Search

The electromagnetic calorimeter of the PANDA detector at the future Facility for Antiproton and Ion Research is one of the central components to measure high-energy photons over a wide dynamic range down to a few tens of mega-electron volts. The calorimeter comprises almost 16 000 PWO-II crystals of 200 mm length with high quality standards in optical performance, light output, and radiation hardness. The running mass production has passed more than 7000 crystals. The observation of stimulated recovery even of cooled crystals by illumination with external light sources integrated into the detector modules has opened up a new design concept for PANDA and future calorimeters.

The response function of a 3 times 3 matrix of 200-mm-long PWO-II crystals has been measured with energy-marked photons up to 675 MeV energy. For the first time the crystals were readout individually with one large area avalanche photo diode of the second generation operating at a temperature of 0degC. The reconstructed electromagnetic shower distributions show excellent energy resolutions down to 40 MeV. Reducing the temperature and increasing the light collection by an additional large-area avalanche photo diode can achieve further improvement.

For the first time, the response function to high-energy photons of a 3 times 3 matrix comprising large volume LYSO crystals was measured using energy marked photons provided by the tagged photon facility of MAMI. The crystal quality was determined based on the optical transparency, the intrinsic radioactivity and the luminescence yield. Energy and time resolutions for photons up to 490 MeV photon energy have been deduced from the reconstruction of the electromagnetic shower deposited into the crystal array and the data delivers very promising results.

For the first time, full size lead tungstate crystals of different suppliers, quality and dopant concentration have been irradiated with gamma-rays at low temperatures down to -25degC at IHEP Protvino. In contrast to the behavior at room temperature, increased damage and extremely slow recovery processes have been observed. These first results are discussed in the light of several very different interpretations. Further more sensitive measurements are under preparation. The outcome will have a strong impact on the presently assembled ALICE-PHOS detector and the design of the EM calorimeter of PANDA at the future FAIR facility.

In a comparative study, the performance of sub-arrays consisting of large CeF 3 and PbWO 4 crystals has been investigated with high-energy photons below 1 GeV. Energy and time resolutions are determined and compared with the corresponding values for BaF 2 based on the experience of operating the electromagnetic calorimeter Taps .

BaF/sub 2/ has become a very versatile scintillator for particle and photon detection commonly applied in medium and high energy physics experiments. The intrinsic properties allow particle identification via time-of-flight, /spl Delta/E-E and pulse-shape techniques. A new NE102A-BaF/sub 2/ phoswich detector using the standard TAPS crystals has been tested at relativistic energies. The drastically improved particle identification and first results obtained with a large annular forward wall consisting of 120 phoswich modules with 15 mm NE102A attached to the BaF/sub 2/-crystal will be discussed in detail.

The presented paper documents the overall quality of the PWO-II crystals for the PANDA electromagnetic calorimeter focusing in particular on the radiation hardness and the consequences on the operation at T=-25oC. The imposed radiation damage due to γ-rays can be significantly cured applying the process of stimulated recovery, which was observed for the first time for PbWO 4 scintillators. The fast recovery can be achieved even using photons in the infrared region and can be applied to operating detectors parallel to damaging irradiation in case the photo sensor is not sensitive to the external light. The technological application is part of a submitted patent (TM-382-DE).

The PANDA detector will be one of the major experimental installations at the future acceleration facility FAIR at GSI (Darmstadt) for hadron physics studies using a cooled antiproton beam. A new type of the lead tungstate crystals (PWO-II) was developed as the scintillation material for the electromagnetic calorimeter of the target spectrometer of PANDA, which has to provide photon detection in the energy range from 10MeV up to 10GeV with excellent energy resolution operating at high interaction rates. The new PWO-II crystals of improved quality are characterized by light yield of 17–22 photoelectron per MeV of deposited energy and radiation induced absorption coefficient at 420 nm (luminescence maximum) below 1m−1 (integral dose 3krad), both determined at room temperature. The crystals were optimized with respect to light yield and radiation hardness for operation at low temperatures down to T=−25°C. The paper presents studies of the quality parameters of two pre-production lots of 120 and 600 PWO-II full size crystals comprising samples of 11 different shapes for the barrel part of the calorimeter.

The light output of PbWO/sub 4/ crystals, produced at BTCP, has been significantly enhanced by an improved manufacturing technology. First large size crystals of 150 and 200 mm length have been tested assembled in 3/spl times/3 arrays using tagged photons between 64 MeV and 520 MeV energy. The scintillation light has been detected either with commercial photomultiplier tubes or new developed large area silicon avalanche photo diodes of 10/spl times/10 mm/sup 2/ active area. Excellent energy resolutions have been obtained in both cases. For the first time, a timing resolution well below 1 ns has been achieved with diode readout.

A new charged-particle veto detector for the photon spectrometer TAPS has been designed, tested and manufactured. The hexagonal plastic scintillators of 5 mm thickness are read-out via green emitting wavelength-shifting fibers and multi-anode photomultipliers. The concept, the performance of prototypes tested with high energy electrons and cosmic muons and the final design are presented. The limitations of fast and compact multi-anode metal case photomultipliers are discussed in detail.

A microprocessor controlled time measurement system MNSC with eight separate stop channels started in groups of four channels is presented. The system uses integrated ECL counters with built-in gates as first stages counting a 500 MHz clock signal. The further counter stages are built up with STTL and LSTTL. Time intervals up to 20 ms can be measured with a resolution of 2 ns. The result of an experiment is shown where the arrival of a detonation front is measured with MNSC.