PSD-V, London, September 1999 Two dimensional readout in a liquid xenon ionisation chamber V.Solovov, V.Chepel, A.Pereira, M.I.Lopes, R.Ferreira Marques, A.J.P.L.Policarpo LIP-Coimbra and Department of Physics University of Coimbra, Portugal

PSD-V, London, September 1999 Conventional PET: problem of parallax LXe PET detector Goals: obtaining DOI (Depth of Interaction) information, i.e. 3D position sensitivity improve spatial and time resolution Idea: scintillation (30 ns) timing collection of free electrons position

PSD-V, London, September 1999 LXe multiwire PET chamber  x = 0.8 mm (fwhm)  z = 5 mm (DOI) drift time wire number Anger method (there are still hopes) Problem:  y ~10 mm Alternative: Measurement of y using induction signals:  Wires ? Strips ? Wires & strips ?

PSD-V, London, September 1999 Mini-strip plate ICARUS: Idea: replace the system of wire electrodes in LAr TPC by a more reliable and rigid construction LXe PET: 1). G10 ?? - problem of xenon pollution wires strips electrodsprinted circuit (material - G10) (P.Cennini e.a., NIM A346 (1994) 550) (A / V) LXe PET LAr TPC (A / V) ~100:1 A - area of outgassing surface V - volume of working material 2). Energy to be detected: ICARUS PET ~1:10

PSD-V, London, September 1999 Mini-strip plate Desag D263 glass 0.55 mm thick 50x50 mm 2 x y

PSD-V, London, September 1999 Recombination in LXe:  -s and  -s 2 kV/cm 4% E  92% 2 kV/cm E   : 5.44 MeV 14,000 e  : 240 keV (E.Aprile e.a., NIM A307 (1991) 119) (E.Aprile e.a., NIM A302 (1991) 177)

PSD-V, London, September 1999 Mini-strip plate: Computation Electron trajectories and equipotential lines of weighed field calculated for an induction strip (cathode voltage is V) Computed signals (x=y=0) Acquired signals (computed ones are shown in black)

PSD-V, London, September 1999 Signals on the induction strips Strip #0 Amplitude of the charge signal induced on strip #0 (centred at y=0) as a function of y-coordinate of the electron starting position at the cathode (computed for x=0) Scatter plot of the amplitudes of the signals induced on two adjacent back strips. (normalised to the collected charge for every event)

PSD-V, London, September 1999 Amplitude spectra Back strips

PSD-V, London, September 1999 Position resolution in y-direction (across the induction strips) Equivalent  -ray energy ~140keV Obtained with the centre of gravity method: B-D. Only the signals above threshold count A. Sum of the signals in all channels where A i - amplitude of the charge signal on strip i centred at y i A B C D

PSD-V, London, September 1999 Position resolution as a function of energy Equivalent (“effective”)  -ray energy

PSD-V, London, September 1999 Conclusions 1. Mini-strip plate on glass substrate can be operated in liquid xenon, 2. Position resolution  1 mm (fwhm) across the induction strips and localisation precision of 2 mm across the collection strips are achieved, 3. These values are obtained in the equivalent  -ray energy range from 110 keV to 220 keV. For PET it means: 1. Excellent (~1 mm) transaxial and axial position resolution, 2. Depth of Interaction (DOI) can be measured with the accuracy of ~2 mm What else? The fact that good position resolution was obtained with the equivalent  -ray energy as low as ~100 keV, allows us to think of a liquid xenon 2D imaging device (gamma camera) with purely ionisation readout.

PSD-V, London, September 1999 Acknowledgements P.Picchi (ICARUS at CERN) P.Cennini (CERN) F.Pietropaolo (ICARUS at CERN) F.Fraga (LIP-Coimbra) L.Margato (University of Minho)

PSD-V, London, September 1999 Position resolution in y-direction across the induction strips (2) E=220 keVE=110 keV

PSD-V, London, September 1999