|
| The Field Grandient Lattice Detector is a complete gas detection system in that it comprises in a single flexible foil of 100 microns, a gas-amplification mechanism and a 3D (3 axes) readout. |
The FGLD consists of two or more layers of tracks or wires spaced apart by uniform distance and electrically isolated. When a voltage is applied across the layers, the resultant high electric field gradient between the tracks or wires is capable of producing an electron avalanche in a gas medium.
The avalanche of electrons is collected on the anode layer (designated 'BOT') of wires or tracks while the ionized gas molecules recombine on the upper cathode layers ('MID' and 'TOP'). When operated in the proportional region, the amount of charge in each collected pulse gives a measure of the energy lost by the original particle incident in the detector. Suitable readout electronics, connected to each of the tracks of all three layers, can be used to reconstruct the trajectory of the incident particle.
The FGLD consists of a thin, flexible polyimide foil of only 100 microns thickness. The triple-
layer structure is made using photo-lithographic techniques similar to those used in
high-resolution printed-circuit board (PCB) production. Removal of the polyimide in the active area is accomplished
with a
wet-etching chemistry patented by CERN.
The same technique is used in the fabrication of other technolgies, such as
the Gas Electron Multiplier (GEM) and
ChemcialVias.
|
| A close-up of the active area of the FGLD showing the lattice of the 3 readout axis and the form of the polyimide after chemcial etching. |
The FGLD has applications in the detection of charged particles and photons. Shown below is the pulse height spectrum recorded from an Fe55 radioactive source. The source emits soft X-rays of 6keV energy. This spectrum shows a clear distinction between the 6keV X-rays and the 3keV escape peak which results from the interaction of the X-rays in Argon gas. The separation between the two peaks corresponds to an energy resolution of about 25% FWHM.
The FGLD idea was first developed by Louis Dick of the PH department
and by Rui de Oliveira, section leader of the PCB workshop (building 102).
As of September 2003,
David Watts has
been handling the majority of the R&D efforts, which includes mainly the fabrication of the
detectors themselves in the PCB workshop.
Material available on this site copyright
Ó
2004 European Organisation for Nuclear Research.
All rights reserved.