Constant Temperature Fermi Gas Model Research Articles

Investigation of level density and Gama strength function for photoneutron reaction in medical linacs in Beamline

Photoneutron reaction cross-sections of 197Au, 187Re, 186W, 181Ta, 94,95,96,97,98,100Mo isotopes were calculated through the TALYS 1.95 nuclear reaction code. The energy range of the incident photon chosen as 7 MeV–30 MeV corresponded to the range of the giant dipole resonance region, which is also an applicable energy range in radiotherapy for many commercial medical linear accelerators. Calculations were performed using three phenomenological level density models available in code, namely the Constant Temperature Fermi Gas Model, the Back-shifted Fermi Gas Model, and the Generalized Superfluid Model. The most convenient level density model for each reaction was chosen using relative variance calculations. The cross-section calculations were repeated using gamma strength function models, Kopecky-Uhl generalized Lorentzian model, Brink-Axel Lorentzian model, and Goriely's hybrid model and the best level density model was kept constant. The calculated data and the experimental data from the international Experimental Nuclear Reaction Data Library were analysed and compared graphically.

Estimation of (n,p) reaction cross sections at 14.5 [formula omitted] MeV neutron energy by using artificial neural network

The aim of this study is to develop an accurate artificial neural network algorithm for the cross-section of (n,p) reactions at 14.5 ∓0.5 MeV neutron energy which is important to developing materials for fusion reactor design. The experimental data used at artificial Neural network calculations have been taken from the Experimental Nuclear Reaction Data (EXFOR) database. Bayesian algorithm has been used at training section of artificial neural network. Regression (R) values of artificial neural network calculations have been found as 0.99363, 0.98574 and 0.99257 for training, testing and all process respectively. In addition to artificial neural network calculations, TALYS 1.95 nuclear reaction code has been used to reproduce (n,p) reactions at 14.5 ∓0.5 MeV. Two-component exciton model and Constant Temperature Fermi Gas Model have been used as pre-equilibrium and level density models respectively. Mean square errors of our calculations have been found 48.51 and 495.06 for artificial neural network and TALYS 1.95 respectively. Artificial Neural network estimations have been compared and analyzed with the TALYS 1.95 calculations and the experimental data taken from EXFOR database.

Cross sections of 56Fe(n, p)56Mn, 55Mn(n, p)55Cr, 52Cr(n, p)52V, 56Fe(n, α)53Cr, 55Mn(n, α)52V and 52Cr(n, α)49Ti reactions using phenomenological level density models from threshold to 20 MeV

56Fe(n,p)56Mn, 55Mn(n,p)55Cr, 52Cr(n,p)52V, 56Fe(n, α)53Cr, 55Mn(n, α)52V and 52Cr(n, α)49Ti reactions are evaluated using four phenomenological nuclear level density models from reaction threshold to 20 MeV. The calculated data is compared with the experimental nuclear reaction data from EXFOR database. Statistical factors H, D and R are computed to identify the best fit. Level density parameters are adjusted for further improvement of the fitting. Back shifted Farmi-gas model gives a resemblance of neutron-induced 56Fe, 55Mn and constant temperature Fermi-gas model gives a closeness for 52Cr reaction with our new parameter values.

Investigation of gamma strength functions and level density models effects on photon induced reaction cross–section calculations for the fusion structural materials 46,50Ti, 51V, 58Ni and 63Cu

Scientists have been focused on fusion reactor studies to overcome the increasing energy demand. The materials, which have the potential to be used in fusion reactors must be resistant to the harmful effects of radiation in the manner of material itself. Selection of the appropriate materials to be used in nuclear reactors has a crucial importance to achieve the maximum efficiency and security. Ti, V, Ni and Cu are known as some of the constructional fusion materials. Existence of many knowledge about those materials provides countless advantages to the researchers and one of them is the cross–section, which basically means the probability of a nuclear reaction's occurrence. In addition to the cross–section, there exist some other parameters, which could be pointed as gamma strength function and level density models that affect the theoretical calculations. In this study, photon induced reaction cross–sections of 46,50Ti, 51V, 58Ni and 63Cu target isotopes have been calculated by using TALYS 1.8 code with different gamma strength functions in the giant dipole resonance region. For gamma strength functions Kopecky-Uhl generalised Lorentzian Model, Brink-Axel Lorentzian Model, Hartree-Fock BCS tables, Hartree-Fock-Bogolyubov tables and Goriely's Hybrid Model have been employed. To appoint the best gamma strength function model, the relative variance calculations have been performed. Also, reaction cross–sections have been recalculated by using the best gamma strength function models through the different level density options. Constant Temperature Fermi Gas Model, Back Shifted Fermi Gas Model and Generalised Super Fluid Model have been employed for level density calculations. Experimental data for the investigated reactions have been taken from EXFOR library and used for comparisons of the obtained calculation results.

Theoretical calculations of production cross–sections for the 201Pb, 111In 18F and 11C radioisotopes at proton induced reactions

Production of radioisotopes that used in medical diagnosis and treatment are mostly based on the nuclear reactions. The cross–section data are important to understand nuclear reaction mechanisms. In this study TALYS 1.8 code has been used to calculate production cross–sections of 201Pb, 111In, 18F and 11C radioisotopes at proton induced reactions. Constant Temperature Fermi Gas Model (CTFGM), Back Shifted Fermi Gas Model (BSFGM) and Generalised Super Fluid Model (GSM) have been employed as a level density models for computations. Relative variance calculations have been carried out to determine the best level density model. In addition to cross–section calculations, total activities of radioisotopes have been presented. Production cross–section calculation results have been compared with experimental data taken from Experimental Nuclear Reaction Database (EXFOR).

Investigation of level density parameter effects on (p,n) and (p,2n) reaction cross–sections for the fusion structural materials 48Ti, 63Cu and 90Zr

The materials used in fusion reactor must be resistance to the harmful effects of radiation in the manner of material itself. Selection of the appropriate materials used in nuclear reactor has a crucial importance to achieve the maximum efficiency and security. Ti, Cu and Zr are known to be employed as first wall materials in fusion reactors. In this study, level density parameter effects on (p,n) and (p,2n) reaction cross–section calculations have been investigated by employing different level density models within TALYS 1.8 computer code for 48Ti, 63Cu and 90Zr selected as target materials. Also, for these isotopes (p,n) and (p,2n) reaction cross–section calculations have been done by using two different level density models of EMPIRE 3.2 code. For calculations; Constant Temperature Fermi Gas Model, Back Shifted Fermi Gas Model, Generalised Super Fluid Model and Microscopic level densities (temperature dependent Hartree Fock Bogolyubov, Gogny Force) from Hilaire's combinatorial tables have been used from TALYS 1.8. In addition, Generalised Superfluid Model and Hartree Fock Bogolyubov Model have been selected for calculations from EMPIRE 3.2 code. To appoint the best level density model, the relative variance analyses have been done. The cross–section calculations have been repeated via TALYS 1.8 level density models by changing the a parameter replacing with the obtained one from the best level density model result and value taken from the literature for each isotope. To analyze and comment about the outcomes of the study, a comparison of the results have been done with each other and the experimental data taken from the literature.

(γ, 2n)-Reaction cross-section calculations of several even-even lanthanide nuclei using different level density models

There are several level density models that can be used to predict photo-neutron cross sections. Some of them are Constant Temperature + Fermi Gas Model (CTFGM), Back-Shifted Fermi Gas Model (BSFM), Generalized Superfluid Model (GSM), Hartree-Fock-Bogoliubov microscopic Model (HFBM). In this study, the theoretical photo-neutron cross sections produced by (γ, 2n) reactions for several eveneven lanthanide nuclei such as 140,142Ce, 142,144,146,148,150Nd, 144,148,150,152,154Sm, and 160Gd have been calculated on the different level density models as mentioned above by using TALYS 1.6 and EMPIRE 3.1 computer codes for incident photon energies up to 30 MeV. The obtained results have been compared with each other and available experimental data existing in the EXFOR database. Generally, at least one level density model cross-section calculations are in agreement with the experimental results for all reactions except 144Sm(γ, 2n)142Sm along the incident photon energy, TALYS 1.6 BSFM option for the level density model cross-section calculations can be chosen if the experimental data are not available or are improbable to be produced due to the experimental difficulty.

Levels of 159Gd populated in average resonance neutron capture

The primary γ-rays and energy levels in 159Gd were investigated in average resonance neutron capture using tailored neutron beams at 2 keV and 24 keV and a pair spectrometer at the high flux reactor at Brookhaven. Nearly 200 levels with spin up to 5 2 are reported below 3 MeV. The distribution of radiative strength in this nucleus was obtained and is compared with a giant dipole resonance and single-particle strength models. The density of observed levels was determined and is described in terms of the constant temperature Fermi gas model. The neutron binding energy in 159Gd was determined to be 5943.32(12) keV.

Primary gamma transitions in 159Gd after isolated resonance neutron capture

Energy levels and transitions in 159Gd were studied by means of radiative capture of resonance neutrons at 12 isolated resonances of 158Gd. The time-of-flight technique was used on an enriched target at the IBR-30 reactor at JINR Dubna. A total of 80 primary gamma-transitions were recorded and their absolute intensities were determined resulting in the observation of 1 2 ±, 3 2 ± levels up to 2.4 MeV. The observed level density is described in terms of the constant temperature Fermi gas model. The neutron binding energy was determined at (5943.1±0.2) keV. The photon strength is derived and compared with a giant dipole resonance of standard Lorentzian shape for E1 and M1 radiation. The sum of observed gamma-ray intensity amounts to about 30% of the total gamma width. The remaining gamma-ray intensity above 2.4 MeV is estimated by extrapolating the level density and photon strength models to high excitation energies.

Spin-dependent level density in interacting boson-fermion-fermion model

The level density of the odd-odd nucleus 132Pr is investigated in the interacting boson-fermion-fermion model (IBFFM) which accounts for collectivity and complex interaction between quasiparticle and collective modes. The IBFFM total level density is fitted by a Gaussian and its tail is also fitted by Bethe formula and constant temperature Fermi gas model. The IBFFM spin-dependent level densities show high-spin reductions with respect to Bethe formula. This can be well accounted for by a modified spin-dependent level density formula.

Neutron-capture gamma-ray study of levels in 135Ba and description of nuclear levels in the interacting-boson-fermion model.

We have performed neutron-capture gamma-ray studies on natural and enriched targets of $^{134}\mathrm{Ba}$ in order to investigate the nuclear levels of $^{135}\mathrm{Ba}$. The low-energy level spectra were compared with the calculations using the interacting-boson-fermion model (IBFM) and the cluster-vibration model. The level densities up to 5 MeV that are calculated within the IBFM are in accordance with the constant temperature Fermi gas model. From the spin distribution we have determined the corresponding spin cutoff parameter \ensuremath{\sigma} and compared it to the prediction from nuclear systematics.

Double neutron capture in62Ni

The γ-radiation following single and double neutron capture in isotopically enriched62Ni was studied at the high flux reactor of the Institut Laue-Langevin, using a pair and Compton suppressed germanium detector. Measurements before and after 170 d of breeding were performed. The γ-ray fluxes through63Ni and64Ni are discussed; several new levels and spin-parity assignments were found. On the basis of the known discrete levels and the low-energy neutron resonances, level density parameters were determined within the Constant Temperature Fermi Gas model. The neutron binding energies were measured asBn (63Ni)=6837.92(18) keV andBn (64Ni)=9657.64(24) keV. The63Ni (n, γ) cross section for reactor neutrons was measured to be σ=20−2+5 b.

High-resolution spectroscopy of 32P : (II). Level density and primary transition strengths observed after thermal neutron capture in 31P

The -γ-ray spectrum emitted after thermal neutron capture in 31P was studied at the ILL high flux reactor with a pair spectrometer and an intrinsic Ge detector. A total of 212 transitions were assigned to the decay of 32P and 155 of these, representing 96.7% of the observed flux, were placed in a level scheme of 38 states. The neutron binding energy was determined as 7935.74 (16) keV. The densities of states observed in this reaction and in a recent (d, p) study are analyzed in the constant temperature Fermi-gas model. The primary E1 and M1 transition strengths in 32P are discussed and are compared to other sd-shell nuclei.

Spectroscopy of 41K by thermal neutron capture in 40K

The γ-ray spectrum emitted after thermal neutron capture in 40K has been studied at the ILL high flux reactor with curved crystal Bragg, pair and Ge(Li) spectometers. 585 transitions were assigned to the reaction 40K(n, γ) 41K and 490 of them were placed into a 41K level scheme; 68 new states are proposed. On the basis of γ-ray branches to states with established spin and parity, many new spin-parity assignments were made. The level energies up to 4 MeV were measured with a precision of 8–50 eV relative to the 411.8 keV 198Au standard, those above 4 MeV with a precision of 50–100 eV. The spin of the capture state was found to be I = 7 2 ; the neutron binding energy was determined to E B = 10095.25(10) keV. The level density of I π = 5 2 ±, 7 2 ±, 9 2 ± states was analyzed in terms of the constant-temperature Fermi gas model. It was shown that in this spin window the level scheme is almost complete up to an excitation energy of 5 MeV.