THERMONUCLEAR REACTIONS IN MEDIUM AND HEAVY NUCLEI

1966 ◽  
Vol 44 (1) ◽  
pp. 151-174 ◽  
Author(s):  
J. W. Truran ◽  
C. J. Hansen ◽  
A. G. W. Cameron ◽  
A. Gilbert
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Level Density ◽  
Strength Function ◽  
Mass Range ◽  
Reaction Rates ◽  
Nuclear Radiation ◽  
Heavy Nuclei ◽  
Nuclear Level Density ◽  
The Cross

A method is outlined by which thermonuclear reaction rates can be determined from the statistical properties of nuclei. Assuming that the contribution to the cross section of a given resonance is given by the Breit–Wigner single-level formula, the total rate is determined by integrating the product of the cross section, weighted by the nuclear level density, and the velocity over energy. The nuclear radiation widths were calculated on the assumption that electric-dipole transitions are dominant. The particle widths were determined by approximating the nuclear strength function by that value calculated for a black nucleus. Nuclear cross sections calculated in this manner are compared with experiment both for charged-particle reactions on lighter nuclei and for neutron-capture reactions proceeding on nuclei in the mass range A > 60. Good agreement is obtained in both cases.

scholarly journals Gamma-widths, lifetimes and fluctuations in the nuclear quasi-continuum

2018 ◽  
Vol 178 ◽  
pp. 06001
Author(s):  
M. Guttormsen ◽  
A. C. Larsen ◽  
J. E. Midtbø ◽  
L. Crespo Campo ◽  
A. Görgen ◽  
...  
Keyword(s):  
Excited States ◽  
Level Density ◽  
Strength Function ◽  
Reaction Rates ◽  
Theoretical Description ◽  
Nuclear Level Density ◽  
Capture Process ◽  
Structure And Dynamics ◽  
Continuum Region ◽  
First Time

Statistical γ-decay from highly excited states is determined by the nuclear level density (NLD) and the γ-ray strength function (γSF). These average quantities have been measured for several nuclei using the Oslo method. For the first time, we exploit the NLD and γSF to evaluate the γ-width in the energy region below the neutron binding energy, often called the quasi-continuum region. The lifetimes of states in the quasi-continuum are important benchmarks for a theoretical description of nuclear structure and dynamics at high temperature. The lifetimes may also have impact on reaction rates for the rapid neutron-capture process, now demonstrated to take place in neutron star mergers.

scholarly journals 237Np reactions with fast neutrons: a phenomenological study

2020 ◽  
Vol 27 ◽  
pp. 14
Author(s):  
I. Sideris ◽  
S. Kolovi ◽  
A. Khaliel ◽  
A. Stamatopoulos ◽  
T. J. Mertzimekis
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Phenomenological Study ◽  
Theoretical Calculations ◽  
Level Density ◽  
Strength Function ◽  
Space Mission ◽  
Fast Neutrons ◽  
Spent Fuel ◽  
Section Data

Neptunium presents various opportunities as nuclear fuel, especially in deep–space mission power generators. As it is part of the nuclear spent fuel in PWR, waste management concerns due to 237Np long α-emitting half-life have attracted some attention recently. The scarcity of experimental data in the fast neutron energy range highlights the necessity to investigate the radiative neutron capture and neutron–induced fission cross sections of this radioisotope. In the present work, statistical modeling of these reactions is performed using TALYS in an extended range of neutron energies between 10 keV and 20 MeV. In total, 72 different combinations of code parameters were selected to study the level density and γ-strength function dependence of the cross section in 238Np. Preequilibrium and compound nucleus formation phenomena are also examined. Theoretical calculations are compared to available experimental total cross section data found in literature in an attempt to investigate any discrepancies between experiment and theory and validate statistical uncertainties.

scholarly journals The effect of deformation parameter of heavy nuclei on level density parameter

2019 ◽  
Vol 12 (25) ◽  
pp. 38-43
Author(s):  
Mahdi Hadi Jasim
Keyword(s):  
Cross Sections ◽  
Collective Motion ◽  
Level Density ◽  
Reaction Cross ◽  
Neutron Resonance ◽  
Density Parameter ◽  
Heavy Nuclei ◽  
Nuclear Level Density ◽  
S Wave ◽  
Level Density Parameter

The possible effect of the collective motion in heavy nuclei has been investigated in the framework of Nilson model. This effect has been searched realistically by calculating the level density, which plays a significant role in the description of the reaction cross sections in the statistical nuclear theory. The nuclear level density parameter for some deformed radioisotopes of (even- even) target nuclei (Dy, W and Os) is calculated, by taking into consideration the collective motion for excitation modes for the observed nuclear spectra near the neutron binding energy. The method employed in the present work assumes equidistant spacing of the collective coupled state bands of the considered isotopes. The present calculated results for first excited rotational band have been compared with the accumulated values from the literature for s-wave neutron resonance data, and were in good agreement with those data.

Systematic study of the (n,2n) reaction cross section for 121Sb and 123Sb isotopes

2022 ◽  
Author(s):  
RATANKUMAR SINGH ◽  
N.L. Singh ◽  
Rakesh Chauhan ◽  
Mayur Mehta ◽  
Saraswatula suryanarayan ◽  
...  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Systematic Study ◽  
Reaction Cross Section ◽  
Level Density ◽  
Reaction Cross ◽  
Measured Cross Section ◽  
Model Calculations ◽  
The Cross ◽  
Equilibrium Emission

Abstract The cross sections of the 121Sb(n,2n) 120Sbm and 123Sb(n,2n) 122Sb reactions were measured at 12.50, 15.79 and 18.87 MeV neutron energies relative to the standard 27Al(n,α) 24Na monitor reaction using neutron activation and offline γ-ray spectrometry technique. Irradiations of the samples were performed at the BARC-TIFR Pelletron Linac Facility, Mumbai, India. The quasi-monoenergetic neutron was generated via the 7Li(p,n) reaction. Statistical model calculations were performed by nuclear reaction codes TALYS (ver. 1.9) and EMPIRE (ver. 3.2.2) using various input parameters and nuclear level density models. The cross sections of the ground and the isomeric state as well as the isomeric cross section ratio were studied theoretically from reaction threshold to 26 MeV energies. The effect of pre-equilibrium emission is also discussed in detail using different theoretical models. The present measured cross section were discussed and compared with reported experimental data and evaluation data of the JEFF-3.3, ENDF/B-VIII.0, JENDL/AD-2017 and TENDL-2019 libraries. A detailed analysis of the uncertainties in the measured cross section data was performed using the covariance analysis method. Furthermore, a systematic study of the (n,2n) reaction cross section for 121Sb and 123Sb isotopes were also performed within 14-15 MeV neutron energies using various systematic formulae. This work helps to overcome discrepancies in Sb data and illustrate a better understanding of pre-equilibrium emission in (n,2n) reaction channel.

scholarly journals The 55Mn(p,?)56Fe and 55Mn(p,n)55Fe Cross Sections

1983 ◽  
Vol 36 (1) ◽  
pp. 1 ◽  
Author(s):  
LW Mitchell ◽  
DG Sargood
Keyword(s):  
Statistical Model ◽  
Energy Range ◽  
Cross Section ◽  
Cross Sections ◽  
Reaction Rates ◽  
Significant Part ◽  
Thermonuclear Reaction ◽  
Model Calculations ◽  
The Cross

The cross section of the reaction 55Mn(p, y)56Pe has been measured in the energy range 0�80-2�04 MeV and of the reaction 55Mn(p, n)55Pe from threshold to 2� 04 MeV. Statistical model calculations reproduce the (p, n) cross section to within a factor of 1� 4, but with the (p, y) reaction they fail by a factor ;;;:2 over a significant part of the energy range. Thermonuclear reaction rates are calculated from the data for temperatures in the range (1-5) x 109 K.

scholarly journals Cross sections of the 89Y(p,γ) reaction relevant to the p process

2019 ◽  
Vol 11 ◽  
Author(s):  
P. Tsagari ◽  
M. Kokkoris ◽  
E. Skreti ◽  
P. Demetriou ◽  
S. Galanopoulos ◽  
...  
Keyword(s):  
Statistical Theory ◽  
Angular Distribution ◽  
Cross Section ◽  
Cross Sections ◽  
Relative Efficiency ◽  
Reaction Rates ◽  
Hpge Detectors ◽  
The Cross ◽  
Good Agreement

The cross section of the 89Y(p,7)90Zr reaction was determined at Ep=l.4-4.8 MeV via angle-integrated measurements carried out by means of a 4π Nal summing detector as well as via angular distribution measurements using an array of 4 HPGe detectors with 100% relative efficiency. The resulting cross sections vary from 0.5 to 5 mb. Astrophysical S factors and reaction rates have also been derived. A good agreement between the experimental rates and and the predictions of statistical theory has been found.

ELECTROMAGNETIC STRENGTH IN HEAVY NUCLEI – EXPERIMENTS AND A GLOBAL FIT

2011 ◽  
Vol 20 (02) ◽  
pp. 431-442 ◽  
Author(s):  
R. BEYER ◽  
E. BIRGERSSON ◽  
A. R. JUNGHANS ◽  
R. MASSARCZYK ◽  
G. SCHRAMM ◽  
...  
Keyword(s):  
Cross Sections ◽  
Ground State ◽  
Level Density ◽  
Strength Function ◽  
Model Parameters ◽  
Heavy Nuclei ◽  
Dipole Strength ◽  
Dipole Resonance ◽  
Radiative Neutron ◽  
Radiative Neutron Capture

A global parameterization is presented for the electromagnetic strength in heavy nuclei which gives a rather good fit to respective data in nuclei with mass numbers A between 50 and 240. It relies on a Lorentzian description of the isovector giant dipole resonance and it needs only a very small number of parameters to describe the electric dipole strength down to low excitation energy of importance for radiative capture processes. The resonance energies are chosen to be in accordance to liquid drop model parameters adjusted to ground state masses and to rotation invariant determinations of ground state deformation and triaxiality. By a straightforward use of this information a surprisingly smooth variation of the GDR width with A and Z is found and a full agreement to the predictions of the electromagnetic sum rule is assured. Predictions for radiative neutron capture cross sections compare well to respective data, when the proposed photon strength function is combined with standard prescriptions for the level density in the product nuclei.

Experimental Studies Of Multilayer Glass Structures On Compression, Compression With Bending And Simple Bending

2019 ◽  
pp. 22-30
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Applied Load ◽  
Experimental Studies ◽  
Strength Properties ◽  
Research Topic ◽  
Normative Values ◽  
Laminated Glass ◽  
The Cross ◽  
Experimental Values

The work of multilayer glass structures for central and eccentric compression and bending are considered. The substantiation of the chosen research topic is made. The description and features of laminated glass for the structures investigated, their characteristics are presented. The analysis of the results obtained when testing for compression, compression with bending, simple bending of models of columns, beams, samples of laminated glass was made. Overview of the types and nature of destruction of the models are presented, diagrams of material operation are constructed, average values of the resistance of the cross-sections of samples are obtained, the table of destructive loads is generated. The need for development of a set of rules and guidelines for the design of glass structures, including laminated glass, for bearing elements, as well as standards for testing, rules for assessing the strength, stiffness, crack resistance and methods for determining the strength of control samples is emphasized. It is established that the strength properties of glass depend on the type of applied load and vary widely, and significantly lower than the corresponding normative values of the strength of heat-strengthened glass. The effect of the connecting polymeric material and manufacturing technology of laminated glass on the strength of the structure is also shown. The experimental values of the elastic modulus are different in different directions of the cross section and in the direction perpendicular to the glass layers are two times less than along the glass layers.

scholarly journals Total cross sections of eγ → $$ eX\overline{X} $$ processes with X = μ, γ, e via multiloop methods

2021 ◽  
Vol 2021 (1) ◽  
Author(s):  
Roman N. Lee ◽  
Alexey A. Lyubyakin ◽  
Vyacheslav A. Stotsky
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Elliptic Integral ◽  
High Energy ◽  
Calculation Methods ◽  
Complete Elliptic Integral ◽  
Total Cross Sections ◽  
Multiloop Calculation ◽  
The Cross ◽  
Analytical Expressions

Abstract Using modern multiloop calculation methods, we derive the analytical expressions for the total cross sections of the processes e−γ →$$ {e}^{-}X\overline{X} $$ e − X X ¯ with X = μ, γ or e at arbitrary energies. For the first two processes our results are expressed via classical polylogarithms. The cross section of e−γ → e−e−e+ is represented as a one-fold integral of complete elliptic integral K and logarithms. Using our results, we calculate the threshold and high-energy asymptotics and compare them with available results.

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