Tomas Kvalheim Eriksen

• Markova, Maria; Larsen, Ann-Cecilie; Neumann-Cosel, P. von; Litvinova, E.; Goriely, S. & Bell, Lauren Tracy [Vis alle 17 forfattere av denne artikkelen] (2026). Exploring the statistical properties of the neutron-deficient 109In isotope with the Oslo method. Physical Review C. ISSN 2469-9985. 113(4). doi: 10.1103/qrvh-s12k. Fulltekst i vitenarkiv Vis sammendrag

  The nuclear level density and the 𝛾-ray strength function of the neutron-deficient 109In isotope were extracted for the first time with data from the 106Cd⁢(𝛼,𝑝⁢𝛾)⁢109In reaction using a combination of the Oslo and the shape methods. Both quantities are consistent with those of neighboring Cd and Sn nuclei but show substantial discrepancies with currently available model predictions. In contrast to earlier observations in the neighboring isotopic chains, 109In does not exhibit any significant enhancement of the dipole strength near the neutron separation energy. To interpret this feature, random-phase time-blocking approximation calculations have been performed for 109In and the neighboring 110,112Sn nuclei. The experimental data were also employed to estimate cross sections and rates of the radiative neutron- and proton-capture reactions, 108In⁢(𝑛,𝛾)⁢109In and 108Cd⁢(𝑝,𝛾)⁢109In, respectively, with the reaction code talys. Our (𝑝,𝛾) cross section is in excellent agreement with direct measurements over a wide range of proton energies, while the (𝑛,𝛾) cross section demonstrates notable deviations from predictions in the jina reaclib library. The new results on the statistical properties of 109In provide valuable constraints that may help address the problem of large model uncertainties compromising the accuracy of astrophysical 𝑝-process simulations.

• Paulsen, Wanja; Li, Kevin Ching Wei; Siem, Sunniva; Ingeberg, Vetle Wegner; Larsen, Ann-Cecilie & Eriksen, Tomas Kvalheim [Vis alle 15 forfattere av denne artikkelen] (2025). Remeasuring the γ-decay branching ratio of the Hoyle state. Physical Review C. ISSN 2469-9985. 112. doi: 10.1103/2h2s-sbyx. Fulltekst i vitenarkiv
• Gheorghe, I.; Goriely, S.; Wagner, N.; Aumann, T.; Baumann, M. & Beek, Beek Van [Vis alle 19 forfattere av denne artikkelen] (2024). Photoneutron cross section measurements on Pb 208 in the giant dipole resonance region. Physical Review C. ISSN 2469-9985. 110(1). doi: 10.1103/PhysRevC.110.014619. Fulltekst i vitenarkiv
• 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.

• Pogliano, Francesco; Larsen, Ann-Cecilie; Markova, Maria; Garrote, Frank Leonel Bello; Bjørøen, Marianne Møller & Eriksen, Tomas Kvalheim [Vis alle 17 forfattere av denne artikkelen] (2022). Indirect measurement of the (n,γ) Sb 127 cross section. Physical Review C. ISSN 2469-9985. 106(1). doi: 10.1103/PhysRevC.106.015804. Fulltekst i vitenarkiv Vis sammendrag

  Nuclei in the 135I region have been identified as being a possible bottleneck for the i process. Here we present an indirect measurement for the Maxwellian-averaged cross section of 126Sb(n,γ). The nuclear level density and the γ-ray strength function of 127Sb have been extracted from 124Sn(α,pγ)127Sb data using the Oslo method. The level density in the low-excitation-energy region agrees well with known discrete levels, and the higher-excitation-energy region follows an exponential curve compatible with the constant-temperature model. The strength function between Eγ≈1.5–8.0 MeV presents several features, such as an upbend and a possibly double-peaked pygmy-like structure. None of the theoretical models included in the nuclear reaction code talys seem to reproduce the experimental data. The Maxwellian-averaged cross section for the 126Sb(n,γ)127Sb reaction has been experimentally constrained by using our level-density and strength-function data as input to talys. We observe a good agreement with the jina reaclib, tendl, and bruslib libraries, while the endf/b-viii.0 library predicts a significantly higher rate than our results.

• Markova, Maria; Larsen, Ann-Cecilie; Neumann-Cosel, Peter von; Bassauer, Sergej; Görgen, Andreas & Guttormsen, Magne Sveen [Vis alle 23 forfattere av denne artikkelen] (2022). Nuclear level densities and γ -ray strength functions in Sn 120,124 isotopes: Impact of Porter-Thomas fluctuations. Physical Review C. ISSN 2469-9985. 106(3). doi: 10.1103/PhysRevC.106.034322. Fulltekst i vitenarkiv Vis sammendrag

  Nuclear level densities (NLDs) and γ-ray strength functions (GSFs) of 120,124Sn have been extracted with the Oslo method from proton-γ coincidences in the (p,p′γ) reaction. The functional forms of the GSFs and NLDs have been further constrained with the Shape method by studying primary γ-transitions to the ground and first excited states. The NLDs demonstrate good agreement with the NLDs of 116,118,122Sn isotopes measured previously. Moreover, the extracted partial NLD of 1− levels in 124Sn is shown to be in fair agreement with those deduced from spectra of relativistic Coulomb excitation in forward-angle inelastic proton scattering. The experimental NLDs have been applied to estimate the magnitude of the Porter-Thomas (PT) fluctuations. Within the PT fluctuations, we conclude that the GSFs for both isotopes can be considered to be independent of initial and final excitation energies, in accordance with the generalized Brink-Axel hypothesis. Particularly large fluctuations observed in the Shape-method GSFs present a considerable contribution to the uncertainty of the method and may be one of the reasons for deviations from the Oslo-method strength at low γ-ray energies and low values of the NLD (below ≈1×103–2×103MeV−1).

• Cook, K.J.; Chevis, A.; Eriksen, Tomas Kvalheim; Simpson, E.C.; Kibédi, T. & Bezzina, L.T. [Vis alle 17 forfattere av denne artikkelen] (2021). High-precision proton angular distribution measurements of C 12 (p,p′) for the determination of the E0 decay branching ratio of the Hoyle state. Physical Review C. ISSN 2469-9985. 104(2). doi: 10.1103/PhysRevC.104.024620. Fulltekst i vitenarkiv
• Markova, Maria; Neumann-Cosel, Neumann-Cosel von; Larsen, A.C.; Bassauer, S.; Görgen, A. & Guttormsen, Magne Sveen [Vis alle 25 forfattere av denne artikkelen] (2021). Comprehensive Test of the Brink-Axel Hypothesis in the Energy Region of the Pygmy Dipole Resonance. Physical Review Letters. ISSN 0031-9007. 127(18). doi: 10.1103/PhysRevLett.127.182501. Fulltekst i vitenarkiv Vis sammendrag

  The validity of the Brink-Axel hypothesis, which is especially important for numerous astrophysical calculations, is addressed for 116,120,124Sn below the neutron separation energy by means of three independent experimental methods. The γ-ray strength functions (GSFs) extracted from primary γ-decay spectra following charged-particle reactions with the Oslo method and with the shape method demonstrate excellent agreement with those deduced from forward-angle inelastic proton scattering at relativistic beam energies. In addition, the GSFs are shown to be independent of excitation energies and spins of the initial and final states. The results provide a critical test of the generalized Brink-Axel hypothesis in heavy nuclei, demonstrating its applicability in the energy region of the pygmy dipole resonance.

• 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.

• McCormick, Brendan P.; Stuchbery, A.E.; Brown, BA; Georgiev, G; Coombes, BJ & Gray, TJ [Vis alle 18 forfattere av denne artikkelen] (2019). First-excited state g factors in the stable, even Ge and Se isotopes. Physical Review C. ISSN 2469-9985. 100(4). doi: 10.1103/PhysRevC.100.044317. Fulltekst i vitenarkiv
• Zeiser, Fabio; Tveten, Gry Merete; Potel, Gregory; Larsen, Ann-Cecilie; Guttormsen, Magne Sveen & Laplace, Thibault A. [Vis alle 22 forfattere av denne artikkelen] (2019). Restricted spin-range correction in the Oslo method: The example of nuclear level density and γ-ray strength function from 239Pu(d, pγ) 240Pu. Physical Review C. ISSN 2469-9985. 100:024305(2), s. 1–9. doi: 10.1103/PhysRevC.100.024305. Fulltekst i vitenarkiv
• Evitts, Lee J.; Garnsworthy, Adam B.; Kibédi, Tibor; Smallcombe, James; Reed, Matthew W. & Stuchbery, Andrew E. [Vis alle 24 forfattere av denne artikkelen] (2019). E0 transition strength in stable Ni isotopes. Physical Review C. ISSN 2469-9985. 99:024306(2), s. 1–11. doi: 10.1103/PhysRevC.99.024306. Fulltekst i vitenarkiv
• 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.

• 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.

• 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.

• 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.

• Laplace, Thibault A.; Zeiser, Fabio; Guttormsen, Magne Sveen; Larsen, Ann-Cecilie; Bleuel, Darren L. & Bernstein, Lee A. [Vis alle 27 forfattere av denne artikkelen] (2016). Statistical properties of Pu 243, and Pu 242 (n,γ) cross section calculation. Physical Review C. Nuclear Physics. ISSN 0556-2813. 93(1). doi: 10.1103/PhysRevC.93.014323. Fulltekst i vitenarkiv Vis sammendrag

  The level density and γ -ray strength function (γ SF) of 243Pu have been measured in the quasicontinuum using the Oslo method. Excited states in 243Pu were populated using the 242Pu(d,p) reaction. The level density closely follows the constant-temperature level density formula for excitation energies above the pairing gap. The γ SF displays a double-humped resonance at low energy as also seen in previous investigations of actinide isotopes. The structure is interpreted as the scissors resonance and has a centroid of ωSR = 2.42(5) MeV and a total strength of BSR = 10.1(15) μ2 N , which is in excellent agreement with sum-rule estimates. The measured level density and γ SF were used to calculate the 242Pu(n,γ ) cross section in a neutron energy range for which there were previously no measured data.

• Larsen, Ann-Cecilie; Guttormsen, Magne Sveen; Schwengner, Ronald; Bleuel, Darren L.; Goriely, Stephane & Harrisopulos, Sotirios [Vis alle 21 forfattere av denne artikkelen] (2016). Experimentally constrained (p,γ) y 89 and (n,γ) y 89 reaction rates relevant to p -process nucleosynthesis. Physical Review C. Nuclear Physics. ISSN 0556-2813. 93(4). doi: 10.1103/PhysRevC.93.045810. Fulltekst i vitenarkiv Vis sammendrag

  The nuclear level density and the γ -ray strength function have been extracted for 89Y by using the Oslo method on 89Y(p,p γ ) 89Y coincidence data. The γ -ray strength function displays a low-energy enhancement consistent with previous observations in this mass region (93–98Mo). Shell-model calculations support the conclusion that the observed enhancement is due to strong, low-energy M1 transitions at high excitation energies. The data were further used as input for calculations of the 88Sr(p,γ ) 89Y and 88Y(n,γ ) 89Y cross sections with the TALYS reaction code. Comparison with cross-section data, where available, as well as with values from the BRUSLIB library, shows a satisfying agreement.

• 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
• Larsen, Ann-Cecilie; Goriely, Stephane; Bernstein, L. A.; Bleuel, D. L.; Bracco, A. & Brown, B. A. [Vis alle 25 forfattere av denne artikkelen] (2015). Upbend and M1 scissors mode in neutron-rich nuclei — consequences for r-process (n,gamma) reaction rates. Acta Physica Polonica B. ISSN 0587-4254. 46(3), s. 509–512. doi: 10.5506/APhysPolB.46.509. Fulltekst i vitenarkiv Vis sammendrag

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

• Tveten, Gry Merete; Garrote, Frank Leonel Bello; Campo, Lucia Crespo; Eriksen, Tomas Kvalheim; Giacoppo, Francesca & Guttormsen, Magne Sveen [Vis alle 18 forfattere av denne artikkelen] (2015). The statistical properties of 111,112,113Sn studied with the Oslo method. The European Physical Journal Conferences. ISSN 2101-6275. 93. doi: 10.1051/epjconf/20159304004. Fulltekst i vitenarkiv Vis sammendrag

  The γ-ray strength function and level density of 111, 112, 113Sn are being studied at the Oslo Cyclotron Laboratory (OCL) up to the neutron binding energy by applying the Oslo method to particle-γ coincidence data. The preliminary results for the γ-ray strength function are discussed in the context of the results for the more neutron-rich Sn-isotopes previously studied at OCL.

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

  The γ-ray strength functions and nuclear level densities of 138La and 139La have been measured below the neutron separation energies. These new data were used to calculate astrophysical Maxwellian-averaged () cross-sections to investigate the production and destruction of the p-nucleus 138La in the photodisintegration process. The results confirm the underproduction of 138La in the p-process with respect to the observed abundances and strongly support the ν-process through capture on 138Ba as the main contributor to the synthesis of 138La in Type II supernovae.

• Garrote, Frank Leonel Bello; Görgen, Andreas; Mierzejewski, Jan; Mihai, Corina Mihaela; Delaroche, Jean Paul & Girod, Michel [Vis alle 24 forfattere av denne artikkelen] (2015). Lifetime measurement for the 21+ state in Sm 140 and the onset of collectivity in neutron-deficient Sm isotopes. Physical Review C. Nuclear Physics. ISSN 0556-2813. 92:024317(2). doi: 10.1103/PhysRevC.92.024317. Fulltekst i vitenarkiv Vis sammendrag

  Background: The chain of Sm isotopes exhibits a wide range of nuclear shapes and collective behavior. While the onset of deformation for N > 82 has been well studied both experimentally and theoretically, fundamental data is lacking for some Sm isotopes with N < 82. Purpose: Electromagnetic transition rates represent a sensitive test of theoretical nuclear structure models. Lifetime measurements are furthermore complementary to Coulomb excitation experiments, and the two methods together can give access to spectroscopic quadrupole moments. Method: The lifetime of the 2+ 1 state in 140Sm was measured with the recoil-distance Doppler shift technique using the reaction 124Te( 20Ne, 4n) 140Sm at 82 MeV. Theoretical calculations were performed based on a mapped collective Hamiltonian in five quadrupole coordinates (5DCH) and the Gogny D1S interaction. Results: The lifetime of the 2+ 1 state in 140Sm was found to be 9.1(6) ps, corresponding to aB(E2; 2+ 1 → 0+ 1 ) value of 51(4) Weisskopf units. The theoretical calculations are in very good agreement with the experimental result. Conclusions: The B(E2; 2+ 1 → 0+ 1 ) value for 140Sm fits smoothly into the systematic trend for the chain of Sm isotopes. The new beyond-mean field calculations are able to correctly describe the onset of collectivity in the Sm isotopes below the N = 82 shell closure for the first time.

• 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
• 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
• 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, 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

• Tornyi, Tamas Gabor; Guttormsen, Magne Sveen; Eriksen, Tomas Kvalheim; Görgen, Andreas; Giacoppo, Francesca & Hagen, Trine Wiborg [Vis alle 12 forfattere av denne artikkelen] (2014). Level density and gamma-ray strength function in the odd-odd 238Np nucleus. Physical Review C. Nuclear Physics. ISSN 0556-2813. 89(4). doi: 10.1103/PhysRevC.89.044323. Fulltekst i vitenarkiv
• Larsen, Ann-Cecilie; Blasi, Nives; Bracco, Angela; Bürger, Arnold; Camera, Franco & Eriksen, Tomas Kvalheim [Vis alle 25 forfattere av denne artikkelen] (2014). Low-energy enhancement of nuclear γ strength and its impact on astrophysical reaction rates. The European Physical Journal Conferences. ISSN 2101-6275. doi: 10.1051/epjconf/20146607014. Fulltekst i vitenarkiv Vis sammendrag

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

• Larsen, Ann-Cecilie; Blasi, Nives; Bracco, Angela; Camera, Franco; Eriksen, Tomas Kvalheim & Görgen, Andreas [Vis alle 19 forfattere av denne artikkelen] (2013). Evidence for the dipole nature of the low-energy γ enhancement in 56Fe. Physical Review Letters. ISSN 0031-9007. 111(24). doi: 10.1103/PhysRevLett.111.242504. Fulltekst i vitenarkiv Vis sammendrag

  The γ-ray strength function of 56Fe has been measured from proton-γ coincidences for excitation energies up to ≈11  MeV. The low-energy enhancement in the γ-ray strength function, which was first discovered in the (3He,αγ)56Fe reaction, is confirmed with the (p,p′γ)56Fe experiment reported here. Angular distributions of the γ rays give for the first time evidence that the enhancement is dominated by dipole transitions. © 2013 American Physical Society

• Larsen, Ann-Cecilie; Bürger, Alexander; Goriely, Stephane; Guttormsen, Magne Sveen; Görgen, Andreas & Eriksen, Tomas Kvalheim [Vis alle 16 forfattere av denne artikkelen] (2013). Astrophysical reaction rates and the low-energy enhancement in the γ strength. Acta Physica Polonica B. ISSN 0587-4254. 44(3), s. 563–566. doi: 10.5506/APhysPolB.44.563. Fulltekst i vitenarkiv

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• Paulsen, Wanja; Li, Kevin Ching Wei; Siem, Sunniva; Ingeberg, Vetle Wegner; Larsen, Ann-Cecilie & Eriksen, Tomas Kvalheim [Vis alle 15 forfattere av denne artikkelen] (2026). CLUSTER'26. Fulltekst i vitenarkiv
• Paulsen, Wanja; Li, Kevin Ching Wei; Siem, Sunniva; Ingeberg, Vetle Wegner; Larsen, Ann-Cecilie & Eriksen, Tomas Kvalheim [Vis alle 20 forfattere av denne artikkelen] (2023). Remeasuring the gamma-decay branching ratio of the Hoyle state. 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.

• 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
• 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
• Larsen, Ann-Cecilie; Bürger, Alexander; Eriksen, Tomas Kvalheim; Görgen, Andreas; Guttormsen, Magne Sveen & Hagen, Trine Wiborg [Vis alle 29 forfattere av denne artikkelen] (2011). Experiments of reaction model inputs: level density and gamma strength. Fulltekst i vitenarkiv
• Larsen, Ann-Cecilie; Guttormsen, Magne Sveen; Bürger, Alexander; Eriksen, Tomas Kvalheim; Görgen, Andreas & Hagen, Trine Wiborg [Vis alle 16 forfattere av denne artikkelen] (2011). Level density and gamma strength - achievements and challenges. Fulltekst i vitenarkiv
• Paulsen, Wanja; Siem, Sunniva; Li, Kevin Ching Wei & Eriksen, Tomas Kvalheim (2025). A saga on the γ-decay branching ratio of the Hoyle state at the Oslo Cyclotron Laboratory. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  The triple-α process is a fundamental cornerstone of stellar nucleosynthesis, facilitating the production of 12C, a vital building block for life. Through the triple-α process, three helium nuclei can fuse to ultimately produce a stable 12C nuclide. At medium stellar temperatures between 0.1–2.0 GK, the Hoyle state in 12C mediates the triple-α reaction, making a comprehensive understanding of its properties essential for accurately modeling the stellar production of 12C, as well as the subsequent stellar nucleosynthesis. Numerous measurements of the decay modes of the Hoyle state have been conducted since its discovery, yielding a relatively well-constrained value of for it’s radiative branching ratio, describing the probability of producing 12C through the triple-α process. However, a recent measurement published by Kibédi et al. [Phys. Rev. Lett. 125, 182701 (2020)] reported a highly discrepant value of Γrad/Γ = 6.2(6) × 10−4 for the radiative branching ratio from the Hoyle state. Given the astrophysical significance of the Hoyle state, resolving this conflict is crucial. This study seeks to address this discrepancy through a new measurement of the γ-decay branching ratio of the Hoyle state, together with a comprehensive reanalysis of the data published by Kibédi et al. [Phys. Rev. Lett. 125, 182701 (2020)].

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