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Positron Emission
Particle Tracking |
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Positron emission particle tracking or PEPT is a technique for studying the
flow of particulate systems such as tumbling mills in the minerals industry.
Initially developed for the medical imaging industry, positron emission
tomography has been adapted for engineering applications at the University of
Birmingham. The particular value of PEPT is the ability to look deep within the
particulate system for extended periods of time thereby elucidating the in-situ
kinematics and dynamics of the flow. The basic principle of PEPT is based on
positron annihilation. A single (“tracer”) particle is labelled with a
radionuclide that decays via beta-plus decay, resulting in two gamma rays, each
of energy 511 keV travelling in exactly opposite directions. Simultaneous
detection of the two gamma rays in an array of detectors (a PET “camera”)
defines a line along which the annihilation occurred. Detection of a few such
events in a very short time interval allows the position of the tracer particle
to be triangulated in three dimensions. Location in space of the tracer particle
may be achieved at a frequency up to 250 Hz with an accuracy which depends on
the speed and activity of the tracer particle.
PEPT is currently the only
non-invasive technique capable of mapping the in-situ flow fields in robust,
industrial systems to the level of detail that is demanded for mechanistic
modelling. Advances in computing have made numerical modelling of complex
flows conceivable. However, realistic simulation of industrial systems is still
decades away from being achieved. Consequently, most numerical modelling work
still employs simplifying assumptions that ultimately make the computing tasks
tractable. The integrity of these assumptions requires validation if they are to
gain confidence within industry. PEPT offers detailed validation of the flow
field and related parameters.
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Academic and Research staff at UCT |
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UCT Students involved in PEPT |
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L. Bbosa |
Validating numerical
simulations of tumbling mills with PEPT |
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A.J. Morrison |
Optimisation of trajectory fields derived from PEPT |
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D. Kallon |
Circulation rate modelling in tumbling mills using PEPT |
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H. Brodner |
Velocity field modelling in tumbling mills using PEPT |
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M. Bickell |
An investigation into PET imaging |
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A PEPT laboratory at |
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The Positron Emission
Particle Tracking laboratory at iThemba LABS cyclotron centre
was opened in August 2009. The PEPT laboratory at iThemba LABS
has all the
obvious advantages with respect to radiation handling and licensing, and will be
available for research use by local and international scientists. This is a
large inniative which presently includes the
UCT Physics PEPT group
(Dr Indresan Govender
and
Prof Andy Buffler), the
Centre
for Minerals Research (Dr Aubrey Mainza and Mr Andre van der Westhuizen), the
Minerals to Metals Initiative
at UCT (Prof J-P Franzidis),
Department of Earth Science and
Engineering at
Imperial College London (Prof Jan Cilliers), the
Positron Imaging Centre
at the
University of Birmingham (Prof David Parker),
the
Julius Kruttschnitt Mineral
Research Centre (Prof
Malcolm Powell)
and
iThemba LABS. PEPT experiments
require positron-emitting radioisotopes which are produced by cyclotron proton
beams. iThemba LABS routinely produces radioisotopes such as F-18 and Ga-68 for medical PET use.
The "EXACT3D" (Model: CTI/Siemens
966) positron emission tomography scanner was designed with the aim of achieving
high sensitivity and resolution using available detector technology. The device
consists of 48 rings of standard bismuth germinate detector elements (each 4.39
mm transaxial x 4.05 mm axial x 30 mm deep, grouped in blocks of 8 x 8) with a
ring diameter of 82 cm, producing an axial field of view of 23.4 cm. Attenuation
correction is carried out with a small Cs-137 source which moves under hydraulic
pressure in a helical tube. The I/O and computing hardware can maintain a
sustained acquisition rate of about 4 million coincidence events per second. The
mean spatial resolution is 4.8 ±
0.2 mm FWHM (transaxial, 1 cm off-axis) and 5.6 ±
0.5 mm (axial, on-axis). The scanner has been used for clinical research use at
Hammersmith Hospital, London, since 1995, and may still be the most sensitive 3D
PET scanner in operation today.
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A flavour of our research |
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Mechanistic
transport modelling of rheologically complex slurry mixtures
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Experimental
validation of Discrete Element Models applied to tumbling mills
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Flow characterisation in mining
equipment (chutes, mills, pipelines)
- Flow dynamics in the upper
airway of patients suffering from obstructive sleep apnoea
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| News |
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| A new PET scanner was commissioned
early 2012
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