scholarly journals Statistical Hauser-Feshbach Model Description of (n,α) Reaction Cross Sections for the Weak s-Process

Universe ◽  
2022 ◽  
Vol 8 (1) ◽  
pp. 25
Author(s):  
Sema Küçüksucu ◽  
Mustafa Yiğit ◽  
Nils Paar
Keyword(s):  
Cross Sections ◽  
Density Functional ◽  
Experimental Studies ◽  
Reaction Cross ◽  
Model Description ◽  
Energy Density Functional ◽  
Model Calculations ◽  
Level Densities ◽  
Environment Model ◽  
Reaction Cross Sections

The (n,α) reaction contributes in many processes of energy generation and nucleosynthesis in stellar environment. Since experimental data are available for a limited number of nuclei and in restricted energy ranges, at present only theoretical studies can provide predictions for all astrophysically relevant (n,α) reaction cross sections. The purpose of this work is to study (n,α) reaction cross sections for a set of nuclei contributing in the weak s-process nucleosynthesis. Theory framework is based on the statistical Hauser-Feshbach model implemented in TALYS code with nuclear masses and level densities based on Skyrme energy density functional. In addition to the analysis of the properties of calculated (n,α) cross sections, the Maxwellian averaged cross sections are described and analyzed for the range of temperatures in stellar environment. Model calculations determined astrophysically relevant energy windows in which (n,α) reactions occur in stars. In order to reduce the uncertainties in modeling (n,α) reaction cross sections for the s-process, novel experimental studies are called for. Presented results on the effective energy windows for (n,α) reaction in weak s-process provide a guidance for the priority energy ranges in the future experimental studies.

scholarly journals Pygmy and giant resonances: connecting the nuclear structure to stellar astrophysics

2018 ◽  
Vol 194 ◽  
pp. 04001
Author(s):  
Nadia Tsoneva
Keyword(s):  
Cross Sections ◽  
Density Functional ◽  
Reaction Cross ◽  
Giant Resonances ◽  
Energy Density Functional ◽  
Theoretical Investigations ◽  
Dipole Response ◽  
The Impact ◽  
Reaction Cross Sections ◽  
Phonon Model

Systematic theoretical investigations of dipole response in neutron-rich nuclei of importance for day-one photonuclear experiments at ELI-NP are presented. The calculations are performed in advanced mi- croscopic theory based on energy-density functional and three-phonon quasiparticle-phonon model. The model basis accounts for a large range of nuclear excitations with different spin and parity. In the focus of the studies are electric and magnetic dipole modes with energies up to 25 MeV. Of special interest are pygmy dipole and giant dipole resonances. The impact of different low-energy excitations and in particular of the PDR on radia- tive neutron-capture reaction cross sections in nuclei of key importance for nucleosynthesis is investigated.The obtained results are compared to available experimental data.

scholarly journals (p,γ) Reaction Cross Sections Relevant to the p process: First Results for the Se Isotopes

2020 ◽  
Vol 13 ◽  
pp. 161
Author(s):  
A. Lagoyannis ◽  
A. Spyrou ◽  
S. Harissopulos ◽  
S. Galanopoulos ◽  
R. Kunz ◽  
...  
Keyword(s):  
Cross Sections ◽  
Optical Model ◽  
Reaction Cross ◽  
Activation Technique ◽  
Nuclear Level ◽  
Proton Capture ◽  
Model Calculations ◽  
Level Densities ◽  
First Results ◽  
Reaction Cross Sections

Proton-capture reaction cross sections of Se isotopes were determined in the 1-6 MeV energy range by means of γ-angular distribution measurements as well as via the activation technique. In this report we compare our first cross-section results with statistical model calculations performed using various microscopic and phenomenological approaches of Optical Model Potentials and Nuclear Level Densities.

scholarly journals Proton-capture Reaction Cross Sections on the Sr Isotopes Relevant to the p-process Nucleosynthesis

2020 ◽  
Vol 13 ◽  
pp. 153
Author(s):  
S. Galanopoulos ◽  
S. Harissopulos ◽  
J. W. Hammer ◽  
R. Kunz ◽  
P. Demetriou
Keyword(s):  
Cross Sections ◽  
Reaction Cross ◽  
Tandem Accelerator ◽  
Proton Capture ◽  
Model Calculations ◽  
Capture Reaction ◽  
Level Densities ◽  
Theoretical Predictions ◽  
The University ◽  
Reaction Cross Sections

Proton-capture reaction cross sections on the 86,87,88Sr isotopes have been determined at energies from 1.4 to 5 MeV by measuring γ-angular distributions at the 4 MV single-ended Dynamitron accelerator of the University of Stuttgart as well as at the 5 MV VdG Tandem accelerator of NCSR "Demokritos", Athens. In the former case an array of 4 HPGe detectors with relative efficiency εr≈100%, each shielded with BGO crystals, were used. In the case of the measurements carried out at "Demokritos" we used only one HPGe detector (εr≈80%) with no BGO shield. Cross sections ranging from 0.5 μb to 5 mb as well as the relevant S factors were obtained. The data were compared with statistical model calculations using the code MOST. In the calculations, various combinations of microscopic and phe- nomenological models of the nucleon-Nucleus Optical Model Potentials (OMP) and Nuclear Level Densities (NLD) were used and a good agreement between the data and theoretical predictions was found.

scholarly journals Statistical model calculations of 72,73Ge(n,p) and 72,74Ge(n,α) reactions on natural Ge

2020 ◽  
Vol 15 ◽  
pp. 104
Author(s):  
S. Galanopoulos ◽  
R. Vlastou ◽  
P. Demetriou ◽  
M. Kokkoris ◽  
C. T. Papadopoulos ◽  
...  
Keyword(s):  
Statistical Model ◽  
Energy Range ◽  
Neutron Energy ◽  
Cross Sections ◽  
Reaction Cross ◽  
Model Calculations ◽  
Monoenergetic Neutron ◽  
Theoretical Investigations ◽  
Equilibrium Emission ◽  
Reaction Cross Sections

Systematic experimental and theoretical investigations of the 72,73Ge(n,p)72,73 Ga and 72,74Ge(n,α)69,71Znm reaction cross sections are presented in the energy range from thresh- old to about 17 MeV neutron energy. The above reaction cross sections were measured from 8.8 to 11.4 MeV by using the activation method, relative to the 27Al(n,α)24Na refer- ence reaction. The quasi-monoenergetic neutron beams were produced via the 2H(d,n)3He reaction at the 5 MV VdG Tandem T11/25 accelerator of NCSR “Demokritos”. Statisti- cal model calculations using the code EMPIRE-II (version 2.19) taking into consideration pre-equilibrium emission were performed on the data measured in this work as well as on data reported in literature.

(n, p) Reaction Cross Sections Calculations of Some Stellar Iron Group Fusion Materials

2017 ◽  
Vol 6 (1) ◽  
pp. 18-25 ◽  
Author(s):  
Tarik Siddik
Keyword(s):  
Cross Sections ◽  
Reaction Cross ◽  
Nuclear Model ◽  
Incident Neutron ◽  
Excitation Functions ◽  
Model Calculations ◽  
Model Code ◽  
Group Target ◽  
Reaction Cross Sections ◽  
Group Fusion

The excitation functions for (n, p) reactions from reaction threshold to 24 MeV on some important iron (Fe) group target elements (20 ≤ Z ≤ 28) for astrophysical (n, p) reactions such as Si, Ca, Sc, Ti, Cr, Fe, Co and Ni were calculated using TALYS-1.0 nuclear model code. The new calculations on the excitation functions of 28Si(n, p)28Al, 29Si(n, p)29Al, 42Ca(n, p)42K, 45Sc(n, p)45Ca, 46Ti(n, p)46Sc, 53Cr(n, p)53V, 54Fe(n, p)54Mn, 57Fe(n, p)57Mn, 59Co(n, p)59Fe, 58Ni(n, p)58Co and 60Ni(n, p)60Co reactions have been carried out up to 24 MeV incident neutron energy. In these calculations, the compound nucleus and pre-equilibrium reaction mechanism studied extensively. According to these calculations, we assume that these model calculations can be applied to some heavy elements, ejected into interstellar medium by dramatic supernova events.

scholarly journals Microscopie Calculations of Nuclear Level Densities and Astrophysical Applications

2019 ◽  
Vol 11 ◽  
Author(s):  
P. Demetriou ◽  
S. Goriely
Keyword(s):  
Cross Sections ◽  
Level Density ◽  
Reaction Cross ◽  
Neutron Resonance ◽  
Thermodynamic Quantities ◽  
Microscopic Approach ◽  
Level Densities ◽  
Hartree Fock ◽  
The Impact ◽  
Reaction Cross Sections

A new level density formula based on a microscopic calculation of the thermodynamic quantities using the deformed Hartree-Fock-BCS method is proposed. In the microscopic approach shell, pairing and deformation effects on the thermodynamic quantities are treated consistently. The final level density formula is shown to be in close agreement with experimental neutron resonance spacings and low energy states. The impact of the newly-determined level densities on nuclear reaction cross sections and rates of relevance in astrophysics applications is presented.

scholarly journals Thermonuclear Reaction Rates for Reactions Leading to N = 28 Nuclei

1995 ◽  
Vol 48 (1) ◽  
pp. 125
Author(s):  
A.J Morton ◽  
DG Sargood
Keyword(s):  
Statistical Model ◽  
Nuclear Reaction ◽  
Cross Sections ◽  
Optical Model ◽  
Reaction Rates ◽  
Reaction Cross ◽  
Model Parameters ◽  
Thermonuclear Reaction ◽  
Model Calculations ◽  
Reaction Cross Sections

Nuclear reaction cross sections derived from statistical-model calculations have been used in the calculation of thermonuclear reaction rates for 36 nuclei at temperatures that are representative of the interiors of evolving stars and supernovae as nucleosynthesis approaches the production of nuclei with N = 28. The statistical-model calculations used optical-model parameters in the particle channels which had been selected to give the best overall agreement between theoretical and experimental cross sections for reactions on stable target nuclei in the mass and energy ranges of importance for the stellar conditions of interest. The optical-model parameters used, and the stellar reaction rates obtained, are tabulated. Comparisons are made between these stellar rates and those from other statistical-model calculations in the literature.

scholarly journals Study of the photon strength functions and level density in the gamma decay of the n + 234U reaction

2019 ◽  
Vol 211 ◽  
pp. 02002 ◽  
Author(s):  
J. Moreno-Soto ◽  
E Berthoumieux ◽  
E Dupont ◽  
F Gunsing ◽  
O Serot ◽  
...  
Keyword(s):  
Gamma Rays ◽  
Cross Sections ◽  
High Efficiency ◽  
Level Density ◽  
Reaction Cross ◽  
Level Densities ◽  
Strength Functions ◽  
Gamma Decay ◽  
Reaction Cross Sections ◽  
Nuclear Applications

The accurate calculations of neutron-induced reaction cross sections are relevant for many nuclear applications. The photon strength functions and nuclear level densities are essential inputs for such calculations. These quantities for 235U are studied using the measurement of the gamma de-excitation cascades in radiative capture on 234U with the Total Absorption Calorimeter at n_TOF at CERN. This segmented 4π gamma calorimeter is designed to detect gamma rays emitted from the nucleus with high efficiency. This experiment provides information on gamma multiplicity and gamma spectra that can be compared with numerical simulations. The code DICEBOXC is used to simulate the gamma cascades while GEANT4 is used for the simulation of the interaction of these gammas with the TAC materials. Available models and their parameters are being tested using the present data. Some preliminary results of this ongoing study are presented and discussed.

scholarly journals The Neutron Facility at NCSR "Demokritos"- Implementation in the Case of the 232Th(n,2n) and 241Am(n,2n) Reactions

2020 ◽  
Vol 13 ◽  
pp. 136
Author(s):  
R. Vlastou ◽  
C. T. Papadopoulos ◽  
G. Perdikakis ◽  
M. Kokkoris ◽  
S. Kossionides ◽  
...  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Computer Code ◽  
Reaction Cross ◽  
Cross Section Data ◽  
Model Calculations ◽  
Section Data ◽  
Neutron Facility ◽  
Mev Protons ◽  
Reaction Cross Sections

In the 5.5 MV tandem T11/25 Accelerator Laboratory of NCSR "Demokritos" monoenergetic neutron beams can be produced in the energy ranges 120-650 keV, 4-11.5 MeV and 16-20.5 MeV by using the 7Li(p,n), 2H(d,n) and 3H(d,n) reactions, respectively. The corresponding beam energies and ions delivered by the accelerator, are 1.92-2.37 MeV protons, 0.8-9.6 MeV deuterons and 0.8-3.7 MeV deuterons, for the three reactions, respectively. Experimental results for neutron energies from threshold up to 11.5 MeV and at 17.1 MeV will be given for the 232Th(n,2n)231Th reaction, while for the 241 Am(n,2n)240 Am reaction, preliminary cross section data at 10.4, 10.6 and 17.1 MeV will be discussed. In the framework of the CERN n-TOF collaboration, the cross section of these reactions have been measured relative to the 197Au(n,2n)196Au, 27Al(n,a)24Na and 93Nb(n,2n) reaction cross sections, by using the activation method. In addition to the experimental work, theoretical Statistical model calculations are being carried out using the computer code STAPRE/F. The results are compared to the experimental data.

Sign in / Sign up

Export Citation Format

Share Document