L. H. Toburen

Differential Cross Sections for Ionization of Methane, Ammonia, and Water Vapor by High Velocity Ions,

Cross sections, differential in the energy of secondary electrons, for ionization of methane, ammonia, and water vapor by high energy protons are presented. The results are based on a model that uses photoabsorption and ion impact ionization data to evaluate the coefficients in Bethe’s asymptotic cross section for inelastic scattering of high velocity ions. Model cross sections are compared with previously published data and new data on ionization of methane and water vapor by 3.0 and 4.2 MeV protons. The simple, analytic model should be very useful in transport calculations where differential ionization cross sections over a broad range of primary and secondary energies are needed.

Differential Cross Sections for Electron Emission in Heavy Ion-Atom Collisions

The systematics of differential ionization cross sections are explored for incident charged particles which possess atomic structure. Although little has been published regarding outer shell ionization by structured projectiles, sufficient data are becoming available to provide some insight into the collision process. This discussion concentrates on systematics of emission cross sections for the intermediate and high energy projectiles where the applicability of high energy approximations can be tested and the dramatic changes in emission spectra observed as the projectile energies decrease. Since heavy ion interactions are important in many research fields, it is particularly useful to determine where simple methods of cross section scaling may be appropriate.

Dynamic Screening by Projectile Electrons in Heavy Ion Collisions

Anaysis of recent helium and oxygen ion data has shown that the degree of screening of the ion charge can be represented approximately by a model based on the spatial distribution of bound electrons. This screening model is introduced into the binary encounter approximation to account for screening for projectile electrons, and calculated single and double differential cross sections are compared for He/sup +/, He/sup 2 +/ ionization of argon and O/sup 5 +/ ionization of oxygen. Cross sections for ionization including contributions from both target and projectile are calculated. (GHT)

Multiple Ionization of Atomic Targets by Proton Impact

We have combined experimental measurements of multiply charged ion production, doubly differential electron emission cross sections and Auger electron spectra produced in fast-proton noble-gas collisions with theoretical inner and outer shell ionization cross sections in an effort to provide a unified description of the ionization process. A detailed analysis is provided for 1-4 MeV proton ionization of krypton. Our measured relative yields of Kr+2 and Kr+3 ions are in approximate agreement with the photoionization results of Krause and Carlson. If we assume nearly half of the 3d vacancies created in Kr are filled through multiple (3dNNN) Auger transitions, the M-subshell ionization cross sections that we derive from our Auger electron spectra are in good agreement with theoretical calculations. The measured absolute yields of Kr+2 and Kr+3 are, however, a factor of 2 smaller than those derived from the decay of inner shell vacancies. This discrepancy leads us to believe that multiple ionization in the initial interaction is a significant contribution to the observed yields.

Effect of the cooper minimum on charged particle ionization

Abstract The energy distribution of electrons produced by 1 MeV proton impact ionization on Ne, Ar, H 2 , N 2 , and C 2 H 6 has been measured at 130°. The curves show similar shapes with the exception of Ar due to a Cooper minimum in the 3p → ϵd channel.