REPOSITORY > RESULTS

Abstract

An experimental set-up for the detection of scattered projectile ions was constructed at the
external (in air) beamline of the Microanalytical Center at the Jožef Stefan Institute. The
system is composed of a detector for the analysis of back-scattered projectiles, casually
called the RBS detector, a precise positioning system and a meter of impact charge. The
RBS detector was placed in a prototype holder made of aluminium with a constant He
flush to reduce stopping of the back-scattered protons. The precise proton dose
measurement was accomplished with the implementation of an in-vacuum wire-mesh
based charge-collecting device. For a possible future implementation of an external
micro-beam, an in-vacuum ion-beam chopper device with an RBS detector was
constructed. The precise positioning system composed of a laser fixed on a XYZ micropositioning
stage and a camera was utilized to achieve reproducible positioning with a
precision of better than 100 μm. Calibration on thick targets was performed at the newly
developed RBS setup. A set of representative samples were analysed, some of historical
and archaeological value. The experimental setup at this stage was found to be a suitable
candidate for the transfer to a digital acquisition system enabling the simultaneous
acquisition of two PIXE, one RBS and a PIGE spectrum at high count-rates.
The analysis of geometrically structured samples in particular of cylindrical geometry,
has been somehow neglected in the past, probably because of mathematical difficulties in
the calculation of matrix effects. A mathematical model for an accurate calculation of
X-ray yields induced in cylindrical targets is proposed and the results are compared to
more routinely used models that can be applied in commercially available software
packages. The light elements emitting fluorescence soft X-rays are in particular affected.
A set of measurements was performed on fibres containing detectable elements from Si
up, with the proposed mathematical model.
The achievements were published in two articles.