Multiple Capture Processes Research Articles

X-ray emission from highly-charged ions after electron transfer in slow collisions: the role of multiple capture processes

We have studied 15 keV/q Ar17+ impact on atomic Ar experimentally and theoretically. Our analysis shows that multiple capture processes followed by autoionization contribute strongly to the measured Lyman X-ray emission intensities in the heliumlike projectile.

Interaction of Multicharged Ions with Molecules (CO2,C60) by Coincident Electron Spectroscopy

First results for the investigation of electron capture processes in collisions between multicharged ions and molecule targets using electron spectroscopy in coincidence with charged fragments, are presented. It is shown that a much more detailed investigation of the capture reaction can be achieved using molecular instead of heavy atomic targets provided that an analysis of the target dissociation is made. The collisional systems 18O8+ + Ar, CO2 and C60 have been studied at 80 keV. Non coincident electron spectra as well as first results of double or triple coincidence experiments are discussed. Kinetic energy distributions of the Cn+ fragments (n = 1 to 8) produced in multiple capture processes from C60 target are given. A detailed investigation of the double capture process with CO2 molecule allows the measurement of kinetic energy release distributions (KERD) which characterize the dissociation of CO22+ molecular ions; our results are found to be very similar to those measured in double photoionisation experiments.

Study of multiple capture processes by recoil ion momentum spectroscopy for 150 keV Ne 10+Ar collisions

We report preliminary investigations of multiple electron capture in the collision of 150 keV Ne 10+ ions with Ar targets. These processes can be described by the following reaction: Ne 10+ + Ar → Ne (10− s)+ + Ar r+ + ( r- s)e −. The Ne 10+ projectile removes r electrons from the Ar target among which s electrons are stabilized on the projectile and ( r- s) are ejected into the continuum. Distributions corresponding to the production of up to septuple-charged recoils were obtained in coincidence with the charge state (10 − s) of the scattered projectiles. Stabilization rates and average scattering angles were also derived from this experiment and given here as preliminary results.

Production of projectile and targetK X-rays by single and multiple electron-capture in collisions of Si14+ and Si13+ ions with argon atoms at 4.5 and 5.5 MeV/amu

Projectile and target X-ray cross-sections have been measured in collisions of bare and hydrogenlike Silicon ions with argon atoms. Projectile energies are 125 MeV and 153 MeV, i.e. the intermediate velocity region forK-shell capture. Coincidence measurements between X-ray photons and the scattered Sin+ projectiles with charge statesn-1,n-2 andn-3 have been made. The relative contribution of charge exchange and direct ionization (or excitation) of the targetK-shell has been obtained directly by this new method. DoubleK-shell electron transfer is demonstrated to be very large in the case of fully stripped Si ions. A thorough theoretical analysis of the data is carried out and multiple capture processes are evaluated using an independent electron model.

Experimental Electron-Transfer Cross Sections for Fluorine Ions in Argon at Energies from 8 to 54 MeV

Electron-capture and -loss cross sections have been measured for fluorine ions passing through argon gas in the energy range from 8 to 54 MeV. Cross sections for single- and multiple-electron capture and loss in a single collision were obtained using a computer analysis in real time for fitting the data with an iterative procedure. A detailed description of the computer analysis is given. The capture of as many as four electrons in a single collision has been observed in several cases. The velocity dependence of the single-capture cross section is described by a power of velocity with the power generally increasing for lower-incident-charge states. For multiple-capture processes the cross section decreases more rapidly than a power of velocity. The capture cross section for the fully stripped fluorine nucleus amounts to less than 50% of the theoretical predictions of Nikolaev scaled from a Brinkman-Kramers calculation for protons in argon. The ratio of double- to single-electron-capture cross sections has been discussed in terms of a geometry-independent component of the capture process. The maxima observed in this ratio were rather sharp and close to the same energy for all incident-charge states, making it impossible to identify from the excitation functions the specific shells involved in the capture process. Electron-loss cross sections generally exhibit a broad maximum at velocities approximately twice the orbital velocity of the electron that is lost in the collision. The velocity dependence of multiple-loss cross sections is generally not similar to those for single loss.

Fluctuations in Multiple Capture Processes

The fluctuation in the number of many-fold captures by an element exposed to a high neutron flux is computed. It is found that the fluctuations are identical to those that would be obtained by selecting nuclei at random from an infinite supply with the appropriate average composition.