Welcome to Physics Group
Variable Energy Cyclotron Centre, Kolkata

Gas detector developement

At VECC, we have an active research program to develop gas detectors for detection of heavy charged particles. After an intensive R and D efforts, few position sensitive Multi-Wire Proportional Counters (MWPC) were designed and fabricated indigenously. These large area detectors (typical area is 20 cm x 6 cm) are proficiently used in experiments at the major accelerator facilities available in our country. The position resolution achieved with these detectors is better than a millimetre and time resolution better than a nanosecond. We have also developed avalanche counters (5 cm x 3 cm active area) that is efficient for ”start time“ measurement in a time of flight setup.

The Breskin type of low pressure multi-wire proportional counters detectors that we have developed consists of 5 wire planes. The central anode wire plane provides the time information. Position information (in both X and Y direction) are achieved by delay line method. Two cathode planes give the energy loss in the detector deposited by the charged particles.

3 dimensional view of the design of the multi-wire proportional counters

For the assembly, fabrication and testing of gas detectors, we have a well equipped gas detector laboratory. We have developed a film stretching unit for the preparation of thin polypropylene foil used as the entrance window for the detectors. The front-end of the detector is usually covered by a polypropylene film that is required to be thin enough to minimize the energy loss of the detected charged particle. Thick polypropylene sheet (~ 20 micron) available in the market are stretched to less than a micron thickness by this film stretching unit. An aluminium plate, covered by teflon sheet are heated at about 60°C, be in a motion slowly upward by controlled pneumatic action. The plate stretches the polypropylene film mounted on a table.

A time of flight setup inside VECC scattering chamber, with the two large area MWPCs developed at our laboratory. In the experiment, masses of the fission fragments were measured from the time of flight difference of the fragments.

The film stretching unit developed at our laboratory. It stretches polypropylene film to less than a micron thickness.

We have also developed our own gas handling system. The detectors are operated in flow mode at a typical pressure of 3 torr of isobutene gas. Since the window of the detector is very thin, it is compulsory that the initial pumping of the detector has to be done very slowly. Any fluctuation of inside gas pressure can tear down the window and thus needs precession flow control.  We have designed a gas handling system for this purpose.  It consists of a mass flow controller and an electronic valve that protects the window/detector even in case of power failure during experiment. The mass flow controller offers automatic maintenance of the inside gas pressure very accurately.

A 16 segment silicon detector which is used as the back side of the hybrid gas detector that provides time, position and energy info of a charged particle.

In our country, in next few years we will have accelerators (Super Conducting Cyclotron at Kolkata, LINACs at Mumbai and Delhi) providing intermediate energy heavy ion beams that may be used for front line research in many challenging areas of nuclear physics. We have a R & D program for the development  of detectors for efficient utilization of these accelerator facilities. Fabrication of an unique hybrid detector, conceptually a combination of gas MWPC backed by segmented silicon strips, capable of providing excellent timing, position and energy resolution for heavy fragments is under way.

The MWPCs were used in several experiments to study fusion fission dynamics [e.g; Phys. Rev. C 92, 041601 (R) (2015), Phys. Rev. C 91, 044620 (2015), Phys. Rev. C 83, 024605 (2011), Phys. Rev. C 79, 054607 (2009)]. 

For more info, you may contact: Tilak Ghosh (tilak@vecc.gov.in) / Chandana Bhattacharya (chandana@vecc.gov.in)