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