We present the first Gogny-Hartree-Fock-Bogoliubov (HFB) model which reproduces nuclear masses with an accuracy comparable with the best mass formulas. In contrast with the Skyrme-HFB nuclear-mass ...models, an explicit and self-consistent account of all the quadrupole correlation energies are included within the 5D collective Hamiltonian approach. The final rms deviation with respect to the 2149 measured masses is 798 keV. In addition, the new Gogny force is shown to predict nuclear and neutron matter properties in agreement with microscopic calculations based on realistic two- and three-body forces.
Nuclear level densities play a key role in many nuclear applications. To go beyond the usual particle-independent approximation, a conceptually new approach based on the boson expansion of QRPA ...excitations is proposed. The calculated nuclear level densities are shown to follow an energy dependence close to a constant-temperature formula at energies above a few MeV, but present a rather narrow spin distribution. They are shown to provide a quite remarkable agreement with s-wave resonance spacings and Oslo data, at least for the 48 even-even nuclei considered in the present study.
Valuable theoretical predictions of nuclear dipole excitations in the whole chart are of great interest for different nuclear applications, including in particular nuclear astrophysics. Here we ...present large-scale calculations of the E1 γ-ray strength function obtained in the framework of the axially symmetric deformed quasiparticle random-phase approximation based on the finite-range Gogny force. This approach is applied to even-even nuclei, the strength function for odd nuclei being derived by interpolation. The convergence with respect to the adopted number of harmonic oscillator shells and the cutoff energy introduced in the 2-quasiparticle (2-qp) excitation space is analyzed. The calculations performed with two different Gogny interactions, namely D1S and D1M, are compared. A systematic energy shift of the E1 strength is found for D1M relative to D1S, leading to a lower energy centroid and a smaller energy-weighted sum rule for D1M. When comparing with experimental photoabsorption data, the Gogny-QRPA predictions are found to overestimate the giant dipole energy by typically ∼2 MeV. Despite the microscopic nature of our self-consistent Hartree-Fock-Bogoliubov plus QRPA calculation, some phenomenological corrections need to be included to take into account the effects beyond the standard 2-qp QRPA excitations and the coupling between the single-particle and low-lying collective phonon degrees of freedom. For this purpose, three prescriptions of folding procedure are considered and adjusted to reproduce experimental photoabsorption data at best. All of them are shown to lead to somewhat similar predictions of the E1 strength, both at low energies and for exotic neutron-rich nuclei. Predictions of γ-ray strength functions and Maxwellian-averaged neutron capture rates for the whole Sn isotopic chain are also discussed and compared with previous theoretical calculations.
Context. Nuclear reaction rates of astrophysical applications are traditionally determined on the basis of Hauser-Feshbach reaction codes. These codes adopt a number of approximations that have never ...been tested, such as a simplified width fluctuation correction, the neglect of delayed or multiple-particle emission during the electromagnetic decay cascade, or the absence of the pre-equilibrium contribution at increasing incident energies. Aims. The reaction code TALYS has been recently updated to estimate the Maxwellian-averaged reaction rates that are of astrophysical relevance. These new developments enable the reaction rates to be calculated with increased accuracy and reliability and the approximations of previous codes to be investigated. Methods. The TALYS predictions for the thermonuclear rates of relevance to astrophysics are detailed and compared with those derived by widely-used codes for the same nuclear ingredients. Results. It is shown that TALYS predictions may differ significantly from those of previous codes, in particular for nuclei for which no or little nuclear data is available. The pre-equilibrium process is shown to influence the astrophysics rates of exotic neutron-rich nuclei significantly. For the first time, the Maxwellian-averaged ($n,2n$) reaction rate is calculated for all nuclei and its competition with the radiative capture rate is discussed. Conclusions. The TALYS code provides a new tool to estimate all nuclear reaction rates of relevance to astrophysics with improved accuracy and reliability.
A new parameterization of the effective nucleon–nucleon Gogny interaction is proposed. It reproduces the neutron matter equation of state much better than the commonly used D1S Gogny interaction and ...furthermore reduces the binding energies' drift for the major part of the isotopic chains. Other important nuclear properties related both to nuclear matter and finite nuclei are studied and shown to be of similar quality as with D1S.
Reference database for photon strength functions Goriely, S.; Dimitriou, P.; Wiedeking, M. ...
The European physical journal. A, Hadrons and nuclei,
10/2019, Letnik:
55, Številka:
10
Journal Article
Recenzirano
Odprti dostop
.
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 of 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 (
http://www-nds.iaea.org/PSFdatabase
).
The rapid growth and intensification of aquaculture industries have led to an increased use of antibiotics. Consequently, growing concerns have mounted over the environmental contamination of these ...drugs from medicated feeds and the risk that this poses for antimicrobial resistance. To circumvent environmental leaching, farmers topcoat medicated feeds with oil; however, this only partially addresses the issue. This study investigated the potential of food-grade pregelatinized corn starch (PGS) as a second top-coating agent to reduce oxytetracycline (OTC) leaching from the hand-mixed medicated feed. We immersed top-coated medicated feeds for different periods of time and measured the concentration of OTC in the water to determine leaching. We found a significantly lower level of OTC in water samples collected from the PGS-coated medicated feed compared to the non-PGS-coated medicated feed, with concentrations of OTC approximately 4 and 2.6 times the latter after 5 min and 2 h of water immersion, respectively. We also fed PGS-coated antibiotic feed to jade perch to determine if fish accepted the top-coating and whether they absorbed the OTC. Results from a feeding trial suggested no difference in palatability between PGS and non-PGS-coated medicated feed. We also found that muscle tissue from fish fed with the aforementioned diets had similar levels of OTC concentrations, suggesting that PGS coating does not alter the gastrointestinal absorption of this medication. From our experiment, we conclude that PGS is potentially a new top-coating agent to reduce leaching in hand-mixed OTC medicated feed.
•Reliable results require good replication and detection of pre-existing variation.•Severe summer (or fall) grazing increased SOC accrual in US Northern Great Plains.•SOC accrual was negatively (not ...positively) associated with root biomass.•SOC accrual was positively associated with soil N and density.•Management heterogeneity is likely necessary to sustainably maximize SOC accrual.
Identifying grazing practices that maximize food production and soil carbon sequestration is of global importance. Currently, we cannot reliably predict which grazing practice will accrue the most soil organic carbon (SOC) partly because of confusion created by an abundance of low-quality experiments. Data quality has likely suffered because adequate treatment replication requires a lot of land, meaningful scale introduces heterogeneity among replicates, and pre-existing differences are often not taken into account. Here we tested the effects of five grazing treatments on SOC stocks with a gold standard randomized controlled trial (RCT) with pre-treatment data. Treatments were no grazing, severe summer grazing, moderate fall grazing, severe fall grazing, and the conventional approach for the system of moderate summer grazing. Because grazing experiments are often little-replicated, we also gauged the dependence of results on pre-treatment data by comparing the results of analyses with vs without pre-treatment data. We also tested for relationships between plant (root biomass, plant species composition) and soil properties (mass, nitrogen concentration) and SOC. After applying treatments for 5-yr, the no grazing and severe summer and fall grazing treatments accrued 0.85 to 1.22 kg × m−2 (0–60 cm soil depth) more SOC than conventional moderate summer grazing and represent appreciable (i.e. >4 per mille per yr) increases in SOC stocks. Furthermore, the entire portfolio of new grazing practices increased SOC accrual compared to conventional management. Given the divergent characteristics of the newly applied practices, sustainable accrual of SOC may depend on management heterogeneity. Accrual of SOC was likely driven by a reduction in SOC mineralization related to increased soil density and nitrogen, decreased root biomass, and change in plant species composition. Our findings counter the prevailing view that plant material inputs are the primary driver of SOC accrual in grazing lands. In other words, SOC accrual was mainly associated with indicators of decreased SOC mineralization (C outputs). We also found unique results for analyses with and without pre-treatment data, thereby indicating the risk of unreliable results for little-replicated RCTs without pre-treatment data. Robust generalizations on grazing practices that will reliably and sustainably maximize the rate of SOC accrual for a specific system, climate and timeline are still lacking, but further focus on factors affecting SOC mineralization will facilitate their development.
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