Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userEffect of gamma-strength on nuclear reaction calculations
168
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
The results of the study of gamma-transition description in fast neutron capture and photofission are presented. Recent experimental data were used, namely, the spectrum of prompt gamma-rays in the energy range 2{div}18 MeV from 14-MeV neutron capture in natural Ni and isomeric ratios in primary fragments of photofission of the isotopes of U, Np and Pu by bremsstrahlung with end-point energies $E_e$= 10.5, 12 and 18 MeV. The data are compared with the theoretical calculations performed within EMPIRE 3.2 and TALYS 1.6 codes. The mean value of angular momenta and their distributions were determined in the primary fragments $^{84}$Br, $^{97}$Nb, $^{90}$Rb, $^{131,133}$Te, $^{132}$Sb, $^{132,134}$I, $^{135}$Xe of photofissions. An impact of the characteristics of nuclear excited states on the calculation results is studied using different models for photon strength function and nuclear level density.
rate research
Read More
A closed-form thermodynamic pole approach,TPA, is developed for average description of the E1 radiative strength functions using the microcanonical ensemble for initial states. A semiclassical description of the collective excitation damping in this method is based on modern physical notion on the relaxation processes in Fermi systems.The TPA model gives rather accurate means of simultaneous description of the gamma- decay and photoabsorption strength functions in the medium and heavy nuclei. It is able to cover a relatively wide energy interval, ranging from zeroth gamma-ray energy to values above GDR peak energy, as compared with the others closed-form models for calculation of the E1 strength.
We present here a first application of the Fermionic Molecular Dynamics (FMD) approach to low-energy nuclear reactions, namely the $^3$He($alpha$,$gamma$)$^7$Be radiative capture reaction. We divide the Hilbert space into an external region where the system is described as $^3$He and $^4$He clusters interacting only via the Coulomb interaction and an internal region where the nuclear interaction will polarize the clusters. Polarized configurations are obtained by a variation after parity and angular momentum projection procedure with respect to the parameters of all single particle states. A constraint on the radius of the intrinsic many-body state is employed to obtain polarized clusters at desired distances. The boundary conditions for bound and scattering states are implemented using the Bloch operator. The FMD calculations reproduce the correct energy for the centroid of the $3/2^-$ and $1/2^-$ bound states in $^7$Be. The charge radius of the ground state is in good agreement with recent experimental results. The FMD calculations also describe well the experimental phase shift data in the $1/2^+$, $3/2^+$ and $5/2^+$ channels that are important for the capture reaction at low energies. Using the bound and scattering many-body wave functions we calculate the radiative capture cross section. The calculated $S$ factor agrees very well, both in absolute normalization and energy dependence, with the recent experimental data from the Weizmann, LUNA, Seattle and ERNA experiments.
The nuclear level density and the gamma-ray strength function have been determined for 43Sc in the energy range up to 2 MeV below the neutron separation energy using the Oslo method with the 46Ti(p,alpha)43Sc reaction. A comparison to 45Sc shows that the level density of 43Sc is smaller by an approximately constant factor of two. This behaviour is well reproduced in a microscopical/combinatorial model calculation. The gamma-ray strength function is showing an increase at low gamma-ray energies, a feature which has been observed in several nuclei but which still awaits theoretical explanation.
Nuclear reaction rate ($lambda$) is a significant factor in the process of nucleosynthesis. A multi-layer directed-weighted nuclear reaction network in which the reaction rate as the weight, and neutron, proton, $^4$He and the remainder nuclei as the criterion for different reaction-layers is for the first time built based on all thermonuclear reactions in the JINA REACLIB database. Our results show that with the increase of the stellar temperature ($T_{9}$), the distribution of nuclear reaction rates on the $R$-layer network demonstrates a transition from unimodal to bimodal distributions. Nuclei on the $R$-layer in the region of $lambda = [1,2.5times10^{1}]$ have a more complicated out-going degree distribution than the one in the region of $lambda = [10^{11},10^{13}]$, and the number of involved nuclei at $T_{9} = 1$ is very different from the one at $T_{9} = 3$. The redundant nuclei in the region of $lambda = [1, 2.5times10^{1}]$ at $T_{9} = 3$ prefer $(gamma,p)$ and $({gamma,alpha})$ reactions to the ones at $T_{9}=1$, which produce nuclei around the $beta$ stable line. This work offers a novel way to the big-data analysis on nuclear reaction network at stellar temperatures.
Particle-$gamma$ coincidence experiments were performed at the Oslo Cyclotron Laboratory with the $^{181}$Ta(d,X) and $^{181}$Ta($^{3}$He,X) reactions, to measure the nuclear level densities (NLDs) and $gamma$-ray strength functions ($gamma$SFs) of $^{180, 181, 182}$Ta using the Oslo method. The Back-shifted Fermi-Gas, Constant Temperature plus Fermi Gas, and Hartree-Fock-Bogoliubov plus Combinatorial models where used for the absolute normalisations of the experimental NLDs at the neutron separation energies. The NLDs and $gamma$SFs are used to calculate the corresponding $^{181}$Ta(n,$gamma$) cross sections and these are compared to results from other techniques. The energy region of the scissors resonance strength is investigated and from the data and comparison to prior work it is concluded that the scissors strength splits into two distinct parts. This splitting may allow for the determination of triaxiality and a $gamma$ deformation of $14.9^{circ} pm 1.8^{circ}$ was determined for $^{181}$Ta.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
