Experiments at the APBF

1
Experiments at the APBF
From Atoms to Materials Fundamental to Applied
Science
Positron binding
Interaction fundamentals
Positron binding has been predicted for a number
of atomic systems. Experimental verification of
this process is still lacking. The high
resolution positron beam allows the design of
experiments to measure positron binding to atomic
systems and study of this type of exotic ion.
The atomic and molecular physics program will
initially concentrate on the measurement of low
energy positron scattering cross sections. We
will be able to measure positron cross sections o
unprecedented accuracy and precision, shedding
new light on the fundamental interactions between
positrons and matter. We also plan to develop new
experimental and analysis techniques to extend
the range of cross sections measured.
Studies of biosystems
Bio-materials design
Positron interactions with biomolecules are the
fundamental drivers of PET (positron emission
tomography). However, there have been no studies
of these interactions and the way in which they
can affect the ultimate resolution of this
imaging technique. A program of study of
positron interactions with relevant molecules,
such as water and typical positron delivery
drugs, will shed light on the possibility of
improvements to PET through the understanding of
the underlying, fundamnetal interactions.
New materials are being developed to
revolutionise drug delivery. The function of
these materials depend critically on the open
volume present and the interplay between this and
the desired drug molecule. The positron beam can
aid in the design of these materials by analysing
the pore size, distribution and connectivity,
allowing the tailoring of drug delivery to
optimise drug effectiveness and minimise side
effects.
Materials analysis
Positrons can be used for the analysis of
materials and material structure. Two main
techniques are planned for experiments at the
APBF, PALS and 2D-Doppler. Positron annihilation
lifetime Spectroscopy, or PALS, measures the time
it takes for positrons to annihilate inside a
material. The lifetime of the positrons is
related to the vacancy structure. Positrons are
particularly sensitive to nanometre scale
defects, which have an important role in
determining material properties, such as
permeability.
The 2-D Doppler broadening technique gives
information about the chemical environment of the
annihilation site. Annihilation of a positron
with an inner shell electron produces a
distinctive doppler shift to the annihilation
gamma ray energies, which can be related to the
atom at which the annihilation took place. This
technique can give important information about
the make up of impurity clusters in metals.
The variable energy of the positron beam will
allow us to do materials experiments as a
function of depth. As the energy of the incident
positrons is increased to 10 keV, different
depths of the materials are sampled. This
capacity will be the first of its kind in
Australia and allow studies of thin films and
defects as a function of depth in materials.