Incident Charge State Research Articles

Nonmonotonic Target Dependence of ClKX-Ray-Production Cross Sections in Single Heavy-Ion-Atom Collisions

Chlorine $K$ x-ray-production cross sections have been measured in single collisions of chlorine ions in low incident charge states with gas targets at MeV energies. The cross sections are nonmonotonic as a function of target atomic number, but they approach monotonicity with increasing projectile energy. To explain these results in terms of $2p\ensuremath{\sigma}\ensuremath{-}2p\ensuremath{\pi}$ transitions in nearly symmetric collisions effectively requires $2p$ vacancy production simultaneous with the promotion of Cl $1s$ electrons.

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.

Dependence of ArgonK-Shell Vacancy Production on the Electronic Structure of Swift Heavy Projectiles

Thin gas targets of argon were bombarded with C, N, O, and F projectiles of various incident charge states at energies from l to 2 MeV/amu. Argon K x rays were observed with a Si(Li) detector, and x-ray-production cross sections were obtained. For a given-energy projectile. the cross sections decrease approximately exponentially as the number of electrons bound to the incident projectile increases from 0 to 3. For three or more electrons. the measured cross sections change very little. Hartree-Fock calculations of fluorescence yields as a function of target configuration were used to obtain argon K-shell vacancy- production cross sections. Target configurations were chosen by comparing the experimental argon K alpha and K BETA x-ray energies and K BETA /K alpha relative intensities with the values obtained by Hartree-Fock calculations. For projectiles with more than one electron, the vacancy-production cross sections scale as the square of projectile nuclear charge as expected for Coulomb ionization. but the absolute magnitudes of the cross sections do not agree with Coulomb-ionization results. For projectiles with 0 to 1 electron. however, Coulomb ionization alone cannot explain the observed cross sections. Charge exchange from the argon K shell to projectile bound states has been proposed asmore » a significant vacancy-producing mechanism for collisions involving highly charged projectiles. Although calculations of the charge-exchange cross sections are in reasonable relative agreement with the data, additional vacancy-producing mechanisms cannot be ignored. (auth)« less

Auroral helium precipitation

Several measurements of the flux and charge state of auroral helium precipitation have been made and reported between 1967 and 1972. The primary purpose of these experiments has been to deduce the source location of auroral ions by comparison of auroral helium populations with those measured in the ionosphere and the solar wind. Accordingly, results of these experiments are reviewed and summarized, along with measurements of solar wind and ionospheric helium abundances. It is concluded that the available data suggest a solar wind origin of auroral ions and in addition place certain constraints on the acceleration mechanism. The problem of modification of the incident charge state of a helium beam by atmospheric charge exchange is discussed, and it is shown that auroral helium measurements should be made at altitudes above 400 km to insure that the measurements are a true indication of the original beam charge state composition. Attempts to measure optical emissions of auroral helium are also reviewed, with the conclusion that definitive reproducible detection of such emissions has not been accomplished to date.

Dependence of X-Ray Yields in Argon, Krypton, and Xenon upon the Charge State of Fluorine Ions at 35.7 MeV

In high-velocity ion-atom single collisions, a strong dependence of target x-ray production cross sections upon the ionic charge state has been observed. Experiments were performed in thin gas targets of argon, krypton, and xenon with 35.7-MeV fluorine ions incident in charge states +5 to +9. Production cross sections for Ar $K$, Kr $L$, and Xe $L$ characteristic lines increase by as much as a factor of 5 with increasing incident charge state but cannot be fitted by a ${q}^{2}$ dependence.

Charge Exchange of Fast Iodine Ions in a Dense Jet of Carbon Dioxide

Charge distribution measurements were made with 10-75 MeV iodine ions of various incident charge states traversing either a supersonic CO2-jet of variable density in the range 5 x 1014 to 1.5 x 1017 molecules/cm3 or a target of dilute CO2 with a maximum density of 5 x 1014 molecules/cm3. The equilibrium mean charge ts of the iodine ions in the jet is found to be higher than in the dilute gas. The maximum difference of about one charge unit is observed at 75 MeV. Ihere is no indication for a further increase of Lat gas densities above 5 x 1016 molecules/cm3. Cross sections for electron capture and loss were determined by means of a least-squares-evaluation of non-equilibrium charge distributions. Considerable decrease of the capture cross sections for some lower charge states has proved to be responsible for the increase ?, whereas the loss cross sections do not change measurably with increasing target density.

Measurement of Charge-Changing Cross Sections for 0.4-4.0-MeV Aluminum Ions in Nitrogen

Absolute cross sections for single- and multiple-electron capture and loss by fast aluminum ions in collisions with ${\mathrm{N}}_{2}$ gas molecules have been measured. Data were taken at nine projectile energies between 0.4 and 4.0 MeV, for several incident charge states at each energy. Cross sections were determined from the initial behavior of charge-fraction growth curves under thin-target conditions.