Feshbach Theory Research Articles

Calculations and analysis of n+52Cr reactions below 20 MeV

ABSTRACT Chromium is one of the important structural materials in the process of nuclear reaction, and the precise nuclear data of n + 52Cr reaction is very important. On the basis of the spherical optical model, the unified Hauser–Feshbach theory and exciton model, all reaction cross sections, angular distributions, energy spectra, and double-differential cross sections were calculated and analysed for n + 52Cr reactions below 20 MeV. The theoretical calculations were compared with the available experimental data and other evaluation data from ENDF/B-VIII.0 and JENDL-5.

Potential and Feshbach s-wave resonances in coupled atomic collision channels

We discuss s-wave scattering in an atomic binary collision with two coupled channels, tunable by an external magnetic field, one channel open and the other closed for the incident energies considered. The analysis is performed with a stylized model of square-well potentials. This simplification allows for a pedagogically thorough discussion of the different scattering resonances that appear in coupled channels. One of them, the potential resonances at vanishing energy, occurs as a bound state of the coupled system emerges, in turn, tuned at a very precise value of the external field. The other resonances, described by Feshbach theory, occur when the incident energy is near a bound state of the closed channel, as if it were decoupled from the open channel. These resonances exist for values of the external field above a particular threshold value. Besides the potential intrinsic value of this study in a quantum mechanics course, as the analysis can be performed with minor numerical calculations, it is also an aid for the understanding of current research advances in the exciting field of ultracold gases.

Pre-Equilibrium Differential and Double Differential Cross Sections of Neutrons Induce Nuclear Reactions in 64Zn Nucleus

The pre - equilibrium and equilibrium differential and double differential cross sections have been calculated for 2MeV neutrons induced reactions in 64Zn nucleus using Kalbach Systematic approach in terms of Exciton model with Feshbach, Kerman and Koonin (FKK) statistical theory. The two-component exciton model and some corrections have been implemented in the calculation the particle-hole state density. In this work, Isospin, finite well depth, and shell effects are considered. The obtained results were compared with the available published experimental and theoretical data that in the international libraries such as TENDL, ENDF, and JEFF. The comparisons with these available data showed an acceptable agreement especially for the reactions: 64Zn(n,n)64Zn, 64Zn(n,p)64Cu, 64Zn(n,D)63Cu, 64Zn(n,T)62Cu, 64Zn(n,3He)62Ni, and 64Zn(n,4He)61Ni at different emission angles.

Study of the (n,2n) reaction cross section on 174,176Hf isotopes

Cross section measurements of the 174Hf(n,2n)173Hf and 176Hf(n,2n)175Hf reactions have been performed at the VdG Tandem accelerator of NCSR “Demokritos” in Athens, in the neutron energy region from 8.8 to 11.5 MeV, using the activation technique. Statistical model calculations based on the Hauser - Feshbach theory have also been implemented by using the code EMPIRE-II with different sets of input parameters. The predictions were compared to the data of the present work as well as data from literature.

Theoretical calculations for the reaction 241Am(n, 2n) in the framework of the Hauser-Feshbach model

The cross section of the reaction 2ilAm(n, 2n), has been measured by the activation method in the range from 9.6 to 11.4 MeV, at the Tandem accelerator facility of NCSR Demokritos. Statistical model calculations in the framework of the Hauser- Feshbach theory have been performed, and the first results are presented. Experimental data on the neutron induced fission cross section of 241Am, have been used as a constraint for the calculations. The results of the investigation are presented in comparison with experimental data and previous theoretical evaluations.

Experimental Study of the Astrophysically Interesting 112Cd(p,γ)113In Reaction

An experimental study of the astrophysically interesting 112Cd(p,γ)113In reaction, conducted at INPP, NCSR “Demokritos”, is presented. The purpose of the experiment was to study the total cross section and the angular distribution of the de-excited nuclei. The experiment aimed at both gaining knowledge of proton capture at low energies and serving as a validity test for the Hauser–Feshbach theory, a statistical model of compound reactions of high importance. Both in–beam and activation techniques were used during the experiment and the results are compared to TALYS calculations.

Branching ratios for de-excitation processes of daughter nuclei following invisible dinucleon decays in 16O

Various theories beyond the standard model of particle physics predict the existence of baryon number violating processes resulting in nucleon decay. When occurring within an atomic nucleus, such a decay will be followed by secondary decays of the daughter nucleus unless its ground state is directly populated. In this paper, we estimate branching ratios for processes associated with dinucleon decays of the 16O nucleus. To this end, we use a simple shell model for the ground state of 16O. For decays from the configuration, which result in highly excited states in the daughter nucleus, we employ a statistical model with the Hauser–Feshbach theory. Our analysis indicates that the branching ratio for gamma-ray emission in the energy range between 5 and 9 MeV, which is relevant to low-threshold water Cherenkov experiments such as SNO+, is 4.53%, 35.7%, and 20.2% for the nn, pp, and pn decays in 16O, respectively. In particular, emission of 6.09 and 7.01 MeV gamma-rays from 14C, and 6.45 and 7.03 MeV gamma-rays from 14N, have branching ratios of as large as 10.9%, 20.1%, 7.73% and 8.90%, respectively.

235U(n, f) Independent fission product yield and isomeric ratio calculated with the statistical Hauser–Feshbach theory

ABSTRACT We have developed a Hauser–Feshbach fission fragment decay model, HF3D, which can be applied to the statistical decay of more than 500 primary fission fragment pairs (1,000 nuclides) produced by the neutron induced fission of 235U. The HF3D model numerically integrates fission fragment yield and their initial excitation energy, spin and parity distributions for these 1,000 nuclides. The fission fragment yield Y(A) and the total kinetic energy are model inputs, and we estimate them from available experimental data for the 235U(nth,f) system. The model parameters in the statistical decay calculation are adjusted to reproduce some fission observables, such as the neutron emission multiplicity , its distribution P(ν), and the mass dependence (A). The calculated fission product yield (FPY) and isomeric ratio (IR) are compared with experimental data. The calculated independent FPY YI (A) at the thermal energy reproduces the experimental data well, while the calculated IRs tend to be lower than the Madland–England model prediction. The HF3D model is extended to higher incident neutron energies up to the second-chance fission threshold. We demonstrate for the first time that most of the IRs stay constant, although the production of isomeric state changes as the incident energy increases.

Thick Target Neutron Production on Aluminum and Copper by 40 MeV Deuterons**Supported by the Project of China Academy of Engineering Physics under Grant No 2013B0103015.

The thick target neutron yields (TTNYs) of deuteron-induced reaction on Al and Cu isotopes are analyzed by combining the improved nuclear models and particle transport effects. The modified Glauber model is employed mainly to produce the peak of double differential cross section for the breakup process, and the exciton model and the Hauser–Feshbach theory are used for the statistical processes. The thin-layer accumulation method is used to calculate the TTNYs considering the neutron attenuation effects in the target. The calculated results are compared with the existing experimental data, and the analysis method can predict the TTNY data well at the deuteron energy of 40 MeV.

Theoretical approach to study the light particles induced production routes of 22Na

To create a roadmap for the industrial-scale production of sodium-22, various production routes of this radioisotope involving light charged-particle-induced reactions at the bombarding energy range of threshold to a maximum of 100MeV have been calculated. The excitation functions are calculated by using various nuclear models. Reaction pre-equilibrium process calculations have been made in the framework of the hybrid and geometry dependent hybrid models using ALICE/ASH code, and in the framework of the exciton model using TALYS-1.4 code. To calculate the compound nucleus evaporation process, both Weisskopf–Ewing and Hauser–Feshbach theories have been employed. The cross sections have also separately been estimated with five different level density models at the whole projectile energies. A comparison with calculations based on the codes, on one hand, and experimental data, on the other hand, is arranged and discussed.

Theoretical calculations of n+232Th reaction for energies up to 150 MeV

All reaction cross sections, angular distributions, energy spectra and double differential cross sections of neutron, proton, deuteron, triton, and alpha-particle emission for n+232Th reaction are consistent calculated and analyzed in the energy range of En⩽150MeV. The optical model, the intra-nuclear cascade model, the fission model, the unified Hauser–Feshbach theory and the exciton model which included the improved Iwamoto–Harada model, and the distorted wave Born approximation theory are used. Theoretical calculated results are compared with recent experimental data and other evaluated data from ENDF/B-VII and JENDL-3.

Calculation and analysis for p + 50,52,53,54,natCr reactions

All cross sections, elastic and inelastic scattering angular distributions, energy spectra and double differential cross sections of six outgoing particles (n, p, d, t, helium-3 and α) for p+50,52,53,54,natCr reactions are calculated and analyzed at incident proton energies below 150MeV. The optical model, the intra-nuclear cascade model, evaporation model, Hauser–Feshbach theory with width fluctuation correction, exciton model which includes the improved Iwamoto–Harada model and distorted Born approximation theory are involved in the calculation. The calculated results are compared with existing experimental data.

Overlapping-Resonance Scattering and Statistical Theory of Unimolecular Decomposition

A random matrix model of unimolecular decomposition is investigated based on the Feshbach theory of resonant scattering. Energies of zero-th order quasi-bound states are randomly distributed, and coupling matrix elements between these quasi-bound states and continua are generated by Gaussian random numbers. The average decay rate of the quasi-bound states exhibits systematic behavior as a function of density of quasi-bound states, average magnitude of the coupling and number of continua. The average decay rate coin­ cides with the one predicted by the statistical theory of unimolecular decomposition (RRKM theory) when the mean spacing of the quasi-bound states is comparable with the average resonance width. Under this condition, the spectrum of the quasi-bound states is most diffuse, and we can neither resolve each quasi-bound state nor even distinguish resonant collision from direct one clearly.

Weisskopf–Ewing and Hauser–Feshbach calculations of photonuclear cross sections used for electromagnetic dissociation

The Weisskopf–Ewing (WE) and Hauser–Feshbach (HF) theory are statistical methods, which are often used to calculate photonuclear cross sections for compound nucleus reactions. In our past work, WE methodology was presented and photonuclear reaction cross sections for nucleon emission were calculated using WE theory. Here, our previous results, which neglect pre-equilibrium emissions and do not include multiple particle emission, are compared to those calculated with HF theory and experimental data. For the reactions considered herein, it is found that the WE theory and HF method are in reasonable agreement below the two neutron separation energy assuming an energy dependent branching ratio for intermediate and heavy nuclei. In addition, qualitative confidence of WE theory for electromagnetic dissociation (EMD) cross section calculations was found.

Double differential cross sections of light charged particle emission of n + 27Al reaction

All cross sections, angular distributions, energy spectra and double differential cross sections are consistently calculated and analyzed for n+27Al reaction at incident neutron energies below 200MeV based on the nuclear theoretical models. The optical model, the unified Hauser–Feshbach theory and the exciton model which includes the improved Iwamoto–Harada model, and the distorted wave Born approximation theory are used. Theoretical calculated results of the energy spectra and double differential cross sections of proton, deuteron, triton, helium and alpha-particle emissions are compared with the experimental data.

The analysis of n+237Np reactions for energies up to 200 MeV

All cross sections, angular distributions, energy spectra and double differential cross sections of neutron, proton, deuteron, triton, alpha-particle emission and the prompt fission neutron spectra for n+237Np reactions are consistently calculated and analyzed. The optical model, the intra-nuclear cascade model, the unified Hauser–Feshbach theory and the exciton model which includes the improved Iwamoto–Harada model, the fission model, the linear angular momentum dependent exciton density model and the distorted wave Born approximation theory are used in the energy range of En⩽200MeV. Theoretical calculations are compared with recent experimental data and other evaluated data from ENDF/B-VII and JENDL-3.

Double differential cross sections of proton emission in neutron induced reaction on27Al

Double differential sections for proton emission on aluminium are presented for 40 MeV incident neutron energies. Angular distributions, energy differential and total production cross sections are obtained. The results are compared to existing data and to nuclear model calculations which include preequilibrium and compound decay mechanisms. The EMPIRE code treats these mechanisms in the framework of TUL model for multistep direct and NVWY model for multistep compound. The Hauser Feshbach theory is used to calculate emission from the compound nucleus, with a full conservation of spin and parity.

The theoretical calculation of p+ 232Th reaction for energies up to 250 MeV

All reaction cross sections, energy spectra and double differential cross sections of neutron, proton, deuteron, triton, and alpha-particle emission for p+ 232Th reaction are consistent calculated and analyzed with the optical model, the intranuclear cascade model, the unified Hauser–Feshbach theory and the exciton model which included the improved Iwamoto–Harada model, the fission model and the distorted wave Born approximation theory in the energy range of E p ⩽ 250 MeV . Theoretical calculations are compared with existing experimental data.

Calculation and analysis of n+ 90,91,92,94,96,natZr reactions in the En ⩽ 250 MeV energy range

All of reaction cross sections, angular distributions, energy spectra, γ-ray production cross sections, and the double differential cross section for neutron, proton, deuteron, triton, helium and alpha emission are calculated and analyzed for n+ 90,91,92,94,96,natZr at incident neutron energies from 0.1 to 250 MeV. The optical model, intranuclear cascade model, the unified Hauser–Feshbach theory and the exciton model which included the improved Iwamoto–Harada model are used. Theoretical calculated results are compared with existing experimental data and other evaluated data from ENDF/B-VI.8, ENDF/B-VII.0 and JENDL-3.3. The optical model potential parameters are obtained according to the experimental data of total, nonelastic cross sections and elastic scattering angular distributions.

Complete Feshbach-type projection method to compute autoionizing states in Li-like atomic systems

A fully ab initio method of solution to compute autoionizing states in Li-like atomic systems based on the application of the Feshbach projection formalism is proposed. Applications of the Feshbach formalism, which in principle is a complete many-particle theory, to systems of more than two-active electrons are very scarce due to the limitations imposed by the practical construction of correct projection operators \U0001d4ab and \U0001d4ac inherent to the theory. We include rigorously all the ingredients required by the Feshbach theory in order to compute accurate resonance parameters for the lowest autoionizing states of Li and Ne7+, for the 2Se, 2P° and 2De symmetries.