A. Policarpo

Perspectives for positron emission tomography with RPCs

Abstract In this study, we address the feasibility and main properties of a positron emission tomograph (PET) based on RPCs. The concept, making use of the converter-plate principle, takes advantage of the intrinsic layered structure of RPCs and its simple and economic construction. The extremely good time and position resolutions of RPCs also allow the TOF-PET imaging technique to be considered. Monte-Carlo simulations, supported by experimental data, are presented and the main advantages and drawbacks for applications of potential interest are discussed.

An EPR experiment testing the non-separability of the wave function

Abstract The EPR-type strangeness correlation in the K0 K 0 system produced in the reaction p p → K 0 K 0 at rest has been tested using the CPLEAR detector. The strangeness was tagged via strong interaction with absorbers away from the creation point. The results are consistent with the QM non-separability of the wave function and exclude a spontaneous wave-function factorisation at creation (CL >99.99%).

Tests of CPT symmetry and quantum mechanics with experimental data from CPLEAR

Abstract We use fits to recent published CPLEAR data on neutral kaon decays to π + π − and πeν to constrain the CPT-violation parameters appearing in a formulation of the neutral kaon system as an open quantum-mechanical system. The obtained upper limits of the CPT-violation parameters are approaching the range suggested by certain ideas concerning quantum gravity.

A spark-protected high-rate detector

We developed a very low resistivity RPC-type detector, the anode of which was a plate made from materials with resistivity up to 5]107 ) cm, the cathode being a metallic mesh preceded by a drift region. In such a detector it was actually possible to combine the versatility and high counting-rate capability of metallic PPACs with the extreme robustness and ‘protectivenessa of Resistive Plate Chambers. Occasional discharges triggered by large deposits of primary ionisation or by extreme counting rates are quenched by the resistive anode and are constrained to the streamer phase of the sparking process. The study shows that this discharge a!ects the detector only locally and that the charge released is limited to a few tens of nC. Proportional counting rates up to 105 Hz/mm2 were achieved at gains above 104. The energy resolution at 6 keV was 20% FWHM. The observed gain-rate trade-o! is well described by an analytic model and further improvements may be expected by lowering the resistivity of the anode material. The properties of several custom-made, controllable resistivity, anode materials are described and prospects of improvement in the performance of the detector are discussed. ( 1999 Elsevier Science B.V. All rights reserved.

The GEM scintillation in He–CF4, Ar–CF4, Ar–TEA and Xe–TEA mixtures

Light emitted during the development of electron avalanches in a gas electron multiplier (GEM) can be efficiently used for optical readout of the detector. We report on measurements of total light yields in Ar/CF 4 , He/CF 4 , Ar/TEA and Xe/TEA mixtures. Information on the energy resolution obtained with low-energy X-ray photons is also presented. The spectral distribution of the light produced in the GEM is analysed and the mechanisms associated with the process of light production are considered.

Measurement of the refractive index and attenuation length of liquid xenon for its scintillation light

Abstract The attenuation length and refractive index of liquid xenon for its intrinsic scintillation light (λ=178 nm ) have been measured in a single experiment. The value obtained for the attenuation length is 364±18 mm . The refractive index is found to be 1.69±0.02. Both values were measured at a temperature of 170±1 K .

Performance study of liquid xenon detector for PET

The coincidence time resolution and the intrinsic position resolution along the electron drift direction of a liquid xenon multiwire ionization chamber for PET were measured, being, respectively, 1.5 ns (fwhm) and 0.5 mm (fwhm). Data on the low temperature performance of a photomultiplier tube operating on the VUV are presented.

Purification of liquid xenon and impurity monitoring for a PET detector

Abstract The purification system and the method of impurity monitoring developed for a positron emission tomography (PET) scanner based on liquid xenon position sensitive detectors are described. The present results show that an attenuation length of the scintillation photons in the liquid of the order of 50 cm can be reached by using only commercial purifiers. Although our preliminary measurements show that a strong electron attachment exists in liquid xenon, the electron attenuation length of 2 cm achieved is sufficient for the PET detectors.

Fano factors of rare gases and their mixtures

Abstract Measurements of FW (Fano factor × mean energy to make an ion-pair) for several non metastable Penning gas mixtures were made using the proportional scintillation process. Taking for W the values that correspond to 5.3 MeV alpha particles, upper limits of F were determined. The following results were obtained: 100% Xe, FW = 3.247, F ⩽ 0.15 ± 0.03 100% Ar, FW = 10.536, F ⩽ 0.40 ± 0.03 Ar + 80% Xe, FW = 4.635, F ⩽ 0.21 ± 0.03 Ar + 5% Kr, FW = 9.397, F ⩽ 0.37 ± 0.06 Ar + 24% Xe, FW = 5.093, F ⩽ 0.23 ± 0.02 Ar + 20% Kr, FW = 3.038, F ⩽ 0.12 ± 0.03 Ar + 20% Xe, FW = 3.582, F ⩽ 0.16 ± 0.02 Ar + 79% Kr, FW = 3.113, F ⩽ 0.13 ± 0.02 Ar + 5% Xe, FW = 3.204, F ⩽ 0.14 ± 0.03 100% Kr, FW = 4.584, F ⩽ 0.19 ± 0.02

Observation of electron multiplication in liquid xenon with a microstrip plate

Abstract We report here on the observation of electron multiplication in liquid xenon in a microstrip chamber with an amplification factor of the order of 10. The measurements were carried out at a temperature between 208 and 215 K (liquid density of about 2.7 g/cm 3 ).