page_title: AGATA (gamma-ray detector)
section_title: High-fold segmented Ge detectors
hierarchical_section_title: AGATA (gamma-ray detector) / High-fold segmented Ge detectors
context_page_description: Advanced GAmma Tracking Array is a highly developed detector system to track gamma rays. It is a European collaboration project funded by twelve countries in Europe. The project was proposed in 2001 and in 2002 it was signed by the participant countries; in 2005 the first detector showed its result. It is expected that the complete AGATA will be ready within 2018. The spectrometer is 4π gamma-ray detector which is a combination of several Germanium detectors. It is a major instrument to study nuclear structure ray tracking by measuring the γ-radiation. AGATA will have very good full energy peak efficiency with high peak-to-total ratio and angular resolution. The system will be capable of high event rates with ancillary detectors to measure light charged particles or neutron.
context_section_description: It is important to know the position of the γ-ray interaction inside the detector with high accuracy (1–2 mm) to get a high efficiency. For this purpose, one Ge detector should consist of 30000 voxels. It is almost impossible to get such a high granularity by a physical segmentation of the crystal. But, the pulse shape analysis method developed for AGATA can provide the position accuracy with high resolution and time information. This method requires only 20-40 segments per detector. The AGATA detectors are Ge-detectors that are 36-fold segment with six-fold azimuthal and six-fold longitudinal segmentation.
  The detector is 10 cm long and is circular at the rear side with a diameter of 8 cm and hexagonal at the front face. A common inner electrode and 36 segments are read out via individual preamplifiers. The segments can then be considered as separate detectors. 
  The parameters for the hexagonal crystals are:
  Maximum cylinder size: 90.0 mm length, 40.00 mm radius.
  Coaxial hole size: 10.0 mm diameter, extension to 13.00 mm from the front face.
  Passivated areas: 1.0 mm at the back of the detector, 0.6 mm around the coaxial hole.
  Encapsulation: 0.8 mm thickness with a 4.0 mm crystal-can distance-
  Cryostat: 1.0 mm thickness with a 2.0 mm capsule-cryostat distance.
  By exploiting the spatial information contained in the detector signal we can more accurately localize the γ-ray interaction than is possible by the geometry of the segments. A photoelectron or Compton electron generates electrons and holes which induce image charges of opposite signs on the detector electrodes when a signal is produced. The change of the image charge causes a flow of currents into or out of the electrodes. The induced charge is distributed over several electrodes for the large distance in a multi-segmented detector. For the closer distance an increase and decrease of induced charges of the electrodes continue until the primary charge finally reaches to its destination electrodes and neutralizes the image. To identify the detector sector where the interaction took place we have to observe the net charge on the charge-collecting electrode simply observing the polarity of the induced signal. This allows for distinguishing between interactions at small and large radii.
caption: Detector, Ge detectors are 6-folds azimuthal and 6-folds longitudinal total 36 fold. 10 cm long and 8 cm diameter at the rear. This is not the file should be shown. The original file has the same name. The original file link: http://commons.wikimedia.org/wiki/File:Detector.jpg
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