Nuclear moments: An effective probe of nuclear stucture

Magnetic dipole and electric quadrupole moments are discussed in nuclei near doubly-closed shell nuclei (the T1 nuclei) and in nuclei along series of single-closed shell nuclei (plus of minus a few nucleons) (the In odd-mass and odd-odd nuclei). We discuss the “additivity” rules for nuclear moments. We also address the EO moment: the liquid drop model and the shell-model are discussed and compared to measurements of nuclear radii in the Ca, Sn and Pb region. In the latter region, the importance of intruder states across the Z=82 proton closed shell is emphasized.     

Deformed relativistic mean-field calculations on nuclei near Z = 50 with FSUGold

The ground-state properties of Sn, Te, Xe, and Ba isotopes have been systematically investigated in the framework of the deformed relativistic mean-field theory with the new parameter set FSUGold. The results show that FSUGold is as successful as NL3 ^* in reproducing the ground-state binding energies of the nuclei. The calculated two-neutron separation energies, quadrupole deformations, and root-mean-square (rms) charge radii are in good agreement with the experimental data. The parameter set FSUGold can successfully describe the shell effect of the neutron magic number N = 82 . Detailed discussions on the binding energies, two-neutron separation energies, quadrupole deformations, rms charge radii and “binding energies” of the last neutrons are given.     

Laser spectroscopy of high spin isomers – a review

This review summarizes the experimental data on charge radii differences among ground state and high spin isomeric states determined by high-resolution laser spectroscopic methods. A comparison is presented between radii changes obtained from the isomeric shifts in the atomic spectra and from the quadrupole moments of both ground and isomeric states under the assumption that the radii changes are determined by the difference of the quadrupole deformations. Special attention is paid to isomers arising from the break-up of nucleon pairs and isomers of odd–odd nuclei. The characteristic features of the radii changes for isomeric states of different origin are discussed.     

Nuclear structure studies at Saha Institute of Nuclear Pysics using gamma detector arrays

In-beam gamma-ray spectroscopy, carried out at the Saha Institute of Nuclear Physics in the recent past, using heavy-ion projectiles from the pelletron accelerator centres in the country and multi-detector arrays have yielded significant data on the structure of a large number of nuclei spanning different mass regions. The experiments included the study of two-fold γγ-coincidence events for establishing decay schemes, directional correlation of oriented nuclei (DCO) for help in spin assignments and Doppler shift attenuation for lifetime information. The studies have led to the observation of rotational sequences of states in nuclei near closed shell in the mass A=110 region, vibrational spectra in nuclei with A ∼ 60, interplay between single-particle and collective modes of excitation in the doubly-odd bromine isotopes, decoupled bands with large quadrupole deformation in ⁷⁷Br, shape transition with rotational frequency within a band in ¹³⁵Pm and octupole collectivity in ¹⁵³Eu. Particle-rotor-model and cranked-shell-model calculations have been carried out to provide an understanding of the underlying nuclear structure.     

Static Moments of Neutron-Rich Ground States and Isomers Produced by Projectile Fragmentation

New achievements in nuclear moment measurements on nuclei produced and spin-oriented in intermediate energy (50–80 MeV/u) projectile fragmentation reactions are presented. By combining different types of spin-orientation with different experimental techniques, we show that the magnetic dipole moments and electric quadrupole moments of exotic neutron rich nuclei in their ground state as well as in their excited isomeric states can be measured. A selection of recent experiments performed at the LISE spectrometer at GANIL (Caen, France) is described. This revised version was published online in September 2006 with corrections to the Cover Date.     

Odd-even staggering in nuclear charge radii of neutron-rich europium isotopes

Nuclear magnetic dipole and electric quadrupole moments and changes in mean square charge radii for the neutron-rich^155–159Eu isotopes have been measured using resonance ionization spectroscopy at the IRIS facility. It has been found that the isotopes withN>92, unlike the isotopes with 89≦N≦92, have an ordinary character of odd-even staggering in nuclear charge radii. This means that the octupole deformation attributed previously to the europium nuclei around¹⁵⁴Eu does not display itself in the charge radii of heavier europium isotopes.     

On the sensitivity of the spatial-angular distribution of the Cherenkov light in extensive air showers to the mass composition of primary cosmic rays with energies of 10<Superscript>15</Superscript>–10<Superscript>16</Superscript> eV

This paper analyses the possibility of separating distinct groups of nuclei of primary cosmic rays with energies of 10¹⁵–10¹⁶ eV from the data on the spatial-angular distribution of Cherenkov light in extensive air showers. The paper shows that using an array of a few (3–4) telescopes with a moderately sized angular cell ∼0.5° placed at a distance ∼100 m from one another, one can achieve almost complete separation of the showers initiated by these nuclei (the Bayesian classification error is a few percentage points for the case of separating primary protons and nitrogen nuclei). The authors propose new parameters of the angular Cherenkov image that can greatly enhance the separability of the shower classes as compared to the approach based on the traditional parameters.     

Heat conductivity and the Lorentz number of the Sm1−x GdxS “black” phase

Measurement of the heat conductivity and electrical resistivity of two Sm_1−x Gd_xS compositions with x=0.1 and 0.14 is reported within the 80–300 K interval. An analysis of experimental data on the electronic component of heat conductivity permits a conclusion that the d subband of “heavy” carriers in the conduction band of these materials lies above the s “light”-carrier subband. Fiz. Tverd. Tela (St. Petersburg) 41, 26–29 (January 1999)     

Laser photoionization spectroscopy of rare-earth elements: New results on nuclear electromagnetic moments and charge radii of Eu,Gd and Tb isotopes

New results on spins, electromagnetic moments and isotopic changes of nuclear charge radii for ₆₃ ^157–159 Eu, ₆₄ ^{146, 148, 150} Cd and ₆₅ ^{147–155, 157, 159} Tb have been obtained from hyperfine structure and isotope shifte measured with laser resonance photoionization technique. These results complement two-dimensional picture (with respect to H and Z) of the changes of nuclear ground state properties near the “critical” neutron numbers N=88–90 in the vicinity of the “magric” proten number Z=64.     

Isotopic and Isotonic Chains of Nuclei in the 2p−1f−1gRegion in the Relativistic Mean Field Approach

A complete systematic set of relativistic mean field calculations are presented for the 2p−1f−1gshell nuclei with 28Z40; 26N50, both for isotopic and isotonic chains. Two sets of Lagrangian parameters NL1 (most successfully used in the past) and NL-SH (recently proposed) are used. Also sensitivity of the calculated results on the gaps required to account for pairing is investigated. The calculated binding energies, one (two) nucleon separation energies, the deformations and quadrupole moments, the point and the charge radii, isotopic shifts, densities, alpha staggering and the related quantities are systematically analyzed. The calculations are in good agreement with the experiment. The set Nl-SH seems to have an edge over the set NL1 especially for the neutron rich nuclei.     

Diffraction at HERA, Color Opacity and Nuclear Shadowing in DIS off nuclei

The QCD factorization theorem for diffractive processes in DIS is used to derive formulae for the leading twist contribution to the nuclear shadowing of parton distributions in the low thickness limit (due to the coherent projectile (photon) interactions with two nucleons). Based on the current analyzes of diffraction at HERA we find that the average strength of the interactions which govern diffraction in the gluon sector at x≤ 10⁻³, Q ₀= 2 GeV is ∼50mb. This is three times larger than in the quark sector and suggests that applicability of DGLAP approximation requires significantly larger Q ₀ in the gluon sector. We use this information on diffraction to estimate the higher order shadowing terms due to the photon interactions with N≥ 3 nucleons which are important for the scattering of heavy nuclei and to calculate nuclear shadowing and Q ² dependence of gluon densities. For the heavy nuclei the amount of the gluon shadowing: G _A(x,Q ₀ ²) /AG _N(x,Q ₀ ²)_{|x ≤ 10−3}∼ 0.25–0.4 is sensitive to the probability of the small size configurations within wave function of the gluon “partonometer” at the Q ₀ scale. At this scale for A∼ 200 the nonperturbative contribution to the gluon density is reduced by a factor of 4–5 at x≤ 10⁻³ unmasking PQCD physics in the gluon distribution of heavy nuclei. We point out that the shadowing of this magnitude would strongly modify the first stage of the heavy ion collisions at the LHC energies, and also would lead to large color opacity effects in eA collisions at HERA energies. In particular, the leading twist contribution to the cross section of the coherent J/ψ production off A≥ 12 nuclei at s ⁻²≥ 70 GeV is strongly reduced as compared to the naive color transparency expectations. The Gribov black body limit for F _2A(x,Q ²) is extended to the case of the gluon distributions in nuclei and shown to be relevant for the HERA kinematics of eA collisions. Properties of the final states are also briefly discussed. Received: 12 March 1999     

Decay of an electronic vortex of a collisionless shock wave as a possible mechanism of a “Coulomb explosion”

A new mechanism of a “Coulomb explosion,” where ions are accelerated by the electric field separating charges at the magnetic Debye radius r _B∼B/4πen _e, is proposed on the basis of a nonquasineutral model of electronic vortices in a magnetic field. It is shown by means of numerical calculations that in the process of acceleration of the ions a collisionless shock wave, whose front has an effective width of the order of δ∼r _B, determined by the breakdown of quasineutrality, is formed in a time of the order of ω _pi ⁻¹ , where ω_pi is the ion plasma frequency. The origin of such explosive dynamics is the formation of “holes” in the electron density at characteristic times of the order of ω _pe ⁻¹ (ω_pe is the electronic plasma frequency) as a result of the generation of electronic vorticity by the Weibel instability of an electromagnetic wave. Calculations for a laser pulse with intensity J∼6×10¹⁸ W/cm² show that the ions expand in the radial direction with velocities up to 3.5×10⁸ cm/s. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 10, 669–674 (25 November 1999)     

Charge radii and quadrupole-deformation parameters of high-spin isomers

Experimental data on the differences of charge radii of nuclei in the ground and high-spin isomeric states are surveyed. High-resolution laser-spectroscopy methods were used for measurements. The results obtained for the differences of these radii by two methods—from measurements of isomeric shifts of the levels of atoms containing the nuclei being studied and from measurements of their quadrupole moments in both states under the assumption that the differences of the radii are determined by the difference in their quadrupole deformations—were compared. Two-particle isomers in odd—odd nuclei, isomers formed upon the break of one or several nucleon pairs, and isomers featuring the 1i _13/2 configuration of the odd neutron in mercury nuclei were considered. The observed distinctions between the aforementioned differences of charged radii are discussed for isomeric states of different nature.     

Unparticles in gauge theory

A field model for a quark and an antiquark binding is described. Quarks interact via a gauge unparticle (“ungluon”). The model is formulated in terms of Lagrangian which features the source field S(x) which becomes a local pseudo-Goldstone field of conformal symmetry — the pseudodilaton mode and from which the gauge non-primary unparticle field is derived by B _μ(x) ∼ ∂_μ S(x). Because the conformal sector is strongly coupled, the mode S(x) may be one of new states accessible at high energies. We have carried out an analysis of the important quantity that enters in the “ungluon” exchange pattern — the “ungluon” propagator.     

Spin-parity measurements in the neutron-rich N ∼ 20 34P and 36S nuclei

Yrast and near-yrast energy levels in the neutron-rich N ∼ 20 nuclei ³⁴P, ³⁶S were populated using transfer/deep-inelastic processes following the ³⁴S + ¹¹⁵In reaction at an incident energy of 140MeV. The use of a multi-clover array has facilitated polarization measurements of the observed γ-rays and necessitated some changes in the previously known level scheme. The observation of the negative-parity levels in these nuclei on the periphery of the “island of inversion” is indicative of the influence of the intruder orbitals on the level structure at low spins. Shell-model calculations indicate that the inclusion of the orbitals from the upper pf shell is important even for the low-lying positive-parity states.     

Irreducible tensor operators and selective/hard single and double resonance experiments in insulators: Applications to NMRON and MQ-NMR

Recently, pulsed NMRON experiments have been carried out on trace amounts of radioactive⁵⁴Mn in the antiferromagnet MnCl₂4H₂O at 500 MHz (Le Gros et al. [1]). In this compound, the quadrupole splitting between the two lowest NMR transitions is ≈3 MHz, which precludes the use of non-selective (hard) rf pulses. Yet within the restricted 2*2 manifold, associated with a given transition, the nuclear rotation is “hard”. In this paper, the theory of “selective-hard” NMRON and MQ-NMR experiments is developed within the framework of irreducible tensor operators. In essence, the theory extends the early work of Jaynes [4] to deal with the higher-order multipolar states created during the course of a given NMR experiment. Several new pulsed NMRON and MQ-NMR experiments are proposed. For example, it is demonstrated how “ouble resonance”, “selective-hard” experiments on the pseudo spin-1 manifold spanned by |±1> and |0> Zeeman states of any integer spinI could be used to extract small chemical shifts in the face of very large quadrupole splittings.     

Investigation of neutron and proton distributions of He,Li, and Be isotopes using the new Skyrme-Force parameters

The proton and neutron densities, root-mean-square (rms) radii of proton density and neutron density, and neutron skin thickness of ^4–10He, ^6–11Li, and ^7–12Be isotopes are calculated using Skyrme-Hartree-Fock method with SLy4, SLy5, SLy6, and SLy7 force parameters. The evaluated results are compared with experimental data. Also, the results of halo nuclei (^6,8He, ¹¹Li, and ¹¹Be) are compared with the results of other isotopes for selected nuclei having the same neutron configuration.     

Influence of the quantum size effect for grazing electrons on the electronic conductivity of metal films

The thickness dependence of the electronic conductivity of thin (5–150 nm) single-crystal (100) films of refractory metals is investigated at different temperatures ranging from 4.2 K to room temperature. Regions of square-root, quasilinear, and quadratic dependences are observed. The quasilinear thickness dependence is explained by the influence of quantum effects on the transverse motion of electrons in the case when electron scattering by the film surfaces dominates. For macroscopic film thicknesses 30–50 nm, much greater than the Fermi wavelength of an electron, quantum corrections to the electronic conductivity reach values of the order of 50%. This is a consequence of the quantum size effect for grazing electrons, which leads to an anomaly in electron scattering by the film surfaces. The region of the quadratic thickness dependence corresponds to the quantum limit, and the square-root region corresponds to the classical limit. The effect is explained in a quasiclassical two-parameter model (the effective angle α* for small-angle electrons and the parameter γ, equal to the ratio of this angle to the diffraction angle) that takes into account the diffraction angular limits for grazing electrons. The effect occurs for parameters α*≪1 and γ∼1 and differs from the “ordinary” quantum size effect. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 11, 693–698 (10 December 1997)     

Gravity waves accompanying supernova explosions

Gravitational radiation arising during the formation of a protoneutron star is studied. Here it is mainly large-scale nonuniformities that develop inside the star. The entropy and density profiles of such nonuniformities resemble the “mushroom cloud” of a nuclear explosion. A bubble of hot neutron matter floats to the surface of the star, like the “mushroom cloud” of an explosion in the earth’s atmosphere. Depending on the symmetry of the problem, from two to six bubbles can float upward at the same time. The characteristic masses of such bubbles are 0.01M _⊗ and the radial velocities reach ∼0.1c. The energy radiated in the form of gravitational waves in one cycle of bubbles floating to the surface is ∼10⁻² M _⊗ c ²−10⁻¹⁰ M _⊗ c ². Such cycles occur repeatedly as the neutron star cools. This phase can last up to seconds. The total energy radiated in the form of gravitational radiation can reach 10⁻¹ M _⊗ c ². Pis’ma Zh. éksp. Teor. Fiz. 64, No. 12, 817–822 (25 December 1996)