Double electron capture cross-sections by protons in collisions with He

Double electron capture (DEC) by protons from He was studied in collisions at energies in the keV regime, theoretically and experimentally. Theoretical cross-sections were calculated using the electron nuclear dynamic approach and a binomial distribution method in the energy range 1–100 keV. Experimental cross-sections were measured by means of the grow-rate method in the energy range of 4–10 keV. The cross-sections measured are consistent with those of the previous data at the high energies of the measured interval and show a different trend for the low energy. This behavior is consistent with those of other DEC cross-sections measured by protons from He-like targets. With the two collision models, it is proven that the reference data for this system are consistent only with the assumption of uncorrelated electrons and with independent target-projectile nuclei dynamics.     

Coherent electron density distribution oscillations in electron capture by fast protons in helium

Assuming the validity of a recent model of Lyman-α beat behaviour from fast H atoms under conditions of reversal of an applied electric field, we find strong electric dipole density distribution oscillations in electron capture to n=2 levels of hydrogen by fast protons (≈ 2 au) in helium. Possibilities for testing relative orbital phase calculations in charge-transfer theory, and for making comparisons between beam-surface and single ion-atom collision models of projectile passage through solids exist.     

Projectile angular distribution in single electron capture from helium by fast protons

The phenomenon of stochastic resonance (SR) driven by time-delayed feedback in a bistable system with colored noise is investigated. Combining the small time delay and unified colored noise approximation, the Fokker-Planck equation is obtained. The different effects of time delay and noise correlation time on stationary probability density and signal-to-noise ratio (SNR) are discussed respectively. It is found that time delay can markedly improve the output SNR. This method can be practically applied to many fields such as weak signal extraction, recovery and so on. Numerical simulations are presented and are in agreement with the approximate theoretical results.     

On the capture of protons by magnetic monopoles

The cross sections for the formation of monopole proton bound states are calculated in the dipole approximation and found to be of the order of the proton Compton wavelength squared, weakly dependent on the relative velocity and on the binding energy of the system. Cross sections for the inverse (photodetachment) process are also given.     

Isotope effect in nuclear capture of negative muons in xenon

The lifetime of negative muons in the ¹²⁹Xe 1_s state was measured. The muon capture rate in ¹²⁹Xe is compared with that in the ^{132, 136}Xe isotopes. The capture rate was found to depend on the mass number of the cited isotopes. The experimental results are compared with the results of calculations by the semiempirical Goulard-Primakoff formula.     

Search for axions in thermal neutron capture by protons

A search for axions at a 500 MW light water power reactor was performed. From the measured upper limit on the n + p → d + a cross section the “standard” axion is ruled out.     

Radiative capture of protons by the deformed nuclide232Th

The excitation function for the radiative capture²³²Th(p, γ)²³³Pa has been determined in the proton energy range 7 to 20 MeV by an activation method. The results are compared with a compound nucleus model prediction and earlier experimental data for another deformed nuclide¹⁷⁶Yb. As in previous cases an enhancement over the CN-model prediction is observed and the excitation of the giant dipole resonance via the direct-semidirect reaction process is a likely explanation. Supplementary measurements of the²³²Th (p, f) excitation function in the proton energy range 11–20 MeV have been performed.     

Glauber exchange effect in the excitation of hydrogen by electron impact

The Glauber exchange effect is included into the calculations of differential cross sections in an analysis of 1–2 excitation of the hydrogen atom by electron impact within the conventional Glauber theory. An improvement of the theoretical results is obtained.     

Electron capture by fast protons from helium-like ions

Four-body formalism of boundary corrected continuum intermediate state (BCCIS-4B) approximation have been applied to calculate the single-electron capture cross sections by fast protons through some helium-like ions in a large energy range from 30–1000 keV. In this model, distortion has been taken into account in the entrance channel. In the final channel, the passive electron plays the role of screening of the target ion. However, continuum states of the projectile and the electron in the field of the residual target ion are included. The comparison of the results is made with those of other theoretical investigations and experimental findings. The present calculated results are found to be in good agreement with the available experimental findings.     

The radiative capture of fast protons by medium-mass nuclei

High-energy photon spectra were obtained with moderate resolution for a number of neighboring nuclei: ⁵⁶Fe, ⁵⁹Co, ⁵⁸Ni, ⁶⁰Ni, ⁶¹Ni, ⁶³Cu and ⁶⁴Zn in bombardments with protons (8 to 22 MeV). The shapes, magnitudes and energy dependence of the observed spectra are found to be consistent in most of their essential features with the implications of the semidirect model for fast nucleon capture.     

The effect of pressure on orbital electron capture

The effect of pressure on the decay rate by electron capture has been estimated on the basis of certain simplifying assumptions. For the case of ⁷Be the order-of-magnitude agreement is found.     

Remarks on the theory of electron capture into shallow donors in GaAs

A new model for low-temperature recombination of conduction electrons to ionized donors in GaAs is proposed. It assumes that the conduction electron is captured into the ground state of shallow impurity by simultaneous emission of two LA phonons. From a comparison of computed capture rate with recent experimental results the estimated value of the two-phonon deformation potential is d_2LA = 0.02 eV.     

Isotope effects in the diffusion of hydrogen

Isotope effects in diffusion of hydrogen atoms are investigated theoretically. It is shown that isotope effect is reduced by a nonadiabatic effect of the heat bath so that the classical‐quantum crossover temperature and quantum tunneling rate lose their mass dependence. On the other hand, isotope effect is reversed in classical hopping rate under strong spatial confinement at the barrier top. These results indicate that isotope effects can be the means of observing influences of many degrees of freedom characterizing environment in diffusion process. This revised version was published online in August 2006 with corrections to the Cover Date.     

On the classical-trajectory eikonal approximation for electron capture into multicharged ions

The eikonal approach to electron capture developed in earlier publications is analyzed with respect to its physical content using the Born series as a reference expansion. In the language of perturbation theory, the eikonal approach describes a close collision between electron and projectile followed by multiple distant collisions between electron and target nucleus. The distant encounters have a large weight in phase space and therefore dominate capture at intermediate energies. The post-prior discrepancy is shown to be fairly small for nonresonant 1s-1s capture.     

Thermal electron capture by some chlorobromopropanes

Thermal electron attachment rate constants for CH₂ClCHBrCH₃ and CH₂ClCH₂CH₂Br have been measured using electron swarm method. Corresponding rate constants are equal to 3.5×10^-10 and 2.5×10^-10 cm³ molec^-1 s^-1, respectively. Parallely, negative ion mass spectra of these compounds as well as CH₂FCH₂Br, CH₂ClCH₂Br, CH₂BrCH₂Br and CF₃CHClBr has been measured with negative ion mass spectrometry method. The rate constants have been compared with the negative ion mass spectra.     

Interference effect in electron emission in heavy ion collisions with h2 detected by comparison with the measured electron spectrum from atomic hydrogen

Direct evidence of the interference effect in the electron emission spectra from ionization of molecular hydrogen in collisions with bare C and F ions at relatively low collision energies is presented. Oscillations due to the interference are deduced by comparing the measured double differential cross sections of the electrons emitted from molecular hydrogen to those emitted from atomic hydrogen, rather than using the calculated cross sections for H as in a previous report. We believe these experimental data provide stronger support for the evidence of the interference effect. We show that it is not only a feature of very high energy collisions, but also a feature to be observed in relatively lower energy collisions.