Ion Beam - basic research

spectrum of Ca Ka line

In figure 1 we can see the high energy resolution spectrum of Ca Ka line induced with X-rays and O ions. The level of the multiple ionization manifested through satellite lines on the high energy side of the Ka parent line is changing dramatically with different type of excitation.

Basic Introduction:

In experiments involving high energy ion beams we are mainly studying the inner-shell ionization induced in collisions of ions with the target atoms. Inner-shell ionization induced in collisions of charged projectile with an atom is one of the basic processes studied in the field of atomic physics. It helps us to understand interaction of charged particles with matter. It also leads to better description and understanding of the atomic processes and ionization mechanisms. Results obtained from inner-shell ionization studies induced in collisions with ions are very useful also in other fields such as trace element analysis. Efficiency of such a method directly depends on our knowledge about basic atomic properties: energy levels, transition probabilities, ionization cross sections, natural linewidths, etc.

Multiple inner shell ionization:

Inner-shell electron excitation probability depends strongly on type and energy of the projectile. Besides single also multiple inner-shell ionization can very likely occur in collisions of atom with a few MeV/amu ion. Excited atomic state with inner-shell vacancies decays by an electron or photon emission. Energies of the emitted photons are in the X-ray region. Characteristic X-ray spectra are therefore composed from different contributions (spectral lines) originating from radiative transitions in atoms with different number of inner-shell vacancies and different distributions of vacancies among the atomic (sub)shells. If one wants to resolve spectral lines originating from transitions within multiply ionized atom from the diagram lines originating from transitions within singly ionized atom high-resolution X-ray spectroscopy is essential. Energy resolution of semiconductor detectors is not high enough to resolve different contributions therefore Bragg crystal spectrometer whose resolution can come close to the natural linewidths needs to be applied.

Experiments with protons:

Experiments with protons are performed at our 2MV Tandetron accelerator employing high resolution crystal Bragg spectrometer in Johansson geometry. We are studying mainly multiple ionization (1s2p, double1s) of some 3d transition elements and some other low-Z elements. We are also studying the importance of multiple ionization contributions in the PIXE elemental analysis as well as employing high resolution PIXE measurements to study chemical effects in the emitted x-ray spectra.

Experiments with Heavy Ions:

This work has been performed in a collaboration with the group for Atomic Physiscs from University of Fribourg (http://www.unifr.ch/home/welcome.html). The measurements with the high-resolution von Hamos crystal spectrometer were performed at the Paul Scherrer Institute (http://www.psi.ch) using their Philips variable energy cyclotron. We were extending our study of L shell ionization with protons towards heavier ions and higher projectile velocities. The results of this work can be found in

Contact person:

Dr. Matjaž Kavčič

Last updated: 01/22/2014