Influence Of Nuclear Deformation Research Articles

Effects of nuclear deformation in U$+$U collisions at the intermediate energy

Nuclear deformation is an important topic in the study of nuclear structure. The influence of nuclear structure on nuclear reactions and heavy-ion collisions has attracted considerable attention recently. Based on the ultra-relativistic quantum molecular dynamics (UrQMD) model, the effect of nuclear deformation in $^{238}$U$+$$^{238}$U at the beam energy of łinebreak 0.4 GeV/nucleon is investigated and several observables, such as the stopping power, collective flow, and $\pi^{-}/\pi^{+}$ yield ratio, are calculated. It is found that the stopping power obtained with tip-tip (the two nuclei with their long axes head-on) collisions is the largest among collisions with different deformations. For belly-belly (the two nuclei with their short axes head-on and long axes parallel in the reaction plane) collisions, the elliptic flow exists even for the most central collision ($b$=0 fm). $\pi^{-}/\pi^{+}$yield ratio obtained with tip-tip collision is larger than that obtained with belly-belly collision. In addition, the influence of nuclear deformation on the elliptic flow of free protons is stronger than that of nuclear symmetry energy in $^{238}$U$+$$^{238}$U collisions at 0.4 GeV/nucleon, while the elliptic flow ratio between neutrons and protons shows hardly any sensitivity to different deformations of uranium.

α-decay chains and cluster radioactivity of 295−299119 and 298−302120 isotopes using zero- and finite-range NN interactions

The α-decay half-lives of the superheavy nuclei (SHN) with Z = 119 and 120 are investigated by employing the density dependent cluster model. Within the double-folding model, the α-nucleus interaction potential is calculated microscopically using a realistic nucleon–nucleon (NN) interaction. The exchange part of the interaction potential is evaluated within a local density formalism, using the finite-range as well as the ordinary zero-range exchange components of the NN interaction. The influence of nuclear deformation is presented. The calculated values of α-decay half-lives for five isotopes of each of the SHN with Z = 119 and 120 have been compared with those values evaluated using other theoretical models. It was found that our theoretical values are in good agreement with their counterparts. The competition between α-decay and spontaneous fission is investigated and predictions for possible decay modes for the unknown nuclei 295−299119 and 298−302120 are presented. The probable cluster decay half-lives of 295119 and 298120 have been studied within the previously mentioned double-folding model as well as the unified formula (UF) of half-lives for α decay and cluster radioactivity, the scaling law by Horoi (Horoi) and the universal decay law (UDL). The cluster decay half-lives derived from the former three models are too large compared to α-decay half-lives, but the UDL formula predicts the possibility of heavy cluster emission. The mass number variations of the microscopic shell correction energy for different α-decay chains of Z = 119 and 120 isotopes are presented. The possible correlations between the shell effect and each of α-decay and cluster decay half-lives are discussed. We hope that the proposed theoretical predictions for α-decay chains and cluster radioactivity provide a new perspective to experimentalists.

Cluster decay half-lives of trans-lead nuclei based on a finite-range nucleon–nucleon interaction

Nuclear cluster radioactivity is investigated using microscopic potentials in the framework of the Wentzel–Kramers–Brillouin approximation of quantum tunneling by considering the Bohr–Sommerfeld quantization condition. The microscopic cluster–daughter potential is numerically constructed in the well-established double-folding model. A realistic M3Y-Paris NN interaction with the finite-range exchange part as well as the ordinary zero-range exchange NN force is considered in the present work. The influence of nuclear deformations on the cluster decay half-lives is investigated. Based on the available experimental data, the cluster preformation factors are extracted from the calculated and the measured half lives of cluster radioactivity. Some useful predictions of cluster emission half-lives are made for emissions of known clusters from possible candidates, which may guide future experiments.

Deformation dependence of symmetry energy coefficients of nuclei

Based on the semi-classical Thomas-Fermi approximation together with the Skyrme energy-density functional, we study the deformation dependence of symmetry energy coefficients of finite nuclei. The symmetry energy coefficients of nuclei with mass number A = 40, 100, 150, 208 are extracted from two-parameter parabola fitting to the calculated energy per particle. We find that the symmetry energy coefficients decrease with the increase of nuclear quadrupole deformations, which is mainly due to the isospin dependence of the difference between the proton and neutron surface diffuseness. Large deformations of nuclei can cause the change of the symmetry energy coefficient by about 0.5 MeV and the influence of nuclear deformations on the symmetry energy coefficients is more evident for light and intermediate nuclei.

Investigation of dipole strength up to the neutron separation energy atγELBE

The bremsstrahlung facility at the ELBE accelerator offers the possibility to investigate dipole strength distributions up to the neutron-separation energies with photon up to 16 MeV in energy. The facil- ity and various results for nuclides measured during recent years are presented. One example is the study of the N = 80 nuclide 136 Ba. The other presented example is the study of the chain of xenon isotopes from N = 70 to N = 80 which aimed to investigate the influence of nuclear deformation an neutron excess on the dipole strength in the pygmy region. An overview of the analysis is given. GEANT4 simulations were performed to determine the non-nuclear background that has to be removed from the measured spectra. This opens up the possibility to take into account also the strength of unresolved transitions. Simulations of gamma-ray cascades were carried out that consider the transitions from states in the quasi-continuum and allow us to estimate their branching ratios. As a result, the photoabsorption cross sections obtained from corrected intensities of ground- state transitions are compared with theoretical predictions and results within the chain of isotopes. With the help of the measured dipole distribution it is possible to describe gamma-ray spectra following neutron capture more precisely.

Fusion at near-barrier energies within the quantum diffusion approach

The nuclear deformation and neutron-transfer process have been identified as playing a major role in the magnitude of the sub-barrier fusion (capture) cross sections. There are a several experimental evidences which confirm the importance of nuclear deformation on the fusion. The influence of nuclear deformation is straightforward. If the target nucleus is prolate in the ground state, the Coulomb field on its tips is lower than on its sides, that then increases the capture or fusion probability at energies below the barrier corresponding to the spherical nuclei. The role of neutron transfer reactions is less clear. The importance of neutron transfer with positive Q-values on nuclear fusion (capture) originates from the fact that neutrons are insensitive to the Coulomb barrier and therefore they can start being transferred at larger separations before the projectile is captured by target-nucleus. Therefore, it is generally thought that the sub-barrier fusion cross section will increase because of the neutron transfer. The fusion (capture) dynamics induced by loosely bound radioactive ion beams is currently being extensively studied. However, the long-standing question whether fusion (capture) is enhanced or suppressed with these beams has not yet been answered unambiguously. The study of the fusion reactions involving nuclei at the drip-lines has led to contradictory results.

SKYRME-RANDOM-PHASE-APPROXIMATION DESCRIPTION OF E1 STRENGTH IN 92–100Mo

The isovector dipole E1 strength in 92,94,96,98,100 Mo is analyzed within the self-consistent separable random-phase approximation (SRPA) model with Skyrme forces SkT6, SkM*, SLy6, and SkI3. The special attention is paid to the low-energy region near the particle thresholds (4-12 MeV), which is important for understanding of astrophysical processes. We show that, due to a compensation effect, the influence of nuclear deformation on E1 strength below 10-12 MeV is quite modest. At the same time, in agreement with previous predictions, the deformation increases the strength at higher energy. At 4-8 MeV the strength is mainly determined by the tail of E1 giant resonance. The four Skyrme forces differ in description of the whole giant resonance but give rather similar results below 12 MeV.

Global calculation of α-decay half-lives with a deformed density-dependent cluster model

A global calculation of favored \ensuremath{\alpha}-decay half-lives of both even-$A$ and odd-$A$ deformed nuclei is carried out in the framework of a deformed version of the density-dependent cluster model (DDCM). The influence of nuclear deformation on \ensuremath{\alpha}-decay half-lives is taken into account in the deformed DDCM. The microscopic potential between the spherical \ensuremath{\alpha} particle and the deformed daughter nucleus is evaluated numerically from the double-folding model by the multipole expansion method. The deformation and orientation dependence of the \ensuremath{\alpha}-core potential is analyzed and discussed. The formulas of the deformed DDCM are presented in detail, and a large number of numerical calculations of medium and heavy nuclei with available data are completed. The total number of \ensuremath{\alpha} emitters calculated in this article is 485, and this covers the nuclei with $Z=52\text{\ensuremath{-}}110$. This is a complete study of \ensuremath{\alpha}-decay half-lives on both even-$A$ and odd-$A$ nuclei with deformed microscopic potentials. The numerical results obtained by the deformed DDCM are in good agreement with the experimental data.

Influence of Nuclear Deformation on the Potential EnergySurface in Di-Nuclear Model

Influence of the nuclear deformation on the potential energy surface(PES) in a di-nuclear system is studied in details. It is found that thePES shape changes greatly due to the deformation effect. The top pointof the PES could be reduced significantly, which implies that theoptimum excitation energy could also be reduced greatly and may enhancethe formation probability of the compound nucleus. The dynamicaldeformation as a function of the reaction time in the reaction processis dramatic. The Z/N ratios of fragments tend to follow that of thecompound nucleus during the nucleon exchange process, but to fluctuate.

Interaction cross sections and matter radii of A = 20 isobars

Abstract High-energy interaction cross sections of A = 20 nuclei (20N, 20O, 20F, 20Ne, 20Na, 20Mg) on carbon were measured with accuracies of ≈ 1%. The nuclear matter r.m.s. radii derived from the measured cross sections show an irregular dependence on isospin projection. The largest difference in radii, which amounts to approximately 0.2 fm, has been obtained for the mirror nuclei 20O and 20Mg. The influence of nuclear deformation and binding energy on the radii is discussed. By evaluating the difference in r.m.s. radii of neutron and proton distributions, evidence has been found for the existence of a proton skin for 20Mg and of a neutron skin for 20N.

Preequilibrium emission in (p, x n) reactions on palladium isotopes

Energy spectra of neutrons from the104, 105, 106, 108, 110pd(p, xn) reactions atEp=26.1 MeV have been measured using the time-of-flight technique with good overall energy resolution (< 250 keV). The hard part of angle-integrated spectra corresponding to low residual excitations (U≦6MeV) exhibits pronounced structure varying from isotope to isotope. The observed structure can be reasonably well described by preequilibrium-model calculations with two-quasiparticle state densities for proton-particle neutron-hole configurations based on Nilsson-model single-particle levels instead of equidistant ones. The influence of nuclear deformation and pairing on preequilibrium particle emission is explored.

Influence of nuclear deformation on the correlation of protons emitted from compound nuclei

The angular correlations of protons evaporated from the compound nucleus124Ce exhibit strong anisotropies which are inconsistent with the emission from a spherical source. The data can be explained by an enhanced emission probability due to a lower Coulomb barrier perpendicular to the spin axis of strongly deformed nuclei.

Exact finite range DWBA calculations for heavy-ion induced nuclear reactions

Nuclear cluster radioactivity is investigated using microscopic potentials in the framework of the Wentzel–Kramers–Brillouin approximation of quantum tunneling by considering the Bohr–Sommerfeld quantization condition. The microscopic cluster–daughter potential is numerically constructed in the well-established double-folding model. A realistic M3Y-Paris NN interaction with the finite-range exchange part as well as the ordinary zero-range exchange NN force is considered in the present work. The influence of nuclear deformations on the cluster decay half-lives is investigated. Based on the available experimental data, the cluster preformation factors are extracted from the calculated and the measured half lives of cluster radioactivity. Some useful predictions of cluster emission half-lives are made for emissions of known clusters from possible candidates, which may guide future experiments.

Time-of-flight measurement of the evaporation residues from fusion of 5.9 mev/u 84kr and 27al

Mass and Z-distributions of the evaporation residues from compound-nucleus formation in the reaction 5.9 MeV/u 84Kr on 27Al were measured using a time-of-flight ΔE − E telescope, which is described in detail. The high recoil velocity attained by choosing the heavy reaction partner as projectile made it possible to resolve the reaction products by mass and atomic number. Data were taken in the angular range from 1.5 to 6°. The residue distributions are compared to evaporation calculations assuming the statistical decay by fission and particle evaporation of the compound nucleus 111Mn formed at an excitation energy of 108 MeV with angular momenta up to L CN ≈ 69 h ̵ . The data are consistent with the assumption of statistical equilibrium. Details of the de-excitation process, in particular the fission competition and the influence of nuclear deformations at high angular momenta, are discussed.

Influence of nuclear deformation on the neutron wave strength functions of heavy doubly even rotor nuclei

The neutron s-, p- and d-wave strength functions for 15 heavy doubly even rotor nuclei from 226Ra to 244Cm were calculated with a deformed nucleus optical model using the deformations of Stelson and Grodzins. Repetition of the analyses with reduced deformations, as suggested by considerations of the multipole moments of diffuse-edged charge distributions and the potential scattering radius data, produced an improved agreement with experimental measurements. The reduced deformations were essentially equivalent to the ground state equilibrium deformations calculated from the Bardeen-Cooper-Schrieffer theory using projected wave functions including an explicit Coulomb term. Comparative analyses with a single-particle vibrator model, as well as a spherical nucleus with a diffuse edge, are presented.