Deuterium state and the possibility for cold nuclear synthesis in solids

We calculate the deuteron potential and the probability for cold nuclear synthesis for deuterium in the TiD₂ compound and its alloys with 3d-period elements. In the band model of a deuteron gas in a solid we examine the influence of the diffusion currents on the reaction rate. We show that by itself being in the solid state the Coulomb barrier for nuclear reactions is lowered in comparison with the deuterium gas. However, in a solid a necessary condition is the presence of physical processes and fields which lead to a nonequilibrium state for the deuterium subsystem.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 20–30, October, 1993.     

核聚变中的核物理问题

采用标准的量子力学方位阱加库伦位垒,计算了氘-氘聚变截面。给出了0．2～280keY能区内的截面数据。与实验符合得很好。此模型说明了不可用Breit-Wigner公式来讨论轻核聚变反应。将此模型运用于束缚态带电粒子之间的核反应。可以解释一系列“异常现象”。并展现了开发不带强放射性的聚变能的前景。     

A model for annealing of nuclear tracks in solids

A mathematical formula is derived for annealing of radiation induced damage in solids starting with the empirical equation having a form of the Arrhenius equation. This formula is transformed into a practical relationship in the usable form to fit the experimental track annealing data by making use of a relationship between fractional defect density in the latent track and etched track length. Calculated lengths of fission fragment tracks in annealed CR-39 based on the proposed model are compared with corresponding experimental measurements (our previously published results). A very good agreement is found between calculated results and experimental measurements. Physical meanings of parameters involved in the proposed model are given with appropriate theoretical explanation guided by analysis based on the model-fit on track annealing measurements. The results in this paper are useful for a wide spectrum of researchers including cosmic-ray physicists, geologists, nuclear track methodologists and semiconductor/accelerator physicists using ions implantation for doping semiconductors and materials modifications.     

加速器核物理大科学平台现状及展望

文章首先回顾了加速器核物理大科学平台的发展历史,随后总结了核物理研究前沿对加速器平台的需求,介绍了不稳定核束的产生和加速方法,综述了现有的加速器装置情况,最后给出了在建的和计划中的加速器装置展望。     

Spectral densities and nuclear spin relaxation in solids

We investigate the properties of ten spectral densities relevant for nuclear spin relaxation studies in solids. This is preceded by a brief review of nuclear spin relaxation in solids which includes a discussion of the appropriate spin-dependent interactions and the various relaxation rates which can be measured. Also, the link between nuclear spin relaxation and dielectric relaxation is discussed. Where possible and/or appropriate each of the spectral densities is expressed as a continuous distribution of Bloembergen-Purcell-Pound (or Debye) spectral densities 2ξ /(1 + ξ² ω²) for nuclear Larmor angular frequency ω and correlation time ξ. The spectral densities are named after their originators or the shape of the distributions of correlation times or both and are (1) Bloembergen-Purcell-Pound or δ-function, (2) Havriliak-Negami, (3) Cole-Cole, (4) Davidson-Cole, (5) Fang, (6) Fuoss-Kirkwood, (7) Bryn Mawr, (8) Wagner or log-Gaussian, (9) log-Lorentzian, and (10) Fröhlich or energy box. The Havriliak-Negami spectral density is related to the Dissado-Hill theory for dielectric relaxation. The spectral densities are expressed in a way which makes them easy to compare with each other and with experimental data. Many plots of the distributions of correlation times and of the spectral densities vs. various correlation times characterizing the distributions are given.     

Nuclear tracks in solids: registration physics and the compound spike

Observations of GeV heavy ion and MeV cluster-ion tracks in crystalline solids give us new insight into registration physics. Thermal and ion explosion spikes no longer compete; a ‘compound spike’ accounts for both. Ion explosion dominates for surface tracks (electronic sputtering). And there can also be transient plasma stopping in the bulk. For clusters there are ‘vicinage effects’—both electronic and nuclear—which can influence track dimensions and structure. Displacement cascades in large energetic clusters may lead to projectile “fission” and coherent flow into sub-tracks. The absence of tracks in certain targets, and their size/structure in others, leads to a model of projectile assisted prompt anneal (PAPA) in 10⁻¹¹s, either partial or complete, often by swift epitaxy, on elemental lattices (e.g. silicon) or on compound sublattices (e.g. fluorite). Phase transformations are important, but simple target amorphization is rare—the exception, not the rule. For many targets the thermal spike (macroscopic) fails, since ‘point’ defects (atomistic) characteristic of the target, their motion, and the electronic band structure, determine latent track detail. Circumstances in which the Bragg Rule of Additivity fails completely are revealed, and the kinetic threshold for constructive phase transitions in tracks described. This same track physics applies generally also to geothermometry—the opposite time extremum (10⁺¹¹s)—where annealing is due to defect assisted delayed anneal (DADA). Differences between etching rates of induced and spontaneous fission tracks can be explained. The geothermobarometric “Wendt/Vidal effect” (2002)—combined pressure, temperature and stress (with time) influences on fission track annealing (in e.g. apatite)—is briefly discussed.     

Science and technology with nuclear tracks in solids

Fission track dating has greatly expanded its usefulness to geology over the last 40 years. It is central to thermochronology—the use of shortened fission tracks to decipher the thermal history, movement, and provenance of rocks. When combined with other indicators, such as zircon color and (U–Th)/He, a range of temperatures from C to C can be studied. Combining fission track analysis with cosmogenic nuclide decay rates, one can study landscape development and denudation of passive margins. Technological applications have expanded from biological filters, radon mapping, and dosimetry to the use of ion track microtechnology in microlithography, micromachining by ion track etching, microscopic field emission tips, magnetic nanowires as magnetoresistive sensors, microfluidic devices, physiology of ion channels in single cells, and so on. In nuclear and particle physics, relatively insensitive glass detectors have been almost single-handedly responsible for our knowledge of cluster radioactivity, and plastic track detectors together with automated measuring systems have been used at the Bevalac, Brookhaven, CERN, and GSI, mainly to study fragmentation of high-energy heavy nuclei. Almost everything we know about the ultraheavy cosmic rays has been learned using Lexan on the Long Duration Exposure Facility and BP-1 phosphate glass on the Mir Station. New topics include development of calorimetric aerogels capable of measuring kinetic energies of hypervelocity interstellar and interplanetary dust grains in space and research on identification of strains of Bacillus spores by measurements of their size and swelling rates when humidified.     

Nanojunctions as logic operators for the spintronics

We propose two all-electrical nanodevices where the spin properties of an incoming electron are modified by the spin-orbit interaction (SOI), resulting in a transformation of the qubit state carried by the spin. Our proposal is essentially based on nanojunctions made of crossing quantum wires patterned in a two dimensional electron gas where the Rashba SOI is present. We investigate in detail the spin precession of one electron traveling in the proposed nanodevices. The nanojunctions acts as spin filters or ballistic spin rotators whose properties can be varied by tuning the strength of the SOI, by changing the geometry of the junctions. Two different basic mechanism in order to obtain in plane or out of the plane rotations are discussed. We show that, starting from the spin rotators, a large class of unitary transformations can be attained with one or more nanojunctions in series. By choosing appropriate parameters the spin transformations can be made unitary, which corresponds to lossless operators.     

Problems and prospects for an AB-Initio Hartree-FockPerturbed-Cluster treatment of local defects in ionic solids

Abstract

This paper presents a new theoretical technique for the study of defects in crystals. The methods is based on an ab-initio Hartree-Fock perturbed-cluster (PC) scheme¹. A prerequisite for this technique is the availability of a model for the host, perfect crystal, that must be obtained with the same Hamiltonian and the same computational conditions (basis set, accuracy etc.). This information is provided by CRYSTAL, an ab-initio periodic Hartree-Fock code².     

Nuclear clusters and nuclear molecules

Clustering has long been known to be influential in the structure of ground and excited states of N=Z$N=Z$ nuclei. States close to the decay thresholds are of particular interest, as clustering becomes dominant. Recent studies of loosely bound light neutron-rich nuclei have focused attention on structures based on clusters and additional valence neutrons, which give rise to covalent molecular binding effects. These nuclear molecules appear only at the extremes of deformation, in the deformed shell model they are referred to as super- and hyper-deformed. The beryllium isotopes provide the first examples of such states in nuclear physics. Further nuclear molecules consisting of unequal cores and also with three centres can be considered. These arise in the isotopes of neon and carbon, respectively. Molecular states in intrinsically asymmetric configurations give rise to parity (inversion) doublets. Examples of recent experiments demonstrating the molecular structure of the rotational bands in beryllium isotopes are presented. Further experimental evidence for bands as parity doublets in nuclei with valence neutrons in molecular orbits is also analysed. Work on chain states (nuclear polymers) in the carbon isotopes is discussed. These are the first examples of hyper-deformed structures in nuclei with an axis ratio of 3:1. Future perspectives are outlined based on a threshold diagram for covalent nuclear molecules with clusters bound via neutrons in covalent molecular configurations.     

Nuclear orientation and nuclear structure

The purpose of this paper is to demonstrate how recent experimental results of¹⁵¹Eu and⁵⁷Fe high pressure Mössbauer studies in 4f and 3d metallic magnetic systems can contribute to a deeper understanding of the nature of local moment (4f) and itinerant (3d) magnetism in these systems. Special emphasis is given on the comparison of the experimental results with related theoretical models.     

Nuclear moments and nuclear structure

Research activities of the Osaka Sugimoto group in the past 30 years are summarized. Developments of the perturbed angular correlation method and the new NMR method under the leadership of Sugimoto opened a wide variety of possibilities, not only in the nuclear structure study but also in studies of nuclear reactions, weak interactions and hyperfine interactions.     

Nuclear clusters and nuclear molecules

The idea that clusters of nucleons might exist in the nucleus has a long history and dates back to the earliest days of nuclear physics. Recently there have been significant advances in our theoretical treatment of clustering and in the experimental methods available to identify cluster structure in nuclei. These developments are reviewed with particular reference to the²⁴Mg nucleus where a rich variety of cluster configurations is observed.     

Nuclear orbiting and anomalies in nuclear reactions

In this paper, we report our measurements of back-angle oxygen and carbon particle yields from ¹⁶O+⁸⁹Y, ¹²C+⁹³Nb reactions forming the same compound nucleus ¹⁰⁵Ag at the same excitation energy and spin distribution. We find anomalously large oxygen yield and entrance channel dependence at high excitation energies from ¹⁶O+⁸⁹Y reaction implying formation of a dinuclear orbiting complex. Possible connection between nuclear orbiting and fast fission is also discussed.     

Monte Carlo calculations of electron scattering in solids for nuclear spectroscopy

Direct MC modelling of individual elastic and inelastic scattering events of electrons in solids is described. The examples cover transmission through thin solid layers as well as backscattering from flat surfaces of bulk solids. Divergent beams and isotropic emission of incident electrons with energies from 5 to 200 keV are treated.Presented at the Seminar on Secondary Electrons in Electron Spectroscopy, Microscopy, and Microanalysis, Chlum (The Czech Republic), 21–24 September, 1993.     

Nuclear pears: Recent developments and future prospects

We report studies of examples of reflection-asymmetric nuclei which are difficult to access using compound nucleus reactions. The octupole radium isotopes withN>132 and radon isotopes are not accessible by reactions employing stable targets and beams; we have shown that multinucleon transfer reactions can populate these nuclei with sufficient yield for their structure to be determined. We report high-spin studies in^{218, 220, 222}Rn and^{222, 224, 226, 228, 230}Ra: these show that the Ra isotopes withA<228 have the characteristics of octupole deformed nuclei whereas the Rn isotopes behave like octupole vibrators. Measurements of theB(E1)/B(E2) ratios indicate that the electric dipole moment in these nuclei is constant with spin. The most octupole deformed nuclei are predicted to be uranium isotopes withN≈132; measurements of the very fissile nucleus²²⁶U suggest that it is octupole deformed and has a large intrinsic electric dipole moment. Finally, we speculate that the best examples of pear shapes are the hyperdeformed minima predicted to lie low in uranium isotopes withN≈140; their signature of high-multiplicity low-energyE1 photon cascades should be detectable using present-day high-efficiency germanium arrays.     

Semiconductor heterostructures for spintronics and quantum information

A selection of optical experiments is presented, demonstrating the utility of semiconductors in two novel areas of research: spintronics and quantum information. First we show examples of spin manipulation in semiconductor quantum wells. The light is used to generate a spin polarization and to detect it. Next we discuss application of optical methods in studies of carrier-induced ferromagnetism in quantum wells. Finally, we present examples of single quantum dot spectroscopy related to perspectives of application of quantum dots in quantum information, and, in particular, the use of photon correlation measurements as a tool to study the quantum dot excitation mechanisms. To cite this article: J.A. Gaj et al., C. R. Physique 8 (2007).