Observation of the neutron radiative decay

The aim of this work is the experimental observation of and research into a rare neutron mode, the radiative beta decay, where a new particle, the radiative gamma quantum, is formed along with the expected decay products: a beta electron, a recoil proton, and an antineutrino. The discovery of this rare neutron decay mode was conducted through identification of triple-coincidence events: simultaneous registration of a beta electron, a proton, and a radiative gamma quantum. The ordinary neutron decay was registered by double coincidences of a beta electron and a recoil proton. The statistics collected allow one to deduce the branching ratio (BR) BR = (3.2 ± 1.6) × 10⁻³ (90% C.L.) in the gamma energy region greater than 35 keV. This value of BR is consistent with standard electroweak theory. The text was submitted by the authors in English. An erratum to this article is available at .     

Cyclotron spin-flip mode in the extreme quantum limit

In a two-dimensional electron system, the combined excitation (the cyclotron spin-flip mode) associated with changes in both orbital and spin quantum numbers is investigated. The energy of the cyclotron spin-flip mode is studied as a function of the electron filling factor. Comparative dependences of the decay times of the cyclotron spin-flip mode and the magnetoplasmon are measured. It is shown that, as the filling factor increases from v = 0 or decreases from v = 1, the damping of the cyclotron spin-flip mode increases significantly, while the magnetoplasma mode remains undamped.     

Beta decay of highly charged ions

Ion storage rings and ion traps provide the very first opportunity to address nuclear beta decay under conditions prevailing in hot stellar plasmas during nucleosynthesis, i.e. at high atomic charge states. Experiments are summarized that were performed in this field during the last decade at the ion storage-cooler ring ESR in Darmstadt. Special emphasis is given to the first observation of bound-state beta decay, where the created electron remains bound in an inner orbital of the daughter atom. The impact of this specific ‘stellar’ decay mode for s-process nucleosynthesis as well as for nuclear ‘eon clocks’ is outlined. Finally, a new technique, single-ion decay spectroscopy, is presented, where one observes two-body beta decay characteristics (i.e. orbital electron capture or bound-state beta decay) of highly charged, single ions for well-defined nuclear and atomic quantum states of both the mother – and the daughter – ion.     

Scattering of electrons in image-potential states by steps

Image-potential states on several stepped copper surfaces were studied by time, energy, and angle-resolved two-photon photoelectron spectroscopy. For different step densities binding energies and effective masses were determined in the energy-resolved and decay rates in the time-resolved mode of two-photon photoemission. The asymmetry with respect to the electron motion up or down the steps of the total decay rates is enhanced for less-ordered step arrangements. Elastic interband scattering strongly depends on details of the backfolding of the bands by the periodic step structure. Elastic intraband scattering is of similar importance as inelastic decay may contribute significantly to the asymmetry of the decay rates. PACS 73.20.At; 79.60.Bm; 72.10.Fk     

Acoustic phonon impact on the inter-Coulombic decay process in charged quantum dot pairs

ABSTRACT

Recently, highly accurate multi-configuration time-dependent Hartree electron dynamics calculations demonstrated the efficient long-range energy transfer inter-Coulombic decay (ICD) process to happen in charged semiconductor quantum dot (QD) pairs. ICD is initiated by intraband photoexcitation of one of the QDs and leads to electron emission from the other within a duration of about 150 ps. On the same time scale electronically excited states are reported to relax due to the coupling of electrons to acoustic phonons. Likewise, phonons promote ionisation. Here, the QDs' acoustic breathing mode is implemented in a frozen-phonon approach. A detailed comparison of the phonon effects on electron relaxation and emission as well as on the full ICD process is presented, which supports the previous empirical finding of ICD being the dominant decay channel in paired QDs. In addition the relative importance of phonon–phonon, phonon–electron and electron–electron interaction is analysed.     

Decays of Z Bosons into Triple-Quark and Double-Quark Structures

This paper presents a mechanism of decay of elementary particles, which has been developed based on a new approach. The results obtained may be of interest to experimenters engaged in the decay of Z ⁰ bosons. Schemes and modes of the structural decay of gamma structures, one of which is the Z ⁰ boson, are given. Analysis of the schemes and modes of the structural decay has shown that the decays of the product triple-quark particles (products of the decay of a Z ⁰ boson into triple-quark particles) result in the occurrence of a new mode of decay – the decay of one triple-quark particle into three triple-quark particles. According to the proposed mechanism of the decay of particles, an electron, a muon, a triton, and a gamma photon are particles consisting of a quark–antiquark pair and having a spin equal to unity.     

Confinement time exceeding one second for a toroidal electron plasma

Nearly steady-state electron plasmas are trapped in a toroidal magnetic field for the first time. We report the first results from a new toroidal electron plasma experiment, the Lawrence Non-neutral Torus II, in which electron densities on the order of 10(7) cm(-3) are trapped in a 270-degree toroidal arc (670 G toroidal magnetic field) by application of trapping potentials to segments of a conducting shell. The total charge inferred from measurements of the frequency of the m=1 diocotron mode is observed to decay on a 3 s time scale, a time scale that approaches the predicted limit due to magnetic pumping transport. Three seconds represents approximately equal to 10(5) periods of the lowest frequency plasma mode, indicating that nearly steady-state conditions are achieved.     

Evolution of the density profiles and flows of charged particles during the diffusive decay of an electronegative gas plasma

Different scenarios of the spatiotemporal evolution of the parameters of the diffusive decay of a pulsed electronegative gas plasma in the absence of plasma chemical processes are studied. It is shown that nonlinear diffusion in a plasma with negative ions occurs in several stages. The rate of electron density decay increases with time and, in the beginning of the second stage, almost all the electrons escape from the discharge volume. On the other hand, the ion density profile is smoothed out due to ion-ion ambipolar diffusion and the flow of negative ions toward the wall is absent in the first stage of decay. In the second stage, the main diffusion mode is first established and then the ion-ion (electronless) plasma decays exponentially with a characteristic time determined by ion-ion ambipolar diffusion.     

Resonant decay of a Langmuir wave in the presence of dust grains in a cylindrical plasma

The resonant parametric decay of a Langmuir wave into a backward propagating Langmuir wave and an ion acoustic (IA) wave is studied in a cylindrical dusty plasma. The analysis shows that the frequency of the IA mode decreases with the parameter δ_c (where δ_c is the ratio of the ion density to the electron density) for negatively charged dust grains. The growth rate of the resonance decay instability (RDI) and the threshold required for its onset also decrease with δ_c and are strongly dependent on the electron to ion temperature ratio for both positively and negatively charged dust grains. The results obtained also illustrate the dependence of the threshold of the resonance decay instability (μ_th) on the plasma cylinder radius.     

Nonequilibrium nuclear-electron spin dynamics in semiconductor quantum dots

We study the spin dynamics in charged quantum dots in the situation where the resident electron is coupled to only about 200 nuclear spins and where the electron spin splitting induced by the Overhauser field does not exceed markedly the spectral broadening. The formation of a dynamical nuclear polarization as well as its subsequent decay by the dipole-dipole interaction is directly resolved in time. Because not limited by intrinsic nonlinearities, almost complete nuclear polarization is achieved, even at elevated temperatures. The data suggest a nonequilibrium mode of nuclear polarization, distinctly different from the spin temperature concept exploited on bulk semiconductors.     

Parametric excitation of electrostatic whistler wave and electronBernstein wave by extraordinary EM wave

In the present paper, the parametric decay instability of an extraordinary electromagnetic wave (X-wave) into an electron Bernstein wave (EBW) and an electrostatic whistler wave (W-wave) has been studied. Expressions are derived for homogeneous threshold, growth rate, and convective threshold for this instability. The relevance of the present parametric process has been pointed out to explain the generation of whistler mode radiations in the SL-2 experiment, ionospheric modification experiment, in the polar cusp region of the magnetosphere, as well as during intense electron cyclotron resonance heating in the MTX tokamak     

Fluorescence spectrum due to surface plasmon polariton emission in a three level atom

The dynamics of a V-type three level atom positioned inside a metallic slab sandwiched between two asymmetric infinite dielectrics is studied. The surface plasmon polaritons supported by this structure are calculated, quantized and their dispersions are found to exhibit plasmonic band gaps which in turn modify the spontaneous transition rates and the fluorescence spectrum. Interesting features arise from the variations of the decay rate and spectrum with the mode frequency and electron density including local field effects.     

Multiphonon decay of strong mode in quantum lattice

A nonperturbative theory of multiphonon anharmonic decay of strongly excited local mode is developed whereby the mode is considered classically and phonons, quantum mechanically. The decay rate of the mode is expressed via the negative frequency parts of the phonon pair correlation functions. In the case of two-phonon decay the later satisfy the linear integral equations while in the case of two- and more-phonon decay they satisfy the nonlinear integral equations. As a result, the processes mentioned differently depend on the mode amplitude A: two-phonon processes smoothly deminish if A → ∞ while three- and more-phonon processes are fully switched-off at large amplitudes and they abruptly switch-on if the amplitude approaches the critical value. At that the decay rate gets rather high value (of the order of the mode quantum per period). The final stage of the relaxation is well described by the perturbation theory.     

Decay Mode Solutions for Kadomtsev-Petviashvili Equation

The decay mode solutions for the Kadomtsev-Petviashvili (KP) equation are derived by Hirota method (direct method). The decay mode solution is a new set of analytical solutions with Airy function.     

Measured lifetime of SF6-

The lifetime of the SF6 anion was measured at the electrostatic ion storage ring ELISA, where decays in the time span from 100 mus to a few seconds were recorded. We find a nonexponential decay with an approximate t(-1.5) power-law dependence. The observed decay rate is accounted for by a model for thermionic emission that takes into account the initial energy spread of the SF6 molecule prior to electron capture as well as some kinetic energy of the captured electron in the applied plasma-ion source. The energy dependent decay rate is described by an Arrhenius decay constant with a pre-exponential factor and the electron affinity.     

束缚态β-衰变及其天体物理意义

束缚态β-衰变是一种特殊的弱相互作用衰变模式,对某些高电离态重原子的β-衰变有重要或决定性的贡献.从理论和实验两方面介绍了束缚态β-衰变研究的进展及其对恒星中的慢中子俘获过程和187Re 187Os宇宙核钟的影响.     

反射式GaN光电阴极表面势垒对量子效率衰减的影响

针对反射式GaN光电阴极长波段量子效率衰减较大, 短波段量子效率衰减较小的实验现象, 在考虑谷间散射的情况下, 利用玻尓兹曼分布和基于Airy函数的传递矩阵法, 计算了发射电子能量分布, 分析了表面势垒变化对量子效率衰减的影响, 理论与实验符合较好. 激活层有效偶极子数的减少使表面势垒宽度和高度增加, 引起长波光子激发产生的发射电子能量分布衰减较大, 短波光子激发产生的发射电子能量分布衰减较小, 这是量子效率在长波段衰减较大, 短波段衰减较小的根本原因.     

Measurement of the beta+ and orbital electron-capture decay rates in fully ionized, hydrogenlike, and heliumlike 140Pr ions

We report on the first measurement of the beta+ and orbital electron-capture decay rates of 140Pr nuclei with the simplest electron configurations: bare nuclei, hydrogenlike, and heliumlike ions. The measured electron-capture decay constant of hydrogenlike 140Pr58+ ions is about 50% larger than that of heliumlike 140Pr57+ ions. Moreover, 140Pr ions with one bound electron decay faster than neutral 140Pr0+ atoms with 59 electrons. To explain this peculiar observation one has to take into account the conservation of the total angular momentum, since only particular spin orientations of the nucleus and of the captured electron can contribute to the allowed decay.     

EBIC investigations of GaN layers prepared by epitaxial lateral overgrowth

GaN films prepared by lateral overgrowth are investigated by scanning electron microscopy in the electron beam induced current (EBIC) mode. A comparison of experimental and simulated dependences of induced current on beam energy has allowed us to determine not only the diffusion length, but also the donor concentration in different areas of a film. It has been found that the donor distribution is inhomogeneous and this inhomogeneity increases under fast neutron irradiation. This is indicative of the significant influence of structural defects on the rate of radiation defect accumulation. An anomalously slow signal decay outside the Schottky barrier has been found, which can be determined by charged defects formed at the merger boundary.     

Phenomenology of the new light Higgs boson search

We study the feasibility of two experiments to test the existence of the new light Higgs boson (Higglet) h: (1) the observation servation of Higglets produced in high energy proton reactions using the Bethe-Heitler process h + Fe → ?⁺?^? + Fe for detection; (2) the production of Higglets using low energy intensive electron beam with detection using the two photon decay mode.