We describe the physics and data included in the Reference Input Parameter Library, which is devoted to input parameters needed in calculations of nuclear reactions and nuclear data evaluations. ...Advanced modelling codes require substantial numerical input, therefore the International Atomic Energy Agency (IAEA) has worked extensively since 1993 on a library of validated nuclear-model input parameters, referred to as the Reference Input Parameter Library (RIPL). A final RIPL coordinated research project (RIPL-3) was brought to a successful conclusion in December 2008, after 15 years of challenging work carried out through three consecutive IAEA projects. The RIPL-3 library was released in January 2009, and is available on the Web through
http://www-nds.iaea.org/RIPL-3/
. This work and the resulting database are extremely important to theoreticians involved in the development and use of nuclear reaction modelling (ALICE, EMPIRE, GNASH, UNF, TALYS) both for theoretical research and nuclear data evaluations.
The numerical data and computer codes included in RIPL-3 are arranged in seven segments:
MASSES contains ground-state properties of nuclei for about 9000 nuclei, including three theoretical predictions of masses and the evaluated experimental masses of Audi
et al. (2003).
DISCRETE LEVELS contains 117 datasets (one for each element) with all known level schemes, electromagnetic and
γ-ray decay probabilities available from ENSDF in October 2007.
NEUTRON RESONANCES contains average resonance parameters prepared on the basis of the evaluations performed by Ignatyuk and Mughabghab.
OPTICAL MODEL contains 495 sets of phenomenological optical model parameters defined in a wide energy range. When there are insufficient experimental data, the evaluator has to resort to either global parameterizations or microscopic approaches. Radial density distributions to be used as input for microscopic calculations are stored in the MASSES segment.
LEVEL DENSITIES contains phenomenological parameterizations based on the modified Fermi gas and superfluid models and microscopic calculations which are based on a realistic microscopic single-particle level scheme. Partial level densities formulae are also recommended. All tabulated total level densities are consistent with both the recommended average neutron resonance parameters and discrete levels.
GAMMA contains parameters that quantify giant resonances, experimental gamma-ray strength functions and methods for calculating gamma emission in statistical model codes. The experimental GDR parameters are represented by Lorentzian fits to the photo-absorption cross sections for 102 nuclides ranging from
51V to
239Pu.
FISSION includes global prescriptions for fission barriers and nuclear level densities at fission saddle points based on microscopic HFB calculations constrained by experimental fission cross sections.
On the basis of soft-rotor model, a good description of nucleon scattering on tungsten and neighboring nuclei was achieved in J. Phys. G: Nucl. Part. Phys.
48
, 075101 (2021), and the nuclear volume ...conservation condition was introduced. The effect of volume conservation on calculations for tungsten isotopes is further investigated by defining the ratio R for cross sections, scattering angular distributions and analyzing powers. The results show that the volume conservation effect cannot be ignored. This effect is more significant in the low-energy region of cross sections and at extrema of angular distributions. Comparison between the calculated results and existing nuclear data evaluations in different evaluated nuclear data libraries is shown.
Abstract
Nucleon scattering on tungsten and neighboring nuclei are analyzed with a coupled-channels method based on a soft-rotator structure model. The multiple band couplings and nuclear stretching ...factors are built using nuclear wave functions of the soft-rotator model with the Hamiltonian parameters adjusted to reproduce the energy of low-lying collective levels of corresponding nuclei. A regional lane-consistent dispersive coupled-channels optical-model potential is derived to reproduce the neutron total cross sections, nucleon elastic and inelastic scattering angular distributions, and analyzing powers. Excellent agreement with measurements is obtained for neutron total cross sections of
182,183,184,186
W,
178
Hf, and
181
Ta targets in the whole energy range from 100 keV to 200 MeV; other scattering data are found to be in good agreement with measurements. A deformation-dependent nuclear radius correction arising from the volume conservation condition is introduced and allowed to remove phenomenological radii dependencies on nuclear mass from the potential geometry.
A global dispersive coupled-channel optical model (DCCOM) potential is proposed to describe neutron and proton interactions with actinide nuclei in the 0.001 to 200MeV range. A linear dependence of ...the geometrical parameters on the mass number A is employed, and deformation parameters are adjusted for each nucleus to extend the DCCOM determined previously for
238
U and
232
Th to neighboring nuclei,
237
Np,
241
Am,
242,240,239
Pu, and
235,233
U. Fitted deformations are in reasonable agreement with those derived theoretically. The present DCCOM is capable of describing not only the cross sections but also the total cross section differences between
232
Th and
238
U up to 200 MeV within experimental uncertainty, verifying that the isovector potential and assumed geometrical parameters are adequate for describing the minute difference between the cross sections of actinide nuclei and their energy dependence. The present results are compared with calculations obtained using non-dispersive potentials frequently employed in this mass range to reveal the advantage of employing a dispersion relation.
The previously derived Lane consistent dispersive coupled-channel optical model for nucleon scattering on 232Th and 23Su nuclei is extended to describe scattering on even-even actinides with Z=90-98. ...A soft-rotator- model （SRM） description of the low-lying nuclear structure is used, where the SRM Hamiltonian parameters are adjusted to the observed collective levels of the target nucleus. SRM nuclear wave functions （mixed in K quantum number） have been used to calculate the coupling matrix elements of the generalized optical model. The ＂effective＂ deformations that define inter-band couplings are derived from the SRM Hamiltonian parameters. Conservation of nuclear volume is enforced by introducing a dynamic monopolar term to the deformed potential, leading to additional couplings between rotational bands. The fitted static deformation parameters are in very good agreement with those derived by Wang and collaborators using the Weizs~cker-Skyrme global mass model （WS4）, allowing use of the latter to predict cross sections for nuclei without experimental data. A good description of the scarce ＂optical＇experimental database is achieved. SRM couplings and volume conservation allow a precise calculation of the compound-nucleus formation cross sections, which is significantly different from that calculated with rigid-rotor potentials coupling the ground-state rotational band. The derived parameters can be used to describe both neutron- and proton-induced reactions.
Tamura's coupling formalism has been extended to consider low-lying rotational bands built on vibrational (single-particle) band heads in well-deformed even-even (odd) actinides. These additional ...excitations are introduced as a perturbation to the underlying rigid rotor structure that is known to describe well the ground state rotational band of major actinides. Coupling matrix elements needed in extended Tamura's formalism are derived for both even-even and odd actinides. Employed dispersive optical model (DCCOMP) replaces the incident proton energy Ep (for proton induced reactions) by the equivalent Coulomb subtracted energy in all potential terms including both the imaginary and real potentials with the corresponding dispersive corrections. Therefore, the optical potential becomes fully symmetric for protons and neutrons. This potential is used to fit simultaneously all the available optical experimental databases (including neutron strength functions) for nucleon scattering on 238U and 232Th (even even) nuclei. Quasi-elastic (p,n) scattering data to the isobaric analogue states of the target nuclei are also used to constrain the isovector part of the optical potential. Derived Lane-consistent DCCOMP is based on coupling of almost all levels below 1 MeV of excitation energy. The ground state, octupole, beta, gamma and non-axial rotational bands are considered for even nuclei, and rotational bands built on single-particle levels – for odd nuclei. Application of derived potential to odd targets based on a new coupling scheme is foreseen.
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