Welcome to the Website of the

Section of Atomic Collisions




I. Introduction

The main research activity of the Section of Atomic Collisions is the study of fast atomic collisions. We mostly use accelerators for production of fast particles, therefore our research field is often called as "accelerator-based atomic physics". The basic collision processes are as follows:

  • excitation
  • ionization
  • electron capture (charge-exchange)
  • relaxation.

 

We are mainly interested in the dynamical aspect of the collision. The most direct information on the dynamics can be obtained by observing the primarily ejected electrons having continuous energy distribution. The dynamics particularly for the ionization of inner atomic shells can also be studied by detection of the decay products (photons, Auger- or autoionization electrons) emitted from the excited states. In our research of the collision dynamics we use both approaches, applying the methods of x-ray and electron spectrometry.

The primary aim of the investigations is the better understanding of the dynamics of the fast atomic collisions by studying, first of all, collisions involving a few particles. Furthermore, by performing electron- and x-ray spectroscopic measurements of the atomic (molecular) states excited in the collisions, we wish to explore more deeply the electronic structure of the atoms and molecules. Besides the investigations of the simple collision systems carried out on free atoms and molecules, we study also the interactions of more complex systems, like the collisions of photons, electrons, light and heavy ions with solids. As a further example, we may mention our research work exploring the properties of some mesoscopic systems (fullerene molecules, micro-capillaries).

 

Our approach is primarily experimental, but the theoretical work carried out in connection with our own and other's experiments is also remarkable.

 

A significant part of the activity of the Section of Atomic Collisions is the development of new research instruments methods. Due to the experimental character of most of the research work, this activity primarily implies the development of experimental tools, first of all, construction of electron spectrometers. At the same time, it is worth mentioning the development of the theoretical methods for the description of the various collision processes, too.

 

II. Historical review

Our research work in the field of the atomic collisions started about 40 years ago. At that time many groups in the world working in the field of nuclear physics realized that their experimental techniques (particle accelerators, detectors, etc.) can effectively be used to explore the so far unknown properties of the structure and dynamics of atoms and molecules.  The research activity of our group has also roots in nuclear physics, specifically in the field of b spectroscopy.  Quite naturally, our first “atomic physics” experiments represented a transition between the old and new research subjects of the group: Electrons and positrons originating from radioactive sources were used to ionize the inner shells of atoms [1].

Despite of the tradition and experience in the field of electron spectroscopy, the first “true” collision experiments were carried out with use of the x-ray spectroscopy method. In these experiments energetic beams of electrons, protons, alpha particles and heavier ions provided by the accelerators of ATOMKI (the Cockroft-Walton generator, the 5-MV Van de Graaff generator, and later the cyclotron) were used to ionize the K, L and M shell of atoms. The ionization cross sections were determined by measuring the yield of the x-ray photons emitted following the ionization. Later the angular distribution of the x-rays was also measured by which the alignment parameter characterizing the charge-cloud asymmetry of the ionized atom was established.

In parallel with the x-ray spectroscopic experiments, soon an electron spectrometer suitable for the study of collisions has been constructed. In the following decades further electron spectrometers – in some cases with unique parameters – have been built. With use of these spectrometers and other instruments and devices developed by our group (ion beam cleaner, charge-state analyzer, fast particle detector, recoil-ion detector, time-of-flight electron spectrometer, etc.) we performed systematic experiments for a large variety of collision processes and phenomena. Just to mention the most important ones: Auger electron emission; continuum electron emission including the “cusp” phenomenon; post-collision interaction; multiple ionization; photoionization; positron-impact ionization. For the results achieved in the field of the electron spectroscopic investigations of the collision processes our group earned a world-wide reputation.

 

 

References

  [1] S. A. H. Seif El-Nasr, D. Berényi and Gy. Bibók, Z. Phys. 267 (1974) 169 and ibid 271 (1974) 207