R.L. Watson

Ionization and fragmentation of some simple molecules in collisions with 40 MeV Ar13+ ions

Abstract The ionization and fragmentation produced in collisions of 40 MeV Ar13+ projectiles with O2, CO, CO2, N2O and SO2 have been identified by time-of-flight mass spectrometry. In each case, the singly ionized molecular ion is observed to have the highest yield, while substantial yields of doubly charged molecular ions appear in the spectra for CO, CO2 and SO2. Peaks have been identified for atomic ions up to charge 5 +, and those arising from the dissociation of the two diatomic molecules and the nonlinear triatomic molecule SO2 are split into doublets.

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.

Model calculations of multi-ionization cross sections in high velocity ion-cluster collisions

Abstract A model is presented for predicting, on the basis of known ion-atom elementary processes, related cross sections in ion-cluster collisions. The method is particularly suitable in high velocity collisions for which individual impact parameter probabilities of electron capture, excitation and ionization processes, are better known. Application to multi-ionization of 25 MeV C + 60 in collisions with an H 2 target (quasi-perturbative regime) is given. The question of the stability of the C 60 n + projectiles, in connection with predicted multi-ionization cross sections in some specific sites, is discussed.

Recoil-ion kinetic energies for 96 MeV Ar collisions

Abstract The kinetic energies of He, Ne, and Ar recoil-ions produced in single collisions with 96 MeV Ar 4+ and Ar 15+ projectiles have been determined from high resolution time-of-flight measurements. They were found to vary from the ambient thermal energy for charge 1 recoil-ions to 5 eV for Ar 11+ recoil-ions. Average impact parameters were deduced from these results.

Atomic physics with the Texas A&M ECR ion source

Abstract An electron-cyclotron-resonance (ECR) ion source has been constructed to provide highly charged ions for injection into the K500 superconducting cyclotron. The source is also available approximately 30% of the time for use in experiments independent of the cyclotron. An atomic physics beamline has been constructed for this purpose and is now operational. A variety of experiments pertaining to neutralization processes, laser spectroscopy and charge exchange are currently in progress.

Two-fragment coincidence studies of molecular coulomb explosions induced by heavy ion impact

Abstract Time-of-flight (TOF) spectroscopy was used to study the ionic species produced in collisions of 40 MeV Ar13+ with molecular oxygen. Ions from the dissociation of molecular ions having charges as high as 10 + were observed. The flight times of the first ion and the difference in flight times between the first and second ions of binary dissociation events were recorded event-by-event, thereby retaining their correlation. Off-line sorting of the data provided TOF and time difference spectra containing well resolved peaks associated with each of the charge division pairs produced in the dissociation process.

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.

Beam-foil spectroscopy in the EUV employing a position sensitive microchannel plate

Abstract A 50 mm long microchannel plate was adapted to a 1-m grazing incidence spectrometer equipped with a 1200 l/mm grating and applied to the measurement of beam-foil spectra of highly ionized neon in the EUV. A wavelength resolution of better than 1.0 A was achieved using a 100 μm entrance slit for spectra that sampled a wavelength region spanning approximately 100 A. The overall counting efficiency of the spectrometer system operating in a multichannel analysis mode improved by two orders of magnitude relative to that obtained by single channel scan mode analysis. Wavelength accuracies on the order of 0.1 A were achieved.

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.