Influence Of Nuclear Structure 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.

Mapping quasifission characteristics and timescales in heavy element formation reactions

Background: The formation of superheavy elements by fusion of two massive nuclei is severely inhibited by the competing quasifission process.Purpose: Through extensive mass-angle distribution measurements, we map out the systematic dependence of quasifission characteristics as a function of the identity of the colliding nuclei.Methods: The Australian National University's Heavy Ion Accelerator Facility and CUBE spectrometer have been used to measure mass-angle distributions for 42 reactions forming heavy elements. Beam energies above their respective capture barriers were used to minimize the known influence of nuclear structure effects.Results: Different mappings of mass-angle distribution characteristics (including timescales) over the nuclear landscape show a systematic dependence on entrance channel and compound nucleus fissilities.Conclusions: The results provide an empirical baseline to assess effects of nuclear structure at lower beam energies, and motivate the testing and validation of complete dynamical models of heavy element fusion through comparison of mass-angle distributions.

Fusion of40Ca +40Ca,40Ca +48Ca and48Ca +48Ca

The recent experiment on fusion of 40 Ca + 40 Ca is described in some detail and the results are reported. A full excitation function has been measured from well above the Coulomb barrier, down to low energies where the cross section reduces to ≃20 µ b. A comparison is done with the recently published data on fusion of 40 Ca + 48 Ca and of 48 Ca + 48 Ca. The trends are different, in particular as far as the logarithmic derivatives (slopes) are concerned, in the interesting energy region below the barrier. The slope for systems where 40 Ca is involved, show a characteristic behavior with a tendency to saturate in a limited energy range just below the main barrier. The slopes resume increasing at lower energies, possibly indicating the influence of nuclear structure (the strong octupole vibration of 40 Ca) at such low energies, together with the clear presence of the fusion hindrance phenomenon. The results of coupled-channels calculations are presented.

Light charged particle emission in heavy-ion reactions — What have we learnt?

Light charged particles emitted in heavy-ion induced reactions, their spectra and angular distributions measured over a range of energies, carry the signature of the underlying reaction mechanisms. Analysis of data of light charged particles, both inclusive and exclusive measured in coincidence with gamma rays, fission products, evaporation residues have yielded interesting results which bring out the influence of nuclear structure, nuclear mean field and dynamics on the emission of these particles.

The influence of nuclear structure on the Lamb shift in hydrogenlike heavy atoms

We evaluate and list the various contributions to the Lamb shift in hydrogenlike heavy atoms which arise from parameters describing shape, size and structure of the nucleus. We compare these contributions with those obtained from quantum electrodynamics. It is found that in heavy nuclei, nuclear contributions depending on experimental parameters and nuclear models are of the same size as QED contributions of order a2. Therefore, in these systems the theoretical predictions for binding energies are limited by the exact knowledge of the nuclear parameters.

Influence of nuclear structure on the characteristics of light pionic atoms.

An extended version of the standard pion-nucleus optical potential is presented using the momentum-space formulation of the multiple scattering theory. This potential is used for studying the influence of nonlocal effects and nuclear structure on the characteristics of light pionic atoms. A method is suggested to treat the long-range two-nucleon correlations involved in the second order optical potential. Particularly, the spin-orbital Fermi motion correction to the first-order optical potential, the center-of-mass correlations, and the spin-isospin corrections to the second-order optical potential are discussed in some detail. The results are presented in comparison with the experimental data for the 1s and 2p levels of light pionic atoms up to $^{44}\mathrm{Ca}$.

Detour transitions in forbidden radiative electron capture decay

The observed excess of electromagnetic radiation accompanying the first forbidden unique electron capture in 41Ca and the second forbidden nonunique electron capture in 59Ni is interpreted as the contribution of detour transitions via virtual nuclear states. Contrary to previous theories, we suggest that this contribution is important for forbidden transitions in the whole range of photon energies. New formulae for the shape factors of the spectra including the detour transitions are presented. The influence of nuclear structure on the intensity of the detour transition is discussed.

Elastic and inelastic pion scattering and nuclear structure

The influence of nuclear structure upon calculated angular distributions and cross sections of pion scattering off light nuclei is studied within the framework of Glauber theory. Both spin-flip and non-flip processes are included. Results obtained using simple shell-model configurations as well as more realistic shell-model wave functions which may involve particle-hole components are compared. The effects of using realistic single-particle wave functions generated from Woods-Saxon potentials, effects of antisymmetry, renormalisation of the properties of the Δ( 3 2 , 3 2 ) isobar in the nucleus and renormalisation of the effective charge are investigated. Results are given for elastic scattering on 12C, 16O and 24Mg and inelastic scattering on 7Li, 12C, 15N, 20Ne and 24Mg. It is shown that pion-inelastic scattering to excited levels in 15N can give important details of the nature of the particle-hole admixtures. Large effects were found for the calculated angular distributions in 20Ne when the model space was enlarged to include the d 3 2 orbit.

Pion-induced single charge exchange and nuclear structure

The influence of nuclear structure upon calculated angular distributions and cross sections of pion-induced single charge exchange on light nuclei is studied within the framework of Glauber theory. Results obtained using simple shell-model configurations as well as more realistic shellmodel wave functions which involve particle-hole components where appropriate are compared. In all cases the use of better wave functions enhance the ( π +, π 0) cross sections and suppress ( π −, π 0) cross sections. The effects of using realistic single-particle wave functions generated from WoodsSaxon potentials and the effects of the antisymmetry of the nuclear wave functions are also investigated. Renormalisation of the properties of the Δ ( 3 2 , 3 2 ) in the nucleus has also been considered and is shown to be essential to understand the behaviour of the experimental integrated cross section. Results are given for (π +, π 0) on 7 Li, 13 C, 15 N, 16 O, 17 O and 39 K and (π −, π 0) on 13 C, 15 N and 17 O leading to the ground state and excited states of the final nucleus. A comparison with experiment is made where possible.

Influence of nuclear structure on widths of π-atomic terms

The authors calculate the widths of 2p and 3d pi -atomic states in the nuclei 12C, 16O, 32S, 40Ar, 40-48Ca, 46-50Ti and 52Cr assuming the 'two-nucleon' mechanism to be the doorway process for nuclear pion absorption. The results are in good agreement with experiment.

Influence of nuclear structure on binding energy

Influence of nuclear structure on binding energy

Experimental and theoretical particle parameters for L electrons. Directional correlations in Hg 199

Publisher Summary This chapter discusses the experimental and theoretical particle parameters for L electrons. During directional correlation studies, conversion electrons that were involved have achieved increased importance not only because they make correlation measurements in a complex decay feasible but also because of the information gained about the conversion process itself. The existence of so-called penetration effects—such as influence of nuclear structure on the atomic electrons—has made the electron correlation method even more important. The usefulness of this method is based on existing tabulations of theoretically calculated particle parameters bσνλ. The particle parameters involve the same matrix elements as the internal conversions coefficients (ICCs). The nuclear structure when present influences and changes the conversion matrix elements. These are detected in the particle parameters and the ICCs.

The Influence of Nuclear Structure on the Hyperfine Structure of Heavy Elements

The influence on the h.f.s. of the finite size of the nucleus is considered and the effect is calculated for simple models of the nuclear magnetism. It is pointed out that the distribution of magnetic dipole density over the nuclear volume may vary greatly from nucleus to nucleus depending on the relative contributions of spin and orbital magnetic moments to the total nuclear moment. On this basis an attempt is made to interpret the observed discrepancy between the h.f.s. ratio of the Rb isotopes and the ratio of the magnetic moments as determined by the magnetic resonance method. A study of such anomalies may give some information regarding the structure of nuclear moments, in particular, regarding the nuclear ${g}_{L}$-factor.