Positron Emission Particle Tracking

 

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.

 
 
 
Academic and Research staff at UCT  

 

 
  • Dr Indresan Govender
  • Prof Andy Buffler
  • Mr Michael Van Heerden
  • Dr Maximillian Richter
  • Dr Kate Cole
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    UCT Students involved in PEPT
       
    O. Ogunmodimu Validating numerical simulations of vibrating screens using PEPT  
         
    D.N. De Klerk Ergodicity in granular flows  
         
    D. Blakemore Inverse FEM modelling using PEPT  
         
    B. Baloyi Granular viscosity models for tumbling mill flows using PEPT  
         
    T. Pathmathas Nuclear imaging to validate granular rheology models  
    S. Bremner Granular shear cell modelling using PEPT and DEM  
     
     
       

    UCT
     

    Applied Physics

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    A PEPT laboratory at

     
     

    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.

    A flavour of our research
     
    • Mechanistic transport modelling of rheologically complex slurry mixtures
    • Experimental validation of Discrete Element Models applied to tumbling mills
    • Flow characterisation in mining equipment (chutes, mills, pipelines)
    • Flow dynamics in the upper airway of patients suffering from obstructive sleep apnoea
     
    News
     
     A new PET scanner was commissioned early 2012
       

     

     
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