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• Gheorghe, I.; Ari-Izumi, T.; Goriely, S.; Filipescu, D.; Belyshev, S. & Stopani, K. [Vis alle 15 forfattere av denne artikkelen] (2025). Photoneutron reactions on gold in the giant dipole resonance region: Reaction cross sections and average kinetic energies of (γ,xn) photoneutrons. Physical Review C. ISSN 2469-9985. 111(1). doi: 10.1103/PhysRevC.111.014611. Fulltekst i vitenarkiv
• Utsunomiya, H.; Goriely, S.; Kimura, M.; Shimizu, N.; Utsuno, Y. & Tveten, Gry Merete [Vis alle 9 forfattere av denne artikkelen] (2024). Photoneutron emission cross sections for C 13. Physical Review C. ISSN 2469-9985. 109(1). doi: 10.1103/PhysRevC.109.014617. Fulltekst i vitenarkiv Vis sammendrag

  Photoneutron emission cross sections were measured for 13 C below 2⁢𝑛 threshold using quasimonochromatic 𝛾-ray beams produced in laser Compton scattering at the NewSUBARU synchrotron radiation facility. The data show fine structures in the low-energy tail of the giant-dipole resonance; the integrated strength of the fine structure below 18 MeV is intermediate among the past measurements with bremsstrahlung and the positron annihilation 𝛾 rays. We compare the photoneutron emission data with the talys statistical model calculation implemented with the simple modified Lorentzian model of 𝐸⁢1 and 𝑀⁢1 strengths. We also compare the total photoabsorption cross sections for 13 C with shell model and antisymmetrized molecular dynamics calculations as well as the statistical model calculation. We further investigate the consistency between the present photoneutron emission and the reverse 12C(𝑛,𝛾) cross sections through their corresponding astrophysical rate.

• Lewis, R.; Couture, A.; Liddick, S.N.; Spyrou, A.; Bleuel, D.L. & Campo, Lucia Crespo [Vis alle 18 forfattere av denne artikkelen] (2023). Statistical (n, γ) cross section model comparison for short-lived nuclei. European Physical Journal A. ISSN 1434-6001. 59(3). doi: 10.1140/epja/s10050-023-00920-0. Fulltekst i vitenarkiv Vis sammendrag

  Neutron-capture cross sections of neutron-rich nuclei are calculated using a Hauser–Feshbach model when direct experimental cross sections cannot be obtained. A number of codes to perform these calculations exist, and each makes different assumptions about the underlying nuclear physics. We investigated the systematic uncertainty associated with the choice of Hauser-Feshbach code used to calculate the neutron-capture cross section of a short-lived nucleus. The neutron-capture cross section for 73Zn(n,y)74Zn was calculated using three Hauser-Feshbach statistical model codes: TALYS, CoH, and EMPIRE. The calculation was first performed without any changes to the default settings in each code. Then an experimentally obtained nuclear level density (NLD) and y-ray strength function (ySF) were included. Finally, the nuclear structure information was made consistent across the codes. The neutron-capture cross sections obtained from the three codes are in good agreement after including the experimentally obtained NLD and ySF, accounting for differences in the underlying nuclear reaction models, and enforcing consistent approximations for unknown nuclear data. It is possible to use consistent inputs and nuclear physics to reduce the differences in the calculated neutron-capture cross section from different Hauser-Feshbach codes. However, ensuring the treatment of the input of experimental data and other nuclear physics are similar across multiple codes requires a careful investigation. For this reason, more complete documentation of the inputs and physics chosen is important.

• 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.

• Larsen, Ann-Cecilie; Tveten, Gry Merete; Renstrøm, Therese; Utsunomiya, H.; Algin, E. & Ari-Izumi, T. [Vis alle 31 forfattere av denne artikkelen] (2023). New experimental constraint on the W 185 (n,γ) W 186 cross section. Physical Review C. ISSN 2469-9985. 108(2). doi: 10.1103/PhysRevC.108.025804. Fulltekst i vitenarkiv
• Naqvi, F.; Karampagia, S.; Spyrou, A.; Liddick, S.N.; Dombos, A.C. & Bleuel, D.l. [Vis alle 20 forfattere av denne artikkelen] (2022). Total absorption spectroscopy measurement on neutron-rich 74,75Cu isotopes. Nuclear Physics A. ISSN 0375-9474. A1018(122359). doi: 10.1016/j.nuclphysa.2021.122359. Fulltekst i vitenarkiv
• 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.

• Guttormsen, Magne Sveen; Ay, Kursad Osman; Ozgur, Mustafa; Algin, Emel; Larsen, Ann-Cecilie & Garrote, Frank Leonel Bello [Vis alle 26 forfattere av denne artikkelen] (2022). Evolution of the γ -ray strength function in neodymium isotopes. Physical Review C. ISSN 2469-9985. 106(3). doi: 10.1103/PhysRevC.106.034314. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Persch, C.F.; DeYoung, P.A.; Lyons, S.; Spyrou, Artemis; Liddick, Sean N. & Naqvi, F. [Vis alle 27 forfattere av denne artikkelen] (2021). Beta-decay feeding intensity distributions of 71,73Ni. Physical Review C. ISSN 2469-9985. C103(055808). doi: 10.1103/PhysRevC.103.055808. Fulltekst i vitenarkiv Vis sammendrag

  This paper presents the β-decay feeding intensity distribution and Gamow-Teller transition strength distribution of 71,73Ni. These quantities were measured using the technique of total absorption spectroscopy at the National Superconducting Cyclotron Laboratory with the Summing NaI(Tl) detector. These measurements provide sensitive constraints to theoretical models used to predict β-decay properties far from stability for astrophysical applications. Specifically, for the astrophysical r process, the majority of the involved nuclei are not accessible by current facilities, and the nuclear input is mainly provided by theory. The present work reports on two neutron-rich nickel isotopes in the region where the weak r process is expected to be relevant in stellar nucleosynthesis. The experimental results are compared to two theoretical models, namely the shell model and the quasiparticle random-phase approximation, to help further refine theoretical calculations and aid in future r-process studies.

• Guttormsen, Magne Sveen; Alhassid, Yoram; Ryssens, Wouter; Ay, K.o.; Ozgur, Mustafa & Algin, Emel [Vis alle 22 forfattere av denne artikkelen] (2021). Strong enhancement of level densities in the crossover from spherical to deformed neodymium isotopes. Physics Letters B. ISSN 0370-2693. 816. doi: 10.1016/j.physletb.2021.136206. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Malatji, Kgashane Leroy; Beckmann, Kristine Sønstevold; Wiedeking, Mathis; Siem, Sunniva; Goriely, Stephane & Larsen, Ann-Cecilie [Vis alle 21 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Midtbø, Jørgen E.; Zeiser, Fabio; Lima, Erlend; Larsen, Ann-Cecilie; Tveten, Gry Merete & Guttormsen, Magne Sveen [Vis alle 9 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• 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.

• Kawano, T.; Cho, Y.S.; Dimitriou, Paraskevi; Filipescu, D. M.; Iwamoto, N. & Plujko, V. [Vis alle 28 forfattere av denne artikkelen] (2020). IAEA Photonuclear Data Library 2019. Nuclear Data Sheets. ISSN 0090-3752. 163, s. 109–162. doi: 10.1016/j.nds.2019.12.002. Fulltekst i vitenarkiv
• Utsunomiya, Hiroaki; Renstrøm, Therese; Tveten, Gry Merete; Goriely, Stéphane; Ari-izumi, Takashi & Ingeberg, Vetle Wegner [Vis alle 12 forfattere av denne artikkelen] (2019). γ-ray strength function for barium isotopes. Physical Review C. ISSN 2469-9985. 100(3), s. 034605-1–034605-7. doi: 10.1103/PhysRevC.100.034605. Fulltekst i vitenarkiv Vis sammendrag

  Photoneutron cross sections were measured for 137 Ba and 138 Ba at energies below two-neutron threshold using quasimonochromatic γ -ray beams produced in laser Compton scattering at the NewSUBARU synchrotron radiation facility. The photoneutron data are used to constrain the γ -ray strength function on the basis of the Hartree-Fock-Bogolyubov plus quasiparticle random phase approximation using the Gogny D1M interaction. Supplementing the experimentally constrained γ -ray strength function with the zero-limit E1 and M1 contributions, which are unique to the deexcitation mode, we discuss radiative neutron capture cross sections relevant to the s-process nucleosynthesis of barium isotopes in the vicinity of the neutron magic number 82.

• Kullmann, Ina Kristine Berentsen; Larsen, Ann-Cecilie; Renstrøm, Therese; Beckmann, Kristine Sønstevold; Garrote, Frank Leonel Bello & Campo, Lucia Crespo [Vis alle 13 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Lyons, Stephanie; Spyrou, Artemis; Liddick, Sean N.; Naqvi, Farheen; Crider, Benjamin P. & Dombos, Alexander C. [Vis alle 25 forfattere av denne artikkelen] (2019). 69,71Co β-decay strength distributions from total absorption spectroscopy. Physical Review C. ISSN 2469-9985. 100(2), s. 1–10. doi: 10.1103/PhysRevC.100.025806. Fulltekst i vitenarkiv Vis sammendrag

  Background: The rapid neutron capture process is one of the main nucleosynthesis processes of elements heavier than Fe. Uncertainties in nuclear properties, such as masses, half-lives, and β -delayed neutron probabilities can cause orders of magnitude of variation within astrophysical r-process simulations. Presently, theoretical models are used to make global predictions of various nuclear properties for the thousands of nuclei required for these simulations, and measurements are required to benchmark these models, especially far from stability. Purpose: β -decay strength distributions can be used to not only inform astrophysical r-process simulations, but also to provide a stringent test for theoretical calculations. The aim of this work is to provide accurate strength distributions for 69 , 71 Co β decay. Method: The technique of total absorption spectroscopy was used to measure the β decay of 69 , 71 Co for the first time at the National Superconducting Cyclotron Laboratory. The ions were implanted in a double-sided silicon strip detector at the center of the Summing NaI(Tl) detector and identified using standard particle identification methods. The response of the detection system to the β -decay electron and subsequent γ -ray radiation was fit to the observed experimental data using a χ 2 -minimization technique. Results: β -feeding intensities and Gamow-Teller strength distributions were extracted from the fits of the experimental data. The β -decay intensities show that there is a large percentage of feeding to levels above 2 MeV, which have not been observed in previous studies. The resultant β -feeding intensities and Gamow-Teller strength distributions were compared to shell model and quasiparticle random phase approximation (QRPA) calculations. Conclusions: Comparing experimentally determined β -decay strength distributions provides a test of models, which are commonly used for global β -decay properties for astrophysical calculations. This work highlights the importance of performing detailed comparisons of models to experimental data, particularly far from stability and as close to the r-process path as possible.

• Larsen, Ann-Cecilie; Liddick, Sean N.; Spyrou, Artemis; Guttormsen, Magne Sveen; Garrote, Frank Leonel Bello & Midtbø, Jørgen E. [Vis alle 7 forfattere av denne artikkelen] (2019). The Beta-Oslo Method: ExperimentallyConstrained (n,γ) Reaction RatesRelevant to ther-Process. I Formicola, Alba; Junker, Matthias; Gialanella, Lucio & Imbriani, Gianluca (Red.), Nuclei in the Cosmos XV. Springer. ISSN 9783030138752. s. 137–140. doi: 10.1007/978-3-030-13876-9_22. Fulltekst i vitenarkiv
• Voinov, Alexander; Renstrøm, Therese; Bleuel, D.l.; Grimes, S.M.; Guttormsen, Magne Sveen & Larsen, Ann-Cecilie [Vis alle 23 forfattere av denne artikkelen] (2019). Level densities of 74,76Ge from compound nuclear reactions. Physical Review C. ISSN 2469-9985. 99(5). doi: 10.1103/PhysRevC.99.054609. Fulltekst i vitenarkiv Vis sammendrag

  The level densities of 74 , 76 Ge nuclei are studied with 68 , 70 Zn ( 7 Li , Xp ) reactions. Proton evaporation spectra are measured at backward angles in a wide energy region, from about 2 to 25 MeV. The analysis of spectra allows for the testing of level density models used in modern reaction codes for practical cross-section calculations. Our results show that at excitation energies above the discrete level region, all level density models tested in this work overestimate the level densities that are needed to reproduce proton spectra from these reactions. The Gilbert and Cameron model, which includes the constant-temperature energy dependence of the level density, shows the best agreement with experiment, however, its parameters need to be adjusted to reflect the observed reduction of the level density at higher excitation energies.

• 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 .

• Midtbø, Jørgen E.; Larsen, Ann-Cecilie; Renstrøm, Therese; Garrote, Frank Leonel Bello & Lima, Erlend (2019). Systematic Low-Energy Enhancementof the Gamma-Ray Strength Function. I Formicola, Alba; Junker, Matthias; Gialanella, Lucio & Imbriani, Gianluca (Red.), Nuclei in the Cosmos XV. Springer. ISSN 9783030138752. s. 405–407. doi: 10.1007/978-3-030-13876-9. Fulltekst i vitenarkiv
• Utsunomiya, Hiroaki; Renstrøm, Therese; Tveten, Gry Merete; Goriely, Stéphane; Ari-izumi, Takashi & Filipescu, Dan Mihai [Vis alle 14 forfattere av denne artikkelen] (2019). γ-ray strength function for thallium isotopes relevant to the 205Pb−205Tl chronometry. Physical Review C. ISSN 2469-9985. 99(2), s. 024609-1–023609-8. doi: 10.1103/PhysRevC.99.024609. Fulltekst i vitenarkiv Vis sammendrag

  Photoneutron cross sections were measured for 203Tl and 205Tl at energies between the one- and two-neutron thresholds using quasimonochromatic γ -ray beams produced in laser Compton scattering at the NewSUBARU synchrotron radiation facility. Our measurement results in cross sections significantly different from the previously reported bremsstrahlung experiment, leading to rather different giant dipole resonance (GDR) parameters, in particular to lower GDR peak energies and higher peak cross sections. The photoneutron data are used to constrain the γ -ray strength function on the basis of the Hartree-Fock-Bogolyubov plus quasiparticle random-phase approximation using the Gogny D1M interaction. Supplementing the experimentally constrained γ -ray strength function with the zero-limit E1 and M1 contributions for the de-excitation mode, we estimate the Maxwellian-averaged cross section for the s-process branching-point nucleus 204Tl in the context of the 205Pb-205Tl chronometry.

• 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.

• Guttormsen, Magne Sveen; Goriely, Stephane; Larsen, Ann-Cecilie; Görgen, Andreas; Hagen, Trine Wiborg & Renstrøm, Therese [Vis alle 13 forfattere av denne artikkelen] (2019). Indirect(n,γ)91,92Zr Cross SectionMeasurements for the s-Process. I Formicola, Alba; Junker, Matthias; Gialanella, Lucio & Imbriani, Gianluca (Red.), Nuclei in the Cosmos XV. Springer. ISSN 9783030138752. s. 359–362. doi: 10.1007/978-3-030-13876-9_65. Fulltekst i vitenarkiv
• Krzysiek, Mateusz; Utsunomiya, Hiroaki; Gheorghe, Ioana; Filipescu, Dan Mihai; Renstrøm, Therese & Tveten, Gry Merete [Vis alle 19 forfattere av denne artikkelen] (2019). Photoneutron cross-section measurements for 165HO by the direct neutron-multiplicity sorting at Newsubaru. Acta Physica Polonica B. ISSN 0587-4254. 50(3), s. 487–494. doi: 10.5506/APhysPolB.50.487. Fulltekst i vitenarkiv
• 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
• Lewis, Rebecca; Liddick, Sean N.; Larsen, Ann-Cecilie; Spyrou, Artemis; Bleuel, Darren L. & Couture, Aaron J. [Vis alle 17 forfattere av denne artikkelen] (2019). Experimental constraints on the 73Zn(n,γ)74Zn reaction rate. Physical Review C. ISSN 2469-9985. 99(3). doi: 10.1103/PhysRevC.99.034601. Fulltekst i vitenarkiv Vis sammendrag

  Background: The recent observation of a neutron-star merger finally confirmed one astrophysical location of the rapid neutron-capture process (r-process). Evidence of the production of A < 140 nuclei was seen, but there is still little detailed information about how those lighter elements are produced in such an environment. Many of the questions surrounding the A ≈ 80 nuclei are likely to be answered only when the nuclear physics involved in the production of r-process nuclei is well understood. Neutron-capture reactions are an important component of the r-process, and neutron-capture cross sections of r-process nuclei, which are very neutron rich, have large uncertainties. Purpose: Indirectly determine the neutron-capture cross section and reaction rate of 73Zn(n, γ ) 74Zn. Methods: The nuclear level density (NLD) and γ -ray strength function (γ SF) of 74Zn were determined following a total absorption spectroscopy (TAS) experiment focused on the β decay of 74Cu into 74Zn performed at the National Superconducting Cyclotron Laboratory. The NLD and γ SF were used as inputs in a Hauser-Feshbach statistical model to calculate the neutron-capture cross section and reaction rate. Results: The NLD and γ SF of 74Zn were experimentally constrained for the first time using β-delayed γ rays measured with TAS and the β-Oslo method. The NLD and γ SF were then used to constrain the neutron-capture cross section and reaction rate for the 73Zn(n, γ ) 74Zn reaction. Conclusions: The uncertainty in the neutron-capture cross section and reaction rate of 73Zn(n, γ ) 74Zn calculated in TALYS was reduced to under a factor of 2 from a factor of 5 in the cross section and a factor of 11 in the reaction rate using the experimentally obtained NLD and γ SF.

• Garrote, Frank Leonel Bello; Görgen, Andreas; Mihai, C.; Abraham, T.; Campo, Lucia Crespo & Delaroche, Jean Paul [Vis alle 34 forfattere av denne artikkelen] (2018). Lifetime measurements in 138Nd. Physical Review C. ISSN 2469-9985. 97(6), s. 1–7. doi: 10.1103/PhysRevC.97.064310. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Utsunomiya, Hiroaki; Watanabe, Takahumi; Ari-izumi, Takashi; Takenaka, Daiki; Araki, Takeru & Tsuji, Kazuya [Vis alle 18 forfattere av denne artikkelen] (2018). Photon-flux determination by the Poisson-fitting technique with quenching corrections. Nuclear Instruments and Methods in Physics Research Section A : Accelerators, Spectrometers, Detectors and Associated Equipment. ISSN 0168-9002. 896, s. 103–107. doi: 10.1016/j.nima.2018.04.021. Fulltekst i vitenarkiv Vis sammendrag

  Single- and multi-photon spectra of pulsed -ray beams produced at 17, 34, and 40 MeV in the laser Compton scattering were measured with an 8” 12” NaI(Tl) detector. By using the experimental single-photon spectra as the probability function of generating random numbers, response functions of the NaI(Tl) detector to -fold photons ( = 2, 3, 4 ...) were constructed. The least-square fits to the experimental multi-photon spectra by the Poisson distribution consisting of the response functions were made. The multi-photon spectra measured at 17 and 34 MeV follow the Poisson distribution. A quenching phenomenon of multi-photon spectra was observed for 40 MeV -rays as a result of the saturation at the photomultiplier tube of the NaI(Tl) detector. The original Poisson distributions were restored from the quenched spectra using a saturation curve in the form of with =e. We discuss the accuracy of photon-flux determination.

• Utsunomiya, Hiroaki; Renstrøm, Therese; Tveten, Gry Merete; Goriely, Stéphane; Katayama, Seitaro & Ari-Izumi, Takashi [Vis alle 22 forfattere av denne artikkelen] (2018). Photoneutron cross sections for Ni isotopes: Toward understanding (n, γ ) cross sections relevant to weak s-process nucleosynthesis. Physical Review C. ISSN 2469-9985. 98(5), s. 1–9. doi: 10.1103/PhysRevC.98.054619. Fulltekst i vitenarkiv Vis sammendrag

  Photoneutron cross sections were measured for 58Ni, 60Ni, 61Ni, and 64Ni at energies between the one-neutron and two-neutron thresholds using quasimonochromatic γ -ray beams produced in laser Compton scattering at the NewSUBARU synchrotron radiation facility. These photoneutron data are used to extract the γ -ray strength function above the neutron threshold, complementing the information obtained by the Oslo method below the threshold. We discuss radiative neutron-capture cross sections and the Maxwellian-averaged cross sections for Ni isotopes including 63Ni, a branching point nucleus along the weak s-process path. The cross sections are calculated with the experimentally constrained γ-ray strength functions from the Hartree-Fock-Bogolyubov plus quasiparticle–random-phase approximation based on the Gogny D1M interaction for both E1 and M1 components and supplemented with the M1 upbend.

• 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), s. 064321-1–064321-12. doi: 10.1103/PhysRevC.98.064321. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Larsen, Ann-Cecilie; Midtbø, Jørgen E.; Guttormsen, Magne Sveen; Renstrøm, Therese; Liddick, Sean N. & Spyrou, Artemis [Vis alle 22 forfattere av denne artikkelen] (2018). Enhanced low-energy γ-decay strength of 70Ni and its robustness within the shell model. Physical Review C. ISSN 2469-9985. 97(5), s. 1–9. doi: 10.1103/PhysRevC.97.054329. Fulltekst i vitenarkiv Vis sammendrag

  Neutron-capture reactions on very neutron-rich nuclei are essential for heavy-element nucleosynthesis through the rapid neutron-capture process, now shown to take place in neutron-star merger events. For these exotic nuclei, radiative neutron capture is extremely sensitive to their γ -emission probability at very low γ energies. In this work, we present measurements of the γ -decay strength of 70Ni over the wide range 1.3 Eγ 8 MeV. A significant enhancement is found in the γ -decay strength for transitions with Eγ < 3 MeV. At present, this is the most neutron-rich nucleus displaying this feature, proving that this phenomenon is not restricted to stable nuclei. We have performed E1-strength calculations within the quasiparticle time-blocking approximation, which describe our data above Eγ 5 MeV very well. Moreover, large-scale shell-model calculations indicate an M1 nature of the low-energy γ strength. This turns out to be remarkably robust with respect to the choice of interaction, truncation, and model space, and we predict its presence in the whole isotopic chain, in particular the neutron-rich 72,74,76Ni.

• Guttormsen, Magne Sveen; Larsen, Ann-Cecilie; Midtbø, Jørgen E.; Campo, Lucia Crespo; Görgen, Andreas & Ingeberg, Vetle Wegner [Vis alle 11 forfattere av denne artikkelen] (2018). Gamma-widths, lifetimes and fluctuations in the nuclear quasi-continuum. The European Physical Journal Conferences. ISSN 2101-6275. 178(06001). doi: 10.1051/epjconf/201817806001. Fulltekst i vitenarkiv Vis sammendrag

  Statistical γ-decay from highly excited states is determined by the nuclear level density (NLD) and the γ-ray strength function (γSF). These average quantities have been measured for several nuclei using the Oslo method. For the first time, we exploit the NLD and γSF to evaluate the γ-width in the energy region below the neutron binding energy, often called the quasi-continuum region. The lifetimes of states in the quasi-continuum are important benchmarks for a theoretical description of nuclear structure and dynamics at high temperature. The lifetimes may also have impact on reaction rates for the rapid neutron-capture process, now demonstrated to take place in neutron star mergers.

• 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.

• Renstrøm, Therese; Utsunomiya, H.; Nyhus, Hilde-Therese; Larsen, Ann-Cecilie; Guttormsen, Magne Sveen & Tveten, Gry Merete [Vis alle 16 forfattere av denne artikkelen] (2018). Verification of detailed balance for γ absorption and emission in Dy isotopes. Physical Review C. ISSN 2469-9985. 98(5), s. 1–14. doi: 10.1103/PhysRevC.98.054310. Fulltekst i vitenarkiv Vis sammendrag

  The photoneutron cross sections of 162,163Dy have been measured for the first time in an energy region from the neutron threshold (Sn) up to ≈13MeV. The (γ,n) reaction was induced with quasimonochromatic laser Compton-scattered γ rays, produced at the NewSUBARU laboratory. The corresponding γ -ray strength functions (γ SF) have been calculated from the photoneutron cross sections. The data are compared to reanalyzed γSFs of 160–164Dy, which are measured below Sn. The excellent agreement with the photoneutron data at Sn confirms the principle of detailed balance. Thus, a complete γ SF is established covering in total the energy regionof1 Eγ 13MeV.Thesemid-shellwell-deformeddysprosiumisotopesallshowscissorsresonances with very similar structures. We find that our data predict the same integrated scissors strength as (γ,γ′) data when integrated over the same energy range, which shows that the scissors mode very likely is consistent with the generalized Brink hypothesis. Finally, using the γSFs as input in the reaction code TALYS, we have deduced radiative neutron-capture cross sections and compared them to direct measurements. We find a very good agreement within the uncertainties, which gives further support to the experimentally determined γ SFs.

• Utsunomiya, Hiroaki; Renstrøm, Therese; Tveten, Gry Merete; Gheorghe, Ioana; Filipescu, Dan Mihai & Belyshev, Sergey [Vis alle 22 forfattere av denne artikkelen] (2018). Photoneutron Reaction Data for Nuclear Physics and Astrophysics. The European Physical Journal Conferences. ISSN 2101-6275. 178. doi: 10.1051/epjconf/201817806003. Fulltekst i vitenarkiv Vis sammendrag

  We discuss the role of photoneutron reaction data in nuclear physics and astrophysics in conjunction with the Coordinated Research Project of the International Atomic Energy Agency with the code F41032 (IAEA-CRP F41032).

• Brits, C.P.; Wiedeking, M.; Garrote, Frank Leonel Bello; Bleuel, D. L.; Giacoppo, F. & Görgen, Andreas [Vis alle 22 forfattere av denne artikkelen] (2017). Resonances in odd-odd 182Ta. The European Physical Journal Conferences. ISSN 2101-6275. 146. doi: 10.1051/epjconf/201714605012. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Larsen, Ann-Cecilie; Guttormsen, Magne Sveen; Blasi, Nives; Bracco, Angela; Camera, Franco & Campo, Lucia Crespo [Vis alle 24 forfattere av denne artikkelen] (2017). Low-energy enhancement and fluctuations of γ-ray strength functions in 56,57Fe: test of the Brink–Axel hypothesis. Journal of Physics G: Nuclear and Particle Physics. ISSN 0954-3899. 44(6). doi: 10.1088/1361-6471/aa644a. Fulltekst i vitenarkiv Vis sammendrag

  Nuclear level densities and γ-ray strength functions of 56,57Fe have been extracted from proton-γ coincidences. A low-energy enhancement in the γ-ray strength functions up to a factor of 30 over common theoretical E1 models is confirmed. Angular distributions of the low-energy enhancement in 57Fe indicate its dipole nature, in agreement with findings for 56Fe. The high statistics and the excellent energy resolution of the large-volume LaBr3(Ce) detectors allowed for a thorough analysis of γ strength as function of excitation energy. Taking into account the presence of strong Porter–Thomas fluctuations, there is no indication of any significant excitation energy dependence in the γ-ray strength function, in support of the generalized Brink–Axel hypothesis. This research was first published in Journal of Physics G: Nuclear and Particle Physics. © IOP Publishing.

• Utsunomiya, Hiroaki; Goriely, Stephane; Renstrøm, Therese; Katayama, Seitaro; Gheorghe, Ioana & Filipescu, Dan [Vis alle 8 forfattere av denne artikkelen] (2017). A unified understanding of (?, n) and (n, ?) reactions and direct neutron-multiplicity sorting. The European Physical Journal Conferences. ISSN 2101-6275. 146. doi: 10.1051/epjconf/201714605002. 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.

• Guttormsen, Magne Sveen; Goriely, Stephan; Larsen, Ann-Cecilie; Görgen, Andreas; Hagen, Trine Wiborg & Renstrøm, Therese [Vis alle 13 forfattere av denne artikkelen] (2017). Quasicontinuum γ decay of 91,92Zr: Benchmarking indirect (n,γ ) cross section measurements for the s process. Physical Review C. ISSN 2469-9985. 96(2). doi: 10.1103/PhysRevC.96.024313. Fulltekst i vitenarkiv Vis sammendrag

  Nuclear level densities (NLDs) and γ-ray strength functions (γSFs) have been extracted from particle-γ coincidences of the 92Zr(p,p′γ)92Zr and 92Zr(p,dγ)91Zr reactions using the Oslo method. The new 91,92ZrγSF data, combined with photonuclear cross sections, cover the whole energy range from Eγ≈1.5MeV up to the giant dipole resonance at Eγ≈17 MeV. The wide-range γSF data display structures at Eγ≈9.5 MeV, compatible with a superposition of the spin-flip M1 resonance and a pygmy E1 resonance. Furthermore, the γSF shows a minimum at Eγ≈2–3MeV and an increase at lower γ-ray energies. The experimentally constrained NLDs and γSFs are shown to reproduce known (n,γ) and Maxwellian-averaged cross sections for 91,92Zr using the talys reaction code, thus serving as a benchmark for this indirect method of estimating (n,γ) cross sections for Zr isotopes. This research was originally published in Physical Review C - Nuclear Physics. © American Physical Society

• 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.

• Larsen, Ann-Cecilie; Spyrou, Artemis; Liddick, Sean N.; Guttormsen, Magne Sveen; Ingeberg, Vetle Wegner & Siem, Sunniva [Vis alle 25 forfattere av denne artikkelen] (2017). Novel Techniques for Constraining Neutron-capture Rates relevant to Heavy-element Nucleosynthesis. Proceedings of Science (PoS). INPC2016. doi: 10.22323/1.281.0360. Fulltekst i vitenarkiv Vis sammendrag

  In this contribution we discuss new experimental approaches to indirectly provide information on neutron-capture rates relevant to the r-process. In particular, we focus on applications of the Oslo method to extract fundamental nuclear properties for reaction-rate calculations: the nuclear level density and the γ strength function. Two methods are discussed in detail, the Oslo method in inverse kinematics and the beta-Oslo method. These methods present a first step towards constraining neutron-capture rates of importance to the r-process.

• Spyrou, Artemis; Larsen, Ann-Cecilie; Liddick, Sean N.; Naqvi, Farheen; Crider, Benjamin P. & Dombos, Alexander C. [Vis alle 19 forfattere av denne artikkelen] (2017). Neutron-capture rates for explosive nucleosynthesis: the case of 68Ni(n, γ)69Ni. Journal of Physics G: Nuclear and Particle Physics. ISSN 0954-3899. 44. doi: 10.1088/1361-6471/aa5ae7. Fulltekst i vitenarkiv Vis sammendrag

  Neutron-capture reactions play an important role in heavy element nucleosynthesis, since they are the driving force for the two processes that create the vast majority of the heavy elements. When a neutron capture occurs on a short-lived nucleus, it is extremely challenging to study the reaction directly and therefore the use of indirect techniques is essential. The present work reports on such an indirect measurement that provides strong constraints on the 68Ni(n, γ)69Ni reaction rate. This is done by populating the compound nucleus 69Ni via the β decay of 69Co and measuring the γ-ray deexcitation of excited states in 69Ni. The β-Oslo method was used to extract the γ-ray strength function and the nuclear level density. In addition the half-life of 69Co was extracted and found to be in agreement with previous literature values. Before the present results, the 68Ni(n, γ)69Ni reaction was unconstrained and the purely theoretical reaction rate was highly uncertain. The new uncertainty on the reaction rate based on the present experiment (variation between upper and lower limit) is approximately a factor of 3. The commonly used reaction libraries JINA-REACLIB and BRUSLIB are in relatively good agreement with the experimental rate. The impact of the new rate on weak r-process calculations is discussed. This research was first published in Journal of Physics G: Nuclear and Particle Physics. © IOP Publishing.

• Guttormsen, Magne Sveen; Larsen, Ann-Cecilie; Görgen, Andreas; Renstrøm, Therese; Siem, Sunniva & Tornyi, Tamas Gabor [Vis alle 7 forfattere av denne artikkelen] (2016). Is the generalized Brink-Axel hypothesis valid? Proceedings of Science (PoS). 2016-September, s. 1–8. doi: 10.22323/1.281.0062. Fulltekst i vitenarkiv Vis sammendrag

  Experimental results of the 237Np(d, pγ) 238Np reaction are presented, which verifies the generalized Brink-Axel (gBA) hypothesis for γ transitions between states in the quasi-continuum. The gBA hypothesis holds not only for specific collective resonances, but for the full dipole strength below the neutron separation energy. We discuss the validity of the gBA hypothesis also for lighter systems like 92Zr where the concept of a unique γ-ray strength function (γSF) is problematic due to large Porter-Thomas fluctuations. Methods for studying the γSF and the fluctuations as function of excitation energy are presented.

• Campo, Lucia Crespo; Garrote, Frank Leonel Bello; Eriksen, Tomas Kvalheim; Görgen, Andreas; Guttormsen, Magne Sveen & Hadynska-Klek, Katarzyna [Vis alle 14 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Ay, K.o.; Ozgur, Mustafa; Algin, Emel; Guttormsen, Magne Sveen; Garrote, Frank Leonel Bello & Campo, Lucia Crespo [Vis alle 20 forfattere av denne artikkelen] (2016). Nuclear level densities and gamma-ray strength functions of 145,149,151Nd isotopes. Journal of Physics: Conference Series (JPCS). ISSN 1742-6588. 766(012027). doi: 10.1088/1742-6596/766/1/012027. 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 &lt;sup&gt;237&lt;/sup&gt;U and &lt;sup&gt;239&lt;/sup&gt;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.

• Spyrou, Artemis; Liddick, Sean N.; Naqvi, Farheen; Crider, Benjamin P.; Dombos, Alexander C. & Bleuel, Darren L. [Vis alle 21 forfattere av denne artikkelen] (2016). Strong Neutron-γ Competition above the Neutron Threshold in the Decay of 70Co. Physical Review Letters. ISSN 0031-9007. 117(14). doi: 10.1103/PhysRevLett.117.142701. Fulltekst i vitenarkiv Vis sammendrag

  The β-decay intensity of 70Co was measured for the first time using the technique of total absorption spectroscopy. The large β-decay Q value [12.3(3) MeV] offers a rare opportunity to study β-decay properties in a broad energy range. Two surprising features were observed in the experimental results, namely, the large fragmentation of the β intensity at high energies, as well as the strong competition between γ rays and neutrons, up to more than 2 MeV above the neutron-separation energy. The data are compared to two theoretical calculations: the shell model and the quasiparticle random phase approximation (QRPA). Both models seem to be missing a significant strength at high excitation energies. Possible interpretations of this discrepancy are discussed. The shell model is used for a detailed nuclear structure interpretation and helps to explain the observed γ-neutron competition. The comparison to the QRPA calculations is done as a means to test a model that provides global β-decay properties for astrophysical calculations. Our work demonstrates the importance of performing detailed comparisons to experimental results, beyond the simple half-life comparisons. A realistic and robust description of the β-decay intensity is crucial for our understanding of nuclear structure as well as of r-process nucleosynthesis.

• Clément, Emmanuel; Zielińska, Magdalena; Görgen, Andreas; Körten, Wolfram; Péru, Sophie & Libert, Jacques J. [Vis alle 51 forfattere av denne artikkelen] (2016). Spectroscopic Quadrupole Moments in Sr 96,98: Evidence for Shape Coexistence in Neutron-Rich Strontium Isotopes at N=60. Physical Review Letters. ISSN 0031-9007. 116:022701(2). doi: 10.1103/PhysRevLett.116.022701. Fulltekst i vitenarkiv Vis sammendrag

  Neutron-rich 96;98Sr isotopes have been investigated by safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility. Reduced transition probabilities and spectroscopic quadrupole moments have been extracted from the differential Coulomb excitation cross sections. These results allow, for the first time, the drawing of definite conclusions about the shape coexistence of highly deformed prolate and spherical configurations. In particular, a very small mixing between the coexisting states is observed, contrary to other mass regions where strong mixing is present. Experimental results have been compared to beyond-mean-field calculations using the Gogny D1S interaction in a five-dimensional collective Hamiltonian formalism, which reproduce the shape change at N ¼ 60.

• Larsen, Ann-Cecilie; Spyrou, Artemisia; Liddick, Sean N.; Guttormsen, Magne Sveen; Ingeberg, Vetle Wegner & Siem, Sunniva [Vis alle 25 forfattere av denne artikkelen] (2016). Novel techniques for constraining neutron-capture rates relevant to heavy-element nucleosynthesis. Proceedings of Science (PoS). 2016-September:360, s. 1–9. Fulltekst i vitenarkiv Vis sammendrag

  In this contribution we discuss new experimental approaches to indirectly provide information on neutron-capture rates relevant to the r-process. In particular, we focus on applications of the Oslo method to extract fundamental nuclear properties for reaction-rate calculations: the nuclear level density and the γ strength function. Two methods are discussed in detail, the Oslo method in inverse kinematics and the beta-Oslo method. These methods present a first step towards constraining neutron-capture rates of importance to the r-process.

• 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.

• Guttormsen, Magne Sveen; Larsen, Ann-Cecilie; Görgen, Andreas; Renstrøm, Therese; Siem, Sunniva & Tornyi, Tamas Gabor [Vis alle 7 forfattere av denne artikkelen] (2016). Validity of the Generalized Brink-Axel Hypothesis in Np 238. Physical Review Letters. ISSN 0031-9007. 116(1). doi: 10.1103/PhysRevLett.116.012502. Fulltekst i vitenarkiv Vis sammendrag

  We analyze primary γ-ray spectra of the odd-odd 238Np nucleus extracted from 237Npðd; pγÞ238Np coincidence data measured at the Oslo Cyclotron Laboratory. The primary γ spectra cover an excitationenergy region of 0 ≤ Ei ≤ 5.4 MeV, and allow us to perform a detailed study of the γ-ray strength as a function of excitation energy. Hence, we can test the validity of the generalized Brink-Axel hypothesis, which, in its strictest form, claims no excitation-energy dependence on the γ strength. In this work, using the available high-quality 238Np data, we show that the γ-ray strength function is to a very large extent independent of the initial and final states. Thus, for the first time, the generalized Brink-Axel hypothesis is experimentally verified for γ transitions between states in the quasicontinuum region, not only for specific collective resonances, but also for the full strength below the neutron separation energy. Based on our findings, the necessary criteria for the generalized Brink-Axel hypothesis to be fulfilled are outlined.

• Liddick, Sean N.; Spyrou, Artemisia; Crider, Benjamin P.; Naqvi, Farheen; Larsen, Ann-Cecilie & Guttormsen, Magne Sveen [Vis alle 21 forfattere av denne artikkelen] (2016). Experimental Neutron Capture Rate Constraint Far from Stability. Physical Review Letters. ISSN 0031-9007. 116:242502(24). doi: 10.1103/PhysRevLett.116.242502. Fulltekst i vitenarkiv Vis sammendrag

  Nuclear reactions where an exotic nucleus captures a neutron are critical for a wide variety of applications, from energy production and national security, to astrophysical processes, and nucleosynthesis. Neutron capture rates are well constrained near stable isotopes where experimental data are available; however, moving far from the valley of stability, uncertainties grow by orders of magnitude. This is due to the complete lack of experimental constraints, as the direct measurement of a neutron-capture reaction on a short-lived nucleus is extremely challenging. Here, we report on the first experimental extraction of a neutron capture reaction rate on 69 Ni , a nucleus that is five neutrons away from the last stable isotope of Ni. The implications of this measurement on nucleosynthesis around mass 70 are discussed, and the impact of similar future measurements on the understanding of the origin of the heavy elements in the cosmos is presented.

• Renstrøm, Therese; Nyhus, Hilde-Therese; Utsunomiya, Hiroaki; Schwengner, Ronald; Goriely, Stephane & Larsen, Ann-Cecilie [Vis alle 25 forfattere av denne artikkelen] (2016). Low-energy enhancement in the γ-ray strength functions of Ge73,74. Physical Review C. Nuclear Physics. ISSN 0556-2813. 93(6). doi: 10.1103/PhysRevC.93.064302. Fulltekst i vitenarkiv Vis sammendrag

  The γ -ray strength functions and level densities of 73,74Ge have been extracted up to the neutron-separation energy Sn from particle-γ coincidence data using the Oslo method. Moreover, the γ -ray strength function of 74Ge above Sn has been determined from photoneutron measurements; hence these two experiments cover the range of Eγ ≈ 1–13 MeV for 74Ge. The obtained data show that both 73,74Ge display an increase in strength at low γ energies. The experimental γ -ray strength functions are compared with M1 strength functions deduced from average B(M1) values calculated within the shell model for a large number of transitions. The observed low-energy enhancements in 73,74Ge are adopted in the calculations of the 72,73Ge(n,γ ) cross sections, where there are no direct experimental data. Calculated reaction rates for more neutron-rich germanium isotopes are shown to be strongly dependent on the presence of the low-energy enhancement.

• 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.

• Clement, E; Zielinska, Magdalena; Péru, Sophie; Goutte, Héloïse; Hilaire, Stephane & Görgen, Andreas [Vis alle 51 forfattere av denne artikkelen] (2016). Low-energy Coulomb excitation of 96,98Sr beams. Physical Review C. Nuclear Physics. ISSN 0556-2813. 94(5). doi: 10.1103/PhysRevC.94.054326. Fulltekst i vitenarkiv Vis sammendrag

  The structure of neutron-rich 96,98Sr nuclei was investigated by low-energy safe Coulomb excitation of radioactive beams at the REX-ISOLDE facility, CERN, with the MINIBALL spectrometer. A rich set of transitional and diagonal E2 matrix elements, including those for non-yrast structures, has been extracted from the differential Coulomb-excitation cross sections. The results support the scenario of a shape transition at N = 60, giving rise to the coexistence of a highly deformed prolate and a spherical configuration in 98Sr, and are compared to predictions from several theoretical calculations. The experimental data suggest a significant contribution of the triaxal degree of freedom in the ground state of both isotopes. In addition, experimental information on low-lying states in 98Rb has been obtained.

• 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.

• Negi, D; Wiedeking, M; Lanza, EG; Litvinova, E; Vitturi, A & Bark, RA [Vis alle 35 forfattere av denne artikkelen] (2016). Nature of low-lying electric dipole resonance excitations in Ge 74. Physical Review C. Nuclear Physics. ISSN 0556-2813. 94(2). doi: 10.1103/PhysRevC.94.024332. Fulltekst i vitenarkiv Vis sammendrag

  Isospin properties of dipole excitations in 74 Ge are investigated using the (α , α ′ γ ) reaction and compared to (γ , γ ′ ) data. The results indicate that the dipole excitations in the energy region of 6 to 9 MeV adhere to the scenario of the recently found splitting of the region of dipole excitations into two separated parts: one at low energy, being populated by both isoscalar and isovector probes, and the other at high energy, excited only by the electromagnetic probe. Relativistic quasiparticle time blocking approximation (RQTBA) calculations show a reduction in the isoscalar E1 strength with an increase in excitation energy, which is consistent with the measurement.

• 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
• Gheorghe, I.; Utsunomiya, H.; Filipescu, D.; Glodariu, T.; Nyhus, Hilde-Therese & Renstrøm, Therese [Vis alle 10 forfattere av denne artikkelen] (2015). Absolute photoneutron cross sections of Sm isotopes. AIP Conference Proceedings. ISSN 0094-243X. 1645(1), s. 327–331. doi: 10.1063/1.4909595. 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.

• Nyhus, Hilde-Therese; Renstrøm, Therese; Utsunomiya, H.; Goriely, S.; Filipescu, D. M. & Gheorghe, I. [Vis alle 17 forfattere av denne artikkelen] (2015). Photoneutron cross sections for neodymium isotopes: Toward a unified understanding of (γ,n) and (n,γ) reactions in the rare earth region. Physical Review C. Nuclear Physics. ISSN 0556-2813. 91(1). doi: 10.1103/PhysRevC.91.015808. 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
• Utsunomiya, Hiroaki; Goriely, Stéphane; Filipescu, Dan Mihai; Tesileanu, Ovidiu; Gheorghe, Ioana & Glodariu, Tudor [Vis alle 12 forfattere av denne artikkelen] (2015). Photoneutron reactions in nuclear astrophysics. Journal of Physics: Conference Series (JPCS). ISSN 1742-6588. 590:012023. doi: 10.1088/1742-6596/590/1/012023. 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.

• Filipescu, Dan Mihai; Utsunomiya, Hiroaki; Camera, Franco; Nyhus, Hilde-Therese; Renstrøm, Therese & Gheorghe, Ioana [Vis alle 13 forfattere av denne artikkelen] (2015). Photoneutron cross section measurements on Sm isotopes. The European Physical Journal Conferences. ISSN 2101-6275. 93:02006, s. 1–4. doi: 10.1051/epjconf/20159302006. Fulltekst i vitenarkiv
• Renstrøm, Therese; Nyhus, Hilde-Therese; Utsunomiya, Hiroaki; Larsen, Ann-Cecilie; Siem, Sunniva & Guttormsen, Magne Sveen [Vis alle 25 forfattere av denne artikkelen] (2015). First evidence of low energy enhancement in Ge isotopes. The European Physical Journal Conferences. ISSN 2101-6275. 93. doi: 10.1051/epjconf/20159304003. Fulltekst i vitenarkiv Vis sammendrag

  The γ-strength functions and level densities of 73,74Ge have been extracted from particle-γ coincidence data using the Oslo method. In addition the γ-strength function of 74Ge above the neutron separation threshold, Sn = 10.196 MeV has been extracted from photoneutron measurements. When combined, these two experiments give a γ-strength function covering the energy range of ∼1-13 MeV for 74Ge. This thorough investigation of 74Ge is a part of an international campaign to study the previously reported low energy enhancement in this mass region in the γ-strength function from ∼3 MeV towards lower γ energies. The obtained data show that both 73,74Ge display an increase in strength at low γ energies.

• 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
• Filipescu, D. M.; Gheorghe, I.; Utsunomiya, H.; Goriely, S.; Renstrøm, Therese & Nyhus, Hilde-Therese [Vis alle 16 forfattere av denne artikkelen] (2014). Photoneutron cross sections for samarium isotopes: Toward a unified understanding of (gamma,n) and (n,gamma) reactions in the rare earth region. Physical Review C. Nuclear Physics. ISSN 0556-2813. doi: 10.1103/physrevc.90.064616. 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
• Spyrou, A.; Liddick, S.N.; Larsen, Ann-Cecilie; Guttormsen, Magne Sveen; Cooper, K. & Dombos, A.C. [Vis alle 15 forfattere av denne artikkelen] (2014). Novel technique for Constraining r-Process (n, γ) Reaction Rates. Physical Review Letters. ISSN 0031-9007. 113(232502). doi: 10.1103/PhysRevLett.113.232502. Fulltekst i vitenarkiv Vis sammendrag

  A novel technique has been developed, which will open exciting new opportunities for studying the very neutron-rich nuclei involved in the r process. As a proof of principle, the γ spectra from the β decay of 76Ga have been measured with the SuN detector at the National Superconducting Cyclotron Laboratory. The nuclear level density and γ-ray strength function are extracted and used as input to Hauser-Feshbach calculations. The present technique is shown to strongly constrain the 75Ge(n,γ)76Ge cross section and reaction rate. © 2014 American Physical Society

• Utsunomiya, Hiroaki; Shima, Tatsushi; Takahisa, Keiji; Filipescu, Dan Mihai; Tesileanu, Ovidiu & Gheorghe, Ioana [Vis alle 12 forfattere av denne artikkelen] (2014). Energy calibration of the NewSUBARU storage ring for laser compton-scattering gamma rays and applications. IEEE Transactions on Nuclear Science. ISSN 0018-9499. 61(3), s. 1252–1258. doi: 10.1109/TNS.2014.2312323. Fulltekst i vitenarkiv
• Eriksen, Tomas Kvalheim; Nyhus, Hilde-Therese; Guttormsen, Magne Sveen; Görgen, Andreas; Larsen, Ann-Cecilie & Renstrøm, Therese [Vis alle 11 forfattere av denne artikkelen] (2014). Pygmy resonance and low-energy enhancement in the γ-ray strength functions of Pd isotopes. Physical Review C. Nuclear Physics. ISSN 0556-2813. 90(044311). doi: 10.1103/PhysRevC.90.044311. Fulltekst i vitenarkiv
• Clément, Etebong Peter; Görgen, Andreas; Dijon, A; France, G De; Bastin, B & Blazhev, A [Vis alle 46 forfattere av denne artikkelen] (2014). Onset of collectivity in &lt;sup&gt;96,98&lt;/sup&gt;Sr studied via Coulomb excitation. The European Physical Journal Conferences. ISSN 2101-6275. 66:02021. doi: 10.1051/epjconf/20146602021. 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

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• Staff, Gunnar Andreas; Zarruk, Gustavo A.; Hatleskog, Johan; Stavland, Simon T.; Mcnulty, Henry David Feaver & Ibarra-Hernandez, Roberto Jose [Vis alle 12 forfattere av denne artikkelen] (2020). Physics Guided Machine Learning Significantly Improves Outcomes for Data-Based Production Optimization. Fulltekst i vitenarkiv
• Midtbø, Jørgen E.; Larsen, Ann-Cecilie & Renstrøm, Therese (2018). Extracting γ-strength functions from shell model calculations. Fulltekst i vitenarkiv
• Guttormsen, Magne Sveen; Larsen, Ann-Cecilie; Midtbø, Jørgen E.; Campo, Lucia Crespo; Görgen, Andreas & Ingeberg, Vetle Wegner [Vis alle 11 forfattere av denne artikkelen] (2017). Gamma-widths, lifetimes and fluctuations in the nuclear quasi-continuum. Fulltekst i vitenarkiv
• Renstrøm, Therese & Tveten, Gry Merete (2016). The northern light - science and popular culture. Fulltekst i vitenarkiv
• Guttormsen, Magne Sveen; Larsen, Ann-Cecilie; Görgen, Andreas; Renstrøm, Therese; Siem, Sunniva & Tornyi, Tamas Gabor [Vis alle 7 forfattere av denne artikkelen] (2016). Is the generalized Brink-Axel hypothesis valid? Fulltekst i vitenarkiv
• 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 & Renstrøm, Therese (2015). Preliminary results for 89Y, 203Tl and 205Tl from the November 2015 experiments at the NewSubaru facility. Fulltekst i vitenarkiv
• Guttormsen, Magne Sveen; Larsen, Ann-Cecilie; Blasi, N; Bracco, A; Camera, F & Eriksen, Tomas Kvalheim [Vis alle 19 forfattere av denne artikkelen] (2014). Recent results using large LaBr3 detectors and future perspectives. Fulltekst i vitenarkiv
• Renstrøm, Therese (2014). Level density and strength function of Ge-74. Fulltekst i vitenarkiv
• Renstrøm, Therese (2014). First evidence of low energy upbend in germanium isotopes. Fulltekst i vitenarkiv
• Renstrøm, Therese (2014). Gamma strength function of Ge-74. Fulltekst i vitenarkiv
• 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
• Renstrøm, Therese (2015). Probing Statistical Properties of Ni, Ge, Nd and Sm isotopes. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  Denne avhandlingen er motivert av tidligere resultater fra Oslo syklotronlaboratorium som viser at eksiterte atomkjerner henfaller ved å sende ut et avvikende spekter av gammastråling i forhold til det etablerte teorier forutsier. En sterk økning i sannsynlighet for utsendelse av lavenergetisk gammastråling har blitt påvist. Denne såkalte resonansen ble i dette arbeidet funnet for første gang i både nikkel og germaniumkjerner. Undersøkelser av atomkjernen utføres ved å tilføre energi slik at kjernen settes ut av likevekt. Renstrøm og hennes medarbeidere har oppnådd dette ved å bombardere atomkjerner med høyenergetiske små partikler eller gammastråling. Antall ulike konfigurasjoner en kjerne kan innta når den blir eksitert har blitt målt og spekteret til gammastrålingen i det kjernen kvitter seg med eksitasjonsenergien er blitt registrert. Fra denne informasjonen kan to viktige egenskaper ved kjernen studeres: dens nivåtetthet og gamma-styrkefunksjon. Disse to grunnleggende størrelsene kan gi ny informasjon om kjerners struktur, i tillegg til å belyse et område innen kjerne-astrofysikk. Grunnstoffer tyngre enn jern dannes nesten utelukkende ved nøytroninnfangning. Størrelsene målt i Renstrøms avhandling er viktige kjernefysiske bidrag for å kunne modellere denne prosessen. Det er her blitt vist at den økte sannsynligheten for å sende ut lavenergetisk stråling kan ha stor effekt på dannelsen av nøytronrike germaniumisotoper.

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