Effect of beta decay to bound states in ionized atoms on the fraction of delayed neutrons

The ionization of an atom leads to the appearance of an additional beta-decay channel to a bound state of an electron. It is shown that, for nuclei that are products of uranium fission and which are emitters of delayed neutrons, the fraction of delayed neutrons increases upon taking into account the additional beta-decay channel to bound states.     

Effect of beta-electron capture to a bound state on delayed-neutron emission from fission fragments

The effect of ionization of the atomic electron shell on beta decay is investigated. The change in the beta-decay probability is due primarily to the appearance of the channel involving beta-electron capture to a bound state. It is shown that the effect may be significant at low beta-transition energies. The magnitude of the effect was studied in the case of the emission of one to three delayed neutrons following the beta decay of fission fragments. In the calculations, use was made of the beta-decay strength function with allowance for the population of isobaric resonances in daughter nuclei. The effect proved to be maximal for fragments where the numbers of protons and neutrons approach those in closed shells and subshells, thereby illustrating the role of the shell structure of the nucleus in fission.     

The lifetime of the dimuon atom

Summary The weak decay of a muon in the ground state of a dimuon atom is analysed. Although the two muons are correlated by Fermi-Dirac statistics, it is shown that, in marked contrast to the seemingly analogous case of neutron beta-decay in³H, statistics have no effect on the muon decay rate. The distinction between the two cases is discussed. To speed up publication, the author of this paper has agreed to not receive the proofs for correction.     

Internal Ionization of an Atom in the β Decay of Tritium

The problem of internal ionization in the beta decay of tritium due to the scattering of a β electron off a bound electron is discussed. The total probability of the process per a single decay event is calculated. The distributions over the momentum and the kinetic energy of a liberated electron are plotted. A correction to the β spectrum produced by internal ionization is determined. The identity of electrons is taken into account in all calculations. The results of calculations of the modified spectrum are of interest for the KATRIN experiment aimed at measuring the mass of an electron antineutrino. The high-luminosity source also makes it possible to search for keV-scale sterile neutrinos in the middle part of the β spectrum, where the internal ionization effect is significant.     

Robust Scheme for Entangling Two Distant Atoms

A robust scheme is presented for realizing entangled states for two atoms trapped in separate cavities connected by an optical fiber. The first atom is initially in a superposition of the excited state and an auxiliary ground state not coupled to the first cavity, while the second one is initially in the ground state coupled to the second cavity. The scheme involves two atom-cavity-fiber interactions accompanied by the monitoring of the cavity decay and atomic spontaneous emission. The two atoms evolve to an entangled state through exchanging an excitation after the first interaction. The states with the excitation failing to be transferred are eliminated when a photon is detected during the second interaction. Therefore, the scheme is insensitive to the decoherence effect and detection inefficiency.     

Atomic effects accompanying the beta decay of tritium

The results of the first experiment designed to measure the difference between the beta-decay constants of atomic and molecular tritium Δλ=λ_a–λ_m are presented. The experimental scheme calls for the creation of two identical samples of a gas mixture containing helium-4 and molecular tritium followed by the treatment of one of them for the purpose of bringing the tritium into the atomic state. The value of Δλ is determined by comparing the growth rates of the ratio of the concentration of radiogenic helium-3 to the concentration of helium-4 in the samples with molecular and atomic tritium. The value Δλ=(4.6±0.8)×10⁻¹² s⁻¹, which corresponds o a relative change in the decay constant amounting to ∼0.26%, is obtained. Zh. Tekh. Fiz. 69, 19–21 (September 1999)     

Tunneling and reflection of an exciton incident upon a quantum heterostructure barrier

We investigate, in one spatial dimension, the quantum mechanical tunneling of an exciton incident upon a heterostructure barrier. We model the relative motion eigenstates of the exciton using a form of the one-dimensional hydrogen atom which avoids difficulties previously associated with 1D hydrogenic states. We obtain probabilities of reflection and transmission using the method of variable transmission and reflection amplitudes. Our calculations may be broadly divided into two sets. In the first set, we consider general qualitative aspects of exciton tunneling, such as the effect of different effective masses for electrons and holes and a relative difference in electron and hole barrier strengths. The second set models the tunneling of an exciton in a GaAs/Al(x)Ga(1-x)As heterostructure. In these calculations we find that, for energies such that the two lowest exciton states are coupled, the probability spectrum for transition from the ground state to the first excited state is identical to that for transition from the first excited state to the ground state. In addition, narrow peaks in the probability spectrum for transition are observed across this energy range for low dopant concentration x. Other interesting phenomena correlated with these peaks in the transition probability are reported.     

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.     

Dynamics and post-collision interaction effects in two electron decay from the Xenon 4d hole

Two Auger electrons, one very slow, one fast, have been detected in coincidence following near threshold 4d photoionization of the Xe atom. The distribution in the energy the two electrons share has been measured for the first time revealing the presence of post-collision interaction effects that provide unique information on the decay dynamics of the 4d hole. Analysis of the distorted line shapes indicates that the dominant process is decay of Xe+(4d(-1)) to Xe3+ through cascade emission of a zero kinetic energy Auger electron followed by a fast Auger electron. The widths of the intermediate Xe2+* states are estimated to be about 60 meV.     

New results in the theory of muonic atom formation in molecular hydrogen

Muonic atom formation in molecular hydrogen proceeds in two stages. In the first stage, the mu-molecular complex (abµe)^* is formed due to Coulomb capture of a muon by a hydrogen molecule (abee), and, in the second stage, the decay of the complex leads to exotic-atom formation. We consider various channels for the decay of the complex. The main competition channels are direct dissociation and Auger decay. The primary distribution of muonic atoms over quantum states and kinetic energy has been obtained taking into account the competition of the decay channels.     

Integrales radiales d'un atome hydrogenoide a potentiel Coulombien a ecran

The Schrödinger equation for a hydrogenic atom with a screened Coulomb potential has been solved using both the variation method and the Numerov numerical method. The atomic parameters, such as the eigenvalues, the mean electron radii, the radial integrals and the number of bound states are calculated and compared with the values for the unperturbed atom.

It is found that for a few of the atomic states with positive eigenvalues (metastable states), the preionisation probability is definitely larger than the spontaneous probability of transition toward the lower bound atomic states.

The effect of the screening parameter on the eigenvalues, the mean radii and the radial integrals is illustrated with a few tables and figures.     

Effect of electron exchange on atomic ionization in a strong electric field

Hartree-Fock atom in a strong electric static field is considered. It is demonstrated that exchange between outer and inner electrons, taken into account by the so-called Fock term affects strongly the long-range behavior of the inner electron wave function. As a result, it dramatically increases its probability to be ionized. A simple model is analyzed demonstrating that the decay probability, compared to the case of a local (Har-tree) atomic potential, increases by many orders of magnitude. As a result of such increase, the ratio of inner to outer electrons ionization probability became not too small. It is essential that the effect of exchange upon probability of inner electron ionization by strong electric field is proportional to the square of the number of outer electrons. It signals that in clusters the inner electron ionization by strong field, the very fact of which is manifested by e.g. high energy quanta emission, has to be essentially increased as compared to this process in gaseous atomic objects.     

Intra-acceptor hole relaxation in Be δ-doped GaAs/AlAs multiple quantum wells

This paper studies the dynamics of intra-acceptor hole relaxation in Be δ -doped GaAs/AlAs multiple quantum wells (MQW) with doping at the centre by time-resolved pump-probe spectroscopy using a picosecond free electron laser for infrared experiments. Low temperature far-infrared absorption measurements clearly show three principal absorption lines due to transitions of the Be acceptor from the ground state to the first three odd-parity excited states respectively. The pump-probe experiments are performed at different temperatures and different pump pulse wavelengths. The hole relaxation time from 2p excited state to 1s ground state in MQW is found to be much shorter than that in bulk GaAs, and shown to be independent of temperature but strongly dependent on wavelength. The zone-folded acoustic phonon emission and slower decay of the wavefunctions of impurity states are suggested to account for the reduction of the 2p excited state lifetime in MQW. The wavelength dependence of the 2p lifetime is attributed to the diffusion of the Be atom δ -layer in quantum wells.     

MEASUREMENT OF LOW MAGNETIC FIELD DISTRIBUTION OF A β SPECTROMETER

The low magnetic field distribution of an iron-core double-focusing low-energy β spectrometer is measured with a second harmonic magnetic flux gate magnetometer, the relative measuring precision is better than ±0.05%. The field strength of the spectrometer is about 10G. This spectrometer is used to measure the β spectrum from tritium β decay for estimating the rest mass of electron antineutrion.     

氢原子电子云的计算和可视化分析

介绍了氢原子中"电子云"的计算机基本作图方法,一种是蒙特卡罗法,另一种是逐点扫描法.利用MATLAB软件.从不同角度对氢原子各种状态下的电子云三维立体分布进行了可视化,使氢原子中电子概率密度的教学更加直观.     

Consideration of the theoretical possibility of regulating the nuclear reactor by changing a fraction of delayed neutrons

A lot of theoretical and experimental studies devoted to the effect of external electromagnetic fields and ionization on the beta-decay probability have been published in the past years. The possibility of using this physical effect as the main reactor-regulation mechanism is investigated in this study. A set of equations allowing the operation of a nuclear reactor to be described when the probability for the beta decay of precursors of delayed neutrons and, hence, the fraction of delayed neutrons are functions of time is written and investigated. It is shown that, if the fraction of the delayed neutrons does not change, the proposed set of equations coincides with the generally known one. As follows from the analysis of the solutions to the new set of equations, the proposed reactor-regulation method does not allow reactor runaway driven by prompt neutrons even theoretically. The application of the proposed control method to a circulating-fuel liquid-type reactor is briefly considered.     

用屏蔽法计算较轻元素原子的高次电离能

考虑到离子的相对论效应,依据屏蔽方法,给出了原子第2、1壳层电子电离能的一种表达式.依据较轻元素原子低次(小于13)电离能实验数据,总结出原子(离子)电离第2、1壳层不同电子态电子时,相应的屏蔽系数与电子态及原子序数的函数关系,根据该函数关系,可求出相应原子的高次电离电子的屏蔽系数.计算了原子序数13至23的元素高电荷态离子基态电离能,计算结果与文献可提供的实验数据相符合.     

Effect of various adsorbates in dephasing and population decay of the Cu(1 0 0) image potential states

A theoretical study of the electron dynamics in image potential states on Cu(1 0 0) surfaces with different types of adsorbates is presented. Scattering of the image state electron by an adsorbate induces inter-band and intra-band transitions leading respectively to the population decay and to the dephasing of the image state. We compare results obtained with low coverage (typically 1 adsorbate atom per 1000 surface atoms) Cs, Ar, and a model electronegative adsorbates. As follows from our results, Cs adsorbates lead to both appreciable dephasing and decay, while electronegative adsorbates mostly affect the dephasing rate. The effect of low coverage Ar adsorbates is small, consistent with their neutrality.     

Increase in the probability of forbidden electron beta decays in a superstrong magnetic field

Form factors for unique forbidden electron beta decays in a superstrong constant uniform external magnetic field are considered. The probability of forbidden and allowed electron beta decays increases in a superstrong magnetic field owing to the increase in the density of vacant electron bound states at the nucleus involved. It is shown that, because of the growth of the form factors, the relative increase in the probability of forbidden electron beta decays in a magnetic field exceeds the relative increase in the probability of allowed decays (at identical decay endpoint energies).     

Implications of a 17 keV neutrino for baryogenesis

There is some experimental evidence for a 17 keV component of the electron neutrino, in the form of the recent observations of kinks in the beta-decay spectra of tritium, ¹⁴C, ³⁵S and ⁶³Ni. In this paper I show that most particle-physics models consistent with the 17 keV neutrino require a baryogenesis scale below 10⁶ GeV. Furthermore, models with a 17 keV neutrino typically contain new sources of CP violation, and the cosmological baryon asymmetry could be generated by anomalous electroweak interactions during a first-order weak phase transition.