Single-particle Level Density Parameter Research Articles

Preequilibrium models for 58Ni (n, xp) reaction in Neutrons at 8, 9, 9.4, 11 and 14.8 MeV using the EMPIRE and TALYS codes

In this study, the calculations of proton emission spectra produced by 58Ni (n, xp) reaction are used in the framework of preequilibrium models with the EMPIRE and TALYS codes. Exciton Model predictions combined with the Kalbach angular distributions systematics and statistical Multi-step Direct (MSD) with Multi-step Compound (MSC) processes preequilibrium models were used. Also, some necessary parameters as optical model, level density, level density a-parameter and single-particle level density parameter have been investigated for our calculations. The comparison with experimental data shows clear improvement over the Exciton and MSD with MSC models calculations.

NUCLEAR LEVEL DENSITY OF HEAVY NUCLEI Z≥90 THROUGH SEMICLASSICAL METHOD

The nuclear level density parameters of back shift Fermi gas model, including single-particle level density parameter a and excitation energy shift E1, for some heavy nuclei have been calculated in the framework of semiclassical approach. The single-particle level density have been obtained for mean-field Woods–Saxon potential. By using the obtained values of single-particle level density parameter and excitation energy shift, the spin cut-off factor has been calculated at the neutron binding energy.

NUCLEAR LEVEL DENSITY PARAMETER WITH YUKAWA FOLDED POTENTIAL

The average dependence of the single-particle level-density parameter on mass number A, isospin and deformation is determined using the Yukawa folded mean-field potential for spherical and deformed nuclei at temperatures 0 ≤ T ≤ 5 MeV and elongations ranging from oblate shapes to the scission configuration of fissioning nuclei. The results are compared with similar estimates obtained previously using the relativistic mean-field theory, the Skyrme Hartree-Fock and the Thomas-Fermi approach.

High spin properties of 124Ba

The 124Ba nucleus is investigated on the basis of the method of statistical mechanics by assuming the nucleons to move in triaxially deformed Nilsson potential. The variation in the Fermi energies of protons and neutrons is studied as a function of spin and temperature. The Fermi energies determined as a function of angular momentum is used to study the dependence of shell correction on angular momentum using the Strutinsky smoothing procedure. The most important observation is that the shell correction is almost the same for all spins for 124Ba. The spin cutoff parameter and the single particle level density parameter are studied as a function of spin and temperature. Constant entropy lines drawn by plotting the excitation energy against angular momentum are found to be roughly at constant energy above the yrast line and are almost equally spaced. It is observed that no yrast traps are present for 124Ba.

Microscopic nuclear level densities from Fe to Ge by the shell model Monte Carlo method

We calculate microscopically total and parity-projected level densities for β-stable even-even nuclei between Fe and Ge, using the shell model Monte Carlo methods in the complete ( pf+0 g 9/2)-shell. A single-particle level density parameter a and backshift parameter Δ are extracted by fitting the calculated densities to a backshifted Bethe formula, and their systematics are studied across the region. Shell effects are observed in Δ for nuclei with Z=28 or N=28 and in the behavior of A/ a as a function of the number of neutrons. We find a significant parity dependence of the level densities for nuclei with A≲60, which diminishes as A increases.

Structural properties of hot rotating40Ca

The yrast and yrare lines are obtained for {sup 40}Ca using a statistical method by assuming the nucleons to move in a triaxially deformed Nilsson harmonic oscillator potential. The backbending and yrast traps are observed in the case of {sup 40}Ca at certain spins. A shift in the first yrast minima towards higher angular momentum states with an increase in entropy is observed. A second backbending is found to occur at spin M=17{h_bar} for all entropies. The excitation energy, the nuclear level density, the single-particle level density parameter, and the spin cutoff parameter are determined as functions of temperature and angular momentum by minimizing the free energy. The Strutinsky method is used to study the variation of the shell correction with angular momentum for equilibrium shapes. The Fermi energies obtained as a function of angular momentum are used for calculating this shell correction. The nucleus is found to be spherical up to M=6{h_bar} and becomes oblate with a further increase in angular momentum. The shell correction is found to increase with the deformation having a minimum value for the spherical shape. {copyright} {ital 1997} {ital The American Physical Society}

Structural properties of hot deformed 122Xe at high spins.

The Xe122 nucleus is investigated using statistical theory for studying intrinsic properties as a function of temperature and spin assuming the nucleus to move in a triaxially deformed Nilsson potential. The single particle level density parameter is extracted as a function of temperature for various spins and is found to reach a constant value at higher temperature. The excitation energy is calculated as a function of angular momentum for different entropies and temperatures. The spin cutoff parameter as a function of angular momentum is determined for various temperatures from the rotational energy. The shell correction as a function of angular momentum is determined. The variation of proton and neutron Fermi energies with temperature and angular momentum is studied. The effect of the variation of nuclear level density with excitation energy on nuclear temperature is verified for different spins. © 1995 The American Physical Society.

Shell effects in hot isobaric nuclei.

Level densities for hot isobaric nuclei are investigated by incorporating the isospin fluctuations in the statistical theory of nuclei. The single-particle level density parameter a is extracted as a function of temperature for various isospins of the system. At large temperatures, the empirical value of a\ensuremath{\simeq}A/8 is reproduced. A new method of extracting the neutron-proton asymmetry parameter is proposed. The neutron-proton asymmetry parameter is found to depend very strongly on deformation and isospin at low temperatures. The effect of the shell structure on the asymmetry energy is predominant for certain isospins corresponding to stable neutron-proton combinations. Results are presented for A=42, 44, 46, and 208. The excitation energy versus isospin plot for constant entropy of the system exhibits pockets similar to yrast traps in high-spin states of highly excited nuclei.

Analysis of recent measurement of nuclear level density parameters

Data from experiments leading to values of the nuclear logarithmic level density derivatives are analysed and shown to be reasonably self consistent. A modified form of the curve drawn by Newton for the value of the single particle level density parameter a is found to be in accord with the data. Attention is drawn to the effect of restriction of the allowed angular momentum of the emitted particles on the value found for the temperature in an evaporative process.