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Variable Energy Cyclotron Centre, Kolkata

Charged Particle Detector Array (CPDA)

The forward array will consist of 24  Silicon-Silicon-CsI(Tl) telescopes, each composed of a 50 micron thick  silicon strip (16 segments) detector (delE1), a 500 micron/1 mm ( delE2 / E) thick double sided (16 x 16 segments) silicon strip detector (DSSD), and four 6 cm thick CsI(Tl) detectors.(E). Thus, the E detector will provide two dimensional position information as well as good isotopic identification for the fragments with (Z < 10) produced in low and intermediate energy heavy-ion reactions. In addition to good isotopic resolution, it will also provide a low energy threshold for particle identification. The CsI(Tl) detectors  will detect  proton of  maximum energy of E/A = 140 MeV  and  ¹⁶O ions of energy  E/A = 335 MeV respectively. The angular coverage of the forward array would be ~ 7^o -45^o. The CsI(Tl) crystals are  trapezoidal in shape, having 2.5 x 2.5 cm² front  face and 3.5 x 3.5 cm² back face respectively and coupled to a photodiode due to the excellent linearity of the photodiode over a wide dynamic range and compact size.

 Design view of the CPDA

In-beam performance of a prototype telescope of the forward array has been tested with145 MeV ²⁰Ne beam at VECC. All Strips and the CsI(Tl) detectors were read out individually using standard readout electronics and a VME-based online data acquisition system developed at VECC to collect data on event-by-event basis.

Telescope configuration for CPDA

Photograph of the telescopes

The extreme forward array which will cover the angular range of 3^o -7^o, will be made up of 32  phoswitch detectors (combinations of fast and slow  plastic scintillators). 

Photograph of the Charged Particle Detector Array (CPDA)

The decay time for the fast plastic scintillator is 2 ns while that for slow plastic is 280 ns.  Prototype plastic phoswich detectors have been developed, which consist of fast and slow plastic of thickness 200 mm and 100 mm respectively. The phoswitch detectors were then optically coupled to a low power photomultiplier tube to collect the scintillation light.  Typical energy thresholds in 200mm fast scintillators for different ionizing particles are ~4MeV for proton, ~4MeV/A for alpha and ~7MeV/A for ¹⁶O. In - beam  performance of these detectors have been  carried out  using ¹⁴⁵MeV ²⁰Ne ion beam from the Variable Energy Cyclotron,  Kolkata,  on a  mylar  target and the particle separation obtained is shown below.

Particle separation in phoswich detector

The backword part, covering the angular range 45 degree to 175 degree will consists of 300 CsI(Tl) crystals of different size and shape.