Proton-γ coincidences from (d,p) reactions between a Ni66 beam and a deuterated polyethylene target have been analyzed with the inverse-Oslo method to find the nuclear level density (NLD) and γ-ray strength function (γSF) of Ni67. The Ni66(n,γ) capture cross section has been calculated using the Hauser-Feshbach model in using the measured NLD and γSF as constraints. The results confirm that the Ni66(n,γ) reaction acts as a bottleneck when relying on one-zone nucleosynthesis calculations. However, the impact of this reaction is strongly dampened in multizone models of low-metallicity AGB stars experiencing i-process nucleosynthesis. Published by the American Physical Society 2025

In this work, we present new data on the 197Au photoneutron reactions in and above the giant dipole resonance region, obtained by using 8 to 39 MeV quasimonochromatic gamma-ray beams produced at the NewSUBARU facility in Japan and a high-and-flat efficiency neutron detection system. We report absolute cross sections and mean photoneutron energies for the 197Au(gamma, inX ) reactions with i = 1 to 4. The photoabsorption cross section was obtained as the sum of the (gamma, inX) reaction cross sections. The giant dipole resonance parameter values were obtained by fitting the experimental photoabsorption cross sections. The present photoabsorption cross sections are in good agreement with the Saclay results of Veyssiere et al., Nucl. Phys. A 159, 561 (1970). Thus, our study does not support the recommendation of Berman et al., Phys. Rev. C 36, 1286 (1987), of lowering the Saclay photoabsorption cross sections by 8%. We observed a nonstatistical high-energy neutron emission in the (gamma, n) reaction in the low-energy region between Sn and 10 MeV. The present results are compared with data from the literature and statistical model calculations performed with the TALYS and EMPIRE codes.

The radiative branching ratio of the Hoyle state is crucial to estimate the triple-α reaction rate in stellar environments at medium temperatures of T=0.1 to 2 GK. Knowledge of the γ-decay channel is critical as this is the dominant radiative decay channel for the Hoyle state. A recent study by Kibédi et al. [Phys. Rev. Lett. 125, 182701 (2020)] has challenged our understanding of this astrophysically significant branching ratio and its constraints. The main purpose was to perform a new measurement of the γ-decay branching ratio of the Hoyle state to deduce the radiative branching ratio of the Hoyle state, an additional objective was to independently verify aspects of the measurement conducted by Kibédi et al. For the primary experiment of this work the Hoyle state was populated by the ^12C(p,p') reaction at 10.8 MeV at the Oslo Cyclotron Laboratory. The γ-decay branching ratio was deduced through triple-coincidence events between a proton populating the Hoyle state and the subsequent γ-ray cascade. An independent analysis of the 2014 data published by Kibédi et al. has been carried out. From the main experiment of this work, a γ-decay branching ratio of the Hoyle state was determined as Γ_γ^7.65/Γ^7.65=4.0(3)× 10^-4, yielding a radiative branching ratio of Γ_rad/Γ=4.1(4) × 10^-4. The reanalysis of the 2014 experiment in this work yielded Γ_γ^7.65/Γ^7.65=4.5(6)× 10^-4, with a radiative branching ratio of Γ_rad/Γ=4.6(6) × 10^-4. The measurements of the radiative branching ratio of the Hoyle state in this work is in excellent agreement with several recent studies, as well as the previously adopted ENSDF average of Γ_rad/Γ=4.16(11)× 10^-4.

Received 31 October 2023DOI:https://doi.org/10.1103/PhysRevC.109.019901©2024 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasElectromagnetic transitionsEnergy levelsLevel densitiesNuclear decayNuclear structure & decaysNucleon induced nuclear reactionsProperties90 ≤ A ≤ 149Nuclear Physics

Photoneutron emission cross sections were measured for $^{13}$C below $2n$ threshold using quasi-monochromatic $\gamma$-ray beams produced in laser Compton-scattering at the NewSUBARU synchrotron radiation facility. The data show fine structures in the low-energy tail of the giant-dipole resonance; the integrated strength of the fine structure below 18~MeV is intermediate among the past measurements with bremsstrahlung and the positron annihilation $\gamma$ rays. We compare the photoneutron emission data with the {\sf TALYS} statistical model calculation implemented with the simple modified Lorentzian model of $E1$ and $M1$ strengths. We also compare the total photoabsorption cross sections for $^{13}$C with the shell model and antisymmetrized molecular dynamics calculations as well as the statistical model calculation. We further investigate the consistency between the present photoneutron emission and the reverse $^{12}$C(n,$\gamma$) cross sections through their corresponding astrophysical rate.

A high-and-flat efficiency moderated neutron detection array of 3 He counters has been recently developed for photoneutron cross section measurements at the future ELI-NP gamma-ray beam source. We have designed a three rings geometry of 31 counters with a ˜37% efficiency flat within 5% in the 10 keV to 5 MeV neutron energy interval. A commissioning experiment was performed using proton beams delivered by the 9 MV Tandem accelerator of IFIN-HH. We measured the neutron production cross sections for proton induced reactions on nat Cu and 27 Al. The ( p , xn ) reactions on nat Cu were investigated in the 4.5 MeV to 14 MeV proton energy range with 250 keV steps, using pulsed and continuous proton beams. The low energy measurements below 10 MeV served to validate the detection efficiency calibration against well-known nat Cu ( p , n ) cross sections. The 27 Al( p , n ) reaction was investigated in the 5.8 MeV to 6.75 MeV energy range with 5 keV steps. Preliminary cross section results are here compared with preceding data.

In this work, we present new data on the $^{182,183,184}$W($\gamma,n$) cross sections, utilizing a quasi-monochromatic photon beam produced at the NewSUBARU synchrotron radiation facility. Further, we have extracted the nuclear level density and $\gamma$-ray strength function of $^{186}$W from data on the $^{186}$W($\alpha,\alpha^\prime\gamma$)$^{186}$W reaction measured at the Oslo Cyclotron Laboratory. Combining previous measurements on the $^{186}$W($\gamma,n$) cross section with our new $^{182,183,184}$W($\gamma,n$) and ($\alpha,\alpha^\prime\gamma$)$^{186}$W data sets, we have deduced the $^{186}$W $\gamma$-ray strength function in the range of $1<E_\gamma<6$ MeV and $7<E_\gamma<14$ MeV. Our data are used to extract the level density and $\gamma$-ray strength functions needed as input to the nuclear-reaction code \textsf{TALYS}, providing an indirect, experimental constraint for the $^{185}$W($n,\gamma$)$^{186}$W cross section and reaction rate. Compared to the recommended Maxwellian-averaged cross section (MACS) in the KADoNiS-1.0 data base, our results are on average lower for the relevant energy range $k_B T \in [5,100]$ keV, and we provide a smaller uncertainty for the MACS. The theoretical values of Bao \textit{et al.} and the cross section experimentally constrained on photoneutron data of Sonnabend \textit{et al.} are significantly higher than our result. The lower value by Mohr \textit{et al.} is in very good agreement with our deduced MACS. Our new results could have implications for the $s$-process and in particular the predicted $s$-process production of $^{186,187}$Os nuclei.

The 111,112,113Sn isotopes have been studied with (p, d gamma ), (p, p'gamma ), and (d, p gamma ) reactions to extract the nuclear level densities (NLDs) and gamma -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 approximate to 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 approximate to 3 MeV in 111,113Sn and above approximate to 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.

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 μN2 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.

In this work, we present new data on the $^{182,183,184}\mathrm{W}(\ensuremath{\gamma},n$) cross sections, utilizing a quasi-monochromatic photon beam produced at the NewSUBARU synchrotron radiation facility. Further, we have extracted the nuclear level density and $\ensuremath{\gamma}$-ray strength function of $^{186}\mathrm{W}$ from data on the $^{186}\mathrm{W}(\ensuremath{\alpha},{\ensuremath{\alpha}}^{\ensuremath{'}}\ensuremath{\gamma})^{186}\mathrm{W}$ reaction measured at the Oslo Cyclotron Laboratory. Combining previous measurements on the $^{186}\mathrm{W}(\ensuremath{\gamma},n$) cross section with our new $^{182,183,184}\mathrm{W}(\ensuremath{\gamma},n$) and ($\ensuremath{\alpha},{\ensuremath{\alpha}}^{\ensuremath{'}}\ensuremath{\gamma})^{186}\mathrm{W}$ data sets, we have deduced the $^{186}\mathrm{W}\phantom{\rule{4pt}{0ex}}\ensuremath{\gamma}$-ray strength function in the range of $1<{E}_{\ensuremath{\gamma}}<6$ MeV and $7<{E}_{\ensuremath{\gamma}}<14$ MeV. Our data are used to extract the level density and $\ensuremath{\gamma}$-ray strength functions needed as input to the nuclear-reaction code talys, providing an indirect, experimental constraint for the $^{185}\mathrm{W}(n,\ensuremath{\gamma})^{186}\mathrm{W}$ cross section and reaction rate. Compared to the recommended Maxwellian-averaged cross section (MACS) in the KADoNiS-1.0 database, our results are on average lower for the relevant energy range ${k}_{B}T\ensuremath{\in}[5,100]$ keV, and we provide a smaller uncertainty for the MACS. The theoretical values of Bao et al. [At. Data Nucl. Data Tables 76, 70 (2000)] and the cross section experimentally constrained on photoneutron data of Sonnabend et al. [Astrophys. J. 583, 506 (2003)] are significantly higher than our result. The lower value by Mohr et al. [Phys. Rev. C 69, 032801(R) (2004)] is in very good agreement with our deduced MACS. Our new results provide an improved uncertainty estimate for the ($n,\ensuremath{\gamma})^{186}\mathrm{W}$ reaction rate, which is one important ingredient in simulations for investigating the neutron density and the $^{186,187}\mathrm{Os}$ production in the $s$ process.

In this work, we present new data on the 182,183,184W(& gamma; , n) cross sections, utilizing a quasi-monochromatic photon beam produced at the NewSUBARU synchrotron radiation facility. Further, we have extracted the nuclear level density and & gamma; -ray strength function of 186W from data on the 186W(& alpha;, & alpha;'& gamma; ) 186W reaction measured at the Oslo Cyclotron Laboratory. Combining previous measurements on the 186W(& gamma; , n) cross section with our new 182,183,184W(& gamma; , n) and (& alpha;, & alpha;'& gamma; ) 186W data sets, we have deduced the 186W & gamma; -ray strength function in the range of 1 < E & gamma; < 6 MeV and 7 < E & gamma; < 14 MeV. Our data are used to extract the level density and & gamma; -ray strength functions needed as input to the nuclear-reaction code TALYS, providing an indirect, experimental constraint for the 185W(n, & gamma; ) 186W cross section and reaction rate. Compared to the recommended Maxwellian-averaged cross section (MACS) in the KADoNiS-1.0 database, our results are on average lower for the relevant energy range kBT & ISIN; [5, 100] keV, and we provide a smaller uncertainty for the MACS. The theoretical values of Bao et al. [At. Data Nucl. Data Tables 76, 70 (2000)] and the cross section experimentally constrained on photoneutron data of Sonnabend et al. [Astrophys. J. 583, 506 (2003)] are significantly higher than our result. The lower value ingredient in simulations for investigating the neutron density and the 186,187Os production in the s process.

M. Guttormsen,1, ∗ K. O. Ay,2 M. Ozgur,2 E. Algin,2, 3 A. C. Larsen,1 F. L. Bello Garrote,1 H. C. Berg,1, † L. Crespo Campo,1 T. Dahl-Jacobsen,1 F. W. Furmyr,1 D. Gjestvang,1 A. Görgen,1 T. W. Hagen,1 V. W. Ingeberg,1 B. V. Kheswa,1, 4 I. K. B. Kullmann,5 M. Klintefjord,1 M. Markova,1 J. E. Midtbø,1 V. Modamio,1 W. Paulsen,1 L. G. Pedersen,1 T. Renstrøm,1 E. Sahin,1 S. Siem,1 G. M. Tveten,1 and M. Wiedeking6, 7 1Department of Physics, University of Oslo, N-0316 Oslo, Norway 2Department of Physics, Eskisehir Osmangazi University, Faculty of Science and Letters, TR-26040 Eskisehir, Turkey 3Department of Metallurgical and Materials Engineering, Pamukkale University, 20160 Denizli, Turkey 4Department of Physics, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa 5Institut d’Astronomie et d’Astrophysique, CP-226, Université Libre de Bruxelles, 1050 Brussels, Belgium 6SSC Laboratory, iThemba LABS, P.O. Box 722, Somerset West 7129, South Africa 7School of Physics, University of the Witwatersrand, Johannesburg 2050, South Africa (Dated: April 20, 2022)

Nuclear level densities (NLDs) and $\gamma$-ray strength functions (GSFs) of $^{120,124}$Sn have been extracted with the Oslo method from proton-$\gamma$ coincidences in the ($p,p^{\prime}\gamma)$ reaction. The functional forms of the GSFs and NLDs have been further constrained with the Shape method by studying primary $\gamma$-transitions to the ground and first excited states.The NLDs demonstrate good agreement with the NLDs of $^{116,118,122}$Sn isotopes measured previously. Moreover, the extracted partial NLD of 1$^{-}$ levels in $^{124}$Sn 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 $\gamma$-ray energies and low values of the NLD (below $\approx1\cdot10^{3}-2\cdot10^{3}$ MeV$^{-1}$).

Nuclear level densities (NLDs) and gamma -ray strength functions (GSFs) of 120,124Sn have been extracted with the Oslo method from proton-gamma coincidences in the (p, p'gamma ) reaction. The functional forms of the GSFs and NLDs have been further constrained with the Shape method by studying primary gamma -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 gamma -ray energies and low values of the NLD (below eta 1 x 103-2 x 103 MeV-1).

The experimental gamma-ray strength functions (gamma-SFs) of 142,144-151Nd have been studied for gamma-ray energies up to the neutron separation energy. The results represent a unique set of gamma-SFs 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. The data indicate that the mechanisms behind the low-energy enhancement and the scissors mode are decoupled from each other.

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.

The Oslo method comprises a set of analysis techniques designed to extract nuclear level density and average gamma-decay strength function from a set of excitation-energy tagged gamma-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 gamma-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. Program summary Program Title: OMpy (Midtb empty set et al., 2020) CPC Library link to program files: https://doi.org/10.17632/jbthtbm9bd.1 Code Ocean Capsule: https://doi.org/10.24433/CO.6094094.v1 Licensing provisions: GPLv3 Programming language: Python, Cython Nature of problem: Extraction of the nuclear level density and average gamma-ray strength function from a set of excitation-energy tagged gamma-ray spectra including the quantification of uncertainties and correlations of the results. Solution method: The level density and gamma-ray strength function can be obtained simultaneously using a set of analysis techniques called the Oslo method. To propagate the uncertainty from the counting statistics, we analyze an ensemble of perturbed spectra, which are created based on the experimental input. One obtains a set of level densities and gamma-ray strength functions for each realization from a fit process. The fitting metric (chi(2)) is degenerate, but the degeneracy is removed by a simultaneous normalization of the level density and gamma-ray strength function to external data, such that all correlations are preserved. There have been several modifications to facilitate a modular program flow and to enhance accuracy, reproducibility and transparency of the results. The main revisions in OMpy are that it (i) uses an ensemble based uncertainty quantification throughout whole method, (ii) the fitting is based on well tested external libraries, (iii) corrections for the normalization procedure have been introduced, (iv) the code base is auto-documented with Sphinx and automatically tested. (C)2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

We present the latest development of measuring (γ, n) cross sections and giant dipole resonance (GDR) cross sections in the IAEA photonuclear data project. Photoneutron cross sections were measured for 21 isotopes below 2n threshold to construct the γ-ray strength function (γSF) with the γSF method; (γ, n) cross sections are used as experimental constraints on the model E1 and M1 γSFs from the Hartree–Fock–Bogolyubov plus quasi-particle random phase approximation based on the Gogny D1M interaction supplemented with the M1 upbend. GDR cross sections were measured for 11 nuclei from 9Be to 209Bi by direct neutron-multiplicity sorting with a flat-efficiency neutron detector toward a goal of resolving the long-standing discrepancy between the Livermore and Saclay data. We present γSFs for the Ni isotopic chain and GDR cross sections for 159Tb as well as those updated for 209Bi.

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.

K. L. Malatji,1, 2, ∗ K. S. Beckmann,3, † M. Wiedeking,1, 4, ‡ S. Siem,3 S. Goriely,5 A. C. Larsen,3 K. O. Ay,6 F. L. Bello Garrote,3 L. Crespo Campo,3 A. Görgen,3 M. Guttormsen,3 V. W. Ingeberg,3 P. Jones,1 B. V. Kheswa,1, 7 P. von Neumann-Cosel,8 M. Ozgur,6 G. Potel,9 L. Pellegri,1, 4 T. Renstrøm,3 G. M. Tveten,3 and F. Zeiser3 1Department of Subatomic Physics, iThemba LABS, P.O. Box 722, Somerset West 7129, South Africa 2Physics Department, Stellenbosch University, Matieland 7602, South Africa 3Department of Physics, University of Oslo, N-0316, Oslo, Norway 4School of Physics, University of the Witwatersrand, Johannesburg 2050, South Africa 5Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles, CP 226, B-1050 Brussels, Belgium 6Department of Physics, Faculty of Science and Letters, Eskisehir Osmangazi University, TR-26040 Eskisehir, Turkey 7Department of Applied Physics and Engineering Mathematics, University of Johannesburg, Doornfontein 2028, South Africa 8Institut für Kernphysik, Technische Universität Darmstadt, D-64289 Darmstadt, Germany 9Lawrence Livermore National Laboratory, Livermore, California 94551, USA (Dated: January 11, 2021)