure has been revealed, providing the first information on its behavior below the = 82 shell closure. By a theoretical analysis, it is demonstrated, contrary to previous interpretations, that both the kink at = 126 and the odd-even staggering can be described predominantly at the mean-field level and that pairing does not need to play a crucial role in their origin.
Vermeulen, M. J.; 西尾 勝久; 廣瀬 健太郎; Kean, K. R.; 牧井 宏之; Orlandi, R.; 塚田 和明; Tsekhanovich, I.*; Andreyev, A. N.; 石崎 翔馬*; et al.
Physical Review C, 102(5), p.054610_1 - 054610_11, 2020/11
Fission fragment mass distributions for 23 nuclei (U, Np, Pu, Am, Cm, and Bk) were measured using the multi-nucleon transfer approach in the reaction of O+Np, and their excitation-energy dependence was obtained up to a maximum of 70 MeV. Among them, the low energy fission of Np, Pu, and Cm is reported for the first time. The experimental data for all the studied nuclei were compared to the Langevin calculations. The calculation which takes into account the effects of multi-chance fission well reproduced the peak-to-valley ratio and mass-asymmetric peak positions of the distributions. The angular momenta given to the fissioning nucleus is also discussed.
Carroll, R. J.*; Podolyk, Zs.*; Berry, T.*; Grawe, H.*; Alexander, T.*; Andreyev, A. N.; Ansari, S.*; Borge, M. J. G.*; Brunet, M.*; Creswell, J. R.*; et al.
Physical Review Letters, 125(19), p.192501_1 - 192501_6, 2020/11
The decay of Hg into the one-proton hole, one neutron-particle Tl nucleus was investigated at CERN-ISOLDE. Shell-model calculations describe well the level scheme deduced, validating the proton-neutron interactions used, with implications for the whole of the , quadrant of neutron-rich nuclei. While both negative and positive parity states with spin 0 and 1 are expected within the window, only three negative parity states are populated directly in the decay. The data provide a unique test of the competition between allowed Gamow-Teller and Fermi, and first-forbidden decays, essential for the understanding of the nucleosynthesis of heavy nuclei in the rapid neutron capture process. Furthermore, the observation of the parity changing decay where the daughter state is core excited is unique, and can provide information on mesonic corrections of effective operators.
Cubiss, J. G.*; Andreyev, A. N.; Barzakh, A. E.*; Manea, V.*; Al Monthery, M.*; Althubiti, N. A.*; Andel, B.*; Antalic, S.*; 他39名*
Physical Review C, 102(4), p.044332_1 - 044332_12, 2020/10
A comprehensive study of the isotope Au has been made at the CERN-ISOLDE facility, using resonance laser ionization. Two long-lived states in Au were identified - a low-spin ground state and a high-spin isomer - each of which were produced as pure beams. Using the ISOLTRAP precision Penning trap, the excitation energy of the isomeric state in Au was determined to be 189(14) keV. The -decay fine structure patterns of the two states were studied using the Windmill decay station, providing information on the low-lying states in the daughter nucleus Ir. Nuclear spin assignments of Au and Au are made based on the observed -decay feeding and hyperfine structure intensity patterns.
Harding, R. D.*; Andreyev, A. N.; Barzakh, A. E.*; Atanasov, D.*; Cubiss, J. G.*; Van Duppen, P.*; 他40名*
Physical Review C, 102(2), p.024312_1 - 024312_16, 2020/08
A detailed nuclear spectroscopy study of Au was performed. An -decay branching ratio of % and a half-life of s have been derived. The first measurement of the hyper fine structure for atomic transitions has been also performed, from which the magnetic dipole moment has been extracted. A spin assignment of is proposed for the ground state of Au, with a  configuration.
Stryjczyk, M.*; Andel, B.*; Andreyev, A. N.; Cubiss, J.*; Pakarinen, J.*; 他43名*
Physical Review C, 102(2), p.024322_1 - 024322_9, 2020/08
Decay spectroscopy of the long-lived states in Tl has been performed at ISOLDE, CERN. The decay from the low-spin (2) state in Tl was observed for the first time and a half-life was determined. Based on the -decay energy, the relative positions of the long-lived states were fixed, with the (2) state as the ground state, the 7 state at 77(56) keV, and the 10 state at 451(56) keV. The level scheme of the internal decay of the Tl(10) state, which was known to decay solely through emission of 374-keV -ray transition, was extended and a lower limit for the -decay branching b 5.9(3)% was determined. The extracted retardation factors for the decay of the 10 state were compared to the available data in neighboring odd-odd thallium isotopes indicating the importance of the d shell in the isomeric decay and significant structure differences between Tl and Tl.
Andel, B.*; Andreyev, A. N.; Antalic, S.*; Al Monthery, M.*; Barzakh, A.*; Bissell, M. L.*; Chrysalidis, K.*; 他29名*
Physical Review C, 102(1), p.014319_1 - 014319_12, 2020/07
-delayed fission (DF) decay of a low-spin (ls) and a high-spin (hs) isomer in Bi was studied at the ISOLDE facility at CERN. Their DF partial half-lives were determined: , DF(Bi)= 5.6(8) 10 s and , DF(Bi)=1.7(6) 10 s. This work is the first DF study of two states in one isotope and allows the spin dependence of low-energy fission to be explored. The fission fragment mass distribution of a daughter nuclide Pb, following the decay of the high-spin isomer, was deduced and indicates a mixture of symmetric and asymmetric fission modes.
Benito, J.*; Fraile, L. M.*; Korgul, A.*; Piersa, M.*; Adamska, E.*; Andreyev, A. N.; lvarez-Rodrguez, R.*; 他81名*
Physical Review C, 102(1), p.014328_1 - 014328_18, 2020/07
The structure of the doubly magic Sn has been investigated at the ISOLDE facility at CERN, populated both by the -decay of In and -delayed neutron emission of In. The level scheme of Sn is greatly expanded with the addition of 68 -ray transitions and 17 levels. The identification of particle-hole multiplets both for protons and neutrons and the transition rates connecting different particle-hole configurations may provide input on the two-body matrix elements and single-particle states for state-of-the-art calculations.
Venhart, M.*; Balogh, M.*; Herz, A.*; Wood, J. L.*; Ali, F. A.*; Joss, D. T.*; Andreyev, A. N.; Auranen, K.*; Carroll, R. J.*; Drummond, M. C.*; et al.
Physics Letters B, 806, p.135488_1 - 135488_6, 2020/07
The extremely neutron-deficient isotopes Au were studied by means of in-beam -ray spectroscopy. Specific tagging techniques, -decay tagging in Au and isomer tagging in Au, were used for these studies. Feeding of positive-parity, nearly spherical states, which are associated with 2 and 3 proton-hole configurations, from the 1 proton-intruder configuration was observed in 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.
Barzakh, A. E.*; Atanasov, D.*; Andreyev, A. N.; Al Monthery, M.*; Althubiti, N. A.*; Andel, B.*; Antalic, S.*; Blaum, K.*; 他34名*
Physical Review C, 101(6), p.064321_1 - 064321_7, 2020/06
Hyperfine-structure parameters and isotope shift of the isomeric state in Au relative to Au for the 267.6-nm atomic transition have been measured for the first time using the in-source resonance-ionization spectroscopy technique. The magnetic dipole moment and change in the mean-square charge radius for this isomer have been deduced. The observed large isomer shift relative to the ground state in Au confirms the occurrence of the shape coexistence in Au proposed earlier from the analysis of the nuclear spectroscopic data and particle plus triaxial rotor calculations. The analysis of the magnetic moment supports the previously proposed ,  assignment at moderate prolate deformation for Au.
Barzakh, A. E.*; Atanasov, D.*; Andreyev, A. N.; Al Monthery, M.*; Althubiti, N. A.*; Andel, B.*; Antalic, S.*; Blaum, K.*; 他39名*
Physical Review C, 101(3), p.034308_1 - 034308_9, 2020/03
Hyperfine-structure constants for the = 11/2 gold isomers Au have been measured at CERN-ISOLDE, using the in-source laser resonance-ionization spectroscopy technique. From the measured hyperfine constants the differences between hyperfine anomalies have been deduced. These differential hyperfine anomaly values have been used to determine the hyperfine anomaly relative to the stable Au with advanced atomic calculations. Magnetic dipole moments for the gold isomers in question have been deduced, taking into account the corresponding relative hyperfine-anomaly values. It has been shown that the commonly used prescription for the extraction of the magnetic moment values for the gold isotopes should be reconsidered. The magnetic moments calculated by this prescription have been reevaluated by properly accounting for the hyperfine anomaly, which is as large as 10% for several gold isotopes.
Chrysalidis, K.*; Barzakh, A. E.*; Ahmed, R.*; Andreyev, A. N.; Ballof, J.*; Cubiss, J. G.*; Fedorov, D. V.*; Fedosseev, V. N.*; Fraile, L. M.*; Harding, R. D.*; et al.
Nuclear Instruments and Methods in Physics Research B, 463, p.472 - 475, 2020/01
放射壊変によって生成された多数のジスプロシウム同位体について、ISOLDEのレーザー共鳴イオン源(RILIS)を用いてイオン源内レーザー分光法によって研究した。Dyに対する相対的な同位体シフトを (gs) 共鳴遷移を用いて測定した。電子的因子Fとマスシフト因子Mを導出し、それらを使ってDyとDyの平均自乗荷電半径の変化を初めて決定した。
Cubiss, J. G.*; Harding, R. D.*; Andreyev, A. N.; Althubiti, N.*; Andel, B.*; Antalic, S.*; Barzakh, A. E.*; Cocolios, T. E.*; Day Goodacre, T.*; Farooq-Smith, G. J.*; et al.
Physical Review C, 101(1), p.014314_1 - 014314_4, 2020/01
Sun, M. D.*; Liu, Z.*; Huang, T. H.*; Zhang, W. Q.*; Andreyev, A. N.; Ding, B.*; Wang, J. G.*; Liu, X. Y.*; Lu, H. Y.*; Hou, D. S.*; et al.
Physics Letters B, 800, p.135096_1 - 135096_5, 2020/01
Fine structure in the decay of U was observed in the fusion-evaporation reaction Re(Ar,p3n) by using fast digital pulse processing technique. Two -decay branches of U feeding the ground state and 244 keV excited state of Th were identified by establishing the decay chain UThRaRn. The -particle energy for the ground-state to ground-state transition of U was determined to be 8993(17) keV, 213 keV higher than the previous value, the half-life was updated to be 62s. Evolution of nuclear structure for =131 even- isotones from Po to U was discussed in the frameworks of nuclear mass and reduced -decay width, a weakening octupole deformation in the ground state of U relative to its lighter isotones Ra and Th was suggested.
Ghys, L.*; Andreyev, A. N.; Huyse, M.*; Van Duppen, P.*; Antalic, S.*; Barzakh, A.*; Capponi, L.*; Cocolios, T. E.*; Cubiss, J.*; Derkx, X.*; et al.
Physical Review C, 100(5), p.054310_1 - 054310_13, 2019/11
The aim of this work was to investigate the -decay properties of Fr and daughter products. Neutron-deficient francium nuclei are produced at ISOLDE-CERN bombarding a UCx target with 1.4 GeV protons. Due to the very high statistics and the high beam purity, improved decay data for Fr and its daughters were obtained. The observation of crossover transitions positioned the isomeric high-spin level of At at an excitation energy of 265(3) keV. Half-life values of 4.47(5) s and 1.28(10) s were extracted for the ground state and isomeric state of At and 52(3) ms for the ground-state decay of Fr.