F. W. Saris

An ion-implantation method to measure the fraction of beam carrying inner-shell vacancies when penetrating solids

Abstract It is shown that from the Ar K-shell X-ray emission cross-section in collisions of Ar projectiles with Ar atoms, previously implanted in Si, one can determine the fraction of beam carrying L-shell vacancies. The depth dependence of this fraction can be obtained by varying the implantation energy. The results yield quantitative information on L-shell vacancy lifetimes of Ar ions moving through solids.

An estimate of direct Coulomb K-shell vacancy production in heavy ion-atom collisions

Under conditions in which direct radial or rotational coupling mechanisms are not expected to contribute and for collision velocities for which the MO model is expected to apply, it is proposed that experimental data concerning K-vacancy production in heavy ion-atom collisions can be described in terms of direct Coulomb excitation. Agreement between experimental ionization cross sections and the predictions of the BEA universal curve is demonstrated, with transient molecular effects allowed for by a simple binding-energy modification. This binding-energy-modified BEA is also used as a basis of an explanation of the observed enhancement of K-vacancy production at or near level matching.

Energy spectra of electrons produced in collisions of multiply charged neon ions with noble-gas atoms

Energy spectra of electrons produced in collisions of 100 keV Nen+(n=1, 2, 3, 4) on He, Ne, Ar and Kr have been measured. The experimental data show that capture of two electrons into excited autoionising states of the projectile is important for the Ar and Kr targets. For the Ne and He targets capture of two electrons into excited states is less probable.

New developments for the absolute calibration of light intensities in the far ultraviolet

Abstract New developments are described for the absolute calibration of light intensities in the far ultraviolet. First, we use the microwave cavity as an (almost) monochromatic light source, determining the intensity of its radiation with a thermopile. Secondly, we apply the branching ratio method for molecules. Next we describe two methods which are based on the fact that some cross sections for emission of spectral lines in the vacuum ultraviolet, produced by electron impact on gases, can be theoretically or empirically calculated.

Charge-state dependence of inner-shell vacancy production in heavy ion-atom collisions with atomic number larger than 10

X-ray production cross sections have been measured for Ne K X-rays in Ne-Ar, Kr and Ar-Ne collisions, Kr L X-rays in Ar-Kr and Kr-Kr, Xe and Ar K X-rays in Ar-Ar, Xe. Projectile energies used were 60 to 1150 keV for neon ions, 300 to 2000 keV for argon ions and 175 to 1900 keV for krypton ions. The range of charge states used was 1+ to 4+ for neon and 2+ to 7+ for argon and krypton ions. The vacancy production cross sections extracted from the X-ray data show no charge-state dependence and indicate that two-step processes are not important. It is proposed that near the united-atom limit a direct coupling from molecular orbitals (MO) to the continuum is important. A large difference in the excitation function was seen depending on whether 2p sigma , 3d sigma or 4f sigma MO were involved. It is proposed that this strong dependence is caused by the relative difference in the energy gap and the shape of the MO involved. The data are compared with estimates from the modified BEA scaling law and the statistical model. For the latter model systematic deviations with experiment are found.

Enhanced K-L vacancy-sharing ratios observed in low-velocity Ne-Kr collisions

The Ne K and Kr L X-ray production cross sections were measured for projectile energies of 100 to 1100 keV. The vacancy-production ratios P between Ne 1s and Kr 2p are orders of magnitude higher than calculated vacancy-sharing ratios using the Demkov-Meyerhof estimates. A calculation of P using the Nikitin formalism gives excellent agreement with the data.

The production of K-shell vacancies during collisions of 50-1200 keV Nen+→Ne for n=1, 2, 3 and 4

The production of K-shell vacancies in collisions of Nen+ to Ne has been studied in the energy range 50-1200 keV for n=1, 2, 3 and 4. For this purpose, cross sections for K X-ray and K Auger-electron production have been measured. The results show no indication of an asymmetry effect which was expected to be seen according to calculations of correlation diagrams for the Nen+ to Ne system. On the contrary, the data agree very well with the predictions of the simple one-electron promotion model, i.e. the cross sections scale with the incoming charge state of the projectile. The absolute K-shell ionisation cross sections agree within 20% with cross sections calculated theoretically. From the X-ray and Auger data, fluorescence yields are obtained. These fluorescence yields depend on the projectiles energy as well as on its charge state.

Ion-Induced Continuum X-ray Emission

This paper reviews continuum X-ray emission produced by ion-impact on gaseous and solid targets. Molecular orbital X-rays are considered in detail in order to establish the circumstances under which they can be distinguished from radiative electron capture and from various kinds of bremsstrahlung. The level of understanding of continuum X-ray production appears to parallel that of ion-induced inner-shell ionization in general.

Two-electron-one-photon transitions following double K-shell ionization in symmetric collisions of N, O and Ne

Cross sections for two-electron-one-photon transitions following double K-shell ionization in 200 keV collisions of N++NH3, O++H2O and Ne++Ne are reported. These transitions are of the type (1s)-2 to (2s)-1(2p)-1.

The production mechanism and spectral distribution of K MO X-rays in collisions of 35-200 keV N+-N

By comparing X-ray spectra from N++NH3 and N++N2 it is shown that the continuum X-rays observed during 35-200 keV N+ on N2 collisions can be interpreted as MO X-rays produced in a two-step process. Spectral distributions have been calculated in the quasi-static approximation and a comparison is made with experiment.