Nuclear Structure Models Research Articles

Octupole correlations in the actinides and the spdf-IBA model

The octupole bands in the Z∼88, N∼134 region, with their abundance of experimental information, offer a real challenge for different nuclear structure models. In this region, quasimolecular bands, which are thought to indicate the presence of stable octupole deformation, have been observed. The quantities most often reported are the B(E1)/B(E2) branching ratios from these levels. The calculations in the framework of the spdf model show that the 1-pf boson limit (dipole-octupole vibrations) can describe the essential experimental features related to the octupole bands in the Rn-Th region.

Supersymmetry in some nuclear-structure models

Application of the supersymmetry concept in nuclear-structure physics is considered. A Hamiltonian that is based on the U(6/12) graded algebra and which does not possess, in general, a dynamic symmetry is constructed. However, part of the eigenstates of this Hamiltonian belonging to even-even and odd neighboring nuclei form supersymmetric multiplets. It is also shown that the particle-rotor model description of rotational bands in an odd nucleus that are built on the K=1/2 pseudoorbital singlet Nilsson state belonging to the shell with an even principal pseudooscillator quantum number can be reformulated as a realization of supersymmetry.

Octupole correlations in the transitional actinides and thespdfinteracting boson model

The region of light actinides $(Z\ensuremath{\sim}88,N\ensuremath{\sim}134),$ which is thought to exhibit signs of stable octupole deformation, offers a real challenge for nuclear structure models. We study the even-even Ra-Th nuclei in the framework of the $\mathrm{spdf}$ interacting boson model and we find that while the properties of the low-lying states can be understood without stable octupole deformation, higher spin states $(J\ensuremath{\gtrsim}12\ensuremath{\Elzxh})$ in some of these nuclei (e.g., ${}^{226}\mathrm{Ra})$ suggest that octupole deformation develops with increasing spin. We also discuss how octupole deformation can arise in the rotational (dynamical symmetry) limit.

Overview of nuclear reaction models used in nuclear data evaluation

A brief outline of nuclear reaction mechanisms including the optical model, the Distorted Wave Born Approximation, the Coupled Channels, classical and quantum-mechanical preequilibrium models and the Compound Nucleus is given. The relations among different nuclear reaction and structure models are indicated. The paper is addressed to the users of nuclear data and seeks to explain basic physical concepts and the role of nuclear reaction models in data evaluation.

Covenant Marriage: A New Alternative for Traditional Families

The phrase “alternative family forms” evokes images of family organization that deviate from the so-called “traditional” model of nuclear structure with husband/breadwinner, wife/homemaker. This paper, however, examines a new, alternative form of marriage contract that is highly compatible with that traditional model: “Covenant Marriage,” which is currently available in just two of the fifty U.S. states. We begin by describing features of the covenant marriage alternative in Louisiana, and its supporters early, enthusiastic expectations. We then discuss its very limited adoption, but its much greater appeal to couples with traditional gender role attitudes. We conclude by considering the apparent value of the covenant marriage contract for those couples who wish to practice and promote gendered family roles and responsibilities.

Three-dimensional spectral precision distance microscopy of chromatin nanostructures after triple-colour DNA labelling: a study of the BCR region on chromosome 22 and the Philadelphia chromosome.

Topological analysis of the three-dimensional (3D) chromatin nanostructure and its function in intact cell nuclei implies the use of high resolution far field light microscopy, e.g. confocal laser scanning microscopy (CLSM). However, experimental evidence indicates that, in practice, under biologically relevant conditions, the spatial resolution of CLSM is limited to about 300 nm in the lateral direction and about 700 nm in the axial direction. To overcome this shortcoming, the use of a recently developed light microscopical approach, spectral precision distance microscopy (SPDM) is established. This approach is based on the precise localization of small labelling sites of a given target in spectrally differential images. By means of quantitative image analysis, the bary centres (intensity weighted centroid analogous to the centre of mass) of these independently registered labelling sites can be used as point markers for distance and angle measurements after appropriate calibration of optical aberrations (here, polychromatic shifts). In combination with specific labelling of very small chromatin target sites with dyes of different spectral signatures by fluorescence in situ hybridization (FISH), SPDM presently allows us to analyse the nuclear topology in three-dimensionally conserved nuclei with a 'resolution equivalent', many times smaller than the conventional optical resolution. Chronic myelogeneous leukaemia (CML) is genetically characterized by the fusion of parts of the BCR and ABL genes on chromosomes 22 and 9, respectively. In most cases, the fusion leads to a translocation t(9; 22) producing the Philadelphia chromosome. SPDM was applied to analyse the 3D chromatin structure of the BCR region on the intact chromosome 22 and the BCR-ABL fusion gene on the Philadelphia chromosome (Ph) by using a new triple-colour FISH protocol: two different DNA probes were used to detect the BCR region and the third DNA probe was used to identify the location of the ABL gene. Consistent 3D distance measurements down to values considerably smaller than 100 nm were performed. The angle distributions between the three labelled sites on the Philadelphia chromosome territory were compared to two state-of-the-art computer models of nuclear chromatin structure. Significant differences between measured and simulated angle distributions were obtained, indicating a complex and non-random angle distribution.

Microscopic analysis of the breathing mode in 40Ca and 58Ni

Recent experimental studies of the giant electric resonance region in 58Ni and 40Ca with inelastically scattered α-particles of energy Eα= 240 MeV are analyzed within a microscopic nuclear structure model. The model includes the continuum RPA and more complex 1p1h⊗phonon configurations. By superimposing the contributions of different multipoles up to L = 4 we obtain good agreement with the newest (reanalyzed) data for the isoscalar monopole strength and for the total (α,α′) cross section in 58Ni. Agreement with experiment for the isoscalar monopole resonance in 40Ca is obtained too. We emphasize the necessity of using microscopic transition densities and discuss consequences for the analyses of such experiments in light and medium mass nuclei. It is shown that the gross structure of the isoscalar monopole resonance in 40Ca is caused by the 1p1h⊗phonon configurations.

Sensitivities of the proton-nucleus elastic scattering observables of6Heand8Heat intermediate energies

We investigate the use of proton-nucleus elastic scattering experiments using secondary beams of 6He and 8He to determine the physical structure of these nuclei. The sensitivity of these experiments to nuclear structure is examined by using four different nuclear structure models with different spatial features using a full-folding optical potential model. The results show that elastic scattering at intermediate energies (<100 MeV per nucleon) is not a good constraint to be used to determine features of structure. Therefore researchers should look elsewhere to put constraints on the ground state wave function of the 6He and 8He nuclei.

Localization of radiation-induced chromosomal breakpoints along human chromosome 1 using a combination of G-banding and FISH

Purpose : To determine the exact location of radiation-induced chromosomal breakpoints along the euchromatic or heterochromatic regions: G-light and G-dark bands, respectively. Materials and methods : The distribution of radiation-induced chromosomal breakpoints was scored in human lymphocytes irradiated in vitro with 3 Gy of gamma-radiation. Image analysis was applied to combine G-banded and FISH-painted images of the human chromosome 1. Results : A total of 195 chromosomal breakpoints in 176 cells with structural chromosomal aberrations was used for the present analysis. Radiation-induced breakpoints were found to be distributed randomly with respect to the p or q arms of chromosome 1 and specific band or band length, but more breakpoints were mapped to G-light than to G-dark bands, the difference being statistically significant. Conclusions : The results can well be interpreted in terms of concepts of existing models of nuclear architecture, chromatin structure and transcriptional activities of the chromatin, which can influence the induction of primary chromosomal aberrations by gamma-rays. Differential repair of randomly produced primary aberrations may also explain the non-random distribution of radiation-induced breakpoints.

Lessons to be learned from the coherent photoproduction of pseudoscalar mesons

We study the coherent photoproduction of pseudoscalar mesons---particularly of neutral pions---placing special emphasis on the various sources that put into question earlier nonrelativistic-impulse-approximation calculations. These include: final-state interactions, relativistic effects, off-shell ambiguities, and violations to the impulse approximation. We establish that, while distortions play an essential role in the modification of the coherent cross section, the uncertainty in our results due to the various choices of optical-potential models is relatively small (of at most 30%). By far the largest uncertainty emerges from the ambiguity in extending the many on-shell-equivalent representations of the elementary amplitude off the mass shell. Indeed, relativistic impulse-approximation calculations that include the same pionic distortions, the same nuclear-structure model, and two sets of elementary amplitudes that are identical on-shell, lead to variations in the magnitude of the coherent cross section by up to factors of five. Finally, we address qualitatively the assumption of locality implicit in most impulse-approximation treatments, and suggest that the coherent reaction probes---in addition to the nuclear density---the polarization structure of the nucleus.

Delbrück and nuclear effects in photon scattering: recent developments

Delbrück scattering, which is the elastic scattering of a photon in a Coulomb field, is of interest both as an observable high-order non-linear process in quantum electrodynamics and as an interfering process in studies of nuclear structure. This process has been extensively investigated in the past from theoretical and computational points of view. In this paper, attention is mainly focused on the theoretical features and, in particular, the dispersion relation approach and a critical review of the numerical evaluations of the first-order Born approximation cross-section is presented. Applications and limits of these results are discussed in comparison with experimental data on elastic photon scattering by medium-and heavy-mass nuclei and theoretical models of nuclear structure. Copyright © 1999 John Wiley & Sons, Ltd.

Delbrück and nuclear effects in photon scattering: recent developments

Delbrück scattering, which is the elastic scattering of a photon in a Coulomb field, is of interest both as an observable high-order non-linear process in quantum electrodynamics and as an interfering process in studies of nuclear structure. This process has been extensively investigated in the past from theoretical and computational points of view. In this paper, attention is mainly focused on the theoretical features and, in particular, the dispersion relation approach and a critical review of the numerical evaluations of the first-order Born approximation cross-section is presented. Applications and limits of these results are discussed in comparison with experimental data on elastic photon scattering by medium-and heavy-mass nuclei and theoretical models of nuclear structure. Copyright © 1999 John Wiley & Sons, Ltd.

Is the lattice gas model a unified model of nuclear structure?

It is shown that a 50%-occupied `lattice gas' reproduces the sequence, occupancy and degeneracy of the energy levels of the independent-particle (IP) model due to symmetries inherent to the lattice. Although the lattice gas has thus far been developed solely for simulation of heavy-ion multifragmentation results, the correspondence between the lattice gas and the IP model suggests a convergence of the `strong-interaction' collective approach and the `weak-interaction' microscopic approach to nuclear structure theory. This hybrid model is called the `IP-lattice gas' model.

Visualizing the atomic nucleus

Between the realm of precise few-body calculations and the realm of precise stochastic calculations lie most of the problems of the nuclear realm, where only imperfect models with a variety of adjustable parameters allow for quantitative work. Recent developments in both computer science and nuclear theory, however, have made it possible to visualize the nucleus in a manner consistent among the diverse models of nuclear structure. We discuss the need for visualization at the nuclear level, for both educational and research purposes, and then describe a computer graphics implementation that we call Nuclear Visualization Software.

Detection of δ-electron events in charge coupled devices: a fingerprint of single swift heavy ions

Charge Coupled Devices, an arrangement of a few 100 000 photo-electric cells on a plane, allow the spatially and temporally resolved detection of single swift heavy ions and δ-electrons emitted by projectile-target-interactions from a target foil mounted at a distance of 500 μm above the microchip. This detector system is read out by standard TV technique and the signal is digitized for further processing by image analysis. The δ-electrons can be observed as a halo around the hit of the ion on the corresponding TV frame. The appearance of these halos is determined by the ion parameters velocity and effective charge. Vice versa the δ-electron halos provide information on the projectile within the bounds of the δ-electron statistics. This effect has been described in detail by an appropriate nuclear track structure model, which comprises production, transport and detection of δ-electrons as independent processes. First model calculations have been confirmed by experimental data.

Dependence of direct neutron capture on nuclear-structure models

The prediction of cross sections for nuclei far off stability is crucial in the field of nuclear astrophysics. We calculate direct neutron capture on the even-even isotopes ${}^{124\ensuremath{-}145}$Sn and ${}^{208\ensuremath{-}238}$Pb with energy levels, masses, and nuclear density distributions taken from different nuclear-structure models. The utilized structure models are a Hartree-Fock-Bogoliubov model, a relativistic mean field theory, and a macroscopic-microscopic model based on the finite-range droplet model and a folded-Yukawa single-particle potential. Due to the differences in the resulting neutron separation and level energies, the investigated models yield capture cross sections sometimes differing by orders of magnitude. This may also lead to differences in the predicted astrophysical $r$-process paths.

Intermediate energy charge-exchange reactions induced by polarized 3He

Spin polarization transfer is proven to be very useful in obtaining detailed information of the continuum nuclear responses. The data, taken for the ( p , n ) reactions, have enabled us to separate the response into the spin longitudinal and transverse components. These partial nuclear responses have been successfully used to make critical tests of nuclear structure models. In the present paper, we shall first summarize the results of the data and the theoretical analyses made so far. We shall then discuss information obtainable from the ( 3 H e, t ) reaction, emphasizing on the differences and similarities in comparison with the ( p , n ) reaction. The results of numerical calculations made for ( 3 H e, t ) reactions based on the microscopic distorted wave impulse approximation will also be reported.

Concluding remarks

Concluding remarks

Lattice models for quark, nuclear structure and nuclear reaction studies

Because of their computational simplicity, lattice models have found various uses in quark, nuclear structure and nuclear reaction (multifragmentation and heavy-ion) studies. However, differences in the mean density of particles among crystal types lead to significantly different properties, indicating that simulations using nucleon lattices should compare several lattice structures. The characteristics of five important lattice groups are discussed and fundamental algorithms are provided.

Uncertainties in direct neutron capture calculations due to nuclear structure models

The prediction of cross sections for nuclei far off stability is crucial in the field of nuclear astrophysics. For spherical nuclei close to the dripline the statistical model (Hauser-Feshbach) approach is not applicable and direct contributions may dominate the cross sections. For neutron-rich, even-even Sn targets, we compare the resulting neutron capture cross sections when consistently taking the input for the direct capture calculations from three different microscopic models. The results underline the sensitivity of cross sections calculated in the direct model to nuclear structure models which can lead to high uncertainties when lacking experimental information.