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[Background] Photon strength functions are an important ingredient in calculations relevant for the nucleosynthesis of heavy elements. The relation to the photoabsorption cross section allows to experimentally constrain photon strength functions by investigating the photo-response of atomic nuclei. [Purpose] We determine the photoresponse of $^{66}$Zn in the energy region of 5.6 MeV to 9.9 MeV and analyze the contribution of the "elastic" decay channel back to the ground state. In addition, for the elastic channel electric and magnetic dipole transitions were separated. [Methods] Nuclear resonance fluorescence experiments were performed using a linearly-polarized quasi-monoenergetic photon beam at the High Intensity $\gamma$-ray Source. Photon beam energies from 5.6 to 9.9 MeV with an energy spread of about 3% were selected in steps of 200-300 keV. Two High Purity Germanium detectors were used for the subsequent $\gamma$-ray spectroscopy. [Results] Full photoabsorption cross sections are extracted from the data making use of the monoenergetic character of the photon beam. For the ground-state decay channel, the average contribution of electric and magnetic dipole strengths is disentangled. The average branching ratio back to the ground state is determined as well. [Conclusions] The new results indicate lower cross sections when compared to the values extracted from a former experiment using bremsstrahlung on $^{66}$Zn. In the latter, the average branching ratio to the ground state is estimated from statistical-model calculations in order to analyze the data. Corresponding estimates from statistical-model calculations underestimate this branching ratio compared to the values extracted from the present analysis, which would partly explain the high cross sections determined from the bremsstrahlung data.

Magnetic dipole strength functions are determined for the series of germanium isotopes from $N = Z = 32$ to $N$ = 48 on the basis of a large number of transition strengths calculated within the shell model. The evolution of the strength with increasing neutron number in the $1g_{9/2}$ orbital is analyzed. A bimodal structure comprising an enhancement toward low transition enery and a resonance in the region of the scissors mode is identified. The low-energy enhancement is strongest near closed shells, in particular at the almost completely filled $1g_{9/2}$ orbital, while the scissorslike resonance is most pronounced in the middle of the open shell, which correlates with the magnitude of the also deduced electric quadrupole transition strengths. The results are consistent with previous findings for the shorter series of iron isotopes and proves the occurrence and correlation of the two low-lying magnetic dipole modes as a global structural feature., Comment: Results unchanged. Discussion extended

The dipole strength of the nuclide $^{76}$Ge was studied in photon-scattering experiments using bremsstrahlung produced with electron beams of energies of 7.8 and 12.3 MeV at the $\gamma$ELBE facility. We identified 210 levels up to an excitation energy of 9.4 MeV and assigned spin $J$ = 1 to most of them. The quasicontinuum of unresolved transitions was included in the analysis of the spectra and the intensities of branching transitions were estimated on the basis of simulations of statistical $\gamma$-ray cascades. The photoabsorption cross section up to the neutron-separation energy was determined and is compared with predictions of the statistical reaction model. The derived photon strength function is compared with results of experiments using other reactions., Comment: 12 pages, 9 figures

Recent astronomical data have provided the primordial deuterium abundance with percent precision. As a result, Big Bang nucleosynthesis may provide a constraint on the universal baryon to photon ratio that is as precise as, but independent from, analyses of the cosmic microwave background. However, such a constraint requires that the nuclear reaction rates governing the production and destruction of primordial deuterium are sufficiently well known. Here, a new measurement of the $^2$H($p,\gamma$)$^3$He cross section is reported. This nuclear reaction dominates the error on the predicted Big Bang deuterium abundance. A proton beam of 400-1650keV beam energy was incident on solid titanium deuteride targets, and the emitted $\gamma$-rays were detected in two high-purity germanium detectors at angles of 55$^\circ$ and 90$^\circ$, respectively. The deuterium content of the targets has been obtained in situ by the $^2$H($^3$He,$p$)$^4$He reaction and offline using the Elastic Recoil Detection method. The astrophysical S-factor has been determined at center of mass energies between 265 and 1094 keV, addressing the uppermost part of the relevant energy range for Big Bang nucleosynthesis and complementary to ongoing work at lower energies. The new data support a higher S-factor at Big Bang temperatures than previously assumed, reducing the predicted deuterium abundance., Comment: 13 pages, 9 figures, 4 tables; to be published in Phys. Rev. C

Photon strength functions describing the average response of the nucleus to an electromagnetic probe are key input information in the theoretical modelling of nuclear reactions. Consequently they are important for a wide range of fields such as nuclear structure, nuclear astrophysics, medical isotope production, fission and fusion reactor technologies. They are also sources of information for widely used reaction libraries such as the IAEA Reference Input Parameter Library and evaluated data files such as EGAF. In the past two decades, the amount of reaction gamma-ray data measured to determine photon strength functions has grown rapidly. Different experimental techniques have led to discrepant results and users are faced with the dilemma which (if any) of the divergent data to adopt. We report on a coordinated effort to compile and assess the existing experimental data on photon strength functions from the giant dipole resonance region to energies below the neutron separation energy. The assessment of the discrepant data at energies around or below the neutron separation energy has been possible only in a few cases where adequate information on the model-dependent analysis and estimation of uncertainties was available. In the giant dipole resonance region, we adopt the recommendations of the new IAEA photonuclear data library. We also present global empirical and semi-microscopic models that describe the photon strength functions in the entire energy region and reproduce reasonably well most of the experimental data. The compiled experimental photon strengths and recommended model calculations are available from the PSF database hosted at the IAEA (URL:www-nds.iaea.org/PSFdatabase)., Comment: IAEA Coordinated Research Project on Generating Reference Database for Photon Strength Functions (F41032)

Photo-induced reaction cross section data are of importance for a variety of current or emerging applications, such as radiation shielding design and radiation transport analyses, calculations of absorbed dose in the human body during radiotherapy, physics and technology of fission reactors (influence of photo-reactions on neutron balance) and fusion reactors (plasma diagnostics and shielding), activation analyses, safeguards and inspection technologies, nuclear waste transmutation, medical isotope production and astrophysical applications. Since the release of the IAEA Photonuclear Data Library in 1999 however, new experimental data as well as new methods to assess the reliability of experimental cross sections have become available. Theoretical models and input parameters used to evaluate photo-induced reactions have improved significantly over the years. In addition, new measurements of partial photoneutron cross sections using mono-energetic photon beams and advanced neutron detection systems have been performed allowing for the validation of the evaluations and assessments of the experimental data. Furthermore, technological advances have led to the construction of new and more powerful gamma-beam facilities, therefore new data needs are emerging. We report our coordinated efforts to address these data needs and present the results of the new evaluations of more than 200 nuclides included in the new updated IAEA Photonuclear Data Library, where the photon energy goes up to 200 MeV. We discuss the new assessment method and make recommendations to the user community in cases where the experimental data are discrepant and the assessments disagree. In addition, in the absence of experimental data, we present model predictions for photo-induced reaction cross section on nuclides of potential interest to medical radioisotope production.

The enhancement observed below 2 MeV in the radiative strength function of nuclei near closed shells is explained by shell model calculations as M1 transitions between excited states. In the open-shell a change to a bimodal structure composed of the zero energy spike and a scissors resonance is found. The features are caused by realignment of high-j orbitals.

The gamma-strength functions and level densities in the quasi-continuum of 147;149Sm isotopes have been extracted from particle-coincidences using the Oslo method. The nuclei of interest were populated via (p,d) reactions on pure 148;150Sm targets and the reaction products were recorded by the Hyperion array. An upbend in the low-energy region of the gSF has been observed. The systematic analysis of the gSF for a range of Sm isotopes highlights the interplay between scissors mode and the upbend. Shell-model calculations show reasonable agreement with the experimental gSFs and confirm the correspondence between the upbend and scissors mode.

The $\gamma$-ray strength function, or average reduced $\gamma$-ray transition probability, is a fundamental input in the calculation of $(n,\gamma)$ cross sections used to simulate the nucleosynthesis of elements heavier than Fe. Since 2004, an enhanced probability of $\gamma$-decay with $\gamma$-ray energies below $\approx2 - 4$ MeV has been measured in reaction data for numerous nuclei. This has been observed as an increase in the $\gamma$-ray strength with decreasing $\gamma$-ray energy, often referred to as the low-energy enhancement or \textit{upbend} in the $\gamma$-ray strength. Nevertheless, the available data confirming this enhancement corresponded solely to charged-particle included reactions and no low-energy enhancement had yet been confirmed from neutron-induced reaction measurements. In this work, we present the first evidence of low-energy $\gamma$-ray strength enhancement from neutron-capture reaction data. Gamma-ray spectra following thermal neutron capture on $^{58,60}$Ni have been used to determine the strength for primary and secondary $\gamma$-rays in $^{59,61}$Ni, showing an enhancement for $\gamma$-ray energies below $\approx 3$ MeV and $\approx 2$ MeV for $^{59,61}$Ni, respectively. For the first time, this enhancement is observed down to $\gamma$-ray energies of $\approx0.2$ MeV. Further, available spin-parity assignments have been used to obtain the multipolarity and electromagnetic character of these transitions, showing that this low-energy enhancement is dominated by $M1$ and $E2$ strength, with $E1$ strength also exceeding Standard Lorentzian Model predictions. Finally, large-basis shell-model calculations have been performed, also predicting a strong $M1$ enhancement at low $\gamma$-ray energies., Comment: Article and appendix, 5 figures

The $\gamma$-ray strength function ($\gamma$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-$\gamma$ coincidence events from the $\mathrm{d}(^{86}\mathrm{Kr}, \mathrm{p}\gamma)^{87}\mathrm{Kr}$ reaction were measured at iThemba LABS and the $\gamma$SF and NLD in $^{87}\mathrm{Kr}$ obtained. The low-energy region of the $\gamma$SF is compared to Shell Model calculations which suggest this region to be dominated by M1 strength. The $\gamma$SF and NLD are used as input parameters to Hauser-Feshbach calculations to constrain $(\mathrm{n},\gamma)$ cross sections of nuclei using the TALYS reaction code. These results are compared to $^{86}\mathrm{Kr}(n,\gamma)$ data from direct measurements., Comment: Submitted to EpJ A Letters

In this work, we present new data on the $^{89}$Y($\gamma$,n) cross section studied with a quasi-monochromatic photon beam produced at the NewSUBARU synchrotron radiation facility in Japan contributing torwards resolving a long standing discrepancy between existing measurements of this cross section. Results for $\gamma$-ray strength function below threshold obtained by applying the Oslo method to $^{89}$Y($p,p'\gamma$)$^{89}$Y coincidences combined with the $^{89}$Y($\gamma$,n) data this providing experimental data for the $\gamma$-ray strength function of $^{89}$Y for $\gamma$ energies in the range of $\approx 1.6$ Mev to $\approx$ 20 MeV. A low-energy enhancement is seen for $\gamma$-rays below $\approx 2.5$ MeV. Shell-model calculations indicate that this feature is caused by strong, low-energy $M1$ transitions at high excitation energies. The nuclear level density and $\gamma$-ray strength function have been extracted from $^{89}$Y($d,p \gamma$)$^{90}$Y coincidences using the Oslo method. Using the ($\gamma,n$) and ($d,p\gamma$) data as experimental constraints, we have calculated the $^{89}$Y($n,\gamma$)$^{90}$Y cross section with the TALYS reaction code. Our results have been compared with directly measured (n,$\gamma$) cross sections and evaluations. The $N=50$ isotope $^{89}$Y is an important bottleneck in the s-process and the magnitude of the $^{89}$Y(n,$\gamma)$ cross section is key to understanding how s-process stars produce heavy isotopes., Comment: 18 pages (including references) and 16 figures, to be submitted to PRC

The $^{14}\textrm{N(p,}\gamma\textrm{)}^{15}\textrm{O}$ reaction is the slowest reaction of the carbon-nitrogen cycle of hydrogen burning and thus determines its rate. The precise knowledge of its rate is required to correctly model hydrogen burning in asymptotic giant branch stars. In addition, it is a necessary ingredient for a possible solution of the solar abundance problem by using the solar $^{13}$N and $^{15}$O neutrino fluxes as probes of the carbon and nitrogen abundances in the solar core. After the downward revision of its cross section due to a much lower contribution by one particular transition, capture to the ground state in $^{15}$O, the evaluated total uncertainty is still 8\%, in part due to an unsatisfactory knowledge of the excitation function over a wide energy range. The present work reports precise S-factor data at twelve energies between 0.357-1.292~MeV for the strongest transition, capture to the 6.79~MeV excited state in $^{15}$O, and at ten energies between 0.479-1.202~MeV for the second strongest transition, capture to the ground state in $^{15}$O. An R-matrix fit is performed to estimate the impact of the new data on astrophysical energies. The recently suggested slight enhancement of the 6.79~MeV transition at low energy could not be confirmed. The present extrapolated zero-energy S-factors are $S_{6.79}(0)$~=~1.24$\pm$0.11~keV~barn and $S_{\rm GS}(0)$~=~0.19$\pm$0.05~keV~barn., Comment: Submitted to Phys. Rev. C

Isospin properties of dipole excitations in 74 Ge are investigated using the ({\alpha},{\alpha}'{\gamma}) reaction and compared to ({\gamma},{\gamma}) data. The results indicate that the dipole excitations in the energy region of 6 to 9 MeV adhere to the scenario of the recently found splitting of the region of dipole excitations into two separated parts: one at low energy, being populated by both isoscalar and isovector probes, and the other at high energy, excited only by the electromagnetic probe. Relativistic quasiparticle time blocking approximation (RQTBA) calculations show a reduction in the isoscalar E1 strength with an increase in excitation energy, which is consistent with the measurement., Comment: 7 pages, 7 figures

Low-background experiments with stable ion beams are an important tool for putting the model of stellar hydrogen, helium, and carbon burning on a solid experimental foundation. The pioneering work in this regard has been done by the LUNA collaboration at Gran Sasso, using a 0.4 MV accelerator. In the present contribution, the status of the project for a higher-energy underground accelerator is reviewed. Two tunnels of the Felsenkeller underground site in Dresden, Germany, are currently being refurbished for the installation of a 5 MV high-current Pelletron accelerator. Construction work is on schedule and expected to complete in August 2017. The accelerator will provide intense, 50 uA, beams of 1H+, 4He+, and 12C+ ions, enabling research on astrophysically relevant nuclear reactions with unprecedented sensitivity., Comment: Submitted to the Proceedings of Nuclei in the Cosmos XIV, 19-24 June 2016, Niigata/Japan

One of the greatest questions for modern physics to address is how elements heavier than iron are created in extreme, astrophysical environments. A particularly challenging part of that question is the creation of the so-called p-nuclei, which are believed to be mainly produced in some types of supernovae. The lack of needed nuclear data presents an obstacle in nailing down the precise site and astrophysical conditions. In this work, we present for the first time measurements on the nuclear level density and average strength function of $^{92}$Mo. State-of-the-art p-process calculations systematically underestimate the observed solar abundance of this isotope. Our data provide stringent constraints on the $^{91}$Nb$(p,{\gamma})^{92}$Mo reaction rate, which is the last unmeasured reaction in the nucleosynthesis puzzle of $^{92}$Mo. Based on our results, we conclude that the $^{92}$Mo abundance anomaly is not due to the nuclear physics input to astrophysical model calculations., Comment: Submitted to PRC

The low-lying $M1$-strength of the open-shell nucleus $^{50}$Cr has been studied with the method of nuclear resonance fluorescence up to 9.7 MeV, using bremsstrahlung at the superconducting Darmstadt linear electron accelerator S-DALINAC and Compton backscattered photons at the High Intensity $\gamma$-ray Source (HI$\gamma$S) facility between 6 and 9.7 MeV of the initial photon energy. Fifteen $1^{+}$ states have been observed between 3.6 and 9.7 MeV. Following our analysis, the lowest $1^{+}$ state at 3.6 MeV can be considered as an isovector orbital mode with some spin admixture. The obtained results generally match the estimations and trends typical for the scissors-like mode. Detailed calculations within the Skyrme Quasiparticle Random-Phase-Approximation method and the Large-Scale Shell Model justify our conclusions. The calculated distributions of the orbital current for the lowest $1^{+}$-state suggest the schematic view of Lipparini and Stringari (isovector rotation-like oscillations inside the rigid surface) rather than the scissors-like picture of Lo Iudice and Palumbo. The spin M1 resonance is shown to be mainly generated by spin-flip transitions between the orbitals of the $fp$-shell., Comment: Accepted in PRC as a regular article

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

The nuclear level density and the $\gamma$-ray strength function have been extracted for $^{89}$Y, using the Oslo Method on $^{89}$Y($p,p' \gamma$)$^{89}$Y coincidence data. The $\gamma$-ray strength function displays a low-energy enhancement consistent with previous observations in this mass region ($^{93-98}$Mo). Shell-model calculations give support that the observed enhancement is due to strong, low-energy $M1$ transitions at high excitation energies. The data were further used as input for calculations of the $^{88}$Sr($p,\gamma$)$^{89}$Y and $^{88}$Y($n,\gamma$)$^{89}$Y cross sections with the TALYS reaction code. Comparison with cross-section data, where available, as well as with values from the BRUSLIB library, shows a satisfying agreement., Comment: 12 pages, 10 figures, version accepted for publication in Phys. Rev. C

The stable nucleus $^{15}$N is the mirror of $^{15}$O, the bottleneck in the hydrogen burning CNO cycle. Most of the $^{15}$N level widths below the proton emission threshold are known from just one nuclear resonance fluorescence (NRF) measurement, with limited precision in some cases. A recent experiment with the AGATA demonstrator array determined level lifetimes using the Doppler Shift Attenuation Method (DSAM) in $^{15}$O. As a reference and for testing the method, level lifetimes in $^{15}$N have also been determined in the same experiment. The latest compilation of $^{15}$N level properties dates back to 1991. The limited precision in some cases in the compilation calls for a new measurement in order to enable a comparison to the AGATA demonstrator data. The widths of several $^{15}$N levels have been studied with the NRF method. The solid nitrogen compounds enriched in $^{15}$N have been irradiated with bremsstrahlung. The $\gamma$-rays following the deexcitation of the excited nuclear levels were detected with four HPGe detectors. Integrated photon-scattering cross sections of ten levels below the proton emission threshold have been measured. Partial gamma-ray widths of ground-state transitions were deduced and compared to the literature. The photon scattering cross sections of two levels above the proton emission threshold, but still below other particle emission energies have also been measured, and proton resonance strengths and proton widths were deduced. Gamma and proton widths consistent with the literature values were obtained, but with greatly improved precision., Comment: Final published version, minor grammar changes, 10 pages, 4 figures, 8 tables; An addendum is published where the last section is revised: T. Sz\"ucs and P. Mohr, Phys. Rev. C 92, 044328 (2015) [arXiv:1510.04956]

Electric quadrupole strength functions have been deduced from averages of a large number of $E2$ transition strengths calculated within the shell model for the nuclides $^{94}$Mo and $^{95}$Mo. These strength functions are at variance with phenomenological approximations as provided by the Reference Input Parameter Library RIPL-3 for calculations of reaction rates on the basis of the statistical model., Comment: arXiv admin note: text overlap with arXiv:1310.7667

A pronounced spike at low energy in the strength function for magnetic radiation (LEMAR) is found by means of Shell Model calculations, which explains the experimentally observed enhancement of the dipole strength. LEMAR originates from statistical low-energy M1-transitions between many excited complex states. Re-coupling of the proton and neutron high-j orbitals generates the strong magnetic radiation. LEMAR is closely related to Magnetic Rotation. LEMAR is predicted for nuclides participating in the r-process of element synthesis and is expected to change the reaction rates. An exponential decrease of the strength function and a power law for the size distribution of the $B(M1)$ values are found, which strongly deviate from the ones of the GOE of random matrices, which is commonly used to represent complex compound states., Comment: Proceedings of the conference on Nuclei and Mesoscopic Physics 2014, MSU, to be published AIP Conference Proceedings