Publikasjoner
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Pedersen, Line Gaard; Sahin, Eda; Görgen, Andreas; Garrote, Frank Leonel Bello; Tsunoda, Y. & Otsuka, T.
[Vis alle 67 forfattere av denne artikkelen]
(2026).
Evolution of the nuclear structure in neutron-rich Cu isotopes: first spectroscopy of odd-odd $$^{74}$$Cu and $$^{76}$$Cu.
European Physical Journal A.
ISSN 1434-6001.
62(6).
doi:
10.1140/epja/s10050-026-01873-w.
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Abstract Excited states in the odd-odd isotopes $$^{74}$$ 74 Cu and $$^{76}$$ 76 Cu were observed for the first time in a spectroscopic study following the $$\beta $$ β decay of $$^{74}$$ 74 Ni and $$^{76}$$ 76 Ni. The experiment was performed at the Radioactive Isotope Beam Factory at RIKEN Nishina Center using the EURICA setup and the BigRIPS separator. Level schemes were constructed based on the analysis of $$\gamma $$ γ - $$\gamma $$ γ coincidences. The time correlations between $$\beta $$ β and $$\gamma $$ γ decay showed no evidence for population of isomeric states in either nucleus. The experimental results are compared to large-scale Monte Carlo shell-model calculations with the A3DA-m interaction. The low-lying states in $$^{74}$$ 74 Cu and $$^{76}$$ 76 Cu are interpreted as spin multiplets arising from the coupling of an odd proton in the $$2p_{3/2}$$ 2 p 3 / 2 or $$1f_{5/2}$$ 1 f 5 / 2 orbital with an odd neutron in the $$1g_{9/2}$$ 1 g 9 / 2 or $$2p_{1/2}$$ 2 p 1 / 2 orbital. The results provide information on the evolution of single-particle orbitals along the chain of neutron-rich Cu isotopes and on the proton-neutron interaction in the vicinity of $$^{78}$$ 78 Ni, which serve as important benchmarks for shell-model calculations. The non-observation of the low-energy isomeric state at 65 keV in $$^{76}$$ 76 Cu, combined with the observed decay pattern from higher-lying states, strongly supports a spin-parity assignment of $$3^{(-)}$$ 3 ( - ) for the ground state and ( $$6^{-}$$ 6 - ) for the isomeric state, resolving a long-standing ambiguity discussed in previous studies.
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Heines, J. S.; Modamio, Victor; Görgen, A.; Korten, W.; Clément, E. & Dudouet, J.
[Vis alle 29 forfattere av denne artikkelen]
(2026).
Triaxiality of neutron-rich ruthenium nuclei studied by lifetime measurements.
European Physical Journal A.
ISSN 1434-6001.
62(3).
doi:
10.1140/epja/s10050-025-01782-4.
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Abstract The breaking of axial symmetry in nuclei enables otherwise precluded behaviours, making it an interesting phenomenon to study. Experimental fingerprints such as very low-lying $$2_2^+$$ 2 2 + states suggest pronounced triaxial deformation for the neutron-rich ruthenium isotopes. Nevertheless, theoretical calculations differ in the description of the triaxial deformation and its evolution with neutron number, making experimental data crucial to understanding it. We investigated the evolution of the degree of triaxiality and $$\gamma $$ γ rigidity in neutron-rich ruthenium isotopes by measuring lifetimes of excited states in $$^{108-112}$$ 108 - 112 Ru with the recoil distance Doppler-shift method. The experiment was carried out at the Grand Accélérateur National d’Ions Lourds using the Advanced Gamma Tracking Array coupled to the Variable Mode Spectrometer. We obtained B ( E 2) values for 29 transitions in the studied nuclei and compared them with fully microscopic symmetry conserving configuration mixing calculations, and phenomenological generalized triaxial rotor and triaxial particle-rotor models. The models generally reproduce the measured transition strengths, and show an increase in triaxiality with neutron number, reaching near maximum triaxiality in $$^{112}$$ 112 Ru. The results are consistent with a transition from $$\gamma $$ γ soft to $$\gamma $$ γ rigid motion as the neutron number increases.
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Heines, Johannes Sørby; Modamio, Victor; Görgen, Andreas; Korten, Wolfram; Ljungvall, Joa & Pasqualato, G.
[Vis alle 45 forfattere av denne artikkelen]
(2025).
NEW LIFETIME MEASUREMENTS
IN THE RUTHENIUM CHAIN: INVESTIGATING
THE EVOLUTION OF TRIAXIALITY.
Acta Physica Polonica B, Proceedings Supplement.
ISSN 1899-2358.
18(2).
doi:
10.5506/APhysPolBSupp.18.2-A22.
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We have used the recoil distance Doppler-shift method to measure lifetimes of excited states in 108Ru, 110Ru, and 112Ru. Excited states in these nuclei were populated by fusion–fission reactions between a 238U beam and a 9Be target in an experiment at GANIL. Fission fragments were identified event by event in the VAMOS++ spectrometer, while γ-rays were detected by the Advanced Gamma Tracking Array (AGATA). The lifetimes in the ground state band are consistent with rotational structures and constant B(E2) values indicate that the deformation does not change significantly across the chain of studied ruthenium nuclei. Preliminary results for lifetimes of states in the γ-band indicate a well deformed triaxial shape with a γ parameter close to 30◦ in 110Ru, with a slight change towards oblate deformation in 112Ru.
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Cederlöf, E. Ahlgren; Bäck, T.; Nyberg, J.; Qi, C.; Ataç, A. & Badran, H.
[Vis alle 32 forfattere av denne artikkelen]
(2023).
Lifetime measurement of the yrast 2 <sup>+</sup> state in <sup>118</sup> Te.
European Physical Journal A.
ISSN 1434-6001.
59(12).
doi:
10.1140/epja/s10050-023-01212-3.
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The electromagnetic transition probabilities of the yrast 2+ states in the midshell Te isotopes, two protons above the closed shell at Sn, are of great importance for the understanding of nuclear collectivity in these isotopes and the role played by the neutron-proton interactions and cross-shell excitations. However, the large uncertainty of the experimental data for the midshell nucleus 118Te and the missing data for 116Te make it difficult to pin down the general trend of the evolution of transition probabilities as a function of the neutron number. In this work, the lifetime of the yrast 2+ state in 118Te was measured, with the aim of reducing the uncertainty of the previous measurement. The result is τ2+ = 7.46(19) ps. In addition, the lifetime of the 4+ state was measured to be τ4+ = 4.25(23) ps. The experimental transition rates are extracted from the measured lifetimes and compared with systematic large-scale shell-model calculations. The trend of the B(E2; 0+ → 2+) values in the midshell area is in good agreement with the calculations and the calculated B4/2 ratio provide evidence for 118Te as a near perfect harmonic vibrator.
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Pasqualato, G; Ansari, S.; Heines, Johannes Sørby; Modamio, Victor; Görgen, Andreas & Beckmann, Kristine Sønstevold
[Vis alle 52 forfattere av denne artikkelen]
(2023).
Shape evolution in even-mass <sup>98 - 104</sup> Zr isotopes via lifetime measurements using the γγ -coincidence technique.
European Physical Journal A.
ISSN 1434-6001.
59(11).
doi:
10.1140/epja/s10050-023-01172-8.
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The Zirconium (Z = 40) isotopic chain has attracted interest for more than four decades. The abrupt lowering of the energy of the first 2+ state and the increase in
the transition strength B(E2; 2+→ 0+) going from 98Zr to 100Zr has been the first example of “quantum phase transition” in nuclear shapes, which has few equivalents in the nuclear chart. Although a multitude of experiments have been
performed to measure nuclear properties related to nuclear shapes and collectivity in the region, none of the measured lifetimes were obtained using the Recoil Distance Doppler Shift method in the γγ-coincidence mode where a gate on the direct feeding transition of the state of interest allows a strict control of systematical errors. This work reports the results of lifetime measurements for the first yrast excited states in 98−104Zr carried out to extract reduced transition
probabilities. The new lifetime values in γγ-coincidence and γ -single mode are compared with the results of former experiments. Recent predictions of the Interacting Boson Model with Configuration Mixing, the Symmetry Conserving Configuration Mixing model based on theHartree–Fock–Bogoliubov approach and the Monte Carlo Shell Model are presented and compared with the experimental data.
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Pedersen, Line Gaard; Sahin, Eda; Görgen, Andreas; Garrote, Frank Leonel Bello; Tsunoda, Y. & Otsuka, T.
[Vis alle 67 forfattere av denne artikkelen]
(2023).
First spectroscopic study of odd-odd Cu 78.
Physical Review C.
ISSN 2469-9985.
107(4).
doi:
10.1103/PhysRevC.107.044301.
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Nuclei in the vicinity of 78Ni are important benchmarks for nuclear structure, which can reveal changes in the shell structure far from stability. Spectroscopy of the odd-odd isotope 78Cu was performed for the first time in an experiment with the EURICA setup at the Radioactive Isotope Beam Factory at RIKEN Nishina Center. Excited states in the neutron-rich isotope were populated following the β decay of 78Ni produced by in-flight fission and separated by the BigRIPS separator. A level scheme based on the analysis of γ−γ coincidences is presented. Tentative spin and parity assignments were made when possible based on the β-decay feeding intensities and γ-decay properties of the excited states. Time correlations between β and γ decay show clear indications of an isomeric state with a half-life of 3.8(4) ms. Large-scale Monte Carlo shell-model calculations were performed using the A3DA-m interaction and a valence space comprising the full fp shell and the 1g9/2 and 2d5/2 orbitals for both protons and neutrons. The comparison of the experimental results with the shell-model calculations allows interpreting the excited states in terms of spin multiplets arising from the proton-neutron interaction. The results provide further insight into the evolution of the proton single-particle orbitals as a function of neutron number, and quantitative information about the proton-neutron interaction outside the doubly magic 78Ni core.
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Galtarossa, F.; Scomparin, L.; Angelis, Giacomo de; Marchi, T.; Baumann, T. & Bazin, D.
[Vis alle 24 forfattere av denne artikkelen]
(2023).
Proton inelastic scattering on 68,70,72Ni.
Journal of Physics: Conference Series (JPCS).
ISSN 1742-6588.
doi:
10.1088/1742-6596/2586/1/012086.
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Abstract The proton inelastic scattering on 68,70,72 Ni isotopes was measured at the NSCL at MSU, employing the S800 spectrometer coupled to the GRETINA γ-ray array. The aim of the experiment was to determine the degree of collectivity in these neutron-rich Z = 28 isotopes. The use of a hadronic probe allows to complement previous Coulomb excitation measurements of the reduced transition probability B(E2; 0 + → 2 + ) and deduce the neutron-to-proton transition matrix elements ratio. The high resolution in γ-ray energy achievable with GRETINA gives large control on feeding transitions, thus reducing possible systematics errors in the determination of transition strengths.
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Pogliano, Francesco; Garrote, Frank Leonel Bello; Larsen, Ann-Cecilie; Berg, Hannah Christine; Gjestvang, Dorthea & Görgen, Andreas
[Vis alle 19 forfattere av denne artikkelen]
(2023).
Observation of a candidate for the M1 scissors resonance in odd-odd Ho 166.
Physical Review C.
ISSN 2469-9985.
107(3).
doi:
10.1103/PhysRevC.107.034605.
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The γ -strength function and the nuclear level density for the odd-odd, rare-earth nucleus 166 Ho have been
extracted from 163 Dy(α, pγ ) 166 Ho data using the Oslo method. A structure at ≈3 MeV in the γ -strength function
is interpreted as the M1 scissors resonance. By employing three different methods we find that its strength
depends rather strongly on the modeling of the E 1 strength, while its centroid does not. The 166 Ho scissors
resonance parameters are consistent with previous results on other rare-earth nuclei.
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Garrote, Frank Leonel Bello; Lopez-Martens, Araceli; Larsen, Ann-Cecilie; Deloncle, I.; Péru, Sophie & Zeiser, Fabio
[Vis alle 39 forfattere av denne artikkelen]
(2022).
Experimental observation of the M1 scissors mode in <sup>254</sup>No.
Physics Letters B.
ISSN 0370-2693.
834.
doi:
10.1016/j.physletb.2022.137479.
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We present the first experimental evidence of the scissors mode in the superheavy nucleus 254No produced in the 208Pb(48Ca, 2nγ))254No reaction. The spectrum of γrays emitted by the excited 254No nuclei shows an enhanced γ-ray yield for transition energies of ≈2.5MeV. By measuring the linear polarization properties of the emitted γrays, 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 γ-ray yield, simulations of the electromagnetic decay of 254No were performed. The observed enhancement is reproduced by including an M1component in the γstrength function with total strength B(M1↑)=11.8(19)μ2N. This is in good agreement with the integrated M1strength 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.
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Guttormsen, Magne Sveen; Ay, Kursad Osman; Ozgur, Mustafa; Algin, Emel; Larsen, Ann-Cecilie & Garrote, Frank Leonel Bello
[Vis alle 26 forfattere av denne artikkelen]
(2022).
Evolution of the γ -ray strength function in neodymium isotopes.
Physical Review C.
ISSN 2469-9985.
106(3).
doi:
10.1103/PhysRevC.106.034314.
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The experimental γ-ray strength functions (γSFs) of 142,144–151Nd have been studied for γ-ray energies up to the neutron separation energy using the Oslo method. The results represent a unique set of γSFs for an isotopic chain with increasing nuclear deformation. The data reveal how the low-energy enhancement, the scissors mode, and the pygmy dipole resonance evolve with nuclear deformation and mass number. This indicates that the mechanisms behind the low-energy enhancement and the scissors mode are decoupled from each other.
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Grocutt, L.; Chapman, R.; Bouhelal, M.; Haas, F.; Goasduff, A. & Smith, J.F.
[Vis alle 35 forfattere av denne artikkelen]
(2022).
Lifetime measurements of states of S 35, S 36, S 37, and S 38 using the AGATA γ -ray tracking spectrometer.
Physical Review C.
ISSN 2469-9985.
106(2).
doi:
10.1103/PhysRevC.106.024314.
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Lifetimes or lifetime limits of a small number of excited states of the sulfur isotopes with mass numbers A=35, 36, 37, and 38 have been measured using the differential recoil-distance method. The isotopes of sulfur were populated in binary grazing reactions initiated by a beam of 36S ions of energy 225 MeV incident on a thin 208Pb target which was mounted in the Cologne plunger apparatus. The combination of the PRISMA magnetic spectrometer and an early implementation of the AGATA γ-ray tracking array was used to detect γ rays in coincidence with projectile-like nuclear species. Lifetime measurements of populated states were measured within the range from about 1 to 100 ps. The number of states for which lifetime measurements or lifetime limits were possible was limited by statistics. For 35S, the lifetime was determined for the first 1/2+ state at 1572 keV; the result is compared with a previous published lifetime value. The lifetime of the 3− state of 36S at 4193 keV was determined and compared with earlier measurements. No previous lifetime information exists for the (6+) state at 6690 keV; a lifetime measurement with large associated error was made in the present work. For 37S, the states for which lifetime limits were established were those at 646 keV with Jπ=3/2− and at 2776 keV with Jπ=11/2−; there are no previously published lifetime values for excited states of 37S. Finally, a lifetime limit was established for the Jπ=(6+) state of 38S at 3675 keV; no lifetime information exists for this state in the literature. Measured lifetime values were compared with the results of state-of-the-art shell-model calculations based on the PSDPF, SDPF-U, and FSU effective interactions. In addition, nuclear magnetic-dipole and electric-quadrupole moments, branching ratios, mixing ratios, and electromagnetic transition rates, where available, have been compared with shell-model values. The current work suffers from poor statistics; nevertheless, lifetime values and limits have been possible, allowing a useful discussion of the ability of state-of-the-art shell-model calculations to reproduce the experimental results.
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Guttormsen, Magne Sveen; Alhassid, Yoram; Ryssens, Wouter; Ay, K.o.; Ozgur, Mustafa & Algin, Emel
[Vis alle 22 forfattere av denne artikkelen]
(2021).
Strong enhancement of level densities in the crossover from spherical to deformed neodymium isotopes.
Physics Letters B.
ISSN 0370-2693.
816.
doi:
10.1016/j.physletb.2021.136206.
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Understanding the evolution of level densities in the crossover from spherical to well-deformed nuclei has been a long-standing problem in nuclear physics. We measure nuclear level densities for a chain of neodymium isotopes 142,144−151Nd which exhibit such a crossover. These results represent the most complete data set of nuclear level densities to date for an isotopic chain between neutron shell-closure and towards mid-shell. We observe a strong increase of the level densities along the chain with an overall increase by a factor of ≈150 at an excitation energy of 6 MeV and saturation around mass 150. Level densities calculated by the shell model Monte Carlo (SMMC) are in excellent agreement with these experimental results. Based on our experimental and theoretical findings, we offer an explanation of the observed mass dependence of the level densities in terms of the intrinsic single-particle level density and the collective enhancement.
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Görgen, Andreas; Guttormsen, Magne Sveen; Larsen, Ann-Cecilie; Siem, Sunniva; Adli, Erik & Edin, Nina Frederike J
[Vis alle 14 forfattere av denne artikkelen]
(2021).
The Oslo Cyclotron Laboratory.
The European Physical Journal Plus.
136,
s. 1–13.
doi:
10.1140/epjp/s13360-021-01150-3.
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Research at the Oslo Cyclotron Laboratory at the University of Oslo is focused on spectroscopy experiments for nuclear structure and nuclear astrophysics using the Oslo Scintillator Array OSCAR. Light-ion beams from the K=35 cyclotron are furthermore used for studies in radiation biology and medical physics, for research and development related to medical isotope production, and for irradiation of materials and electronics components. Here we present an overview of the laboratory and its research infrastructure, give a brief discussion of the respective research programs and methods, and present recent highlights.
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Gjestvang, Dorthea; Siem, Sunniva; Zeiser, Fabio; Randrup, Jørgen; Vogt, Ramona & Garrote, Frank Leonel Bello
[Vis alle 20 forfattere av denne artikkelen]
(2021).
The study of prompt fission γ rays at the Oslo Cyclotron Laboratory.
The European Physical Journal Conferences.
ISSN 2101-6275.
doi:
10.1051/epjconf/202125600005.
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The study of prompt fission γ rays (PFGs) is crucial for understanding the energy and angular momentum distribution in fission, and over the last decade there has been an revived interest in this aspect of fission. We present the new experimental setup at the Oslo Cyclotron Laboratory for detecting PFGs resulting from charged particle-induced fission. Additionally, PFGs from the reaction 240 Pu(d,pf) were measured in April 2018, and the fission gated proton- γ coincidence spectrum is shown. In order to explore the dependence of the PFG emission on the excitation energy and angular momentum of the compound nucleus, we plan several experiments where charged particle reactions are used to induce fission in various plutonium isotopes. The final results will be compared to predictions made by the Fission Reaction Event Yield Algorithm (FREYA) in an upcoming publication, to benchmark the current modelling of both the PFGs and the fission process.
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Scomparin, L.; Marchi, T.; Angelis, G. De; Baumann, T.; Bazin, D. & Gade, A.
[Vis alle 24 forfattere av denne artikkelen]
(2021).
Proton inelastic scattering in <sup>68,70,72</sup>Ni isotopes.
Nuovo cimento della societa italiana de fisica. C, Geophysics and space physics.
ISSN 1124-1896.
44(2-3).
doi:
10.1393/ncc/i2021-21077-6.
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A preliminary analysis of the proton inelastic scattering of 68,70,72Ni at intermediate energies will be discussed. This measurement is important for the study of the nuclear shell’s evolution in the nickel isotopic chain. A brief description of the physics case, the setup, and the particle identification methods will be presented.
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Garrote, Frank Leonel Bello; Sahin, Eda; Tsunoda, Y.; Otsuka, T.; Görgen, Andreas & Niikura, M.
[Vis alle 67 forfattere av denne artikkelen]
(2020).
β decay of Ni 75 and the systematics of the low-lying level structure of neutron-rich odd-A Cu isotopes.
Physical Review C.
ISSN 2469-9985.
102(3).
doi:
10.1103/PhysRevC.102.034314.
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Background: Detailed spectroscopy of neutron-rich odd-A Cu isotopes is of great importance for studying the shell evolution in the region of 78Ni. While there is experimental information on excited states in 69−73,77,79Cu isotopes, the information concerning 75Cu is very limited. Purpose: Experimentally observed single-particle, core-coupling, and proton-hole intruder states in 75Cu, will complete the systematics of these states in the chain of isotopes. Method: Excited states in 75Cu were populated in the β decay of 75Ni isotopes. The Ni nuclei were produced by the in-flight fission of 238U projectiles, and were separated, identified, and implanted in a highly segmented Si detector array for the detection of the β-decay electrons. The β-delayed γ rays were detected in a HPGe cluster array. Monte Carlo shell model calculations were performed using the A3DA interaction built on the pfg9/2d5/2 model space for both neutrons and protons. Results: A level scheme of 75Cu was built up to ≈4 MeV by performing a γ−γ coincidence analysis. The excited states below 2 MeV were interpreted based on the systematics of neutron-rich odd-A Cu isotopes and the results of the shell model calculations. Conclusions: The evolution of the single-particle, core-coupling, and proton-hole intruder states in the chain of neutron-rich odd-A Cu isotopes is discussed in the present work, in connection with the newly observed level structure of 75Cu.
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Gottardo, A.; Angelis, G. De; Doornenbal, P.; Coraggio, L.; Gargano, A. & Itaco, N.
[Vis alle 59 forfattere av denne artikkelen]
(2020).
Transition strengths in the neutron-rich 73,74,75Ni isotopes.
Physical Review C.
ISSN 2469-9985.
102.
doi:
10.1103/PhysRevC.102.014323.
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Reduced transition probabilities have been measured for the neutron-rich 73,74,75Ni nuclei with relativistic Coulomb excitation performed at the RIKEN Nishina Center. For the even-even Ni isotope the determined B(E2;0+→2+) value is compatible within errors with the result of a previous intermediate energy Coulomb excitation experiment, although being somewhat larger. For the odd Ni isotopes B(E2) values have been determined for the first time. In the middle νg9/2 shell nucleus 73Ni three peak candidates have been observed and tentatively assigned to the (5/2+), (13/2+), and (11/2+) excitations. Two peak candidates have been observed in 75Ni and tentatively assigned to the (13/2+) and (11/2+) levels. The measured B(E2) values are in line with the large B(E2) reported in 70Ni and at variance with the small strength measured in 72Ni. Excitation energies compare well with the result of large-scale shell-model calculations, while B(E2) values are larger than predicted. This could indicate an increasing contribution of proton excitations across the Z=28 shell closure when approaching 78Ni.
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Litzinger, Julia; Blazhev, Andrey; Dewald, Alfred; Didierjean, Francois; Duchêne, Gaspard G. & Fransen, C.
[Vis alle 67 forfattere av denne artikkelen]
(2018).
Transition probabilities in neutron-rich 80,82Se and the role of the νg9/2 orbital.
Physical Review C.
ISSN 2469-9985.
97:044323(4),
s. 1–13.
doi:
10.1103/PhysRevC.97.044323.
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Transition probabilities of intermediate-spin yrast and non-yrast excitations in 80,82Se were investigated in a recoil distance Doppler-shift (RDDS) experiment performed at the Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro. The Cologne Plunger device for deep inelastic scattering was used for the RDDS technique and was combined with the AGATA Demonstrator array for the γ -ray detection and coupled to the PRISMA magnetic spectrometer for an event-by-event particle identification. In 80Se, the level lifetimes of the yrast (6+ 1 ) and (8+ 1 ) states and of a non-yrast band feeding the yrast 4+ 1 state are determined. A spin and parity assignment of the head of this sideband is discussed based on the experimental results and supported by large-scale shell-model calculations. In 82Se, the level lifetimes of the yrast 6+ 1 state and the yrare 4+ 2 state and lifetime limits of the yrast (10+ 1 ) state and of the 5− 1 state are determined. Although the experimental results contain large uncertainties, they are interpreted with care in terms of large-scale shell-model calculations using the effective interactions JUN45 and jj44b. The excited states’ wave functions are investigated and discussed with respect to the role of the neutron g9/2 orbital.
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Cederwall, Bo; Doncel-Monasterio, Maria; Aktaş, Özge; Ertoprak, Aysegul; Liotta, Roberto & Qi, Chong
[Vis alle 40 forfattere av denne artikkelen]
(2018).
Lifetime measurements of excited states in Pt 172 and the variation of quadrupole transition strength with angular momentum.
Physical Review Letters.
ISSN 0031-9007.
121(2),
s. 1–6.
doi:
10.1103/PhysRevLett.121.022502.
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Lifetimes of the first excited 2þ and 4þ states in the extremely neutron-deficient nuclide 172Pt 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 BðE2∶4þ 1 → 2þ 1 Þ=BðE2∶2þ 1 → 0þ gsÞ ¼ 0.55ð19Þ was found, similar to a handful of other such anomalous cases observed in the entire Segr´e 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 BðE2∶4þ 1 → 2þ 1 Þ=BðE2∶2þ 1 → 0þ gsÞ 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 BðE2∶4þ 1 → 2þ 1 Þ=BðE2∶2þ 1 → 0þ 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.
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Görgen, Andreas; Heines, Johannes Sørby & Modamio, Victor
(2025).
Triaxiality of neutron-rich ruthenium nuclei studied by lifetime measurements.
doi:
https:/indico.ibs.re.kr/event/701/.
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Neutron-rich ruthenium nuclei with mass around A≈110 are considered some of the best examples for nuclei with triaxial shape in their ground state. Quantitative information about the deformation in general and the degree of triaxiality in particular was obtained from lifetime measurements of short-lived excited states in 108Ru, 110Ru, and 112Ru. Lifetimes were measured using the recoil distance Doppler shift (RDDS) technique for states in both the ground-state band and the K=2 gamma band for the Ru isotopes under study. Combining the lifetimes with known branching rations, the measurements provide a multitude of new B(E2) transition strengths. The excited states were populated in fusion-fission reactions between a 238U beam at 6.2 A MeV and a 9Be target in an experiment performed at GANIL. The fission fragments were identified in mass, charge, and atomic number in the magnetic spectrometer VAMOS on an event-by-event basis. The velocity of nuclei exiting the target foil was slowed down in a degrader that was mounted in a plunger device at variable distances from the target. The AGATA gamma-ray tracking array was used to measure picosecond lifetimes with the RDDS method. The experiment produced a wide range of neutron-rich fission fragments, for which lifetimes could be measured under identical experimental conditions. An overview of the results will be presented, with emphasis on the chain of Ru isotopes. The comparison of experimental results with the triaxial rotor model and with beyond-mean field calculations provides quantitative information on the evolution of triaxiality in the chain of Ru isotopes.
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Heines, Johannes Sørby; Görgen, Andreas; Modamio, Victor; Pasqualato, G; Korten, Wolfram & Ljungvall, Joa
(2023).
Lifetime measurements show high triaxiality in ruthenium.
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Heines, Johannes Sørby; Modamio, Victor & Görgen, Andreas
(2023).
Evolution of Triaxiality in Neutron-Rich Ruthenium Isotopes
Lifetime Measurements of excited states.
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Heines, Johannes Sørby; Görgen, Andreas; Modamio, Victor & Sahin, Eda
(2026).
On Triaxiality: Lifetime Measurements in Ruthenium, Molybdenum and Zirconium.
Universitetet i Oslo.
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The atomic nucleus is challenging to understand. The wave functions of the constituent nucleons come together to generate phenomena very similar to the deformation, rotation and vibration of macroscopic bodies. Change the number of protons or neutrons, however, and the quantum nature of the nucleus becomes apparent. This duality is at the centre of nuclear structure physics: macroscopic descriptions fail to capture the strong quantum effects inherent in the system, but equally, single-particle descriptions cannot account for the collective effects, which are just as apparent. The region of neutron-rich nuclei around mass 100 has garnered particular interest as a testing ground for theory due to its variety of shape-related phenomena: a sudden onset of deformation, with some nuclei showing mixing of two coexisting shapes, and some breaking axial symmetry, becoming triaxial.
This thesis reports on lifetime measurements made with the recoil-distance Doppler-shift method (rdds) in zirconium, molybdenum and ruthenium isotopes, and their implications for triaxial shape transitions, with particular focus on 108Mo and 109–112Ru. The experiment, performed at ganil, populated a large number of nuclides in the region, and used the large-acceptance mass spectrometer vamos++ to identify them event-by-event. The γ-raytracking detector array agata obtained high-statistics γ-spectra of the recoiling nuclei.
To analyse these data, we have developed a new method that aims to be more consistent with the physics of the measurement, and to produce more accurate uncertainty estimates. We show that this method yields results consistent with previously measured values, and use it to extract several previously unmeasured lifetimes. Our results are consistent with an increase in triaxiality in ruthenium, reaching near maximum asymmetry in 112Ru. We find slightly less substantial triaxiality in 108Mo.
We outline further opportunities for research on the dataset – many hitherto unknown lifetimes can still be extracted – and suggest several ways in which rdds analyses could be improved beyond what we have done here.
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Heines, Johannes Sørby; Görgen, Andreas & Modamio, Victor
(2022).
Triaxiality in neutron-rich Ruthenium isotopes, New lifetimes measured in Ru-109,110,111.
Universitetet i Oslo.
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This thesis explores the asymmetrical deformation of Ruthenium isotopes, aiming to provide reliable experimental data useful for testing theoretical nuclear structure models. We have obtained reduced transition probabilities B(E2) for a number of transitions in Ru-109,110,111. A fit of the generalised triaxial rotor model indicates Ru-110 is well deformed, with a slightly oblate triaxial shape. The results are compared to various global nuclear structure models. First approximation reveals no evidence of shape changes between Ru-109 and Ru-111, more accurate results will be achieved through triaxial particle rotor calculations. The dataset at the heart of the analysis, obtained with AGATA and VAMOS++ at GANIL in 2017, features much higher statistics for a much larger number of nuclei than have previously been available. This has allowed us to get reliable lifetime measurements for the neutron odd Ru-109,111, and for both the ground- state band and one phonon γ-band in Ru-110. Additionally, it is expected to significantly reduce systematic errors when comparing results from different nuclei. We have developed and applied a new method for extracting lifetimes from the decay curves obtained in recoil distance Doppler shift measurements. By imposing constraints of physicality, it is expected to produce more reliable results than previous methods. A code for simultaneously fitting multiple gamma-spectra with shared parameters has also been developed.
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Publisert
15. juni 2015 10:12
- Sist endret
26. feb. 2026 14:32
