Improvement of the algorithm for the analysis of Level schemes in the GTOL code

The algorithm of the GTOL code used for constructing nuclear level schemes by the measured γ spectra is discussed, and the difficulties arising in the work with complex nuclear level schemes are pointed out. The ways to improve the algorithm are shown, and the NEWGTOL code allowing large arrays of nuclear data to be properly handled is proposed.     

Nuclear hyperpolarization in solids and the prospects for nuclear spintronics

Nuclear hyperpolarization can be achieved in a number of ways. This article focuses on the use of coupling of nuclei to (nearly) pure quantum states, with particular emphasis on those states obtained by optical excitation in bulk semiconductors. I seek an answer to this question: “What is to prevent the design and analysis of nuclear spintronics devices that use the extremely long-lived hyperpolarized nuclear spin states, and their weak couplings to each other, to affect computation, memory, or informational technology schemes?” The answer, I argue, is in part because there remains a lack of fundamental understanding of how to generate and control nuclear polarization with schemes other than with rf coils.     

Nuclear gamma-ray laser: A comparative analysis of various schemes

Four basic schemes for a nuclear gamma-ray laser (NGL) are analyzed using the “NGL-hyper-bola” as a generalized comparative criterion: solid state Mössbauer scheme; stimulated gamma-emission in cooled ensembles of free nuclei with hidden population inversion of nuclear states; nuclear gamma-ray lasing without inversion; and Bose-Einstein condensate as a hypothetical active medium for NGL.     

Efficient dynamic nuclear polarization at high magnetic fields

By applying a new technique for dynamic nuclear polarization involving simultaneous excitation of electronic and nuclear transitions, we have enhanced the nuclear polarization of the nitrogen nuclei in 15N@C60 by a factor of 10(3) at a fixed temperature of 3 K and a magnetic field of 8.6 T, more than twice the maximum enhancement reported to date. This methodology will allow the initialization of the nuclear qubit in schemes exploiting N@C60 molecules as components of a quantum information processing device.     

Atomic nucleus as the laboratory for symmetry tests. The SPIN program

Two complementary facilities for nuclear orientation of radioactive nuclei, based on hyperfine interactions at low temperatures obtained with top loading ³He?⁴He dilution refrigerators, have been developed at JINR Dubna and Charles University in Prague. These facilities are well suited for nuclear orientation studies practically of any nuclei of physical interest, which can be produced on JINR YASNAPP and DRIBs complexes. Wide variety of precise nuclear spectroscopy experiments with oriented nuclei is carried out with this technique-SPIN program at JINR. The physics potential of nuclear orientation experiments and the information, which can be obtained from the study of directional distribution of gamma radiation from oriented nuclei, are summarized. As the result of such nuclear orientation experiments extensive tests of different symmetry and supersymmetry schemes relevant to nuclear physics can be performed. Some examples of such symmetry and supersymmetry schemes in nuclei, which can be tested in the framework of SPIN program, are indicated.     

Pseudo steady-state photo-CIDNP measurements with improved background suppression

Pulse sequences have been developed which considerably increase the background suppression in pseudo steady-state photo-CIDNP experiments (measurements of photochemically induced dynamic nuclear polarization in which several laser flashes are applied during a period smaller than the nuclear spin relaxation times). Quantitative estimates of the errors caused by pulse imperfections and nuclear spin relaxation are given. The feasibility of the schemes is demonstrated with an experimental example (photoreaction of benzophenone with triethylsilane).     

NMR method for amplification of single-spin state

Amplification of a single-spin state using nuclear magnetic resonance (NMR) techniques in a rotating frame is considered. The main aim is to investigate the efficiency of various schemes for quantum detection. Results of numerical simulation of the time dependence of individual and total nuclear polarizations for 1D, 2D, and 3D configurations of the spin systems are presented.     

Two-quantum stimulated emission of gamma radiation

Various schemes exploiting two-quantum nuclear transitions for the generation of coherent gamma radiation (stimulated anti-Stokes and stimulated two-quantum de-excitation of isomeric nuclei in an active medium with the hidden population inversion of nuclear states and the ignition of an avalanche-like stimulated gamma-emission by counterpropagating X-rays) are discussed.     

夸克模型和原子核

本文评述了近年来从夸克模型出发研究原子核的种种尝试,着重讨论了应用夸克型模解释核力的各种方案。     

Solution of Quantum Mechanical Problems Using Finite Element Method and Parametric Basis Functions

New computational schemes, symbolic-numerical algorithms and programs implementing the high-accuracy finite element method (FEM) for the solution of quantum mechanical boundary-value problems (BVPs) are reviewed. The elliptic BVPs in 2D and 3D domains are solved using the multivariable FEM and Kantorovich method using parametric basis functions. We demonstrate and compare the efficiency of the proposed calculation schemes, algorithms, and software by solving the benchmark BVPs that describe the scattering on a barrier and a well, the bound states of a helium atom, and the quadrupole vibration in a collective nuclear model.     

Signal enhancement in solid-state NMR of quadrupolar nuclei

Recent progress in the development and application of signal enhancement methods for NMR of quadrupolar nuclei in solids is presented. First, various pulse schemes for manipulating the populations of the satellite transitions in order to increase the signal of the central transition (CT) in stationary and rotating solids are evaluated (e.g., double-frequency sweeps, hyperbolic secant pulses). Second, the utility of the quadrupolar Carr–Purcell–Meiboom–Gill (QCPMG) and WURST-QCPMG pulse sequences for the rapid and efficient acquisition of particularly broad CT powder patterns is discussed. Third, less frequently used experiments involving polarization transfer from abundant nuclear spins (cross-polarization) or from unpaired electrons (dynamic nuclear polarization) are assessed in the context of recent examples. Advantages and disadvantages of particular enhancement schemes are highlighted and an outlook on possible future directions for the signal enhancement of quadrupolar nuclei in solids is offered.     

Analysis of evaluated nuclear structure data

General analysis of the consistency of nuclear data and verification of the optimal values of excited state energies, presented in the evaluated nuclear structure data file (ENSDF) (October 2005) have been performed. As optimality criteria, we chose the Pearson and Romanovsky criteria. As a result, along with finding some misprints, it was revealed that the level energies are not optimal for a large number of the ADOPTED LEVELS, GAMMAS sets included in the ENSDF. The use of the standard GTOL program (7.1a version), which calculates the optimal values of the nuclear level energies from the energies of the transitions positioned in a scheme, made it possible to significantly improve the statistical consistency of the schemes.     

Possibility of Combining Nuclear Level Pumping in a Plasma with Lasing in a Solid

Nuclear isomers can be used for the storage and release of “clean” nuclear energy and several triggering schemes have been discussed. Here the possibility to utilize resonance between atomic and nuclear transitions in the form of a hybridization of atomic-nuclear excitation is considered. Several isotopes and specific nuclear levels are identified as candidates for triggering via atomic transitions. A variety of ionization states and atomic-shell configurations arises in a hot plasma generated by short high-power pulses of laser light. The non-radiative conversion of the ionization energy within an atom can be suppressed in the hot plasma surroundings. The time scales of different processes in nuclear, atomic and condensed-matter subsystems are compared and the fast ionization in a solid, X-ray radiance in a plasma, and sample melting and recrystallization may precede nuclear fluorescence. A time scale shorter than 0.1 ns makes this sequence promising for the collective excitation of short-lived modes in a nuclear subsystem. This revised version was published online in August 2006 with corrections to the Cover Date.     

Persistent narrowing of nuclear-spin fluctuations in InAs quantum dots using laser excitation

We demonstrate the suppression of nuclear-spin fluctuations in an InAs quantum dot and measure the timescales of the spin narrowing effect. By initializing for tens of milliseconds with two continuous wave diode lasers, fluctuations of the nuclear spins are suppressed via the hole-assisted dynamic nuclear polarization feedback mechanism. The fluctuation narrowed state persists in the dark (absent light illumination) for well over 1 s even in the presence of a varying electron charge and spin polarization. Enhancement of the electron spin coherence time (T2*) is directly measured using coherent dark state spectroscopy. By separating the calming of the nuclear spins in time from the spin qubit operations, this method is much simpler than the spin echo coherence recovery or dynamic decoupling schemes.     

The futility of observing stimulated gamma-ray emission from a long-lived isomeric state

Summary We reveal the fallacies in recent gamma-ray laser schemes that propose to obtain gain by stimulating transitions from a long-lived upper to a short-lived lower nuclear state. We point out the errors in recent derivations of the stimulated-emission coefficients, derive the correct formulae, and submit an alternative explanation for an experiment purported to observe stimulated emission from a long-lived isomer.     

Nuclear level densities and level spacing distributions: Part II

Extensive and complete nuclear level schemes and neutron resonance densities of 75 nuclides have been used to determine parameters of level density formulae, the spacing distribution of levels with equal spins and parities, and spacing correlations. The dependences of the level density parameters on A, on pairing energies and on shell effects are discussed. The spacing distribution is found to lie between a Poisson and Wigner distribution indicating a transitional character between regular and chaotic properties of the nuclear quantum system near the ground state.     

Partial wave contributions to the antikaon potential at finite momentum

The momentum dependence of the antikaon optical potential in nuclear matter is obtained from a microscopic and self-consistent calculation using the meson-exchange Jülich interaction. Two self-consistent schemes are discussed, which would lead to substantially different predictions for the width of nuclear bound states. The effect of higher partial waves of the interaction, beyond the L=0 component, is studied and found to have moderate but nonnegligible effects on the nuclear potential at zero momentum. At momenta as large as 500 MeV/c, relevant in the analysis of heavy-ion collisions, the higher partial partial waves modify the optical potential by nearly a factor of two.     

Numerical techniques for the evaluation of non-adiabatic interactions and the generation of quasi-diabatic potential energy surfaces using configuration interaction methods

CI techniques, based on nearly complete expansions over determinants for subsets of molecular orbitals and electrons, have been extended to evaluate, by finite differences, non-adiabatic interactions arising from the nuclear kinetic energy operator. A functional of the non-adiabatic interactions is defined and, from the minimum condition of the functional, a simple expression is obtained for the transformation matrix to the quasi-diabatic basis. Two different schemes for the minimization of the functional, with and without constraints to the form of the transformation matrix, have been compared. Simple tests are presented to verify the numerical accuracy of the non-adiabatic interactions and to compare the two schemes for the minimization of the functional.