Publications
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Pedersen, Line Gaard; Sahin, Eda; Görgen, Andreas; Garrote, Frank Leonel Bello; Tsunoda, Y. & Otsuka, T.
[Show all 67 contributors for this article]
(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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Piętka, I. Z.; Wrzosek-Lipska, K.; Garrett, P. E.; Zielińska, M.; Próchniak, L. & Nannini, A.
[Show all 94 contributors for this article]
(2025).
PROBING LOW-ENERGY STATES IN<sup>110</sup>Cd USING COULOMB EXCITATION.
Acta Physica Polonica B, Proceedings Supplement.
ISSN 1899-2358.
18(2).
doi:
10.5506/APhysPolBSupp.18.2-A26.
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A campaign of Coulomb-excitation experiments to study the electromagnetic structure of 110Cd was performed using beams of 14N, 32S, and 60Ni. The use of various reaction partners enables disentangling the contributions of individual electromagnetic matrix elements involved in the excitation process, yielding, among others, a precise determination of the lifetime of the 2+2 state in 110Cd.
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Markova, Maria; Larsen, Ann-Cecilie & Garrote, Frank Leonel Bello
(2025).
PYGMY DIPOLE RESONANCE IN Sn ISOTOPES AND ITS ASTROPHYSICAL IMPACT.
Acta Physica Polonica B, Proceedings Supplement.
ISSN 1899-2358.
18(2).
doi:
10.5506/APhysPolBSupp.18.2-A3.
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The low-lying electric dipole strength in 111−113,116−122,124Sn was extracted with the Oslo method to systematically investigate the pygmy dipole resonance (PDR) and its evolution in Sn isotopes. The nuclear level densities (NLD) and the γ-ray strength functions (GSF) obtained from the Oslo data were used as inputs in the TALYS reaction code to produce radiative neutron-capture cross sections, Maxwellian-averaged cross sections, and rates relevant for the heavy-element nucleosynthesis. Despite a relatively small observed impact of the PDR, the experimentally extracted 121,123Sn(n, γ) 122,124Sn cross sections provide a notable reduction of a currently available theoretical uncertainty for the abundances of Sb isotopes in the i-process simulations.
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Heggebø, Liv Cathrine; Garrote, Frank Leonel Bello; Fjæra, Lars Fredrik; Hervani, Maziar; Ramberg, Christina & Ottestad, Andreas
[Show all 14 contributors for this article]
(2025).
Protons or Photons in Pituitary Neuroendocrine Tumors—That Is Not the Question.
International Journal of Particle Therapy (IJPT).
17.
doi:
10.1016/j.ijpt.2025.101194.
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Purpose
With the long-life expectancy of patients with pituitary neuroendocrine tumors (PitNETs), reducing long-term toxicity is essential to preserve quality of life. We aimed to investigate whether 2- or 3-field proton beam therapy (PBT) plans better spare organs at risks (OARs), including healthy tissue, than volumetric modulated arc photon therapy (VMAT).
Materials and Methods
Fifteen consecutive patients who had received radiation therapy for PitNETs were included. We made 4 treatment plans for each patient: one 3-field PBT plan (3F), two 2-field PBT plans (2F-L and 2F-IV), and 1 VMAT plan. Dosing was set to 1.8 Gy × 30 to allow for dosimetric comparisons.
Results
All 4 treatment techniques showed excellent target volume coverage. Compared to VMAT, the 3 PBT techniques had lower doses to OARs. Median D40% to the hippocampi varied from 0.4 to 1.1 Gy (relative biological effectiveness [RBE]) with PBT and was 5.2 Gy for both hippocampi for VMAT. Median mean dose to brain-CTV and head-CTV were lowest for 2F-L (3.1 and 2.3 Gy [RBE]), followed by 3F (3.9 and 2.5 Gy [RBE]), 2F-IV (4.1 and 2.6 Gy [RBE]), and highest for VMAT (4.8 and 4.7 Gy). A relative reduction in integral dose compared to VMAT was seen for all PBT techniques, with a median reduction of 38.5% to 45.9% for head-CTV.
Conclusion
Proton techniques spared OARs better than VMAT; however, absolute dose sparing was relatively small, and the clinical value remains uncertain. Nonetheless, the dose reduction, especially for the hippocampi and integral dose, is probably clinically meaningful. We argue that head-CTV should be assessed, as much of the volume receiving dose is located outside the brain. The size and location of the target volume impacted which proton plan was preferable. We conclude that individualized planning is more important than a mere question on protons or photons in PitNET patients.
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Markova, Maria; Larsen, Ann-Cecilie & Garrote, Frank Leonel Bello
(2025).
Approaching the pygmy dipole resonance in Sn isotopes with the Oslo method.
The European Physical Journal Conferences.
ISSN 2101-6275.
322(04002).
doi:
10.1051/epjconf/202532204002.
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The γ-ray strength functions (GSF) and nuclear level densities (NLD) below the neutron separation energy were extracted for 111−113,116−122,124Sn from particle-γ coincidence data with the Oslo method in a model consistent way. Combined with results of a recent systematic Coulomb excitation study, the Oslo GSFs were used to extract bulk characteristics of the low-lying electric dipole response, commonly associated with the pygmy dipole resonance (PDR). A resonance-like peak on top of the tail of the isovector giant dipole resonance was observed in all of the isotopes. It is centered at 8 MeV and exhausts ≈2% of the classical Thomas-Reiche-Kuhn (TRK) sum. For the heaviest isotopes, the data suggest also a second peak located at ≈6.5 MeV, which might potentially be the isovector component of the PDR. At variance with microscopic calculations, no clear increase of the total low-lying E1 strength with neutron excess was observed in the experimental data. The results also suggest that association of the full low-lying electric dipole strength with the PDR, especially in its neutron skin interpretation, might be unfounded.
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Markova, Maria; Larsen, Ann-Cecilie & Garrote, Frank Leonel Bello
(2024).
The pygmy dipole resonance in Sn isotopes studied with the Oslo method.
Nuovo cimento della societa italiana de fisica. C, Geophysics and space physics.
ISSN 1124-1896.
47(2),
p. 1–4.
doi:
10.1393/ncc/i2024-24033-0.
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The evolution of bulk properties of the low-lying electric dipole response (LEDR) in 111−113,116−122,124Sn has been studied on the basis of the γ-ray strength functions extracted from particle-γ coincidence data with the Oslo method and from Coulomb excitation data. The LEDR was found to be concentrated at ≈ 8.0–8.3 MeV and exhausts ≈ 2–3% of the Thomas-Reiche-Kuhn sum rule in all isotopes. No clear increase of the strength from the lightest 111Sn to the heaviest studied 124Sn, predicted with the majority of theoretical approaches, was observed.
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Markova, Maria; Larsen, Ann-Cecilie; Tveten, Gry Merete; Neumann-Cosel, Peter von; Eriksen, Tomas Kvalheim & Garrote, Frank Leonel Bello
[Show all 16 contributors for this article]
(2023).
Nuclear level densities and γ -ray strength functions of Sn 111,112,113 isotopes studied with the Oslo method.
Physical Review C.
ISSN 2469-9985.
108(1).
doi:
10.1103/PhysRevC.108.014315.
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The 111,112,113Sn isotopes have been studied with (p,dγ), (p,p′γ), and (d,pγ) reactions to extract the nuclear level densities (NLDs) and γ-ray strength functions (GSFs) of these nuclei below the neutron separation energy by means of the Oslo method. The experimental NLDs for all three nuclei demonstrate a trend compatible with the constant-temperature model below the neutron separation energy while also being in good agreement with the NLDs of neighboring Sn isotopes, obtained previously with the Oslo-type and neutron evaporation experiments. The extracted microcanonical entropies yield ≈1.5 kB entropy of a valence neutron in both 111Sn and 113Sn. Moreover, the deduced microcanonical temperatures indeed suggest a clear constant-temperature behavior above ≈3 MeV in 111,113Sn and above ≈4.5 MeV in 112Sn. We observe signatures for the first broken neutron pairs between 2 and 4 MeV in all three nuclei. The GSFs obtained with the Oslo method are found to be in good agreement below the neutron threshold with the strengths of 112,114Sn extracted in the (p,p′) Coulomb excitation experiments.
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Pedersen, Line Gaard; Sahin, Eda; Görgen, Andreas; Garrote, Frank Leonel Bello; Tsunoda, Y. & Otsuka, T.
[Show all 67 contributors for this article]
(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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Magagula, S.P.E.; Malatji, Kgashane Leroy; Wiedeking, M.; Pellegri, L; Beckmann, Kristine Sønstevold & Garrote, Frank Leonel Bello
[Show all 18 contributors for this article]
(2023).
Investigating the strength of the scissors mode in 151Sm.
Journal of Physics: Conference Series (JPCS).
ISSN 1742-6588.
doi:
10.1088/1742-6596/2586/1/012070.
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Change in nuclei deformation leads to changes in statistical properties such as the nuclear level density (NLD) and γ-ray strength function (γSF). The NLD and γSF of 151Sm were extracted using the Oslo method. The strength of the scissors resonance (SR) and its centroid energy for 151Sm were found to be 2.13 ± 0.60 µ2N and 2.48 ± 0.25 MeV, respectively. These results were used to place the SR of 151Sm and its magnetic dipole strength B(M1)SR into the context of previously measured Sm isotopes.
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Pogliano, Francesco; Garrote, Frank Leonel Bello; Larsen, Ann-Cecilie; Berg, Hannah Christine; Gjestvang, Dorthea & Görgen, Andreas
[Show all 19 contributors for this article]
(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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Markova, Maria; Larsen, Ann-Cecilie & Garrote, Frank Leonel Bello
(2023).
Nuclear level densities and γ-ray strength functions of 120,124Sn and their application in astrophysics.
The European Physical Journal Conferences.
ISSN 2101-6275.
275(02007),
p. 1–4.
doi:
10.1051/epjconf/202327502007.
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Nuclear level densities (NLDs) and γ -ray strength functions (GSFs)of 120;124 Sn have been extracted with the Oslo method and additionally constrained with the novel Shape method. The GSFs were found to be in excellent agreement with the strengths from the inelastic relativistic proton scattering experiment. This comparison suggests the validity of the Brink-Axel hypothesisused as one of the key assumptions in astrophysical calculations. The extracted NLDs and GSFs were further used as experimental inputs to constrain the Maxwellian-averaged cross sections (MACS) for the radiative neutron capture process 119;123 Sn ( n, γ ) 120;124 Sn using the the nuclear reaction code TALYS.
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Markova, Maria; Larsen, Ann-Cecilie & Garrote, Frank Leonel Bello
(2023).
Nuclear level densities and γ-ray strength functions of 120,124Sn for astrophysical purposes.
The European Physical Journal Conferences.
ISSN 2101-6275.
279(12001),
p. 1–6.
doi:
10.1051/epjconf/202327912001.
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The nuclear level densities (NLDs) and γ-ray strength functions (GSFs) of 120,124Sn were extracted with the Oslo method, compared and combined with other experimental data to be used as inputs in the TALYS reaction code to constrain the Maxwellian-averaged cross sections (MACS) for the 119,123Sn(n, γ)120,124Sn reactions. For 120Sn, the MACS are in relatively good agreement with the JINA REACLIB, BRUSLIB libraries, while no clear agreement was found for 124Sn. In addition, the pygmy dipole resonance (PDR) was found to contribute with up to ≈ 3 − 8% of the total MACS in these nuclei.
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Pogliano, Francesco; Larsen, Ann-Cecilie; Markova, Maria; Garrote, Frank Leonel Bello; Bjørøen, Marianne Møller & Eriksen, Tomas Kvalheim
[Show all 17 contributors for this article]
(2022).
Indirect measurement of the (n,γ) Sb 127 cross section.
Physical Review C.
ISSN 2469-9985.
106(1).
doi:
10.1103/PhysRevC.106.015804.
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Nuclei in the 135I region have been identified as being a possible bottleneck for the i process. Here we present an indirect measurement for the Maxwellian-averaged cross section of 126Sb(n,γ). The nuclear level density and the γ-ray strength function of 127Sb have been extracted from 124Sn(α,pγ)127Sb data using the Oslo method. The level density in the low-excitation-energy region agrees well with known discrete levels, and the higher-excitation-energy region follows an exponential curve compatible with the constant-temperature model. The strength function between Eγ≈1.5–8.0 MeV presents several features, such as an upbend and a possibly double-peaked pygmy-like structure. None of the theoretical models included in the nuclear reaction code talys seem to reproduce the experimental data. The Maxwellian-averaged cross section for the 126Sb(n,γ)127Sb reaction has been experimentally constrained by using our level-density and strength-function data as input to talys. We observe a good agreement with the jina reaclib, tendl, and bruslib libraries, while the endf/b-viii.0 library predicts a significantly higher rate than our results.
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Yagi, A.; Odahara, A.; Nishibata, H.; Lozeva, R.; Moon, C.-B. & Nishimura, S.
[Show all 53 contributors for this article]
(2022).
Various nuclear structures in Xe 140 studied by β decay of ground and isomeric states in i 140.
Physical Review C.
ISSN 2469-9985.
105(4).
doi:
10.1103/PhysRevC.105.044325.
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Structure of the neutron-rich N=86 isotope 140Xe, located northeast of a doubly-magic nucleus 132Sn, is investigated by β−γ spectroscopy. Two β-decay isomers in 140I are newly found in the study of two different β decays of 140I which were produced by two reactions (i) direct in-flight fission at a primary target and (ii) β decay of 140Te at an active stopper. Half-lives of the β decays of the ground state, the low-spin isomer, and the high-spin isomer are determined to be 0.38(2), 0.91(5), and 0.47(4) s, respectively. Decay schemes of the β decay of the high-spin isomer and of the mixed β decays of the ground state and the low-spin isomer in 140I to 140Xe are constructed using the information on γ-ray coincidence relation and γ-ray intensity. Nuclear structures of the low-lying states in 140Xe and 140I are discussed by comparing the experimental results to two theoretical calculations based on a large-scale shell model and the deformed Skyrme Hartree-Fock-Bogoliubov plus deformed quasiparticle-random-phase approximation. Possible candidates for (quasi-)γ-band members of 2+ and 4+ states and the octupole collective 1− state are proposed in 140Xe. Increase of quadrupole, triaxial, and octupole collectivities is discussed with the increase of neutron and proton numbers.
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Garrote, Frank Leonel Bello; Lopez-Martens, Araceli; Larsen, Ann-Cecilie; Deloncle, I.; Péru, Sophie & Zeiser, Fabio
[Show all 39 contributors for this article]
(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
[Show all 26 contributors for this article]
(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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Markova, Maria; Larsen, Ann-Cecilie; Neumann-Cosel, Peter von; Bassauer, Sergej; Görgen, Andreas & Guttormsen, Magne Sveen
[Show all 23 contributors for this article]
(2022).
Nuclear level densities and γ -ray strength functions in Sn 120,124 isotopes: Impact of Porter-Thomas fluctuations.
Physical Review C.
ISSN 2469-9985.
106(3).
doi:
10.1103/PhysRevC.106.034322.
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Nuclear level densities (NLDs) and γ-ray strength functions (GSFs) of 120,124Sn have been extracted with the Oslo method from proton-γ coincidences in the (p,p′γ) reaction. The functional forms of the GSFs and NLDs have been further constrained with the Shape method by studying primary γ-transitions to the ground and first excited states. The NLDs demonstrate good agreement with the NLDs of 116,118,122Sn isotopes measured previously. Moreover, the extracted partial NLD of 1− levels in 124Sn is shown to be in fair agreement with those deduced from spectra of relativistic Coulomb excitation in forward-angle inelastic proton scattering. The experimental NLDs have been applied to estimate the magnitude of the Porter-Thomas (PT) fluctuations. Within the PT fluctuations, we conclude that the GSFs for both isotopes can be considered to be independent of initial and final excitation energies, in accordance with the generalized Brink-Axel hypothesis. Particularly large fluctuations observed in the Shape-method GSFs present a considerable contribution to the uncertainty of the method and may be one of the reasons for deviations from the Oslo-method strength at low γ-ray energies and low values of the NLD (below ≈1×103–2×103MeV−1).
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Moon, B.; Gargano, A.; Naïdja, H.; Moon, C.-B.; Odahara, A. & Lozeva, R.
[Show all 53 contributors for this article]
(2022).
First observation of the π0h11/2-ν0h9/2 partner orbital configuration in the odd-odd i 138 nucleus.
Physical Review C.
ISSN 2469-9985.
105(3).
doi:
10.1103/PhysRevC.105.034334.
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The β-decay scheme of 138Te and the level structure of 138I is reported for the first time. The experiment was performed at the Radioactive Isotope Beam Factory of RIKEN, as one of the EUROBALL-RIKEN Cluster Array campaigns. Secondary radioactive ions, including 138Te and 138Sb, were produced by the in-flight fission of a 238U beam with the energy of 345 MeV per nucleon. From the β decay of 138Te, the level scheme of 138I was supplemented with new spin and parity assignments, such as the low-lying negative-parity states and a positive-parity 1+ state. This 1+ state can be interpreted as being associated with the π0h11/2⊗ν0h9/2 partner orbital configuration populated by the Gamow-Teller transition between a neutron in the 0h9/2 orbital and a proton in the 0h11/2 orbital. Details of the structure of 138I are discussed in terms of the proton-neutron interactions and Gamow-Teller transition strength within the theoretical context of shell-model calculations.
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Guttormsen, Magne Sveen; Alhassid, Yoram; Ryssens, Wouter; Ay, K.o.; Ozgur, Mustafa & Algin, Emel
[Show all 22 contributors for this article]
(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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Yokoyama, R.; Ideguchi, E.; Simpson, G.S.; Tanaka, Mn.; Sun, Yang & Lv, Cui-Juan
[Show all 55 contributors for this article]
(2021).
Three-quasiparticle isomers in odd-even Pm 159,161: Calling for modified spin-orbit interaction for the neutron-rich region.
Physical Review C.
ISSN 2469-9985.
104(2).
doi:
10.1103/PhysRevC.104.L021303.
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Neutron-rich Pm (Z=61) isotopes were studied by delayed γ-ray spectroscopy at RIBF, RIKEN Nishina Center using the in-flight fission of a 345 MeV/nucleon 238U beam. A cluster-type Ge detector array, EURICA, was used to measure the delayed γ rays from stopped ions. Isomeric γ decays were observed in 159Pm and 161Pm with half-lives of 4.97(12) μs and 0.79(4) μs, respectively. Level schemes for 159Pm and 161Pm were constructed in this study. The isomeric states of 159Pm and 161Pm could be interpreted as two quasiparticle excitations of neutrons with the configurations of ν(7/2[633]⊗5/2[523]) and ν(7/2[633]⊗1/2[521]), respectively. They are analogous to the isomers that have been observed systematically in other even-mass N=98 and N=100 isotones in this region. A projected shell model calculation was performed and it reproduced the order of three-quasiparticle states only if new Nilsson parameters with an N-dependent spin-orbit interaction were used. This work demonstrates that the strength of spin-orbit interactions in standard Nilsson parameters needs to be modified to study the properties of neutron-rich rare-earth nuclei around A=165, and provides new evidence supporting the existence of the deformed N=98 subshell gap in odd-mass nuclei for the first time.
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Malatji, Kgashane Leroy; Beckmann, Kristine Sønstevold; Wiedeking, Mathis; Siem, Sunniva; Goriely, Stephane & Larsen, Ann-Cecilie
[Show all 21 contributors for this article]
(2021).
Statistical properties of the well deformed 153,155Sm nuclei and the scissors resonance.
Physical Review C.
ISSN 2469-9985.
103(1).
doi:
10.1103/PhysRevC.103.014309.
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The nuclear level densities (NLDs) and the γ-ray strength functions (γSFs) of 153,155Sm have been extracted from (d,pγ) coincidences using the Oslo method. The experimental NLD of 153Sm is higher than the NLD of 155Sm, in accordance with microscopic calculations. The γSFs of 153,155Sm are in fair agreement with QRPA calculations based on the D1M Gogny interaction. An enhancement is observed in the γSF for both 153,155Sm nuclei around 3 MeV in excitation energy and is attributed to the M1 scissors resonance (SR). Their integrated strengths were found to be in the range 1.3–2.1 and 4.4–6.4 μ2N for 153Sm and 155Sm, respectively. The strength of the SR for 155Sm is comparable to those for deformed even-even Sm isotopes from nuclear resonance fluorescence measurements, while that of 153Sm is lower than expected.
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Zeiser, Fabio; Tveten, Gry Merete; Garrote, Frank Leonel Bello; Guttormsen, Magne Sveen; Larsen, Ann-Cecilie & Ingeberg, Vetle Wegner
[Show all 8 contributors for this article]
(2021).
The gamma-ray energy response of the Oslo Scintillator Array OSCAR.
Nuclear Instruments and Methods in Physics Research Section A : Accelerators, Spectrometers, Detectors and Associated Equipment.
ISSN 0168-9002.
985.
doi:
10.1016/j.nima.2020.164678.
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The new Oslo Scintillator Array (OSCAR) has been commissioned at the Oslo Cyclotron Laboratory (OCL). It consists of 30 large volume (⌀ 3.5 × 8 inches) LaBr3(Ce) detectors that are used for 𝛾-ray spectroscopy. The response functions for incident 𝛾 rays up to 20 MeV are simulated with Geant4. In addition, the resolution, and the total and full-energy peak efficiencies are extracted. The results are in very good agreement with measurements from calibration sources and experimentally obtained mono-energetic in-beam 𝛾-ray spectra.
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Markova, Maria; Neumann-Cosel, Neumann-Cosel von; Larsen, A.C.; Bassauer, S.; Görgen, A. & Guttormsen, Magne Sveen
[Show all 25 contributors for this article]
(2021).
Comprehensive Test of the Brink-Axel Hypothesis in the Energy Region of the Pygmy Dipole Resonance.
Physical Review Letters.
ISSN 0031-9007.
127(18).
doi:
10.1103/PhysRevLett.127.182501.
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The validity of the Brink-Axel hypothesis, which is especially important for numerous astrophysical calculations, is addressed for 116,120,124Sn below the neutron separation energy by means of three independent experimental methods. The γ-ray strength functions (GSFs) extracted from primary γ-decay spectra following charged-particle reactions with the Oslo method and with the shape method demonstrate excellent agreement with those deduced from forward-angle inelastic proton scattering at relativistic beam energies. In addition, the GSFs are shown to be independent of excitation energies and spins of the initial and final states. The results provide a critical test of the generalized Brink-Axel hypothesis in heavy nuclei, demonstrating its applicability in the energy region of the pygmy dipole resonance.
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Gjestvang, Dorthea; Siem, Sunniva; Zeiser, Fabio; Randrup, Jørgen; Vogt, Ramona & Garrote, Frank Leonel Bello
[Show all 20 contributors for this article]
(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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Gjestvang, Dorthea; Siem, Sunniva; Zeiser, Fabio; Randrup, Jørgen; Vogt, Ramona & Wilson, Jonathan Nicholas
[Show all 19 contributors for this article]
(2021).
Excitation energy dependence of prompt fission γ-ray emission from 241Pu*.
Physical Review C.
ISSN 2469-9985.
103(3).
doi:
10.1103/PhysRevC.103.034609.
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Prompt fission γ rays (PFGs) resulting from the 240Pu(d,pf) reaction have been measured as a function of fissioning nucleus excitation energy Ex at the Oslo Cyclotron Laboratory. We study the average total PFG multiplicity per fission, the average total PFG energy released per fission, and the average PFG energy. No significant changes in these characteristics are observed over the range 5.75
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Moon, B.; Jungclaus, A.; Naïdja, H.; Gargano, A.; Lozeva, R & Moon, C.B.
[Show all 73 contributors for this article]
(2021).
Nuclear structure of Te isotopes beyond neutron magic number N=82.
Physical Review C.
ISSN 2469-9985.
103(3).
doi:
10.1103/PhysRevC.103.034320.
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Newly observed decay schemes of the nuclei 137Sb and 138Sb are reported. The neutron-rich Sb isotopes were produced by the in-flight fragmentation of a 238U primary beam with an energy of 345 MeV/nucleon. Several new excited states of 137Te with tentatively assigned spin-parities of (5/2−), (9/2−), and (7/2) have been established which play an important role in the evolution of neutron levels beyond N=82. The study of the β decay of 138Sb led to a considerable extension of the level scheme of 138Te including the identification of several nonyrast states. The structure of 137Te and 138Te is discussed on the basis of large-scale shell-model calculations performed using two different effective interactions.
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Midtbø, Jørgen E.; Zeiser, Fabio; Lima, Erlend; Larsen, Ann-Cecilie; Tveten, Gry Merete & Guttormsen, Magne Sveen
[Show all 9 contributors for this article]
(2021).
A new software implementation of the Oslo method with rigorous statistical uncertainty propagation.
Computer Physics Communications.
ISSN 0010-4655.
262.
doi:
10.1016/j.cpc.2020.107795.
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The Oslo method comprises a set of analysis techniques designed to extract nuclear level density and average -decay strength function from a set of excitation-energy tagged -ray spectra. Here we present a new software implementation of the entire Oslo method, called OMpy. We provide a summary of the theoretical basis and derive the essential equations used in the Oslo method. In addition to the functionality of the original analysis code, the new implementation includes novel components such as a rigorous method to propagate uncertainties throughout all steps of the Oslo method using a Monte Carlo approach. The resulting level density and -ray strength function have to be normalized to auxiliary data. The normalization is performed simultaneously for both quantities, thus preserving all correlations. The software is verified by the analysis of a synthetic spectrum and compared to the results of the previous implementation, the oslo-method-software.
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Kibédi, T.; Alshahrani, B.; Stuchbery, A.E.; Larsen, Ann-Cecilie; Görgen, Andreas & Siem, Sunniva
[Show all 20 contributors for this article]
(2020).
Radiative Width of the Hoyle State from γ -Ray Spectroscopy.
Physical Review Letters.
ISSN 0031-9007.
125(18).
doi:
10.1103/PhysRevLett.125.182701.
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The cascading 3.21 and 4.44 MeV electric quadrupole transitions have been observed from the Hoyle state at 7.65 MeV excitation energy in 12C, excited by the 12C(p,p′) reaction at 10.7 MeV proton energy. From the proton-γ−γ triple coincidence data, a value of Γrad/Γ=6.2(6)×10−4 was obtained for the radiative branching ratio. Using our results, together with ΓE0π/Γ from Eriksen et al. [Phys. Rev. C 102, 024320 (2020)] and the currently adopted Γπ(E0) values, the radiative width of the Hoyle state is determined as Γrad=5.1(6)×10−3 eV. This value is about 34% higher than the currently adopted value and will impact models of stellar evolution and nucleosynthesis.
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Garrote, Frank Leonel Bello; Sahin, Eda; Tsunoda, Y.; Otsuka, T.; Görgen, Andreas & Niikura, M.
[Show all 67 contributors for this article]
(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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Wrzosek-Lipska, K; Prochniak, L.; Garrett, P.E.; Yates, S. W.; Wood, J.L. & Napiorkowski, P.J.
[Show all 36 contributors for this article]
(2020).
Quadrupole Deformation of 110Cd Studied with Coulomb Excitation.
Acta Physica Polonica B.
ISSN 0587-4254.
51.
doi:
10.5506/APhysPolB.51.789.
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The low-energy electromagnetic structure of 110Cd was studied using safe-energy Coulomb excitation at the Heavy Ion Laboratory, University of Warsaw. The preliminary results on the quadrupole deformation of lowlying 0+ states in 110Cd are presented and compared to the recent beyondmean- field and General Bohr Hamiltonian calculations.
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Wu, J.; Nishimura, S.; Möller, P.; Mumpower, M.r.; Lozeva, R. & Moon, C.B.
[Show all 51 contributors for this article]
(2020).
β-decay half-lives of 55 neutron-rich isotopes beyond the N = 82 shell gap.
Physical Review C.
ISSN 2469-9985.
101.
doi:
10.1103/PhysRevC.101.042801.
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The β-decay half-lives of 55 neutron-rich nuclei 134−139Sn, 134−142Sb, 137−144Te, 140−146I, 142−148Xe, 145−151Cs, 148−153Ba, and 151−155La were measured at the Radioactive Isotope Beam Factory employing the projectile fission fragments of 238U. The nuclear level structure, which relates to deformation, has a large effect on the half-lives. The impact of newly measured half-lives on modeling the astrophysical origin of the heavy elements is studied in the context of r process nucleosynthesis. For a wide variety of astrophysical conditions, including those in which fission recycling occurs, the half-lives have an important local impact on the second (A ≈ 130) peak.
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Gottardo, A.; Angelis, G. De; Doornenbal, P.; Coraggio, L.; Gargano, A. & Itaco, N.
[Show all 59 contributors for this article]
(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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Vaquero, V; Jungclaus, Andrea; Rodriguez-Sanchez, J. L.; Tostevin, J. A.; Doornenbal, P. & Wimmer, K
[Show all 34 contributors for this article]
(2019).
Inclusive cross sections for one- and multi-nucleon removal from Sn, Sb, and Te projectiles beyond the N = 82 shell closure.
Physics Letters B.
ISSN 0370-2693.
795,
p. 356–361.
doi:
10.1016/j.physletb.2019.06.035.
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Inclusive one- and multi-nucleon removal cross sections have been measured for several Sn, Sb and Te isotopes just beyond the neutron shell closure. The beams were produced in the projectile fission of a 238U beam at the Radioactive Isotope Beam Factory at RIKEN. The experimental cross sections are compared to predictions from the most recent version of the Liege intranuclear cascade model. Although the overall agreement is good, severe discrepancies are observed for the cases of one- and two-neutron removal from 134Sn and 135Sb projectiles and one-proton knockout from all measured isotones. These discrepancies, as well as the relevance of quasi-elastic reaction channels to the one-neutron removal cross sections, are discussed. In addition, the measured inclusive one-proton knockout cross section for the semi-magic 134Sn projectile is compared to eikonal direct reaction theory calculations to assess if the suppression factors to these calculated cross sections, deduced from data on reactions of lighter projectile nuclei, are also applicable to heavy nuclei.
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Sahin, Eda; Hadynska-Klek, Katarzyna; Garrote, Frank Leonel Bello & Görgen, Andreas
(2019).
Probing the nuclear structure in the vicinity of 78Ni.
The European Physical Journal Conferences.
ISSN 2101-6275.
223.
doi:
10.1051/epjconf/201922301054.
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Theoretical and experimental studies of neutron-rich nuclei have shown that the general concept of shell structure is not as robust and universal as earlier thought, but can exhibit significant changes as a function of neutron excess. New magic numbers appear and some other conventional ones disappear mainly because of a different ordering of the single-particle orbitals. In the present contribution, recent experimental studies of neutron-rich Cu isotopes, performed at RIKEN using β decay and one-proton knockout reactions, will be discussed. Neutron-rich nuclei near 78Ni were populated through in-flight fission of 238U on thick 9Be targets in both experiments. In the β-decay study, 75,77Ni nuclei were implanted into the WAS3ABi silicon array, while γ rays from excited states in 75,77Cu emitted after β decay of the implanted ions were detected with the EURICA Ge detector array that was surrounding the active stopper. In a second experiment within the SEASTAR campaign at RIKEN, the same 75,77Cu nuclei were produced in (p,2p) knockout reactions from 76,78Zn beam particles at around 250 MeV/nucleon impinging onto the MINOS liquid hydrogen target. In the latter experiment the DALI2 NaI array was used to detect de-excitation γ rays measured in coincidence with Cu nuclei identified in the Zero Degree Spectrometer. Both studies are complimentary and greatly contribute to our understanding on the nuclear structure in the 78Ni region.
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Kullmann, Ina Kristine Berentsen; Larsen, Ann-Cecilie; Renstrøm, Therese; Beckmann, Kristine Sønstevold; Garrote, Frank Leonel Bello & Campo, Lucia Crespo
[Show all 13 contributors for this article]
(2019).
First experimental constraint on the 191Os(n,γ) reaction rate relevant to s-process nucleosynthesis.
Physical Review C.
ISSN 2469-9985.
99(6).
doi:
10.1103/PhysRevC.99.065806.
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The nuclear level density and
γ
-decay strength of
192
Os
have been extracted using particle-
γ
coincidence data from the
192
Os
(
α
,
α
′
γ
)
192
Os
reaction by means of the Oslo method. The level density is found to be a rather smooth function of excitation energy, approximately following the constant temperature model. The
γ
-decay strength is compared to photoneutron cross-section data above the neutron separation energy, and to
E
1
and
M
1
strengths for nuclei in this mass region derived from primary transitions following neutron capture. Our results are in good agreement with these previous data and draw a consistent picture of the
γ
-strength function in the range
E
γ
≈
1.5
–
6
MeV
. Using the measured nuclear level density and
γ
-decay strength as input to the nuclear-reaction code talys, we provide the first experimentally constrained Maxwellian-averaged cross section (MACS) for the
191
Os
(
n
,
γ
)
192
Os
reaction relevant to
s
-process nucleosynthesis. The systematic uncertainties introduced by the normalization procedure of the level density and
γ
-strength function were investigated and propagated to the calculated Maxwellian-averaged cross section. The obtained result of the Maxwellian-averaged cross section at
k
B
T
=
30
keV
,
⟨
σ
⟩
n
,
γ
=
1134
±
375
mb
, is in very good agreement with the theoretical estimate provided by the KADoNiS project, giving experimental support to the adopted KADoNiS value. Good agreement is also found with MACS values obtained from other libraries, such as TENDL-2017, ENDF/B-VII.0, and JEFF.
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Larsen, Ann-Cecilie; Liddick, Sean N.; Spyrou, Artemis; Guttormsen, Magne Sveen; Garrote, Frank Leonel Bello & Midtbø, Jørgen E.
[Show all 7 contributors for this article]
(2019).
The Beta-Oslo Method: ExperimentallyConstrained (n,γ) Reaction RatesRelevant to ther-Process.
In Formicola, Alba; Junker, Matthias; Gialanella, Lucio & Imbriani, Gianluca (Ed.),
Nuclei in the Cosmos XV.
Springer.
ISSN 9783030138752.
p. 137–140.
doi:
10.1007/978-3-030-13876-9_22.
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Brits, C.P.; Malatji, Kgashane L.; Wiedeking, M.; Kheswa, BV; Goriely, S. & Garrote, Frank Leonel Bello
[Show all 27 contributors for this article]
(2019).
Nuclear level densities and γ-ray strength functions of 180,181,182Ta.
Physical Review C.
ISSN 2469-9985.
99(5).
doi:
10.1103/PhysRevC.99.054330.
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Particle- γ coincidence experiments were performed at the Oslo Cyclotron Laboratory with the 181 Ta ( d , X ) and 181 Ta ( 3 He , X ) reactions to measure the nuclear level densities (NLDs) and γ -ray strength functions ( γ SFs ) of 180 , 181 , 182 Ta using the Oslo method. The back-shifted Fermi-gas, constant temperature plus Fermi gas, and Hartree-Fock-Bogoliubov plus combinatorial models were used for the absolute normalizations of the experimental NLDs at the neutron separation energies. The NLDs and γ SFs are used to calculate the corresponding 181 Ta ( n , γ ) cross sections and these are compared to results from other techniques. The energy region of the scissors resonance strength is investigated and from the data and comparison to prior work it is concluded that the scissors strength splits into two distinct parts. This splitting may allow for the determination of triaxiality and a γ deformation of 14 . 9 ∘ ± 1 . 8 ∘ was determined for 181 Ta .
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Midtbø, Jørgen E.; Larsen, Ann-Cecilie; Renstrøm, Therese; Garrote, Frank Leonel Bello & Lima, Erlend
(2019).
Systematic Low-Energy Enhancementof the Gamma-Ray Strength Function.
In Formicola, Alba; Junker, Matthias; Gialanella, Lucio & Imbriani, Gianluca (Ed.),
Nuclei in the Cosmos XV.
Springer.
ISSN 9783030138752.
p. 405–407.
doi:
10.1007/978-3-030-13876-9.
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Liddick, Sean N.; Larsen, Ann-Cecilie; Guttormsen, Magne Sveen; Spyrou, Artemis; Crider, Benjamin P. & Naqvi, Farheen
[Show all 30 contributors for this article]
(2019).
Benchmarking the extraction of statistical neutron capture cross sections on short-lived nuclei for applications using the β-Oslo method.
Physical Review C.
ISSN 2469-9985.
100:024624(2),
p. 1–12.
doi:
10.1103/PhysRevC.100.024624.
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Numerous scientific fields including astrophysics, nuclear power, and nuclear forensics require a knowledge of basic nuclear properties for large numbers of short-lived, radioactive isotopes far removed from stable nuclei. Neutron-capture cross sections are one such piece of nuclear data where direct measurements are not possible and theoretical predictions can vary by orders of magnitude. A recently developed indirect technique for inferring neutron capture rates, the β -Oslo method, has been introduced but not compared against a known, directly measured neutron capture cross section. To provide this benchmark, two indirect methods based on β decay and charged-particle reactions were used to extract the nuclear level density and γ -ray strength function of 51 Ti . The nuclear level density and γ -ray strength function from the two data sets were found to be equivalent and were used to extract the neutron capture cross section of 50 Ti which agrees with previous direct measurements at high neutron energies. The results demonstrate the validity of the β -Oslo method for extracting neutron capture cross sections of short-lived nuclei and provide a sufficiently small uncertainty to be used in various applications.
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Vaquero, Victor; Jungclaus, Andrea; Doornenbal, Pieter C.; Wimmer, Kathrin; Moro, Antônio M. & Ogata, Kazuyuki
[Show all 34 contributors for this article]
(2019).
In-beam γ-ray spectroscopy of 136Te at relativistic energies.
Physical Review C.
ISSN 2469-9985.
99:034306(3),
p. 1–14.
doi:
10.1103/PhysRevC.99.034306.
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The reduced transition probability B(E2;0+1→ 2 + 1 ) to the first excited 2+ state of the neutron-rich nucleus 136 Te , with two protons and two neutrons outside the doubly magic 132 Sn core, was measured via Coulomb excitation at relativistic energies at the RIKEN Radioactive Isotope Beam Factory. A value of B(E2)=0.191 ( 26 ) e2b2 was extracted from the measured inelastic scattering cross section on an Au target taking into account the contributions from both Coulomb and nuclear excitations. In addition, an upper limit for the transition strength to a 2+ state of mixed-symmetry character in the excitation energy range of 1.5–2.2 MeV was determined and compared to the predictions of various theoretical calculations. Because of the high statistics gathered in the present experiment the error of the deduced B(E2) value is dominated by the systematic uncertainties involved in the analysis of Coulomb excitation experiments at beam energies around 150 MeV/u. Therefore, the latter are for the first time assessed in detail in the present work.
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Goasduff, A; Ljungvall, Joa; Rodríguez, Tomás R.; Garrote, Frank Leonel Bello; Etile, Asénath & Georgiev, Georgi
[Show all 14 contributors for this article]
(2019).
B(E2) anomalies in the yrast band of 170Os.
Physical Review C.
ISSN 2469-9985.
100(3),
p. 034302-1–034302-8.
doi:
10.1103/PhysRevC.100.034302.
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Background: The neutron-deficient osmium isotopic chain provides a great laboratory for the study of shape evolution, with the transition from the soft triaxial rotor in 168Os to the well-deformed prolate rotor in 180Os, while shape coexistence appears around N = 96 in 172Os. Therefore, the study of the Os isotopic chain should provide a better understanding of shape changes in nuclei and a detailed scrutiny of nuclear structure calculations. In this paper, the lifetimes of the low-lying yrast states of 170Os have been measured for the first time to investigate the shape evolution with neutron number. Purpose: Lifetimes of excited states in the ground-state band of 170Os are measured to investigate the shape evolution with neutron number in osmium isotopes and compare with state-of-the-art calculations. Methods: The states of interest were populated via the fusion-evaporation reaction 142Nd(32S, 4n) at a bombarding energy of 170 MeV at the ALTO facility from IPN (Orsay, France). Lifetimes of the 2+ 1 and 4+ 1 states in 170Os were measured with the recoil-distance Doppler-shift method using the Orsay universal plunger system. Results: Lifetimes of the two first excited states in 170Os were measured for the first time. A very small B(E2; 4+ 1 → 2+ 1 )/B(E2; 2+ 1 → 0+ 1 ) = 0.38(11) was found, which is very uncharacteristic for collective nuclei. These results were compared to state-of-the-art beyond-mean-field calculations. Conclusions: Although theoretical results give satisfactory results for the energy of the first few excited states in 170Os and the B(E2; 2+ 1 → 0+ 1 ) they fail to reproduce the very small B(E2; 4+ 1 → 2+ 1 ), which remains a puzzle.
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Garrote, Frank Leonel Bello; Görgen, Andreas; Mihai, C.; Abraham, T.; Campo, Lucia Crespo & Delaroche, Jean Paul
[Show all 34 contributors for this article]
(2018).
Lifetime measurements in 138Nd.
Physical Review C.
ISSN 2469-9985.
97(6),
p. 1–7.
doi:
10.1103/PhysRevC.97.064310.
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Lifetimes of several short-lived excited states in 138Nd were measured with the ROSPHERE array at IFIN-HH, Bucharest, using the recoil-distance Doppler shift technique following the 123Sb(19F,4n) reaction. The resulting electromagnetic transition probabilities are compared to large-scale shell model calculations and to constrained Hartree-Fock-Bogoliubov calculations with the Gogny D1S interaction, configuration mixing, and a five-dimensional collective Hamiltonian formalism. The onset of collectivity in Nd isotopes below the N = 82 shell closure and the deformation induced by the alignment of protons and neutron holes in the h11/2 orbitals are discussed.
-
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Midtbø, Jørgen E.; Larsen, Ann-Cecilie; Renstrøm, Therese; Garrote, Frank Leonel Bello & Lima, Erlend
(2018).
Consolidating the concept of low-energy magnetic dipole decay radiation.
Physical Review C.
ISSN 2469-9985.
98(6),
p. 064321-1–064321-12.
doi:
10.1103/PhysRevC.98.064321.
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We have made a thorough study of the low-energy behavior of the γ -ray strength function within the framework of the shell model. We have performed large-scale calculations spanning isotopic and isotonic chains over several mass regions, considering 283 nuclei in total, with the purpose of studying the systematic behavior of the low-energy enhancement (LEE) for M1 transitions. There are clear trends in the calculations: From being nearly absent in the lowest mass region, the LEE becomes steeper and more pronounced as the mass number increases, and for a given mass region it further increases toward shell closures. Moreover, the LEE is found to be steeper in regions near doubly magic nuclei where proton particles couple to neutron holes. These trends enable us to consolidate several previous works on the LEE into a single, consistent concept. We compare the inferred trends to the available experimental data from the Oslo method and find support for the systematic behavior. Lastly, we have compared the calculations to strength functions compiled from discrete, experimental lifetimes and find excellent agreement; the discrete data are consistent with an LEE and indicate that the slope varies as function of mass number.
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Morales, Ana Isabel; Benzoni, G; Watanabe, H; Angelis, G de; Nishimura, S & Coraggio, L
[Show all 63 contributors for this article]
(2018).
Is seniority a partial dynamic symmetry in the first νg9/2 shell?
Physics Letters B.
ISSN 0370-2693.
781,
p. 706–712.
doi:
10.1016/j.physletb.2018.04.049.
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The low-lying structures of the midshell ν g9/2 Ni isotopes 72Ni and 74Ni have been investigated at the RIBF facility in RIKEN within the EURICA collaboration. Previously unobserved low-lying states were accessed for the first time following β decay of the mother nuclei 72Co and 74Co. As a result, we provide a complete picture in terms of the seniority scheme up to the first (8+) levels for both nuclei. The experimental results are compared to shell-model calculations in order to define to what extent the seniority quantum number is preserved in the first neutron g9/2 shell. We find that the disappearance of the seniority isomerism in the (8+ 1 ) states can be explained by a lowering of the seniority-four (6+) levels as predicted years ago. For 74Ni, the internal de-excitation pattern of the newly observed (6+ 2 ) state supports a restoration of the normal seniority ordering up to spin J = 4. This property, unexplained by the shell-model calculations, is in agreement with a dominance of the single-particle spherical regime near 78Ni.
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Campo, Lucia Crespo; Guttormsen, Magne Sveen; Garrote, Frank Leonel Bello; Eriksen, Tomas Kvalheim; Giacoppo, Francesca & Görgen, Andreas
[Show all 15 contributors for this article]
(2018).
Test of the generalized Brink-Axel hypothesis in 64,65Ni.
Physical Review C.
ISSN 2469-9985.
98,
p. 054303-1–054303-10.
doi:
10.1103/PhysRevC.98.054303.
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Previously published particle-γ coincidence data on the 64Ni(p,p′γ)64Ni and 64Ni(d,pγ)65Ni reactions were further analyzed to study the statistical properties of γ decay in 64,65Ni. To do so, the γ decay to the quasicontinuum region and discrete low-lying states was investigated at γ-ray energies of 2.0–9.6 and 1.6–6.1 MeV in 64 Ni and 65 Ni, respectively. In particular, the dependence of the γ -strength function with initial and final excitation energy was studied to test the validity of the generalized Brink-Axel hypothesis. Finally, the role of fluctuations in transition strengths was estimated as a function of γ-ray and excitation energy. The γ -strength function is consistent with the hypothesis of the independence of initial excitation energy, in accordance with the generalized Brink-Axel hypothesis. The results show that the γ decay to low-lying levels displays large fluctuations for low initial excitation energies.
-
-
Brits, C.P.; Wiedeking, M.; Garrote, Frank Leonel Bello; Bleuel, D. L.; Giacoppo, F. & Görgen, Andreas
[Show all 22 contributors for this article]
(2017).
Resonances in odd-odd 182Ta.
The European Physical Journal Conferences.
ISSN 2101-6275.
146.
doi:
10.1051/epjconf/201714605012.
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Enhanced γ -decay on the tail of the giant electric dipole resonance, such as the scissors or pygmy resonances, can have significant impact on (n,γ ) reaction rates. These rates are important input for modeling processes that take place in astrophysical environments and nuclear reactors. Recent results from the University of Oslo indicate the existence of a significant enhancement in the photon strength function for nuclei in the actinide region due to the scissors resonance. Further, the M1 strength distribution of the scissors resonances in rare earth nuclei has been studied extensively over the years. To investigate the evolution and persistence of the scissor resonance in other mass regions, an experiment was performed utilizing the NaI(Tl) γ -ray detector array (CACTUS) and silicon particle telescopes (SiRi) at the University of Oslo Cyclotron laboratory. Particle-γ coincidences from the 181Ta(d,p)182Ta and 181Ta(d,d’)181Ta reactions were used to measure the nuclear level density and photon strength function of the well-deformed 181Ta and 182Ta systems, to investigate the existence of resonances below the neutron separation energy.
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Malatji, Kgashane L.; Kheswa, Bonginkosi Vincent; Wiedeking, M.; Garrote, Frank Leonel Bello; Brits, C.P. & Bleuel, D. L.
[Show all 21 contributors for this article]
(2017).
Nuclear level densities and γ-ray strength functions of 180,181Ta and neutron capture cross sections.
The European Physical Journal Conferences.
ISSN 2101-6275.
146.
doi:
10.1051/epjconf/201714601010.
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The γ -ray strength functions and nuclear level densities in the quasi-continuum of 180,181Ta are extracted from particle-γ coincidence events with the Oslo Method, below the Sn . The data were used as input in the TALYS reaction code for calculations of the astrophysical Maxwellian-averaged (n, γ ) cross-sections to investigate nucleosynthesis of nature’s rarest stable isotope 180Ta.
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Vaquero, V; Jungclaus, A; Doornenbal, P; Wimmer, K; Gargano, A & Tostevin, JA
[Show all 33 contributors for this article]
(2017).
Gamma Decay of Unbound Neutron-Hole States in Sn-133.
Physical Review Letters.
ISSN 0031-9007.
118(20).
doi:
10.1103/PhysRevLett.118.202502.
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Excited states in the nucleus 133Sn, with one neutron outside the doubly-magic 132Sn core, were populated following one-neutron knockout from a 134Sn beam on a carbon target at relativistic energies at the Radioactive Isotope Beam Factory at RIKEN. Besides the γ rays emitted in the decay of the known neutron single-particle states in 133Sn additional γ strength in the energy range 3.5-5.5 MeV was observed for the first time. Since the neutron-separation energy of 133Sn is low, Sn=2.402(4) MeV, this observation provides direct evidence for the radiative decay of neutronunbound states in this nucleus. The ability of electromagnetic decay to compete successfully with neutron emission at energies as high as 3 MeV above threshold is attributed to a mismatch between the wave functions of the initial and final states in the latter case. These findings suggest that in the region south-east of 132Sn nuclear structure effects may play a significant role in the neutron vs. γ competition in the decay of unbound states. As a consequence, the common neglect of such effects in the evaluation of the neutron-emission probabilities in calculations of global β-decay properties for astrophysical simulations may have to be reconsidered.
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Tveten, Gry Merete; Spyrou, Artemis; Schwengner, Ronald; Naqvi, Farheen; Larsen, Ann-Cecilie & Renstrøm, Therese
[Show all 23 contributors for this article]
(2017).
The Statistical Properties Of 92Mo And Implications For The p-process.
Proceedings of Science (PoS).
INPC2016.
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A particularly challenging part of the question of how elements heavier than iron are created in extreme, astrophysical environments is the creation of the so-called p-nuclei, which are believed to be mainly produced in the O-Ne layer of type II supernovae or type Ia supernovae. The lack of needed nuclear data presents an obstacle in nailing down the precise site and astrophysical conditions for the production of these isotopes. Astrophysical model calculations are able to reproduce abundance patterns of most p-isotopes reasonably well, with some pivotal exceptions. In particular, p-isotopes of mass 92 ≤ A ≤ 98 are underproduced in calculations compared to the actual abundance of these isotopes. The p-isotope 92Mo represents one of the most severe cases of underproduction. State-of-the-art p-process calculations systematically underestimate the observed solar abundance of this isotope.
The main destruction mechanism of this isotope in the standard description of the p-process is through the 92Mo(γ, p)91Nb reaction. Measurements on the nuclear level density and average gamma strength function of 92Mo have been carried out at the Oslo Cyclotron Laboratory. TALYS cross section and reaction rate calculations where the experimental results are used as input will be presented. The data provide stringent constraints on the 91Nb(p, γ)92Mo (and consequently the inverse) reaction rate. The reaction rate extracted in this work was used in reaction network calculations for the scenario of a p-process taking place in a type II supernova explosion as the shock front passes through the O-Ne layer of a 25 solar mass star.
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Campo, Lucia Crespo; Larsen, Ann-Cecilie; Garrote, Frank Leonel Bello; Eriksen, Tomas Kvalheim; Giacoppo, Francesca & Görgen, Andreas
[Show all 13 contributors for this article]
(2017).
Investigating the gamma decay of Ni 65 from particle-gamma coincidence data.
Physical Review C.
ISSN 2469-9985.
96(1).
doi:
10.1103/PhysRevC.96.014312.
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The γ decay of 65 Ni has been studied from particle- γ coincidence data on the 64 Ni ( d , p γ ) 65 Ni reaction. γ -ray spectra at excitation energies below Ex≈ 2 MeV have been studied and compared with previous measurements. Coincidences corresponding to Ex≈ 4.4 – 6.1 MeV have been used to constrain the shape of the nuclear level density and γ -strength function of 65 Ni by means of the Oslo method. The experimental γ -strength function presents an enhancement at γ energies below Eγ ≈ 3 MeV . In addition, a resonance-like structure centered at Eγ ≈ 4.6 MeV is seen together with accumulated strength at Eγ ≈ 2.6 – 3.6 MeV . The obtained results contribute to the systematic study of γ decay in the Ni isotopes, which is of great interest for the understanding of both single-particle and collective nuclear structure phenomena.
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Kheswa, Bonginkosi Vincent; Wiedeking, Mathis; Brown, Joshua A.; Larsen, Ann-Cecilie; Goriely, Stéphane & Guttormsen, Magne Sveen
[Show all 25 contributors for this article]
(2017).
137,138,139La(n,γ) cross sections constrained with statistical decay properties of 138,139,140La nuclei.
Physical Review C.
ISSN 2469-9985.
95(4).
doi:
10.1103/PhysRevC.95.045805.
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The nuclear level densities and γ-ray strength functions of 138,139,140La were measured using the 139La(3He,α), 139La(3He,'3He), and 139La(d,p) reactions. The particle-γ coincidences were recorded with the silicon particle telescope (SiRi) and NaI(Tl) (CACTUS) arrays. In the context of these experimental results, the low-energy enhancement in the A∼140 region is discussed. The 137,138,139La(n,γ) cross sections were calculated at s- and p-process temperatures using the experimentally measured nuclear level densities and γ-ray strength functions. Good agreement is found between 139La(n,γ) calculated cross sections and previous measurements. This research was first published in Physical Review C - Nuclear Physics. © American Physical Society.
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Campo, Lucia Crespo; Garrote, Frank Leonel Bello; Eriksen, Tomas Kvalheim; Görgen, Andreas; Guttormsen, Magne Sveen & Hadynska-Klek, Katarzyna
[Show all 14 contributors for this article]
(2016).
Statistical γ -decay properties of Ni 64 and deduced (n,γ) cross section of the s -process branch-point nucleus Ni 63.
Physical Review C. Nuclear Physics.
ISSN 0556-2813.
94(4).
doi:
10.1103/PhysRevC.94.044321.
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Particle-γ coincidence data have been analyzed to obtain the nuclear level density and the γ -strength function of 64Ni by means of the Oslo method. The level density found in this work is in very good agreement with known energy levels at low excitation energies as well as with data deduced from particle-evaporation measurements at excitation energies above Ex ≈ 5.5 MeV. The experimental γ -strength function presents an enhancement at γ energies below Eγ ≈ 3 MeV and possibly a resonancelike structure centered at Eγ ≈ 9.2 MeV. The obtained nuclear level density and γ -strength function have been used to estimate the (n,γ ) cross section for the s-process branch-point nucleus 63Ni, of particular interest for astrophysical calculations of elemental abundances.
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Klintefjord, Malin; Hadynska-Klek, Katarzyna; Görgen, Andreas; Bauer, C; Garrote, Frank Leonel Bello & Bönig, S
[Show all 44 contributors for this article]
(2016).
Structure of low-lying states in Sm140 studied by Coulomb excitation.
Physical Review C. Nuclear Physics.
ISSN 0556-2813.
93(5).
doi:
10.1103/PhysRevC.93.054303.
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The electromagnetic structure of Sm140 was studied in a low-energy Coulomb excitation experiment with a radioactive ion beam from the REX-ISOLDE facility at CERN. The 2+ and 4+ states of the ground-state band and a second 2+ state were populated by multistep excitation. The analysis of the differential Coulomb excitation cross sections yielded reduced transition probabilities between all observed states and the spectroscopic quadrupole moment for the 2+1 state. The experimental results are compared to large-scale shell model calculations and beyond-mean-field calculations based on the Gogny D1S interaction with a five-dimensional collective Hamiltonian formalism. Simpler geometric and algebraic models are also employed to interpret the experimental data. The results indicate that Sm140 shows considerable γ softness, but in contrast to earlier speculation no signs of shape coexistence at low excitation energy. This work sheds more light on the onset of deformation and collectivity in this mass region.
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Laplace, Thibault A.; Zeiser, Fabio; Guttormsen, Magne Sveen; Larsen, Ann-Cecilie; Bleuel, Darren L. & Bernstein, Lee A.
[Show all 27 contributors for this article]
(2016).
Statistical properties of Pu 243, and Pu 242 (n,γ) cross section calculation.
Physical Review C. Nuclear Physics.
ISSN 0556-2813.
93(1).
doi:
10.1103/PhysRevC.93.014323.
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The level density and γ -ray strength function (γ SF) of 243Pu have been measured in the quasicontinuum using the Oslo method. Excited states in 243Pu were populated using the 242Pu(d,p) reaction. The level density closely follows the constant-temperature level density formula for excitation energies above the pairing gap. The γ SF displays a double-humped resonance at low energy as also seen in previous investigations of actinide isotopes. The structure is interpreted as the scissors resonance and has a centroid of ωSR = 2.42(5) MeV and a total strength of BSR = 10.1(15) μ2 N , which is in excellent agreement with sum-rule estimates. The measured level density and γ SF were used to calculate the 242Pu(n,γ ) cross section in a neutron energy range for which there were previously no measured data.
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Larsen, Ann-Cecilie; Guttormsen, Magne Sveen; Schwengner, Ronald; Bleuel, Darren L.; Goriely, Stephane & Harrisopulos, Sotirios
[Show all 21 contributors for this article]
(2016).
Experimentally constrained (p,γ) y 89 and (n,γ) y 89 reaction rates relevant to p -process nucleosynthesis.
Physical Review C. Nuclear Physics.
ISSN 0556-2813.
93(4).
doi:
10.1103/PhysRevC.93.045810.
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The nuclear level density and the γ -ray strength function have been extracted for 89Y by using the Oslo method on 89Y(p,p γ ) 89Y coincidence data. The γ -ray strength function displays a low-energy enhancement consistent with previous observations in this mass region (93–98Mo). Shell-model calculations support the conclusion that the observed enhancement is due to strong, low-energy M1 transitions at high excitation energies. The data were further used as input for calculations of the 88Sr(p,γ ) 89Y and 88Y(n,γ ) 89Y cross sections with the TALYS reaction code. Comparison with cross-section data, where available, as well as with values from the BRUSLIB library, shows a satisfying agreement.
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Tveten, Gry Merete; Spyrou, A; Schwengner, R; Naqvi, F; Larsen, Ann-Cecilie & Eriksen, Tomas Kvalheim
[Show all 23 contributors for this article]
(2016).
Completing the nuclear reaction puzzle of the nucleosynthesis of Mo 92.
Physical Review C. Nuclear Physics.
ISSN 0556-2813.
94(2).
doi:
10.1103/PhysRevC.94.025804.
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One of the greatest questions for modern physics to address is how elements heavier than iron are created in extreme astrophysical environments. A particularly challenging part of that question is the creation of the so-called p-nuclei, which are believed to be mainly produced in some types of supernovae. The lack of needed nuclear data presents an obstacle in nailing down the precise site and astrophysical conditions. In this work, we present for the first time measurements on the nuclear level density and average γ strength function of 92Mo. State-of-the-art p-process calculations systematically underestimate the observed solar abundance of this isotope. Our data provide stringent constraints on the 91Nb(p,γ ) 92Mo reaction rate, which is the last unmeasured reaction in the nucleosynthesis puzzle of 92Mo. Based on our results, we conclude that the 92Mo abundance anomaly is not due to the nuclear physics input to astrophysical model calculations.
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Giacoppo, Francesca; Garrote, Frank Leonel Bello; Bernstein, Lee; Bleuel, D.l.; Firestone, R.B. & Görgen, Andreas
[Show all 16 contributors for this article]
(2015).
Gamma decay from the quasicontinuum of 197,198Au.
Physical Review C. Nuclear Physics.
ISSN 0556-2813.
91.
doi:
10.1103/PhysRevC.91.054327.
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The average electromagnetic dipole response of levels in the quasicontinuum of 197,198Au has been measured using (3He,3He ) and (d,p) reactions. The extracted γ -ray strength functions have been normalized according to three model assumptions for the nuclear spin distribution. An enhancement in the energy region Eγ = 3.0–6.5 MeV is observed for both isotopes. The E1 component of such excess of strength is studied in detail for 198Au and is interpreted as the pygmy dipole resonance with an energy centroid of 5.9(1) MeV and exhausts about 1% of the total integrated strength. The pygmy dipole resonance is shown to have a significant impact on the calculated 197Au(n,γ ) 198Au cross section.
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Tveten, Gry Merete; Garrote, Frank Leonel Bello; Campo, Lucia Crespo; Eriksen, Tomas Kvalheim; Giacoppo, Francesca & Guttormsen, Magne Sveen
[Show all 18 contributors for this article]
(2015).
The statistical properties of 111,112,113Sn studied with the Oslo method.
The European Physical Journal Conferences.
ISSN 2101-6275.
93.
doi:
10.1051/epjconf/20159304004.
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The γ-ray strength function and level density of 111, 112, 113Sn are being studied at the Oslo Cyclotron Laboratory (OCL) up to the neutron binding energy by applying the Oslo method to particle-γ coincidence data. The preliminary results for the γ-ray strength function are discussed in the context of the results for the more neutron-rich Sn-isotopes previously studied at OCL.
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Samorajczyk, J; Klintefjord, Malin; Droste, C.; Görgen, Andreas; Marchlewski, T & Srebrny, J.
[Show all 19 contributors for this article]
(2015).
Revised spin values of the 991 keV and 1599 keV levels in Sm 140.
Physical Review C. Nuclear Physics.
ISSN 0556-2813.
92:044322(4).
doi:
10.1103/PhysRevC.92.044322.
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The previously accepted spin values of the 991 and 1599 keV levels in Sm140 have been revised and established as 2+ and 0(+), respectively. The γ−γ angular correlation method was used to determine the new spin values. The excited low-spin levels in Sm140 were populated in the Eu140→140Sm and Gd140→ Eu140→140Sm decays. The Gd140 and Eu140 nuclei were produced in the Cd112+S32 reaction at a beam energy of 155 MeV. © 2015 American Physical Society
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Kheswa, Bonginkosi Vincent; Wiedeking, Mathis; Giacoppo, Francesca; Goriely, Stephan; Guttormsen, Magne Sveen & Larsen, Ann-Cecilie
[Show all 19 contributors for this article]
(2015).
Galactic production of 138La: Impact of 138,139La statistical properties.
Physics Letters B.
ISSN 0370-2693.
744,
p. 268–272.
doi:
10.1016/j.physletb.2015.03.065.
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The γ-ray strength functions and nuclear level densities of 138La and 139La have been measured below the neutron separation energies. These new data were used to calculate astrophysical Maxwellian-averaged () cross-sections to investigate the production and destruction of the p-nucleus 138La in the photodisintegration process. The results confirm the underproduction of 138La in the p-process with respect to the observed abundances and strongly support the ν-process through capture on 138Ba as the main contributor to the synthesis of 138La in Type II supernovae.
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Klintefjord, Malin; Hadynska-Klek, Katarzyna; Samorajczyk, J; Görgen, Andreas; Droste, C & Srebrny, J
[Show all 40 contributors for this article]
(2015).
Spectroscopy of low-lying states in 140Sm.
Acta Physica Polonica B.
ISSN 0587-4254.
46(3),
p. 607–611.
doi:
10.5506/APhysPolB.46.607.
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Electromagnetic transition strengths and spectroscopic quadrupole moments for 140Sm were measured by means of multi-step Coulomb excitation with radioactive beam at the ISOLDE facility at CERN. A complementary experiment was performed at the Heavy Ion Laboratory in Warsaw to assign spins for non-yrast states using the angular correlation technique. Based on the new experimental data previous spin assignments need to be revised.
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Garrote, Frank Leonel Bello; Görgen, Andreas; Mierzejewski, Jan; Mihai, Corina Mihaela; Delaroche, Jean Paul & Girod, Michel
[Show all 24 contributors for this article]
(2015).
Lifetime measurement for the 21+ state in Sm 140 and the onset of collectivity in neutron-deficient Sm isotopes.
Physical Review C. Nuclear Physics.
ISSN 0556-2813.
92:024317(2).
doi:
10.1103/PhysRevC.92.024317.
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Background: The chain of Sm isotopes exhibits a wide range of nuclear shapes and collective behavior. While the onset of deformation for N > 82 has been well studied both experimentally and theoretically, fundamental data is lacking for some Sm isotopes with N < 82. Purpose: Electromagnetic transition rates represent a sensitive test of theoretical nuclear structure models. Lifetime measurements are furthermore complementary to Coulomb excitation experiments, and the two methods together can give access to spectroscopic quadrupole moments. Method: The lifetime of the 2+ 1 state in 140Sm was measured with the recoil-distance Doppler shift technique using the reaction 124Te( 20Ne, 4n) 140Sm at 82 MeV. Theoretical calculations were performed based on a mapped collective Hamiltonian in five quadrupole coordinates (5DCH) and the Gogny D1S interaction. Results: The lifetime of the 2+ 1 state in 140Sm was found to be 9.1(6) ps, corresponding to aB(E2; 2+ 1 → 0+ 1 ) value of 51(4) Weisskopf units. The theoretical calculations are in very good agreement with the experimental result. Conclusions: The B(E2; 2+ 1 → 0+ 1 ) value for 140Sm fits smoothly into the systematic trend for the chain of Sm isotopes. The new beyond-mean field calculations are able to correctly describe the onset of collectivity in the Sm isotopes below the N = 82 shell closure for the first time.
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Tveten, Gry Merete; Spyrou, Artemis; Schwengner, Ronald; Naqvi, Farheen; Larsen, Ann-Cecilie & Eriksen, Tomas Kvalheim
[Show all 23 contributors for this article]
(2016).
The Statistical Properties Of 92Mo And Implications For The p-process.
Full text in Research Archive
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A particularly challenging part of the question of how elements heavier than iron are created in extreme, astrophysical environments is the creation of the so-called p-nuclei, which are believed to be mainly produced in the O-Ne layer of type II supernovae or type Ia supernovae. The lack of needed nuclear data presents an obstacle in nailing down the precise site and astrophysical conditions for the production of these isotopes. Astrophysical model calculations are able to reproduce abundance patterns of most p-isotopes reasonably well, with some pivotal exceptions. In particular, p-isotopes of mass 92 ≤ A ≤ 98 are underproduced in calculations compared to the actual abundance of these isotopes. The p-isotope 92Mo represents one of the most severe cases of underproduction. State-of-the-art p-process calculations systematically underestimate the observed solar abundance of this isotope.
The main destruction mechanism of this isotope in the standard description of the p-process is through the 92Mo(γ, p)91Nb reaction. Measurements on the nuclear level density and average gamma strength function of 92Mo have been carried out at the Oslo Cyclotron Laboratory. TALYS cross section and reaction rate calculations where the experimental results are used as input will be presented. The data provide stringent constraints on the 91Nb(p, γ)92Mo (and consequently the inverse) reaction rate. The reaction rate extracted in this work was used in reaction network calculations for the scenario of a p-process taking place in a type II supernova explosion as the shock front passes through the O-Ne layer of a 25 solar mass star.
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Garrote, Frank Leonel Bello
(2018).
Studies of single-particle and collective properties of nuclei.
Det matematisk-naturvitenskapelige fakultet.
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Published
Dec. 19, 2012 10:23 AM
- Last modified
Oct. 21, 2019 2:34 PM
