Reference database for photon strength functions Goriely, S.; Dimitriou, P.; Wiedeking, M. ...
European physical journal. A, Hadrons and nuclei,
10/2019, Letnik:
55, Številka:
10
Journal Article
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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 orbital M1 scissors resonance has been measured for the first time in the quasicontinuum of actinides. Particle-γ coincidences are recorded with deuteron and (3)He-induced reactions on (232)Th. ...The residual nuclei (231,232,233)Th and (232,233) Pa show an unexpectedly strong integrated strength of B(M1)=11-15μ(n)(2) in the E(γ)=1.0-3.5 MeV region. The increased γ-decay probability in actinides due to scissors resonance is important for cross-section calculations for future fuel cycles of fast nuclear reactors and may also have an impact on stellar nucleosynthesis.
Abstract
The interaction of a nucleus with photons plays a key role in understanding a competition in nuclear reactions. The photon strength function (PSF) gives the average response of a nucleus to ...an electromagnetic probe. In this study, an estimation is performed of the mean resonance spacing and average radiative width of 22 nuclei in the range A = 46 – 90. The calculations for this analysis are done in TALYS. In addition, a machine-learning driven approach for determining experimentally obtained model parameters from the neutron/proton and mass number is given. A reasonable agreement within the uncertainties is achieved between the model dependent calculations, using TALYS, and results from random forest regression.
Abstract
To expand on its research agenda and meet the growing demand for nuclear medicine products, the South African Isotope Facility (SAIF) was launched. This study focuses on Radiation Protection ...aspects for SAIF Phase 1, specifically the verification of existing- and basis of design for supplementary engineering controls for the retrofitted accelerator complex, housing an IBA C70 Cyclone 70 MeV H-minus cyclotron and four in-house designed high intensity particle beam target stations. For the dosimetric assessment, a selection of calibrated instruments were used to determine the ambient dose equivalent rate
H
*(10) at points of interest. Physical dose rate measurements were performed for various source terms (66 MeV p+ on Cu, Al, Mg, Ga and Li) and beam intensities up to tens of micro Amperes, beyond in-situ bulk shielding material, for compound shielded target stations and streaming through existing labyrinths. Comparisons are drawn between actual measurements and the FLUKA code. Primarily to determine the in-situ shielding characteristics of unverified bulk shielding material cast in the 1980s, as core drill samples yielded vastly divergent aggregate types and material densities.
The nuclear level density (NLD) and γ-ray strength function (γSF) of 63Ni have been investigated using the Oslo method. The extracted NLD is compared with previous measurements using particle ...evaporation and those found from neutron resonance spacing. The γSF was found to feature a strong low-energy enhancement that could be explained as M1 strength based on large-scale shell model calculations. Comparison of γSFs measured with the Oslo method for various Ni isotopes reveals systematic changes to the strength below 5MeV with increasing mass.
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.
Accurate nuclear data is a key factor in determining the suitability and reliability of many theoretical nuclear models and large-scale calculations. One of the main ingredients of these calculations ...is how nuclei respond to an electromagnetic field. The excitation of the isovector giant dipole resonance (GDR) is of particular importance in both nuclear structure studies as well as being the main mode of interaction of ultra-high-energy cosmic rays with the extra-galactic medium. This study investigates the photoabsorption cross section in the region of the GDR in 24Mg through the use of proton inelastic scattering and the equivalent virtual photon method. The K600 spectrometer at the iThemba LABS facility was used to obtain high resolution, low background 24Mg(p,p’)24Mg* inelastic scattering data. The virtual photon absorption method is described and the result of applying the method is presented and compared to a previous real photon absorption cross section.
Knowledge of the low-lying monopole strength in C12—the Hoyle state in particular—is crucial for our understanding of both the astrophysically important 3α reaction and of α-particle clustering. ...Multiple theoretical models have predicted a breathing mode of the Hoyle State at Ex≈9 MeV, corresponding to a radial in-phase oscillation of the underlying α clusters. The C12(α,α′)C12 and C14(p,t)C12 reactions were employed to populate states in 12C in order to search for this predicted breathing mode. A self-consistent, simultaneous analysis of the inclusive spectra with R-matrix lineshapes, together with angular distributions of charged-particle decay, yielded clear evidence for excess monopole strength at Ex≈9 MeV which is highly collective. Reproduction of the experimentally observed inclusive yields using a fit, with consistent population ratios for the various broad states, required an additional source of monopole strength. The interpretation of this additional monopole resonance as the breathing-mode excitation of the Hoyle state would provide evidence supporting a D3h symmetry for the Hoyle state itself. The excess monopole strength may complicate analysis of the properties of the Hoyle state, modifying the temperature dependence of the 3α rate at T9≳2 and ultimately, the predicted nucleosynthesis in explosive stars.
Two nearly degenerate positive-parity bands with the πg9/22⊗νg9/2−1 configuration and three nearly degenerate negative-parity bands with the πg9/2(p3/2,f5/2)⊗νg9/2−1 configuration have been ...identified in 81Kr. They are interpreted as chiral doublet bands and pseudospin-chiral triplet bands, which is supported by the constrained covariant density functional theory and the multiparticle plus rotor model calculations. The present work reports two new chiral configurations πg9/22⊗νg9/2−1 and πg9/2(p3/2,f5/2)⊗νg9/2−1, and the first example of pseudospin-chiral triplet bands involving the π(p3/2,f5/2) pseudospin doublet.
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