Positron Imaging Centre

Mobile Detector Units

Our mobile detector units are versatile, as they can not only be placed in a configuration that suits the experimental setup, but they are not restricted to being used in the PEPT lab. This means they can be treated as stand alone detector modules. Crucially the detector arrangement can be customised to the application in question, allowing both large and small apperatus to be studied in detail. The images to below depict a single unit, an orthoganal configuration and an example of the units used on plant.

   Mobile Detector Module
   Mobile Detector Module: Orthoganal Configuration
   Mobile Detector Module: On Plant

Specifications of the Units

Detector modules consist of 4 detector blocks and the associated electronics (ADC) packaged as individual units. The detector block houses a segmented bismuth germanate (Bi4Ge3O12) scintillator crystal (8 x 4 or 8 x 8 segments are typical) viewed by 4 photomultiplier tubes. The photopeak efficiency (accepted gamma ray detection efficiency) for these scintillator crystals is around 45%. Signal processing on the composite signal from the 4 PMTs allows the excited crystal element (following a gamma ray interaction) to be explicitly defined, thus giving spatial resolution equal to the crystal pitch in the detectors. Typical detector blocks (8 x 8 segments) offer crystal pitches of 6.25 mm transverse and 6.75 mm axial with 30 mm depth.

Measured singles countrates for a detector module approaches 1.5M events per second, with a dead-time parameter of around 0.6us per detector block. By operating an array of modules coincidence data rates up to 4M events per secod have been observed (due to simultaneous acquisition over many parallel channels). This performance allows PEPT locations to be made at a rate of 1k locations per second with an approximate precision of 0.5mm in 3 dimensions.