Ann-Cecilie Larsen

• Dembski, Cade; Spyrou, Artemis; Brown, B. Alex; Liddick, Sean N.; Berg, Hannah C. & Bleuel, Darren L. [Show all 23 contributors for this article] (2026). Total absorption spectroscopy study of the⁷¹Fe →⁷¹Co β decay. Physical Review C. ISSN 2469-9985. 114(2). doi: 10.1103/MS66-LG13. Full text in Research Archive
• Harris, Caley M.; Spyrou, Artemis; Denissenkov, Pavel; Herwig, Falk; Richard, Andrea L. & Uthayakumaar, Sivahami [Show all 23 contributors for this article] (2026). Influence of neutron-capture reactions on the nucleosynthesis of strontium. Communications Physics. 9(1). doi: 10.1038/s42005-026-02713-5. Full text in Research Archive Show summary

  The astrophysical intermediate neutron-capture process (i process) has been reinvoked in recent years to describe stellar observations that cannot be explained by the traditional nucleosynthesis processes. Despite its success, significant uncertainties still remain including the exact astrophysical conditions and site, as well as the nuclear physics input. Available i-process models strongly underproduce the abundance of strontium (Sr) compared to observational data, while successfully describing neighboring elements, like yttrium (Y) and zirconium (Zr). This discrepancy has been attributed to nuclear physics uncertainties, specifically to the unconstrained reaction rate of the neutron-capture on the isotope krypton-88. Here we present an experimental investigation of this reaction and show that our result provides a possible solution to the aforementioned Sr underproduction in i-process models.

• Ronning, E. K.; Richard, A. L.; Liddick, S. N.; Spyrou, A.; Ringle, R. & Arora, H. [Show all 43 contributors for this article] (2026). Magnetic character of the low-energy enhancement in⁷⁰Zn. Nature. ISSN 0028-0836. 655(8124), p. 875–878. doi: 10.1038/s41586-026-10758-3. Full text in Research Archive Show summary

  The transition of an atomic nucleus from an excited state to a state of lower energy is typically accompanied by the emission of photons. The likelihood of photon emission is a function of the photon energy and of properties of the initial and final nuclear states and is known as the photon (or γ-ray) strength function (γSF)1,2. Of the features present in the γSF, an enhancement in the low-energy region has been observed in some nuclei, but the electromagnetic nature of this enhancement remains an open question3,4. This low-energy enhancement in the γSF significantly impacts our understanding of how elements are created in stars and the structure of the nucleus5,6. Here we present the results from an experiment on the γSF of 70Zn that show that the enhancement in the γSF of this nucleus is of magnetic nature. This observation helps address a long-open question about γSFs in atomic nuclei and directly impacts our predictive capabilities in nuclear science.

• Bell, Lauren Tracy; Siem, Sunniva; Larsen, Ann-Cecilie; Bürger, A.; Markova, Maria & Ingeberg, V. W. [Show all 12 contributors for this article] (2026). Extracting the nuclear level density and γ-ray strength function of 90Zr. Physical Review C. ISSN 2469-9985. 114(1). doi: 10.1103/p9y9-xxjf. Full text in Research Archive Show summary

  In this work, we have extracted the nuclear level density (NLD) and 𝛾-ray strength function (𝛾⁢SF) using the Oslo method on particle-𝛾 coincidence data from the 90Zr⁢(𝑝,𝑝′⁢𝛾)90Zr ⁢reaction. We have applied the shape method to the same data set, providing a model-independent 𝛾⁢SF and a cross-check on the slope of the Oslo-method NLD and 𝛾⁢SF. Further, we have combined the 𝛾⁢SF from this work with photonuclear data, thus covering the 2.5<𝐸𝛾<18MeV energy range. We see an increase in strength in the region around 𝐸𝛾≈9MeV, consistent with previous (𝛾,𝛾′) and (𝛾,𝑛) data. On the other hand, surprisingly, we do not observe a strong low-energy increase at low transition energies. The resulting NLD and 𝛾⁢SF were used as inputs to the nuclear reaction code talys to estimate the cross sections and astrophysical reaction rates for the 89Zr(𝑛,𝛾)⁢90Zr 89Y⁡(𝑝,𝛾)90Zr reactions. We find good agreement with available experimental cross sections and JINA calculations for the 89Y⁡(𝑝,𝛾) results, but not for the 89Zr⁢(𝑛,𝛾) reaction rate for stellar temperatures above 0.7 GK. Based on our data, we provide a much more narrow uncertainty band for the 89Zr⁢(𝑛,𝛾) cross section and reaction rate.

• Markova, Maria; Larsen, Ann-Cecilie; Neumann-Cosel, P. von; Litvinova, E.; Goriely, S. & Bell, Lauren Tracy [Show all 17 contributors for this article] (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. Full text in Research Archive Show summary

  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.

• Henriksen, Ellen Karoline; Bøe, Maria Vetleseter; Sørborg, Øystein & Larsen, Ann-Cecilie (2026). Educational reconstruction of nuclear astrophysics in a design-based research project. Physical Review Physics Education Research. 22. doi: 10.1103/ybmb-vknr. Full text in Research Archive Show summary

  This paper presents the first iteration of development and classroom testing of Stars and Elements, a web-based learning resource for Norwegian upper secondary physics students, focused on how heavy elements are produced in stars and neutron star mergers. Combining the Model of Educational Reconstruction (MER) with the pedagogical link-making framework and Design-Based Research (DBR), we identified core ideas to be communicated, reviewed the physics curriculum and research on student understanding and motivation, and formulated design hypotheses that guided development of a 90-minute learning resource with animations, videos, interactive tasks, peer discussion, and teacher consolidation. Six classes (N = 120) participated; data comprised students’ written responses to three open tasks, brief evaluations, and classroom observations. Most students could describe central concepts and processes concerning red giant stars and neutron star mergers as sites for heavy element production, notably the slow and rapid neutron capture processes, and many benefited from animations and varied task formats. Some displayed uncertain grasp of concepts such as fusion and beta decay. Nature of science (NoS) aspects concerning how physics knowledge is developed were found to be insufficiently represented. From these findings we propose design principles for research-based learning resources on similar topics, including emphasizing explicit link‑making across scales and prior knowledge, scaffolding for challenging nuclear concepts, multimodal visualisations, and explicit NoS focus. We argue that combining MER, link-making and DBR is a promising approach for developing learning resources that reflect the frontiers of science while having a solid grounding in the classroom.

• Pathirana, N. D.; Zegers, R. G. T.; Gao, B.; Spyrou, A.; Larsen, Ann-Cecilie & Berg, H. [Show all 19 contributors for this article] (2026). Extraction of neutron-capture cross sections on 92Zr using the charge-exchange Oslo method. Physical Review C. ISSN 2469-9985. 113(1). doi: 10.1103/qdsh-ygry. Full text in Research Archive Show summary

  The 93 Nb (𝑡, 3 He ) reaction at 115 MeV/nucleon was studied to demonstrate that nuclear level densities and 𝛾-ray strength functions can be extracted from charge-exchange reactions at intermediate energies using the Oslo technique. The matrix of excitation energy in 93 Zr , reconstructed from the (𝑡, 3 He ) reaction, versus the energy of 𝛾 rays emitted by the excited 93 Zr nuclei, was obtained in an experiment with the S800 Spectrograph operated in coincidence with the GRETINA 𝛾-ray detector. The extracted level density and 𝛾-ray strength function obtained by applying the Oslo method to this matrix were used to estimate the 92 Zr ⁢(𝑛,𝛾)⁢ 93 Zr cross section by combining the new results with other experimental data and theoretical calculations for 𝐸⁢1 and 𝑀⁢1 strength functions at higher energies. Good agreement with direct measurements of the 92 Zr ⁢(𝑛,𝛾)⁢ 93 Zr cross section was found. The contribution from the upbend in the extracted 𝛾-ray strength function was important to achieve the consistency, as the neutron-capture cross section without this contribution is significantly below the direct measurements otherwise. Since charge-exchange reactions at intermediate energies have long been used for extracting Gamow-Teller strengths, the successful demonstration of the charge-exchange Oslo method enables experiments in which (𝑛,𝛾) cross sections and Gamow-Teller strengths can be measured simultaneously, which is of benefit for astrophysical studies.

• Greaves, B.; Mücher, D.; Spyrou, A.; Goriely, S.; Rochman, D. & Berg, H. C. [Show all 27 contributors for this article] (2025). Probing the limits of statistical neutron capture for the r process: Experimental constraints on¹⁴¹Cs nuclear level densities. Physics Letters B. ISSN 0370-2693. 871. doi: 10.1016/j.physletb.2025.139992. Full text in Research Archive Show summary

  The r-process abundance peaks, particularly near mass number A ∼ 130, reflect underlying nuclear structure effects such as closed neutron shells, yet modeling the nucleosynthesis in this region remains hindered by uncertain neutron-capture rates. These rates are especially sensitive to nuclear level densities (NLDs) and γ-ray strength functions of neutron-rich nuclei, where experimental data are scarce. We present the first experimental constraint on the NLD of 141Cs using the β-Oslo method, extending sensitivity to the neutron-rich regime near the 𝑁 = 82 closed shell. Our data allow for critical calibration of microscopic NLD models and reveal that 141Cs lies near the limit of statistical model applicability. Using this experimental input, we evaluate radiative neutron-capture rates across neighboring isotones using both Hauser–Feshbach (HF) and High Fidelity Resonance (HFR) models. Our results show order-of-magnitude rate increases for nuclei along the 𝑁 = 86 line, signaling a transition to resonance-dominated capture in this region. These findings underscore the importance of constraining NLDs to improve r-process reaction network predictions, particularly in environments where the validity of statistical models breaks down.

• Markova, Maria; Larsen, Ann-Cecilie & Garrote, Frank Leonel Bello (2025). PYGMY DIPOLE RESONANCE IN Sn ISOTOPES AND ITS ASTROPHYSICAL IMPACT. Acta Physica Polonica B, Proceedings Supplement. ISSN 1899-2358. 18(2). doi: 10.5506/APhysPolBSupp.18.2-A3. Full text in Research Archive Show summary

  The low-lying electric dipole strength in 111−113,116−122,124Sn was extracted with the Oslo method to systematically investigate the pygmy dipole resonance (PDR) and its evolution in Sn isotopes. The nuclear level densities (NLD) and the γ-ray strength functions (GSF) obtained from the Oslo data were used as inputs in the TALYS reaction code to produce radiative neutron-capture cross sections, Maxwellian-averaged cross sections, and rates relevant for the heavy-element nucleosynthesis. Despite a relatively small observed impact of the PDR, the experimentally extracted 121,123Sn(n, γ) 122,124Sn cross sections provide a notable reduction of a currently available theoretical uncertainty for the abundances of Sb isotopes in the i-process simulations.

• Wiedeking, Mathis; Goriely, Stephane; Guttormsen, Magne; Herwig, Falk; Larsen, Ann-Cecilie & Liddick, Sean N. [Show all 10 contributors for this article] (2025). Unlocking i-process nucleosynthesis by bridging stellar and nuclear physics. Nature Reviews Physics. 7(12), p. 696–712. doi: 10.1038/s42254-025-00885-7. Full text in Research Archive Show summary

  The origin of chemical elements and their abundances across the cosmos remain one of the central questions in physics. The formation of elements heavier than iron is traditionally attributed to three main mechanisms: the slow and rapid neutron-capture processes (s and r processes) and the p process (mostly driven by photodisintegration reactions). However, certain astronomical observations reveal elemental abundance patterns inconsistent with these processes. These discrepancies prompted the introduction of the intermediate neutron-capture process (i process), which operates at neutron densities between the s and r processes, and which has emerged as a key area of research. Observations of elemental abundances of stars confirm that the i process does indeed take place. Identifying the required astrophysical conditions and contributions of the i process sensitively depend on neutron-capture reaction rates involving unstable atomic nuclei. Important advancements have been achieved through these new astronomical observations and cutting-edge experimental and analytical techniques in nuclear physics, in addition to models of nuclear physics and nucleosynthesis. State-of-the-art facilities and theoretical models are revolutionizing our ability to explore the i process and offer fresh perspectives on the nuclear behaviour under extreme stellar conditions. This Review underscores the synergy between groundbreaking astronomical and nuclear physics research, bridging nuclear physics and observational astrophysics, and advancing our understanding of i-process nucleosynthesis.

• Dembski, Cade; Spyrou, Artemis; Brown, B. Alex; Liddick, Sean N.; Berg, Hannah C. & Bleuel, Darren L. [Show all 25 contributors for this article] (2025). Extreme shape coexistence observed in 70Co. Communications Physics. 8(1). doi: 10.1038/s42005-025-01998-2. Full text in Research Archive Show summary

  The shape of the atomic nucleus is a property that underpins our understanding of nuclear systems, impacts the limits of nuclear existence, and enables probes of physics beyond the Standard Model. Nuclei can adopt a variety of shapes, including spheres, axially deformed spheroids, and pear shapes. In some regions of the nuclear chart where a spherical nucleus would naively be expected, deformed nuclear states can result from the collective action of constituent protons and neutrons. In a small subset of nuclei both spherical and deformed nuclear states have been experimentally observed, a phenomenon termed shape coexistence. We present spectroscopic evidence for the coexistence of Jπ = 1+ spherical and deformed states in 70Co, separated by less than 275 keV. This close degeneracy of levels with the same Jπ and different shapes demonstrates an extreme example of shape coexistence resulting from the interplay of independent particle motion and collective behavior in highly unstable nuclear systems and identifies the Co isotopes as a transition point between deformed ground states observed in the Cr isotopes and spherical configurations observed in the closed-shell Ni isotopes.

• Markova, Maria; Larsen, Ann-Cecilie & Garrote, Frank Leonel Bello (2025). Approaching the pygmy dipole resonance in Sn isotopes with the Oslo method. The European Physical Journal Conferences. ISSN 2101-6275. 322(04002). doi: 10.1051/epjconf/202532204002. Full text in Research Archive Show summary

  The γ-ray strength functions (GSF) and nuclear level densities (NLD) below the neutron separation energy were extracted for 111−113,116−122,124Sn from particle-γ coincidence data with the Oslo method in a model consistent way. Combined with results of a recent systematic Coulomb excitation study, the Oslo GSFs were used to extract bulk characteristics of the low-lying electric dipole response, commonly associated with the pygmy dipole resonance (PDR). A resonance-like peak on top of the tail of the isovector giant dipole resonance was observed in all of the isotopes. It is centered at 8 MeV and exhausts ≈2% of the classical Thomas-Reiche-Kuhn (TRK) sum. For the heaviest isotopes, the data suggest also a second peak located at ≈6.5 MeV, which might potentially be the isovector component of the PDR. At variance with microscopic calculations, no clear increase of the total low-lying E1 strength with neutron excess was observed in the experimental data. The results also suggest that association of the full low-lying electric dipole strength with the PDR, especially in its neutron skin interpretation, might be unfounded.

• Paulsen, Wanja; Li, Kevin Ching Wei; Siem, Sunniva; Ingeberg, Vetle Wegner; Larsen, Ann-Cecilie & Eriksen, Tomas Kvalheim [Show all 15 contributors for this article] (2025). Remeasuring the γ-decay branching ratio of the Hoyle state. Physical Review C. ISSN 2469-9985. 112. doi: 10.1103/2h2s-sbyx. Full text in Research Archive
• Spyrou, A.; Mücher, D.; Denissenkov, P.A.; Herwig, F.; Good, E.C. & Balk, G. [Show all 32 contributors for this article] (2024). First Study of the Ba 139 (n,γ) Ba 140 Reaction to Constrain the Conditions for the Astrophysical i Process. Physical Review Letters. ISSN 0031-9007. 132(20). doi: 10.1103/PhysRevLett.132.202701. Full text in Research Archive
• Sweet, A.; Bleuel, D.L.; Scielzo, N.D.; Bernstein, L.A.; Dombos, A.C. & Goldblum, B.L. [Show all 19 contributors for this article] (2024). Nuclear level density and γ -decay strength of Sr 93. Physical Review C. ISSN 2469-9985. 109(5). doi: 10.1103/PhysRevC.109.054305. Full text in Research Archive Show summary

  This work presents the first experimentally determined nuclear level density and 𝛾-ray strength function of the short-lived fission product 93 Sr, accomplished using the 𝛽-Oslo method. Direct measurement of the 92 Sr ⁢(𝑛,𝛾)⁢ 93 Sr cross section is not currently possible, as the half-life of 2.66 hours is too short; instead, 93 Sr was formed through 𝛽 decay of 93 Rb to excitation energies around the neutron separation energy. The 𝛾-ray spectra were measured using a total absorption spectrometer at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (MSU). The statistical properties of the 93 Sr nucleus were experimentally determined, including the 𝛾-ray strength function and nuclear level density. At low energies, the 𝛾-ray strength function exhibits a constant 𝛾-decay strength, rather than a slightly increasing strength with decreasing 𝛾-ray energy as had been previously observed for several nuclei in this mid-mass region. These statistical properties were then implemented in the reaction code talys1.95 to calculate the 92 Sr ⁢(𝑛,𝛾)⁢ 93 Sr cross section.

• Markova, Maria; Larsen, Ann-Cecilie & Garrote, Frank Leonel Bello (2024). The pygmy dipole resonance in Sn isotopes studied with the Oslo method. Nuovo cimento della societa italiana de fisica. C, Geophysics and space physics. ISSN 1124-1896. 47(2), p. 1–4. doi: 10.1393/ncc/i2024-24033-0. Full text in Research Archive Show summary

  The evolution of bulk properties of the low-lying electric dipole response (LEDR) in 111−113,116−122,124Sn has been studied on the basis of the γ-ray strength functions extracted from particle-γ coincidence data with the Oslo method and from Coulomb excitation data. The LEDR was found to be concentrated at ≈ 8.0–8.3 MeV and exhausts ≈ 2–3% of the Thomas-Reiche-Kuhn sum rule in all isotopes. No clear increase of the strength from the lightest 111Sn to the heaviest studied 124Sn, predicted with the majority of theoretical approaches, was observed.

• Spyrou, A.; Richman, D.; Couture, A.; Fields, C.E.; Liddick, S.N. & Childers, K. [Show all 26 contributors for this article] (2024). Enhanced production of 60Fe in massive stars. Nature Communications. 15(1). doi: 10.1038/s41467-024-54040-4. Full text in Research Archive Show summary

  Massive stars are a major source of chemical elements in the cosmos, ejecting freshly produced nuclei through winds and core-collapse supernova explosions into the interstellar medium. Among the material ejected, long-lived radioisotopes, such as 60Fe (iron) and 26Al (aluminum), offer unique signs of active nucleosynthesis in our galaxy. There is a long-standing discrepancy between the observed 60Fe/26Al ratio by γ-ray telescopes and predictions from supernova models. This discrepancy has been attributed to uncertainties in the nuclear reaction networks producing 60Fe, and one reaction in particular, the neutron-capture on 59Fe. Here we present experimental results that provide a strong constraint on this reaction. We use these results to show that the production of 60Fe in massive stars is higher than previously thought, further increasing the discrepancy between observed and predicted 60Fe/26Al ratios. The persisting discrepancy can therefore not be attributed to nuclear uncertainties, and points to issues in massive-star models.

• Markova, Maria; Larsen, Ann-Cecilie; Neumann-Cosel, Peter von; Litvinova, E.; Choplin, A. & Goriely, S. [Show all 11 contributors for this article] (2024). Systematic study of the low-lying electric dipole strength in Sn isotopes and its astrophysical implications. Physical Review C. ISSN 2469-9985. 109(5). doi: 10.1103/PhysRevC.109.054311. Full text in Research Archive Show summary

  The 𝛾-ray strength functions (GSFs) and nuclear level densities (NLDs) below the neutron threshold have been extracted for 111–113,116–122,124 Sn from particle-𝛾 coincidence data with the Oslo method. The evolution of bulk properties of the low-lying electric dipole response has been investigated on the basis of the Oslo GSF data and results of a recent systematic study of electric- and magnetic dipole strengths in even-even Sn isotopes with relativistic Coulomb excitation. The obtained GSFs reveal a resonance-like peak on top of the tail of the isovector giant dipole resonance centered at ≈8 MeV and exhausting ≈2% of the classical Thomas-Reiche-Kuhn (TRK) sum. For mass numbers ≥118 the data suggest also a second peak centered at ≈6.5 MeV. It corresponds to 0.1%–0.5% of the TRK sum rule and shows an approximate linear increase with the mass number. In contrast with predictions of the relativistic quasiparticle random-phase and time-blocking approximation calculations, no monotonic increase in the total low-lying 𝐸⁢1 strength was observed in the experimental data from 111 Sn to 124 Sn, demonstrating rather similar strength distributions in these nuclei. The Oslo GSFs and NLDs were further used as inputs to constrain the cross sections and Maxwellian-averaged cross sections of (𝑛,𝛾) reactions in the Sn isotopic chain using talys. The obtained results agree well with other available experimental data and the recommended values from the JINA REACLIB, BRUSLIB, and KADoNiS libraries. Despite relatively small exhausted fractions of the TRK sum rule, the low-lying electric dipole strength makes a noticeable impact on the radiative neutron-capture cross sections in stable Sn isotopes. Moreover, the experimental Oslo inputs for the 121,123 Sn ⁢(𝑛,𝛾) 122,124 Sn reactions were found to affect the production of Sb in the astrophysical 𝑖 process, providing new constraints on the uncertainties of the resulting chemical abundances from multizone low-metallicity asymptotic giant branch stellar models.

• Tagliente, G.; Milazzo, P.M.; Paradela, C.; Kopecky, S.; Vescovi, D. & Alaerts, G. [Show all 135 contributors for this article] (2024). High-resolution cross section measurements for neutron interactions on 89Y with incident neutron energies up to 95 keV. European Physical Journal A. ISSN 1434-6001. 60(1). doi: 10.1140/epja/s10050-024-01243-4. Full text in Research Archive Show summary

  The cross section of the 89Y(n,γ) reaction has important implications in nuclear astrophysics and for advanced nuclear technology. Given its neutron magic number N = 50 and a consequent small neutron capture cross section, 89Y represents one of the key nuclides for the stellar s-process. It acts as a bottleneck in the neutron capture chain between the Fe seed and the heavier elements. Moreover, it is located at the overlapping region, where both the weak and main s-process components take place. 89Y, the only stable yttrium isotope, is also used in innovative nuclear reactors. Neutron capture and transmission measurements were performed at the time-of-flight facilities n_TOF at CERN and GELINA at JRC-Geel. Resonance parameters of individual resonances were extracted from a resonance analysis of the experimental transmission and capture yields, up to a neutron incident energy of 95 keV. Even though a comparison with results reported in the literature shows differences in resonance parameters, the present data are consistent with the Maxwellian averaged cross section suggested by the astrophysical database KADoNiS.

• Lewis, R.; Couture, A.; Liddick, S.N.; Spyrou, A.; Bleuel, D.L. & Campo, Lucia Crespo [Show all 18 contributors for this article] (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. Full text in Research Archive Show summary

  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 [Show all 16 contributors for this article] (2023). Nuclear level densities and γ -ray strength functions of Sn 111,112,113 isotopes studied with the Oslo method. Physical Review C. ISSN 2469-9985. 108(1). doi: 10.1103/PhysRevC.108.014315. Full text in Research Archive Show summary

  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. [Show all 31 contributors for this article] (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. Full text in Research Archive
• Pogliano, Francesco & Larsen, Ann-Cecilie (2023). Impact of level densities and γ-strength functions on r-process simulations. Physical Review C. ISSN 2469-9985. 108(2), p. 025807–025807. doi: 10.1103/PhysRevC.108.025807. Full text in Research Archive Show summary

  Studies attempting to quantify the sensitivity of the r-process abundances to nuclear input have to cope with the fact that the theoretical models they rely on, rarely come with confidence intervals. This problem has been dealt with by either estimating these intervals and propagating them statistically to the final abundances using reaction networks within simplified astrophysical models, or by running more realistic astrophysical simulations using different nuclear-physics models consistently for all the involved nuclei. Both of these approaches have their strengths and weaknesses. In this work, we run r-process calculations for five trajectories using 49 different neutron-capture rate models. Our results shed light on the importance of taking into account shell effects and pairing correlations in the network calculations.

• Magagula, S.P.E.; Malatji, Kgashane Leroy; Wiedeking, M.; Pellegri, L; Beckmann, Kristine Sønstevold & Garrote, Frank Leonel Bello [Show all 18 contributors for this article] (2023). Investigating the strength of the scissors mode in 151Sm. Journal of Physics: Conference Series (JPCS). ISSN 1742-6588. doi: 10.1088/1742-6596/2586/1/012070. Full text in Research Archive Show summary

  Change in nuclei deformation leads to changes in statistical properties such as the nuclear level density (NLD) and γ-ray strength function (γSF). The NLD and γSF of 151Sm were extracted using the Oslo method. The strength of the scissors resonance (SR) and its centroid energy for 151Sm were found to be 2.13 ± 0.60 µ2N and 2.48 ± 0.25 MeV, respectively. These results were used to place the SR of 151Sm and its magnetic dipole strength B(M1)SR into the context of previously measured Sm isotopes.

• Pogliano, Francesco; Larsen, Ann-Cecilie; Goriely, Stéphane; Siess, Lionel; Markova, Maria & Görgen, Andreas [Show all 17 contributors for this article] (2023). Experimentally constrained Ho 165,166 (n,γ) rates and implications for the s process. Physical Review C. ISSN 2469-9985. 107(6). doi: 10.1103/PhysRevC.107.064614. Full text in Research Archive
• Mücher, D.; Spyrou, A.; Wiedeking, M.; Guttormsen, Magne Sveen; Larsen, Ann-Cecilie & Zeiser, Fabio Balthasar [Show all 25 contributors for this article] (2023). Extracting model-independent nuclear level densities away from stability. Physical Review C. ISSN 2469-9985. 107(1). doi: 10.1103/PhysRevC.107.L011602. Full text in Research Archive
• Pogliano, Francesco; Garrote, Frank Leonel Bello; Larsen, Ann-Cecilie; Berg, Hannah Christine; Gjestvang, Dorthea & Görgen, Andreas [Show all 19 contributors for this article] (2023). Observation of a candidate for the M1 scissors resonance in odd-odd Ho 166. Physical Review C. ISSN 2469-9985. 107(3). doi: 10.1103/PhysRevC.107.034605. Full text in Research Archive Show summary

  The γ -strength function and the nuclear level density for the odd-odd, rare-earth nucleus 166 Ho have been extracted from 163 Dy(α, pγ ) 166 Ho data using the Oslo method. A structure at ≈3 MeV in the γ -strength function is interpreted as the M1 scissors resonance. By employing three different methods we find that its strength depends rather strongly on the modeling of the E 1 strength, while its centroid does not. The 166 Ho scissors resonance parameters are consistent with previous results on other rare-earth nuclei.

• Markova, Maria; Larsen, Ann-Cecilie & Garrote, Frank Leonel Bello (2023). Nuclear level densities and γ-ray strength functions of 120,124Sn and their application in astrophysics. The European Physical Journal Conferences. ISSN 2101-6275. 275(02007), p. 1–4. doi: 10.1051/epjconf/202327502007. Full text in Research Archive Show summary

  Nuclear level densities (NLDs) and γ -ray strength functions (GSFs)of 120;124 Sn have been extracted with the Oslo method and additionally constrained with the novel Shape method. The GSFs were found to be in excellent agreement with the strengths from the inelastic relativistic proton scattering experiment. This comparison suggests the validity of the Brink-Axel hypothesisused as one of the key assumptions in astrophysical calculations. The extracted NLDs and GSFs were further used as experimental inputs to constrain the Maxwellian-averaged cross sections (MACS) for the radiative neutron capture process 119;123 Sn ( n, γ ) 120;124 Sn using the the nuclear reaction code TALYS.

• Markova, Maria; Larsen, Ann-Cecilie & Garrote, Frank Leonel Bello (2023). Nuclear level densities and γ-ray strength functions of 120,124Sn for astrophysical purposes. The European Physical Journal Conferences. ISSN 2101-6275. 279(12001), p. 1–6. doi: 10.1051/epjconf/202327912001. Full text in Research Archive Show summary

  The nuclear level densities (NLDs) and γ-ray strength functions (GSFs) of 120,124Sn were extracted with the Oslo method, compared and combined with other experimental data to be used as inputs in the TALYS reaction code to constrain the Maxwellian-averaged cross sections (MACS) for the 119,123Sn(n, γ)120,124Sn reactions. For 120Sn, the MACS are in relatively good agreement with the JINA REACLIB, BRUSLIB libraries, while no clear agreement was found for 124Sn. In addition, the pygmy dipole resonance (PDR) was found to contribute with up to ≈ 3 − 8% of the total MACS in these nuclei.

• Markova, Maria; Larsen, Ann-Cecilie & Garrote, Frank Leonel Bello (2023). Evolution of the Pygmy Dipole Resonance in Sn Isotopes. Acta Physica Polonica B, Proceedings Supplement. ISSN 1899-2358. 16(4-A5), p. 1–4. doi: 10.5506/APhysPolBSupp.16.4-A5. Full text in Research Archive
• Pogliano, Francesco; Larsen, Ann-Cecilie; Markova, Maria; Garrote, Frank Leonel Bello; Bjørøen, Marianne Møller & Eriksen, Tomas Kvalheim [Show all 17 contributors for this article] (2022). Indirect measurement of the (n,γ) Sb 127 cross section. Physical Review C. ISSN 2469-9985. 106(1). doi: 10.1103/PhysRevC.106.015804. Full text in Research Archive Show summary

  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.

• Naqvi, F.; Karampagia, S.; Spyrou, A.; Liddick, S.N.; Dombos, A.C. & Bleuel, D.l. [Show all 20 contributors for this article] (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. Full text in Research Archive
• Bernitt, Sonja; Bertone, Gianfranco; Cardoso, Vitor; Emparan, Roberto; Galatyuk, Tetyana & Kurkela, Eero Aleksi [Show all 13 contributors for this article] (2022). Fundamental Physics in the Gravitational-Wave Era. Nuclear Physics News. ISSN 1061-9127. 32(1), p. 16–19. doi: 10.1080/10619127.2021.1988473. Full text in Research Archive
• Goriely, Stephane; Larsen, Ann-Cecilie & Mücher, Dennis (2022). Comprehensive test of nuclear level density models. Physical Review C. ISSN 2469-9985. 106(4). doi: 10.1103/PhysRevC.106.044315. Full text in Research Archive Show summary

  For the last two decades, experimental information on nuclear level densities for about 60 different nuclei has been obtained on the basis of the Oslo method. While each of these measurements has been typically compared to one or a few level density models, a global study including all the measurements has been missing. The present study provides a systematic comparison between Oslo data and six global level density models for 42 nuclei for which s-wave resonance spacings are also available. We apply a coherent normalization procedure to the Oslo data for each of the six different models, all being treated on the same footing. Our quantitative analysis shows that the constant-temperature model presents the best global description of the Oslo data, closely followed by the mean-field plus combinatorial model and Hartree-Fock plus statistical model. Their accuracies are quite similar, so that it remains difficult to clearly favour one of these models. When considering energies above the threshold where the experimental level scheme is complete, all the six models are shown to lead to rather similar accuracies with respect to Oslo data. The recently proposed shape method can, in principle, improve the situation since it provides an absolute estimate of the excitation-energy dependence of the measured level densities. We show for the specific case of 112Cd that the shape method could exclude the Hartree-Fock plus statistical model. Such an analysis remains to be performed for the bulk of data for which the shape method can be applied to the Oslo measurements before drawing conclusions on the general quality of a given nuclear level density model.

• Garrote, Frank Leonel Bello; Lopez-Martens, Araceli; Larsen, Ann-Cecilie; Deloncle, I.; Péru, Sophie & Zeiser, Fabio [Show all 39 contributors for this article] (2022). Experimental observation of the M1 scissors mode in ²⁵⁴No. Physics Letters B. ISSN 0370-2693. 834. doi: 10.1016/j.physletb.2022.137479. Full text in Research Archive Show summary

  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 [Show all 26 contributors for this article] (2022). Evolution of the γ -ray strength function in neodymium isotopes. Physical Review C. ISSN 2469-9985. 106(3). doi: 10.1103/PhysRevC.106.034314. Full text in Research Archive Show summary

  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.

• Markova, Maria; Larsen, Ann-Cecilie; Neumann-Cosel, Peter von; Bassauer, Sergej; Görgen, Andreas & Guttormsen, Magne Sveen [Show all 23 contributors for this article] (2022). Nuclear level densities and γ -ray strength functions in Sn 120,124 isotopes: Impact of Porter-Thomas fluctuations. Physical Review C. ISSN 2469-9985. 106(3). doi: 10.1103/PhysRevC.106.034322. Full text in Research Archive Show summary

  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).

• Persch, C.F.; DeYoung, P.A.; Lyons, S.; Spyrou, Artemis; Liddick, Sean N. & Naqvi, F. [Show all 27 contributors for this article] (2021). Beta-decay feeding intensity distributions of 71,73Ni. Physical Review C. ISSN 2469-9985. C103(055808). doi: 10.1103/PhysRevC.103.055808. Full text in Research Archive Show summary

  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 [Show all 22 contributors for this article] (2021). Strong enhancement of level densities in the crossover from spherical to deformed neodymium isotopes. Physics Letters B. ISSN 0370-2693. 816. doi: 10.1016/j.physletb.2021.136206. Full text in Research Archive Show summary

  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.

• Wiedeking, Mathis; Guttormsen, Magne Sveen; Larsen, Ann-Cecilie; Zeiser, Fabio; Görgen, Andreas & Liddick, Sean N. [Show all 9 contributors for this article] (2021). Independent normalization for gamma-ray strength functions: The shape method. Physical Review C. ISSN 2469-9985. 104(014311). doi: 10.1103/PhysRevC.104.014311. Full text in Research Archive Show summary

  The shape method, a novel approach to obtain the functional form of the γ-ray strength function (γSF), is introduced. In connection with the Oslo method the slope of the nuclear level density (NLD) and γSF can be obtained simultaneously even in the absence of neutron resonance spacing data. The foundation of the shape method lies in the primary γ-ray transitions which preserve information on the functional form of the γSF. The shape method has been applied to 56Fe, 92Zr, and 164Dy, which are representative cases for the variety of situations encountered in typical NLD and γSF studies. The comparisons of results from the shape method to those from the Oslo method demonstrate that the functional form of the γSF is retained regardless of nuclear structure details or Jπ values of the states fed by the primary transitions.

• Malatji, Kgashane Leroy; Beckmann, Kristine Sønstevold; Wiedeking, Mathis; Siem, Sunniva; Goriely, Stephane & Larsen, Ann-Cecilie [Show all 21 contributors for this article] (2021). Statistical properties of the well deformed 153,155Sm nuclei and the scissors resonance. Physical Review C. ISSN 2469-9985. 103(1). doi: 10.1103/PhysRevC.103.014309. Full text in Research Archive Show summary

  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.

• Görgen, Andreas; Guttormsen, Magne Sveen; Larsen, Ann-Cecilie; Siem, Sunniva; Adli, Erik & Edin, Nina Frederike J [Show all 14 contributors for this article] (2021). The Oslo Cyclotron Laboratory. The European Physical Journal Plus. 136, p. 1–13. doi: 10.1140/epjp/s13360-021-01150-3. Full text in Research Archive Show summary

  Research at the Oslo Cyclotron Laboratory at the University of Oslo is focused on spectroscopy experiments for nuclear structure and nuclear astrophysics using the Oslo Scintillator Array OSCAR. Light-ion beams from the K=35 cyclotron are furthermore used for studies in radiation biology and medical physics, for research and development related to medical isotope production, and for irradiation of materials and electronics components. Here we present an overview of the laboratory and its research infrastructure, give a brief discussion of the respective research programs and methods, and present recent highlights.

• Zeiser, Fabio; Tveten, Gry Merete; Garrote, Frank Leonel Bello; Guttormsen, Magne Sveen; Larsen, Ann-Cecilie & Ingeberg, Vetle Wegner [Show all 8 contributors for this article] (2021). The gamma-ray energy response of the Oslo Scintillator Array OSCAR. Nuclear Instruments and Methods in Physics Research Section A : Accelerators, Spectrometers, Detectors and Associated Equipment. ISSN 0168-9002. 985. doi: 10.1016/j.nima.2020.164678. Full text in Research Archive Show summary

  The new Oslo Scintillator Array (OSCAR) has been commissioned at the Oslo Cyclotron Laboratory (OCL). It consists of 30 large volume (⌀ 3.5 × 8 inches) LaBr3(Ce) detectors that are used for 𝛾-ray spectroscopy. The response functions for incident 𝛾 rays up to 20 MeV are simulated with Geant4. In addition, the resolution, and the total and full-energy peak efficiencies are extracted. The results are in very good agreement with measurements from calibration sources and experimentally obtained mono-energetic in-beam 𝛾-ray spectra.

• Markova, Maria; Neumann-Cosel, Neumann-Cosel von; Larsen, A.C.; Bassauer, S.; Görgen, A. & Guttormsen, Magne Sveen [Show all 25 contributors for this article] (2021). Comprehensive Test of the Brink-Axel Hypothesis in the Energy Region of the Pygmy Dipole Resonance. Physical Review Letters. ISSN 0031-9007. 127(18). doi: 10.1103/PhysRevLett.127.182501. Full text in Research Archive Show summary

  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.

• Gjestvang, Dorthea; Siem, Sunniva; Zeiser, Fabio; Randrup, Jørgen; Vogt, Ramona & Garrote, Frank Leonel Bello [Show all 20 contributors for this article] (2021). The study of prompt fission γ rays at the Oslo Cyclotron Laboratory. The European Physical Journal Conferences. ISSN 2101-6275. doi: 10.1051/epjconf/202125600005. Full text in Research Archive Show summary

  The study of prompt fission γ rays (PFGs) is crucial for understanding the energy and angular momentum distribution in fission, and over the last decade there has been an revived interest in this aspect of fission. We present the new experimental setup at the Oslo Cyclotron Laboratory for detecting PFGs resulting from charged particle-induced fission. Additionally, PFGs from the reaction 240 Pu(d,pf) were measured in April 2018, and the fission gated proton- γ coincidence spectrum is shown. In order to explore the dependence of the PFG emission on the excitation energy and angular momentum of the compound nucleus, we plan several experiments where charged particle reactions are used to induce fission in various plutonium isotopes. The final results will be compared to predictions made by the Fission Reaction Event Yield Algorithm (FREYA) in an upcoming publication, to benchmark the current modelling of both the PFGs and the fission process.

• Gjestvang, Dorthea; Siem, Sunniva; Zeiser, Fabio; Randrup, Jørgen; Vogt, Ramona & Wilson, Jonathan Nicholas [Show all 19 contributors for this article] (2021). Excitation energy dependence of prompt fission γ-ray emission from 241Pu*. Physical Review C. ISSN 2469-9985. 103(3). doi: 10.1103/PhysRevC.103.034609. Full text in Research Archive Show summary

  Prompt fission γ rays (PFGs) resulting from the 240Pu(d,pf) reaction have been measured as a function of fissioning nucleus excitation energy Ex at the Oslo Cyclotron Laboratory. We study the average total PFG multiplicity per fission, the average total PFG energy released per fission, and the average PFG energy. No significant changes in these characteristics are observed over the range 5.75

• Midtbø, Jørgen E.; Zeiser, Fabio; Lima, Erlend; Larsen, Ann-Cecilie; Tveten, Gry Merete & Guttormsen, Magne Sveen [Show all 9 contributors for this article] (2021). A new software implementation of the Oslo method with rigorous statistical uncertainty propagation. Computer Physics Communications. ISSN 0010-4655. 262. doi: 10.1016/j.cpc.2020.107795. Full text in Research Archive Show summary

  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.

• Guttormsen, Magne Sveen; Larsen, Ann-Cecilie; Spyrou, Artemis & Liddick, Sean N. (2020). Experimentally constrained (n, γ) reaction rates relevant to r- and i-process nucleosynthesis. Acta Physica Polonica B. ISSN 0587-4254. 56(3), p. 667–676. doi: 10.5506/APhysPolB.51.667. Full text in Research Archive Show summary

  The element distribution that we observe in the Universe today tells a fascinating story of nucleosynthesis events that have taken place throughout the 13.7-billion-years-long history starting with the Big Bang. It has been known for a long time that radiative neutron-capture reactions play a major role in synthesizing elements heavier than iron. However, many questions remain when it comes to our understanding of neutron-capture processes in extreme stellar environments. In particular, the intermediate and rapid neutron-capture processes are very challenging to describe, as there exist little or no data on the much-needed neutron-capture rates. In this work, we discuss possibilities to obtain indirect, experimental constrains on these rates by means of the Oslo and the β-Oslo methods.

• Kibédi, T.; Alshahrani, B.; Stuchbery, A.E.; Larsen, Ann-Cecilie; Görgen, Andreas & Siem, Sunniva [Show all 20 contributors for this article] (2020). Radiative Width of the Hoyle State from γ -Ray Spectroscopy. Physical Review Letters. ISSN 0031-9007. 125(18). doi: 10.1103/PhysRevLett.125.182701. Full text in Research Archive Show summary

  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.

• Scholz, P.; Guttormsen, Magne Sveen; Heim, F.; Larsen, Ann-Cecilie; Mayer, J. & Savran, D. [Show all 12 contributors for this article] (2020). Primary γ-ray intensities and γ-strength functions from discrete two-step γ-ray cascades in radiative proton-capture experiments. Physical Review C. ISSN 2469-9985. doi: 10.1103/PhysRevC.101.045806. Full text in Research Archive Show summary

  Background: Reaction rates of radiative capture reactions can play a crucial role in the nucleosynthesis of heavy nuclei in explosive stellar environments. These reaction rates depend strongly on γ-ray decay widths in the reaction products, which are, for nonresonant capture reactions at high excitation energies, derived from the γ-ray strength function and the nuclear level density. Recently, the ratio method was applied to primary γ rays observed from (d,p) reactions and nuclear resonance fluorescence measurements to extract the dipole strength in atomic nuclei and to test the generalized Brink-Axel hypothesis. Purpose: The purpose of this work is to apply the ratio method to primary γ-ray intensities of the 63,65Cu(p,γ) reactions to extract γ-ray strength information on the nuclei 64,66Zn. The impact of spin distribution, total γ-ray decay widths, level densities, and width fluctuations on the application of the ratio method will be discussed. Additionally, by comparing the relative γ-ray strength at different excitation energies, conclusions on the validity of the generalized Brink-Axel hypothesis can be made. Method: The radiative proton capture reaction measurements have been performed at the HORUS γ-ray spectrometer of the University of Cologne at one excitation energy for each reaction. Primary γ-ray intensities have been determined by normalizing secondary γ-ray transitions in two-step cascades using their absolute branching ratio. The ratio method was applied to the measured primary γ-ray intensities as well as to previous measurements by Erlandsson et al. at different excitation energies. Results: The relative strength function curve for 64Zn from our measurement shows no significant deviation from the previous measurement at a different excitation energy. The same is true for 66Zn where both measurements were at almost the same excitation energy. Absolute γ-strength function values have been obtained by normalizing the relative curves to quasiparticle random phase approximation calculations because of the absence of experimental data in the respective energy region. Conclusion: The generalized Brink-Axel hypothesis, i.e., the independence of the strength function on the excitation energy, seems to hold in the studied energy region and nuclei. The method to obtain primary γ-ray intensities from two-step cascade spectra was shown to be a valuable and sensitive tool although its uncertainties are connected to the knowledge of the low-energy level scheme of the investigated nucleus. The scaling in the ratio method should be taken with care, because the relative strength is not a simple sum of fE1 and fM1 but a somewhat complex linear combination dependent on the excitation energy of the nucleus.

• Ingeberg, Vetle Wegner; Siem, Sunniva; Wiedeking, Mathis; Sieja, Kamila; Bleuel, D.l. & Brits, C.P. [Show all 29 contributors for this article] (2020). First application of the Oslo method in inverse kinematics. European Physical Journal A. ISSN 1434-6001. 56. doi: 10.1140/epja/s10050-020-00070-7. Full text in Research Archive Show summary

  The γ-ray strength function (SF) and nuclear level density (NLD) have been extracted for the first time from inverse kinematic reactions with the Oslo method. This novel technique allows measurements of these properties across a wide range of previously inaccessible nuclei. Proton–γ coincidence events from the d(⁸⁷Kr,p)⁸⁶Kr reaction were measured at iThemba LABS and the γSF and NLD in ⁸⁶Kr was obtained. The low-energy region of the γSF is compared to shell-model calculations, which suggest this region to be dominated by M1 strength. The γSF and NLD are used as input parameters to Hauser–Feshbach calculations to constrain (n,γ) cross sections of nuclei using the TALYS reaction code. These results are compared to ⁸⁶Kr(n,γ) data from direct measurements.

• Kullmann, Ina Kristine Berentsen; Larsen, Ann-Cecilie; Renstrøm, Therese; Beckmann, Kristine Sønstevold; Garrote, Frank Leonel Bello & Campo, Lucia Crespo [Show all 13 contributors for this article] (2019). First experimental constraint on the 191Os(n,γ) reaction rate relevant to s-process nucleosynthesis. Physical Review C. ISSN 2469-9985. 99(6). doi: 10.1103/PhysRevC.99.065806. Full text in Research Archive Show summary

  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.

• Zeiser, Fabio; Tveten, Gry Merete; Potel, Gregory; Larsen, Ann-Cecilie; Guttormsen, Magne Sveen & Laplace, Thibault A. [Show all 22 contributors for this article] (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), p. 1–9. doi: 10.1103/PhysRevC.100.024305. Full text in Research Archive
• Lyons, Stephanie; Spyrou, Artemis; Liddick, Sean N.; Naqvi, Farheen; Crider, Benjamin P. & Dombos, Alexander C. [Show all 25 contributors for this article] (2019). 69,71Co β-decay strength distributions from total absorption spectroscopy. Physical Review C. ISSN 2469-9985. 100(2), p. 1–10. doi: 10.1103/PhysRevC.100.025806. Full text in Research Archive Show summary

  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. [Show all 7 contributors for this article] (2019). The Beta-Oslo Method: ExperimentallyConstrained (n,γ) Reaction RatesRelevant to ther-Process. In Formicola, Alba; Junker, Matthias; Gialanella, Lucio & Imbriani, Gianluca (Ed.), Nuclei in the Cosmos XV. Springer. ISSN 9783030138752. p. 137–140. doi: 10.1007/978-3-030-13876-9_22. Full text in Research Archive
• Voinov, Alexander; Renstrøm, Therese; Bleuel, D.l.; Grimes, S.M.; Guttormsen, Magne Sveen & Larsen, Ann-Cecilie [Show all 23 contributors for this article] (2019). Level densities of 74,76Ge from compound nuclear reactions. Physical Review C. ISSN 2469-9985. 99(5). doi: 10.1103/PhysRevC.99.054609. Full text in Research Archive Show summary

  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 [Show all 27 contributors for this article] (2019). Nuclear level densities and γ-ray strength functions of 180,181,182Ta. Physical Review C. ISSN 2469-9985. 99(5). doi: 10.1103/PhysRevC.99.054330. Full text in Research Archive Show summary

  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. In Formicola, Alba; Junker, Matthias; Gialanella, Lucio & Imbriani, Gianluca (Ed.), Nuclei in the Cosmos XV. Springer. ISSN 9783030138752. p. 405–407. doi: 10.1007/978-3-030-13876-9. Full text in Research Archive
• Larsen, Ann-Cecilie; Spyrou, Artemis; Liddick, Sean N. & Guttormsen, Magne Sveen (2019). Novel techniques for constraining neutron-capture rates relevant for r-process heavy-element nucleosynthesis. Progress in Particle and Nuclear Physics. ISSN 0146-6410. 107, p. 69–108. doi: 10.1016/j.ppnp.2019.04.002. Full text in Research Archive Show summary

  The rapid-neutron capture process (r process) is identified as the producer of about 50% of elements heavier than iron. This process requires an astrophysical environment with an extremely high neutron flux over a short amount of time (∼ seconds), creating very neutron-rich nuclei that are subsequently transformed to stable nuclei via β − decay. In 2017, one site for the r process was confirmed: the advanced LIGO and advanced Virgo detectors observed two neutron stars merging, and immediate follow-up measurements of the electromagnetic transients demonstrated an ”afterglow” over a broad range of frequencies fully consistent with the expected signal of an r process taking place. Although neutronstar mergers are now known to be r-process element factories, contributions from other sites are still possible, and a comprehensive understanding and description of the r process is still lacking. One key ingredient to large-scale r-process reaction networks is radiative neutron-capture (n, γ) rates, for which there exist virtually no data for extremely neutronrich nuclei involved in the r process. Due to the current status of nuclear-reaction theory and our poor understanding of basic nuclear properties such as level densities and average γ-decay strengths, theoretically estimated (n, γ) rates may vary by orders of magnitude and represent a major source of uncertainty in any nuclear-reaction network calculation of rprocess abundances. In this review, we discuss new approaches to provide information on neutron-capture cross sections and reaction rates relevant to the r process. In particular, we focus on indirect, experimental techniques to measure radiative neutron-capture rates. While direct measurements are not available at present, but could possibly be realized in the future, the indirect approaches present a first step towards constraining neutron-capture rates of importance to the r process.

• Utsunomiya, Hiroaki; Renstrøm, Therese; Tveten, Gry Merete; Goriely, Stéphane; Ari-izumi, Takashi & Filipescu, Dan Mihai [Show all 14 contributors for this article] (2019). γ-ray strength function for thallium isotopes relevant to the 205Pb−205Tl chronometry. Physical Review C. ISSN 2469-9985. 99(2), p. 024609-1–023609-8. doi: 10.1103/PhysRevC.99.024609. Full text in Research Archive Show summary

  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 [Show all 30 contributors for this article] (2019). Benchmarking the extraction of statistical neutron capture cross sections on short-lived nuclei for applications using the β-Oslo method. Physical Review C. ISSN 2469-9985. 100:024624(2), p. 1–12. doi: 10.1103/PhysRevC.100.024624. Full text in Research Archive Show summary

  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 [Show all 13 contributors for this article] (2019). Indirect(n,γ)91,92Zr Cross SectionMeasurements for the s-Process. In Formicola, Alba; Junker, Matthias; Gialanella, Lucio & Imbriani, Gianluca (Ed.), Nuclei in the Cosmos XV. Springer. ISSN 9783030138752. p. 359–362. doi: 10.1007/978-3-030-13876-9_65. Full text in Research Archive
• Krzysiek, Mateusz; Utsunomiya, Hiroaki; Gheorghe, Ioana; Filipescu, Dan Mihai; Renstrøm, Therese & Tveten, Gry Merete [Show all 19 contributors for this article] (2019). Photoneutron cross-section measurements for 165HO by the direct neutron-multiplicity sorting at Newsubaru. Acta Physica Polonica B. ISSN 0587-4254. 50(3), p. 487–494. doi: 10.5506/APhysPolB.50.487. Full text in Research Archive
• Wrzosek-Lipska, K.; Rezynkina, K.; Bree, N.; Zielińska, M.; Gaffney, L.P. & Petts, A. [Show all 70 contributors for this article] (2019). Electromagnetic properties of low-lying states in neutron-deficient Hg isotopes: Coulomb excitation of ¹⁸²Hg, ¹⁸⁴Hg, ¹⁸⁶Hg and ¹⁸⁸Hg. European Physical Journal A. ISSN 1434-6001. 55(8), p. 1–23. doi: 10.1140/epja/i2019-12815-2. Full text in Research Archive
• Malatji, Kgashane Leroy; Wiedeking, Mathis; Goriely, Stephane; Brits, Christiaan Petrus; Kheswa, Bonginkosi Vincent & Garrote, Frank Leonel Bello [Show all 22 contributors for this article] (2019). Re-estimation of 180Ta nucleosynthesis in light of newly constrained reaction rates. Physics Letters B. ISSN 0370-2693. 791, p. 403–408. doi: 10.1016/j.physletb.2019.03.013. Full text in Research Archive
• Lewis, Rebecca; Liddick, Sean N.; Larsen, Ann-Cecilie; Spyrou, Artemis; Bleuel, Darren L. & Couture, Aaron J. [Show all 17 contributors for this article] (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. Full text in Research Archive Show summary

  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.

• Utsunomiya, Hiroaki; Renstrøm, Therese; Tveten, Gry Merete; Goriely, Stéphane; Katayama, Seitaro & Ari-Izumi, Takashi [Show all 22 contributors for this article] (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), p. 1–9. doi: 10.1103/PhysRevC.98.054619. Full text in Research Archive Show summary

  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.

• Jones, M.D.; Macchiavelli, Augusto Oswaldo; Wiedeking, Mathis; Bernstein, Lee A.; Crawford, Heather L. & Campbell, C.M. [Show all 30 contributors for this article] (2018). Examination of the Low-Energy Enhancement of the gamma-ray Strength Function of 56Fe. Physical Review C. ISSN 2469-9985. 97(2). doi: 10.1103/PhysRevC.97.024327. Full text in Research Archive Show summary

  A model-independent technique was used to determine the γ -ray strength function ( γ SF ) of 56 Fe down to γ -ray energies less than 1 MeV for the first time with GRETINA using the (p,p′ ) reaction at 16 MeV. No difference was observed in the energy dependence of the γ SF built on 2+ and 4+ final states, supporting the Brink hypothesis. In addition, angular distribution and polarization measurements were performed. The angular distributions are consistent with dipole radiation. The polarization results show a small bias towards magnetic character in the region of the enhancement.

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• Meir, Michaela Georgine & Larsen, Ann-Cecilie (2026). New Nature study solves a decades-old nuclear physics puzzle. doi: https:/www.linkedin.com/feed/update/urn:li:activity:7492893342847123456. Full text in Research Archive
• Larsen, Ann-Cecilie (2026). Gravitasjonsbølger og grunnstoff. doi: https:/www.uio.no/forskning/scene-domus-bibliotheca/arrangementer/2026/gravitasjonsbolger. Full text in Research Archive
• Ingeberg, Vetle Wegner; Görgen, Andreas; Inoue, Azusa; Kumar, Neeraj; Larsen, Ann-Cecilie & Li, Kevin Ching Wei [Show all 9 contributors for this article] (2026). OSCAR at ISOLDE. Full text in Research Archive Show summary

  For the next run period at ISOLDE, the Nuclear Physics group at the University of Oslo are considering proposing a longer experimental campaign with the Oslo SCintillator ARay (OSCAR). The main aims of such a campaign will be to measure the nuclear level density and -ray strength function of key nuclei relevant for nuclear structure and nuclear astrophysics (e.g. i-process nucleosynthesis). Other cases of interest could be spectroscopy of resonances in light exotic nuclei or rare event searches. In addition, we would also invite other interested groups to propose experiments with the setup while it is present at HIE-ISOLDE. The OSCAR array is the largest LaBr:Ce detector array in the world (at least in terms of detector volume). It offers exceptional efficiency for high-energy -rays without compromising on either energy or time resolution. It consists of 30 large 3.5x8-inch large volume LaBr3:Ce detectors, an icosahedron frame with six rings covering polar angles from to . Detectors can be mounted in a distance of 16.3 to 22 cm from the target, resulting in solid angle coverage of 57%. This translates to about 15% full energy efficiency at 1332 keV and close to 5% at 10 MeV in the closest configuration. In this presentation I will present the physics cases and our preliminary plans for such a campaign.

• Paulsen, Wanja; Li, Kevin Ching Wei; Siem, Sunniva; Ingeberg, Vetle Wegner; Larsen, Ann-Cecilie & Eriksen, Tomas Kvalheim [Show all 15 contributors for this article] (2026). CLUSTER'26. Full text in Research Archive
• Mørch, Hedda Hassel; Brodal, Per & Larsen, Ann-Cecilie (2025). Abels tårn: Blir du smartere av mobilspill? [Radio]. Nrk P2. Full text in Research Archive
• Larsen, Ann-Cecilie (2024). Lecture 1: An introduction to nuclear astrophysics + Lecture 2: Nuclear-physics ingredients for heavy-element nucleosynthesis. Full text in Research Archive
• Larsen, Ann-Cecilie (2024). Lecture 1: An introduction to nuclear astrophysics + Lecture 2: Nuclear-physics ingredients for heavy-element nucleosynthesis. Full text in Research Archive
• Skogvoll, Vidar; Larsen, Ann-Cecilie & Kvellestad, Anders (2024). Real læring - Realistfabrikken: Hvordan lage fysiker. [Radio]. Podcast. Full text in Research Archive
• Larsen, Ann-Cecilie (2024). Kjernefysikk - og hva det kan brukes til. Full text in Research Archive
• Larsen, Ann-Cecilie (2024). Kjerne-astrofysikk. Full text in Research Archive
• Larsen, Ann-Cecilie (2024). Forskerlivet til en kjerne-astrofysiker. Full text in Research Archive
• Larsen, Ann-Cecilie (2024). De leter etter grunnstoff-fabrikkene i universet. [Journal]. Apollon. Full text in Research Archive
• Larsen, Ann-Cecilie (2024). Norske forskere leter etter grunnstoff-fabrikkene i universet. [Journal]. Teknisk Ukeblad. Full text in Research Archive
• Larsen, Ann-Cecilie (2024). Indirect measurements of neutron-capture rates for exotic, neutron-rich nuclei relevant to the intermediate and rapid neutron-capture processes. Full text in Research Archive
• Paulsen, Wanja; Li, Kevin Ching Wei; Siem, Sunniva; Ingeberg, Vetle Wegner; Larsen, Ann-Cecilie & Eriksen, Tomas Kvalheim [Show all 20 contributors for this article] (2023). Remeasuring the gamma-decay branching ratio of the Hoyle state. Full text in Research Archive
• Larsen, Ann-Cecilie (2023). Neutron capture rates for i-process and r-process nucleosynthesis. Full text in Research Archive
• Larsen, Ann-Cecilie (2023). Constraining neutron capture rates relevant to r-process and i-process nucleosynthesis. Full text in Research Archive
• Larsen, Ann-Cecilie (2023). Experiments to constrain neutron capture rates for the i- and r-process nucleosynthesis. Full text in Research Archive
• Sørbø, Solveig & Larsen, Ann-Cecilie (2022). Ann-Cecilie Larsen om kjerneastrofysikk, løping og musikk. [Radio]. radiOrakel og podcast. Full text in Research Archive Show summary

  Ann-Cecilie Larsen er på en måte en spesielt speisa gjest siden hun forsker på space!!! I denne episoden snakker vi om musikk som har hjulpet henne tenke klart når hun skulle kna kjerneastrofysiske data eller "bare" løpe halvmaraton! Tung musikk, tunge metaller. Eller heavy metal, heavy metals. Masse sexy vitenskap.

• Larsen, Ann-Cecilie (2021). Abels tårn - om fusjon. [Radio]. NRK P2 Ekko. Full text in Research Archive
• Larsen, Ann-Cecilie (2021). The quest for the origin of heavy elements. Full text in Research Archive
• Larsen, Ann-Cecilie (2021). Solveigs speisa musikk https://radiorakel.no/author/solveigs-speisa-musikk/ Ann-Cecilie Larsen Om Kjerneastrofysikk, Løping Og Musikk. [Radio]. Podkast og radio. Full text in Research Archive
• Larsen, Ann-Cecilie (2021). Abels tårn - om gull og protoner. [Radio]. NRK P2 Ekko. Full text in Research Archive
• Larsen, Ann-Cecilie (2020). A bright-matter mystery: the quest for the origin of the elements. Full text in Research Archive
• Larsen, Ann-Cecilie (2020). Experimentally constrained neutron-capture rates for the intermediate and rapid neutron-capture processes. Full text in Research Archive
• Larsen, Ann-Cecilie (2019). Indirect, experimental constraints of (n,γ) reaction rates for the i- and r-process. Full text in Research Archive
• Larsen, Ann-Cecilie (2019). Constraining neutron-capture rates relevant to r-process and i-process nucleosynthesis. Full text in Research Archive
• Larsen, Ann-Cecilie (2019). Leading an ERC StG research team - some experiences and thoughts. Full text in Research Archive
• Larsen, Ann-Cecilie (2019). Mysteriet i hjertet av atomet - hvor lenge overlever nøytroner på avveie? Full text in Research Archive
• Midtbø, Jørgen E.; Larsen, Ann-Cecilie & Renstrøm, Therese (2018). Extracting γ-strength functions from shell model calculations. Full text in Research Archive
• Larsen, Ann-Cecilie (2018). Constraining neutron-capture rates for r-process scenarios. Full text in Research Archive
• Larsen, Ann-Cecilie (2018). The beta-Oslo method: experimentally constrained (n,gamma) reaction rates relevant to the r-process. Full text in Research Archive

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