V. Horvat

3-D imaging of binary dissociation events induced by heavy ion impact

Abstract Dissociation of CO molecules induced by 96 MeV Ar ions is being studied by simultaneously measuring the times of flight and the positions of the dissociation product ions. The position information is obtained using optical methods, thus overcoming the pile-up problem associated with measurements in which the position is determined using microchannel plate detectors with resistive anodes. For each dissociation event the velocity components of both ions are determined and used to deduce the released kinetic energy and the angular distribution. Preliminary results are shown for the dissociation of CO2+ into C+ and O+.

Molecular imaging with fast beams

Abstract Three dimensional imaging of the molecular dissociation process in fast collisions is presented with two different setups. One setup is for a fast molecular beam from an accelerator colliding with a gas target. The second setup is for a molecular target system and the collision process is with highly ionized fast beam. The advantages of each system are discussed. The three dimensional imaging of the molecular fragments is done with special detectors that combine the CCD image with time of flight data. An example of the molecular beam measurement is given for an 11 MeV B2 beam.

Target-atom inner-shell vacancy distributions created in collisions with heavy ion projectiles

Abstract A model of the evolution of Cu atom inner-shell electron configurations was developed in order to establish the relationship between the original populations created in K-vacancy producing collisions with fast heavy-ion projectiles and those that exist at the time of Cu Kα and Kβ X-ray emission. The model takes into account multi-step vacancy rearrangement processes that may occur prior to K X-ray emission. An iterative procedure is employed in which a set of trial parameters that define the original inner-shell population distributions are varied to obtain satisfactory agreement of the calculated Kα satellite relative intensities and energies, as well as the overall intensity ratio of Kβ satellites to Kα satellites, with the experimental data. In addition to deducing the properties of the original L- and M-shell population distribution, this procedure also provides the average value of the fluorescence yield for conversion between X-ray and K-vacancy production cross sections.

Multiple ionization of He, Ne, and Ar by high velocity N7+ ions

The yields of He, Ne, and Ar recoil ions produced in collisions with 10–40 MeV/amu N7+ projectiles were measured by the time-of-flight technique. The ratio of the yields for double and single ionization of He and Ne were found to be higher than predicted by theoretical and semiempirical calculations. The role of electron correlation in multiple ionization was assessed by comparing the experimental data for Ne and Ar with the results of an independent electron approximation analysis.

Depth profiles of K x-ray emission from highly stripped argon ions traversing solid media

K x-rays emitted at 90° from an Ar beam incident on thick targets of Be, C, NaF, and KCl at an energy of 6-MeV/u were measured with a curved crystal spectrometer. The observed (Doppler shifted) average energies of the H-like Ar 2p(2P) to 1s(2S) and the He-like Ar 1s2p(1P) to 1s2(1S) transitions provided a means of testing the projectile energy dependence of theoretical initial state population fractions. Good agreement was found for all of the targets except Be. These population fractions were used to calculate depth profiles for emission and detection of the x-rays.

Xenon recoil-ion charge distributions produced in electron capture and loss collisions of 8 MeV/u Kr

Recoil-ion charge distributions produced in single collisions of 8 MeV/u Kr13+ and Kr32+ projectiles with Xe atoms have been measured using time-of-flight spectroscopy. The post-collision charge states of the projectile ions were determined by magnetic dispersion onto a position sensitive microchannel plate detector. The recoil-ion distributions for ionization accompanied by electron loss from Kr13+ projectiles were bell-shaped with averages that ranged from 7.4 for 1-electron loss to 13.9 for 5-electron loss. The recoil-ion distributions for ionization accompanied by electron capture to Kr32+ projectiles were also bell-shaped, but had much higher average charges that ranged from 20.4 for 1-electron capture to 28.5 for 4-electron capture. The large difference in the average charges produced in the two types of collisions is mainly attributable to charge magnification by Auger decay. A simple model quantitatively explains the variation of the capture-ionization charge distribution width and average charge as a function of the number of captured electrons.

Ionization of noble gas atoms by alpha particles and fission fragments from the decay of 252Cf1

Abstract Charge state distributions of He, Ne, Ar, Kr, and Xe ions produced in single collisions with alpha particles and fission fragments from the decay of 252 Cf have been measured using time of flight spectrometry. The measurements reveal that the maximum number of electrons removed in a fission fragment collision ranges from eight in the case of Ne to 20 in the case of Xe. Recoil-ion production cross sections have been determined for the resolvable ionic charge states and compared with the predictions of a model based upon the independent electron approximation.

K- plus L-shell ionization of fourth row elements by 30 MeV/amu Ar ions

Abstract Spectra of K X-rays produced by collisions of 30 MeV/amu Ar ions with metallic targets of Ti, V, Cr, Fe, Co, Ni, Cu, and Zn were measured with a Si(Li) detector system. The measured Kα and Kβ transition energies were compared to the results of Dirac-Fock calculations to estimate the average number of L-shell vacancies at the time of K X-ray emission. The target double-to-single K-shell ionization probabilities were also determined, along with the relative probabilities of having single and double K-shell vacancies in the projectile during passage through the metal foils.