Liquid xenon multiwire chamber for positron tomography

The liquid xenon multiwire chamber has been proposed as a detector of 511 keV gamma-photons for positron emission tomography (PET). Both the scintillation and the ionization signal, read from the anode wires, are used. A test chamber of about 300 cm3 and containing six multiwire ionization cells has been built. The cell is formed by two plane cathodes, 10 mm apart, and 20 anode wires spaced by 2.5 mm tied to pairs resulting in 10 channels, read out independently. The first experiments were performed for a single cell. The number of the anode wire on which the signal is induced gives the depth of interaction in the detector with a precision of 5 mm. This is important information allowing one to reduce the parallax error and, therefore, to decrease the tomograph size and improve the solid angle. The position sensitivity across the cell (or along the tomograph ring) is achieved by measurement of the drift time of the electrons from the point of primary ionization to the anode, triggered by the scintillation detected with a photomultiplier tube. The scintillation also supplies a fast trigger for the coincidence analysis.