giacoppo

• Markova, Maria; Larsen, Ann-Cecilie; Tveten, Gry Merete; Neumann-Cosel, Peter von; Eriksen, Tomas Kvalheim & Garrote, Frank Leonel Bello [Vis alle 16 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• 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 ²⁵⁴No. Physics Letters B. ISSN 0370-2693. 834. doi: 10.1016/j.physletb.2022.137479. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Lokotko, T.; Leblond, S.; Lee, J.; Doornenbal, P.; Obertelli, A. & Poves, A. [Vis alle 67 forfattere av denne artikkelen] (2020). Shell structure of the neutron-rich isotopes Co 69,71,73. Physical Review C. ISSN 2469-9985. 101(3). doi: 10.1103/PhysRevC.101.034314. Fulltekst i vitenarkiv
• Frotscher, A; Gomez-Ramos, M; Obertelli, A; Doornenbal, P; Authelet, G & Baba, H [Vis alle 50 forfattere av denne artikkelen] (2020). Sequential Nature of (p,3p) Two-Proton Knockout from Neutron-Rich Nuclei. Physical Review Letters. ISSN 0031-9007. 125(1). doi: 10.1103/PhysRevLett.125.012501. Fulltekst i vitenarkiv
• Kibédi, T.; Alshahrani, B.; Stuchbery, A.E.; Larsen, Ann-Cecilie; Görgen, Andreas & Siem, Sunniva [Vis alle 20 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Taniuchi, R; Santamaria, C; Doornenbal, P.; Obertelli, A.; Yoneda, K. & Authelet, G. [Vis alle 71 forfattere av denne artikkelen] (2019). 78Ni revealed as a doubly magic stronghold against nuclear deformation. Nature. ISSN 0028-0836. 569, s. 53–58. doi: 10.1038/s41586-019-1155-x. Fulltekst i vitenarkiv
• Elekes, Z; Kripkó, Á; Sohler, D; Sieja, K; Ogata, K. & Yoshida, K [Vis alle 67 forfattere av denne artikkelen] (2019). Nuclear structure of 76Ni from the (p,2p) reaction. Physical Review C. ISSN 2469-9985. 99:014312(1), s. 1–7. doi: 10.1103/PhysRevC.99.014312. Fulltekst i vitenarkiv Vis sammendrag

  The nuclear structure of the 76 Ni nucleus was investigated by ( p , 2 p ) reaction using a NaI(Tl) array to detect the deexciting prompt γ rays. A new transition with an energy of 2227 keV was identified by γ γ and γ γ γ coincidences. According to these coincidence spectra the observed transition connects a new state at 4147 keV and the previously known 4+1 state at 1920 keV. Two weaker transitions were also obtained at 2441 and 2838 keV, which could be tentatively placed to feed the known 2+1 state at 990 keV. Our shell-model calculations using the Lenzi, Nowacki, Poves, and Sieja interaction produced good candidates for the experimental proton hole states in the observed energy region, and the theoretical cross sections showed good agreement with the experimental values. Although we could not assign all the experimental states to the theoretical ones unambiguously, the results are consistent with a reasonably large Z=28 shell gap for nickel isotopes in accordance with previous studies.

• Brits, C.P.; Malatji, Kgashane L.; Wiedeking, M.; Kheswa, BV; Goriely, S. & Garrote, Frank Leonel Bello [Vis alle 27 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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 .

• Liddick, Sean N.; Larsen, Ann-Cecilie; Guttormsen, Magne Sveen; Spyrou, Artemis; Crider, Benjamin P. & Naqvi, Farheen [Vis alle 30 forfattere av denne artikkelen] (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), s. 1–12. doi: 10.1103/PhysRevC.100.024624. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Paul, N.; Obertelli, A.; Bertulani, C. A.; Corsi, A.; Doornenbal, P. & Rodriguez-Sanchez, J. L. [Vis alle 92 forfattere av denne artikkelen] (2019). Prominence of Pairing in Inclusive (p,2p) and (p,pn) Cross Sections from Neutron-Rich Nuclei. Physical Review Letters. ISSN 0031-9007. 122(16). doi: 10.1103/PhysRevLett.122.162503. Fulltekst i vitenarkiv Vis sammendrag

  Fifty-five inclusive single nucleon-removal cross sections from medium mass neutron-rich nuclei impinging on a hydrogen target at ∼ 250     MeV / nucleon are measured at the RIKEN Radioactive Isotope Beam Factory. Systematically higher cross sections are found for proton removal from nuclei with an even number of protons as compared to odd-proton number projectiles for a given neutron separation energy. Neutron removal cross sections display no even-odd splitting, contrary to nuclear cascade model predictions. Both effects are understood through simple considerations of neutron separation energies and bound state level densities originating in pairing correlations in the daughter nuclei. These conclusions are supported by comparison with semimicroscopic model predictions, highlighting the enhanced role of low-lying level densities in nucleon-removal cross sections from loosely bound nuclei.

• Malatji, Kgashane Leroy; Wiedeking, Mathis; Goriely, Stephane; Brits, Christiaan Petrus; Kheswa, Bonginkosi Vincent & Garrote, Frank Leonel Bello [Vis alle 22 forfattere av denne artikkelen] (2019). Re-estimation of 180Ta nucleosynthesis in light of newly constrained reaction rates. Physics Letters B. ISSN 0370-2693. 791, s. 403–408. doi: 10.1016/j.physletb.2019.03.013. Fulltekst i vitenarkiv
• Sua, Martha Liliana Cortés; Doornenbal, P; Dupuis, M; Lenzi, SM; Nowacki, F & Obertelli, A [Vis alle 68 forfattere av denne artikkelen] (2018). Inelastic scattering of neutron-rich Ni and Zn isotopes off a proton target. Physical Review C. ISSN 2469-9985. 97(4), s. 1–10. doi: 10.1103/PhysRevC.97.044315. Fulltekst i vitenarkiv Vis sammendrag

  Proton inelastic scattering of 72,74Ni and 76,80Zn ions at energies around 235 MeV/nucleon was performed at the Radioactive Isotope Beam Factory and studied using γ -ray spectroscopy. Angular integrated cross sections for direct inelastic scattering to the 2+ 1 and 4+ 1 states were measured. The Jeukenne-Lejeune-Mahaux folding model, extended beyond 200 MeV, was used together with neutron and proton densities stemming from quasiparticle random-phase approximation (QRPA) calculations to interpret the experimental cross sections and to infer neutron to proton matrix element ratios. In addition, coupled-channels calculations with a phenomenological potential were used to determine deformation lengths. For the Ni isotopes, correlations favor neutron excitations, thus conserving the Z = 28 gap. A dominance of proton excitation, on the other hand, is observed in the Zn isotopes, pointing to the conservation of the N = 50 gap approaching 78Ni. These results are in agreement with QRPA and large-scale shell-model calculations.

• Campo, Lucia Crespo; Guttormsen, Magne Sveen; Garrote, Frank Leonel Bello; Eriksen, Tomas Kvalheim; Giacoppo, Francesca & Görgen, Andreas [Vis alle 15 forfattere av denne artikkelen] (2018). Test of the generalized Brink-Axel hypothesis in 64,65Ni. Physical Review C. ISSN 2469-9985. 98, s. 054303-1–054303-10. doi: 10.1103/PhysRevC.98.054303. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Liu, XY; Liu, Zhong; Ding, B; Doornenbal, P; Obertelli, A & Lenzi, SM [Vis alle 78 forfattere av denne artikkelen] (2018). Spectroscopy of 25,65/67Mn: Strong coupling in the N = 40 "island of inversion". Physics Letters B. ISSN 0370-2693. 784, s. 392–396. doi: 10.1016/j.physletb.2018.06.067. Fulltekst i vitenarkiv Vis sammendrag

  Excited states in 63,65,67Mn were studied via in-beam γ -ray spectroscopy following knockout reactions from 68Fe. Similar level schemes, consisting of the 11/2−, 9/2−, 7/2− and 5/2− g.s. level sequence, connected by I → I − 1 transitions, were established, the first time for 65,67Mn. Their level structures show features consistent with strongly-coupled rotational bands with K = 5/2. State-of-the-art shellmodel calculations with the modified LNPS effective interaction reproduce the observed levels remarkably well and suggest the dominance of 4-particle-4-hole neutron configurations for all the states. The data on the low-lying excited states of odd-mass 53−67Mn provide a textbook example of nuclear structure evolution from weak coupling through decoupling to strong coupling along a single isotopic chain on the n-rich side of the β stability line. These results help to deepen our understanding of the N = 40 “island of inversion”.

• Shand, Callum Macintyre; Podolyák, Zsolt; Górska, Magda; Doornenbal, Pieter C.; Obertelli, Alexandre & Nowacki, Frédéric [Vis alle 96 forfattere av denne artikkelen] (2017). Shell evolution beyond Z = 28 and N = 50: Spectroscopy of 81,82,83,84Zn. Physics Letters B. ISSN 0370-2693. 773, s. 492–497. doi: 10.1016/j.physletb.2017.09.001. Fulltekst i vitenarkiv
• Malatji, Kgashane L.; Kheswa, Bonginkosi Vincent; Wiedeking, M.; Garrote, Frank Leonel Bello; Brits, C.P. & Bleuel, D. L. [Vis alle 21 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Rose, Sunniva Johanne; Zeiser, Fabio; Wilson, JN; Oberstedt, A; Oberstedt, S & Siem, Sunniva [Vis alle 25 forfattere av denne artikkelen] (2017). Energy dependence of the prompt gamma-ray emission from the (d,p)-induced fission of U-234 and Pu-240. Physical Review C. ISSN 2469-9985. 96(1). doi: 10.1103/PhysRevC.96.014601. Fulltekst i vitenarkiv Vis sammendrag

  Prompt-fission γ rays are responsible for approximately 5% of the total energy released in fission, and therefore important to understand when modeling nuclear reactors. In this work we present prompt γ -ray emission characteristics in fission as a function of the nuclear excitation energy of the fissioning system. Emitted γ -ray spectra were measured, and γ -ray multiplicities and average and total γ energies per fission were determined for the 233 U ( d , p f ) reaction for excitation energies between 4.8 and 10 MeV, and for the 239 Pu ( d , p f ) reaction between 4.5 and 9 MeV. The spectral characteristics show no significant change as a function of excitation energy above the fission barrier, despite the fact that an extra ∼ 5 MeV of energy is potentially available in the excited fragments for γ decay. The measured results are compared with model calculations made for prompt γ -ray emission with the fission model code gef. Further comparison with previously obtained results from thermal neutron induced fission is made to characterize possible differences arising from using the surrogate ( d , p ) reaction.

• Tveten, Gry Merete; Spyrou, Artemis; Schwengner, Ronald; Naqvi, Farheen; Larsen, Ann-Cecilie & Renstrøm, Therese [Vis alle 23 forfattere av denne artikkelen] (2017). The Statistical Properties Of 92Mo And Implications For The p-process. Proceedings of Science (PoS). INPC2016. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Campo, Lucia Crespo; Larsen, Ann-Cecilie; Garrote, Frank Leonel Bello; Eriksen, Tomas Kvalheim; Giacoppo, Francesca & Görgen, Andreas [Vis alle 13 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Kheswa, Bonginkosi Vincent; Wiedeking, Mathis; Brown, Joshua A.; Larsen, Ann-Cecilie; Goriely, Stéphane & Guttormsen, Magne Sveen [Vis alle 25 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Olivier, Lauret; Franchoo, Serge; Niikura, Megumi; Vajta, Zsolt; Sohler, Dóra & Doornenbal, Pieter C. [Vis alle 66 forfattere av denne artikkelen] (2017). Persistence of the Z=28 Shell Gap Around Ni 78: First Spectroscopy of Cu 79. Physical Review Letters. ISSN 0031-9007. 119:192501(19), s. 1–6. doi: 10.1103/PhysRevLett.119.192501. Fulltekst i vitenarkiv
• Marini, P.; Ducasse, Q; Jurado, B; Aiche, M; Mathieu, L & Barreau, G. [Vis alle 33 forfattere av denne artikkelen] (2016). First simultaneous measurement of fission and gamma probabilities of <sup>237</sup>U and <sup>239</sup>Np via surrogate reactions. The European Physical Journal Conferences. ISSN 2101-6275. 122. doi: 10.1051/epjconf/201612212004. Fulltekst i vitenarkiv
• Klintefjord, Malin; Hadynska-Klek, Katarzyna; Görgen, Andreas; Bauer, C; Garrote, Frank Leonel Bello & Bönig, S [Vis alle 44 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Laplace, Thibault A.; Zeiser, Fabio; Guttormsen, Magne Sveen; Larsen, Ann-Cecilie; Bleuel, Darren L. & Bernstein, Lee A. [Vis alle 27 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Larsen, Ann-Cecilie; Guttormsen, Magne Sveen; Schwengner, Ronald; Bleuel, Darren L.; Goriely, Stephane & Harrisopulos, Sotirios [Vis alle 21 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Ducasse, Q; Jurado, B; Aiche, M; Marini, P; Mathieu, L & Görgen, Andreas [Vis alle 29 forfattere av denne artikkelen] (2016). Investigation of the U 238 (d,p) surrogate reaction via the simultaneous measurement of γ -decay and fission probabilities. Physical Review C. Nuclear Physics. ISSN 0556-2813. 94(2). doi: 10.1103/PhysRevC.94.024614. Fulltekst i vitenarkiv Vis sammendrag

  We investigated the 238U(d,p) reaction as a surrogate for the n + 238U reaction. For this purpose we measured for the first time the γ -decay and fission probabilities of 239U∗ simultaneously and compared them to the corresponding neutron-induced data. We present the details of the procedure to infer the decay probabilities, as well as a thorough uncertainty analysis, including parameter correlations. Calculations based on the continuumdiscretized coupled-channels method and the distorted-wave Born approximation (DWBA) were used to correct our data from detected protons originating from elastic and inelastic deuteron breakup. In the region where fission and γ emission compete, the corrected fission probability is in agreement with neutron-induced data, whereas the γ -decay probability is much higher than the neutron-induced data. We have performed calculations of the decay probabilities with the statistical model and of the average angular momentum populated in the 238U(d,p) reaction with the DWBA to interpret these results.

• Cortes, ML; Doornenbal, P; Obertelli, A; Pietralla, N; Werner, V & Authelet, G [Vis alle 63 forfattere av denne artikkelen] (2016). Inelastic scattering of 72,74Ni off a proton target. Journal of Physics: Conference Series (JPCS). ISSN 1742-6588. 724(1). doi: 10.1088/1742-6596/724/1/012008. Fulltekst i vitenarkiv
• Tveten, Gry Merete; Spyrou, A; Schwengner, R; Naqvi, F; Larsen, Ann-Cecilie & Eriksen, Tomas Kvalheim [Vis alle 23 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Tveten, Gry Merete; Spyrou, Artemis; Schwengner, Ronald; Naqvi, Farheen; Larsen, Ann-Cecilie & Renstrøm, Therese [Vis alle 23 forfattere av denne artikkelen] (2016). The statistical properties of 92Mo and implications for the p-process. Proceedings of Science (PoS). 2016-September:163. Fulltekst i vitenarkiv
• Werner, Vince; Santamaria, C; Louchart, C; Obertelli, A; Doornenbal, P & Nowacki, F [Vis alle 63 forfattere av denne artikkelen] (2016). Collectivity of neutron-rich Cr and Fe toward N=50. The European Physical Journal Conferences. ISSN 2101-6275. 107:03007. doi: 10.1051/epjconf/201610703007. Fulltekst i vitenarkiv
• Santamaria, Clémentine; Louchart, C.; Obertelli, A; Werner, V.; Doornenbal, P & Nowacki, F [Vis alle 63 forfattere av denne artikkelen] (2015). Extension of the N = 40 Island of Inversion towards N = 50: Spectroscopy of 66Cr, 70,72Fe. Physical Review Letters. ISSN 0031-9007. 115:192501(19). doi: 10.1103/PhysRevLett.115.192501. Fulltekst i vitenarkiv
• Giacoppo, Francesca; Garrote, Frank Leonel Bello; Bernstein, Lee; Bleuel, D.l.; Firestone, R.B. & Görgen, Andreas [Vis alle 16 forfattere av denne artikkelen] (2015). Gamma decay from the quasicontinuum of 197,198Au. Physical Review C. Nuclear Physics. ISSN 0556-2813. 91. doi: 10.1103/PhysRevC.91.054327. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Ariga, Akitaka; Ariga, Tomoko; Braccini, Saverio; Giacoppo, Francesca; Nesteruk, Konrad P. & Pistillo, Ciro [Vis alle 7 forfattere av denne artikkelen] (2015). Characterization of the dose distribution in the halo region of a clinical proton pencil beam using emulsion film detectors. Journal of Instrumentation (JINST). 10:P01007(1). doi: 10.1088/1748-0221/10/01/P01007. Fulltekst i vitenarkiv
• Larsen, Ann-Cecilie; Goriely, Stephane; Bernstein, L. A.; Bleuel, D. L.; Bracco, A. & Brown, B. A. [Vis alle 25 forfattere av denne artikkelen] (2015). Upbend and M1 scissors mode in neutron-rich nuclei — consequences for r-process (n,gamma) reaction rates. Acta Physica Polonica B. ISSN 0587-4254. 46(3), s. 509–512. doi: 10.5506/APhysPolB.46.509. Fulltekst i vitenarkiv Vis sammendrag

  An enhanced probability for low-energy γ-emission (upbend, Eγ < 3 MeV) at high excitation energies has been observed for several light and medium-mass nuclei close to the valley of stability. Also the M1 scissors mode seen in deformed nuclei increases the γ-decay probability for low-energy γ-rays (Eγ ≈ 2–3 MeV). These phenomena, if present in neutron-rich nuclei, have the potential to increase radiative neutron-capture rates relevant for the r-process. The experimental and theoretical status of the upbend is discussed, and preliminary calculations of (n,γ) reaction rates for neutron-rich, mid-mass nuclei including the scissors mode are shown.

• Tveten, Gry Merete; Garrote, Frank Leonel Bello; Campo, Lucia Crespo; Eriksen, Tomas Kvalheim; Giacoppo, Francesca & Guttormsen, Magne Sveen [Vis alle 18 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Guttormsen, Magne Sveen; Aiche, M; Garrote, Frank Leonel Bello; Bernstein, Lee; Bleuel, D.l. & Byun, Y. [Vis alle 27 forfattere av denne artikkelen] (2015). Experimental level densities of atomic nuclei. European Physical Journal A. ISSN 1434-6001. 51(12), s. 1–8. doi: 10.1140/epja/i2015-15170-4. Fulltekst i vitenarkiv
• Kheswa, Bonginkosi Vincent; Wiedeking, Mathis; Giacoppo, Francesca; Goriely, Stephan; Guttormsen, Magne Sveen & Larsen, Ann-Cecilie [Vis alle 19 forfattere av denne artikkelen] (2015). Galactic production of 138La: Impact of 138,139La statistical properties. Physics Letters B. ISSN 0370-2693. 744, s. 268–272. doi: 10.1016/j.physletb.2015.03.065. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Klintefjord, Malin; Hadynska-Klek, Katarzyna; Samorajczyk, J; Görgen, Andreas; Droste, C & Srebrny, J [Vis alle 40 forfattere av denne artikkelen] (2015). Spectroscopy of low-lying states in 140Sm. Acta Physica Polonica B. ISSN 0587-4254. 46(3), s. 607–611. doi: 10.5506/APhysPolB.46.607. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Garrote, Frank Leonel Bello; Görgen, Andreas; Mierzejewski, Jan; Mihai, Corina Mihaela; Delaroche, Jean Paul & Girod, Michel [Vis alle 24 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Moretto, L.G.; Larsen, Ann-Cecilie; Giacoppo, Francesca; Guttormsen, Magne Sveen & Siem, Sunniva (2015). Experimental first order pairing phase transition in atomic nuclei. Journal of Physics: Conference Series (JPCS). ISSN 1742-6588. 580:012048, s. 1–7. doi: 10.1088/1742-6596/580/1/012048. Fulltekst i vitenarkiv Vis sammendrag

  The natural log of experimental nuclear level densities at low energy is linear with energy. This can be interpreted in terms of a nearly 1st order phase transition from a superfluid to an ideal gas of quasi particles. The transition temperature coincides with the BCS critical temperature and yields gap parameters in good agreement with the values extracted from even- odd mass differences from rotational states. This converging evidence supports the relevance of the BCS theory to atomic nuclei.

• Kheswa, Bonginkosi Vincent; Wiedeking, Mathis; Giacoppo, Francesca; Goriely, Stephane; Guttormsen, Magne Sveen & Larsen, Ann-Cecilie [Vis alle 19 forfattere av denne artikkelen] (2015). Statistical nuclear properties and synthesis of La-138. The European Physical Journal Conferences. ISSN 2101-6275. 93. doi: 10.1051/epjconf/20159304005. Fulltekst i vitenarkiv
• Giacoppo, Francesca; Garrote, Frank Leonel Bello; Eriksen, Tomas Kvalheim; Görgen, Andreas; Guttormsen, Magne Sveen & Hagen, Trine Wiborg [Vis alle 16 forfattere av denne artikkelen] (2015). Observation of low-lying resonances in the quasicontinuum of Pt-195,Pt-196 and enhanced astrophysical reaction rates. The European Physical Journal Conferences. ISSN 2101-6275. 93. doi: 10.1051/epjconf/20159301039. Fulltekst i vitenarkiv
• Guttormsen, Magne Sveen; Bernstein, Lee; Görgen, Andreas; Jurado, Beatriz; Siem, Sunniva & Aiche, M [Vis alle 19 forfattere av denne artikkelen] (2014). Scissors resonance in the quasicontinuum of Th, Pa, and U isotopes. Physical Review C. Nuclear Physics. ISSN 0556-2813. 89(014302). doi: 10.1103/PhysRevC.89.014302. Fulltekst i vitenarkiv
• Guttormsen, Magne Sveen; Larsen, Ann-Cecilie; Garrote, Frank Leonel Bello; Eriksen, Tomas Kvalheim; Giacoppo, Francesca & Görgen, Andreas [Vis alle 16 forfattere av denne artikkelen] (2014). Shell-gap-reduced level densities in 89,90Y. Physical Review C. Nuclear Physics. ISSN 0556-2813. 90(044309). doi: 10.1103/PhysRevC.90.044309. Fulltekst i vitenarkiv
• Giacoppo, Francesca; Garrote, Frank Leonel Bello; Bernstein, Lee A.; Bleuel, Darren L.; Firestone, Richard & Görgen, Andreas [Vis alle 16 forfattere av denne artikkelen] (2014). Statistical gamma-ray emission of gold and its astrophysical implications. The European Physical Journal Conferences. ISSN 2101-6275. 66:02041. doi: 10.1051/epjconf/20146602041. Fulltekst i vitenarkiv
• Giacoppo, Francesca; Garrote, Frank Leonel Bello; Bernstein, L. A.; Bleuel, D. L.; Eriksen, Tomas Kvalheim & Firestone, Richard [Vis alle 18 forfattere av denne artikkelen] (2014). Level densities and thermodynamical properties of Pt and Au isotopes. Physical Review C. Nuclear Physics. ISSN 0556-2813. 90(5). doi: 10.1103/PhysRevC.90.054330. Fulltekst i vitenarkiv Vis sammendrag

  The nuclear level densities of 194–196Pt and 197,198Au below the neutron separation energy have been measured using transfer and scattering reactions. All the level density distributions follow the constant-temperature description. Each group of isotopes is characterized by the same temperature above the energy threshold corresponding to the breaking of the first Cooper pair. A constant entropy excess ΔS=1.9kB and 1.1kB is observed in 195Pt and 198Au with respect to 196Pt and 197Au, respectively, giving information on the available single-particle level space for the last unpaired valence neutron. The breaking of nucleon Cooper pairs is revealed by sequential peaks in the microcanonical caloric curve. © 2014 American Physical Society

• Tropea, S; Napoli, M De; Agodi, C; Blancato, A A; Bondi, Marina & Cappuzzello, F [Vis alle 19 forfattere av denne artikkelen] (2014). MEASUREMENT OF FRAGMENT PRODUCTION CROSS SECTIONS IN THE 12C+12C AND 12C+197Au REACTIONS AT 62 A MeV FOR HADRONTHERAPY AND SPACE RADIATION PROTECTION∗. Acta Physica Polonica B. ISSN 0587-4254. 45(2), s. 565–569. doi: 10.5506/APhysPolB.45.565. Fulltekst i vitenarkiv
• Tornyi, Tamas Gabor; Guttormsen, Magne Sveen; Eriksen, Tomas Kvalheim; Görgen, Andreas; Giacoppo, Francesca & Hagen, Trine Wiborg [Vis alle 12 forfattere av denne artikkelen] (2014). Level density and gamma-ray strength function in the odd-odd 238Np nucleus. Physical Review C. Nuclear Physics. ISSN 0556-2813. 89(4). doi: 10.1103/PhysRevC.89.044323. Fulltekst i vitenarkiv
• Ducasse, Quentin; Jurado, Beatriz; Tornyi, Tamas Gabor; Görgen, Andreas; Wilson, J.D. & Giacoppo, Francesca [Vis alle 28 forfattere av denne artikkelen] (2014). Neutron-induced Cross Sections of Actinides via the Surrogate-reaction Method. Nuclear Data Sheets. ISSN 0090-3752. 119, s. 233–233. doi: 10.1016/j.nds.2014.08.064. Fulltekst i vitenarkiv
• Larsen, Ann-Cecilie; Blasi, Nives; Bracco, Angela; Bürger, Arnold; Camera, Franco & Eriksen, Tomas Kvalheim [Vis alle 25 forfattere av denne artikkelen] (2014). Low-energy enhancement of nuclear γ strength and its impact on astrophysical reaction rates. The European Physical Journal Conferences. ISSN 2101-6275. doi: 10.1051/epjconf/20146607014. Fulltekst i vitenarkiv Vis sammendrag

  An unexpected enhancement in the low-energy part of the γ-strength function for light and medium-mass nuclei has been discovered at the Oslo Cyclotron Laboratory. This enhancement could lead to an increase in the neutron-capture rates up to two orders of magnitude for very exotic, neutron-rich nuclei. However, it is still an open question whether this structure persists when approaching the neutron drip line.

• Guttormsen, Magne Sveen; Jurado, Beatriz; Wilson, J. N.; Aiche, M; Bernstein, L. A. & Ducasse, Quentin [Vis alle 19 forfattere av denne artikkelen] (2013). Constant-temperature level densities in the quasicontinuum of Th and U isotopes. Physical Review C. Nuclear Physics. ISSN 0556-2813. 88(2). doi: 10.1103/PhysRevC.88.024307. Fulltekst i vitenarkiv Vis sammendrag

  Particle-γ coincidences have been measured to obtain γ-ray spectra as a function of excitation energy for 231–233Th and 237–239U. The level densities, which were extracted using the Oslo method, show a constant temperature behavior. The isotopes display very similar temperatures in the quasicontinuum, however, the even-odd isotopes reveal a constant entropy increase ΔS compared to their even-even neighbors. The entropy excess depends on available orbitals for the last unpaired valence neutron of the heated nuclear system. Also, experimental microcanonical temperature and heat capacity have been extracted. Several poles in the heat capacity curve support the idea that an almost continuous melting of Cooper pairs is responsible for the constant-temperature behavior. © 2013 American Physical Society

• Ducasse, Q; Jurado, B; Aiche, M; Mathieu, L; Tornyi, Tamas Gabor & Görgen, Andreas [Vis alle 28 forfattere av denne artikkelen] (2013). Neutron-induced cross sections of actinides via the surrogate-reaction method. The European Physical Journal Conferences. ISSN 2101-6275. 42. doi: 10.1051/epjconf/20134201003. Fulltekst i vitenarkiv
• Napoli, M De; Agodi, C; Battistoni, G; Blancato, A A; Cirrone, G A P & Cuttone, G [Vis alle 20 forfattere av denne artikkelen] (2012). Carbon fragmentation measurements and validation of the GEANT4 nuclear reaction models for hadrontherapy. Physics in Medicine and Biology. ISSN 0031-9155. 57(22), s. 7651–7671. doi: 10.1088/0031-9155/57/22/7651. Fulltekst i vitenarkiv

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• Tveten, Gry Merete; Spyrou, Artemis; Schwengner, Ronald; Naqvi, Farheen; Larsen, Ann-Cecilie & Eriksen, Tomas Kvalheim [Vis alle 23 forfattere av denne artikkelen] (2016). The Statistical Properties Of 92Mo And Implications For The p-process. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Tveten, Gry Merete; Campo, L.C.; Eriksen, Tomas Kvalheim; Giacoppo, Francesca; Guttormsen, Magne Sveen & Görgen, Andreas [Vis alle 17 forfattere av denne artikkelen] (2014). The statistical properties of Sn-isotopes studied with the Oslo-method. Fulltekst i vitenarkiv
• Görgen, Andreas; Klintefjord, Malin Linnea; Siem, Sunniva; Giacoppo, Francesca; Hoff, Per & Korten, Wolfram [Vis alle 14 forfattere av denne artikkelen] (2012). Shape transition and coexistence in neutron-deficient rare earth nuclei: Coulomb excitation of 140Sm. Fulltekst i vitenarkiv

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