Search

Changes in the transparency of lead tungstate crystals under continuous ∼1200-h irradiation with γ rays of a radionuclide 60Co source were investigated. The crystal temperature was maintained at a level of −15°C at a dose rate of 0.1 Gy/h. The crystal transparency recovery process was investigated after the irradiation at temperatures varying from −15 to +38°C. The study was performed while preparing for the PANDA experiment in the FAIR project in Germany.

The momentum dispersion of the proton beam extracted from the vacuum chamber of the U-70 accelerator by channeling was measured for the first time. At an 80-mrad bending angle of the Si single crystal, the following beam parameters were attained: an intensity of 107 protons/s for 1012 protons/s hitting the crystal, momentum dispersion of the beam Δp/p = 0.13%, and a background particle admixture of 0.03% or less.

The radiation hardness of a test batch of lead tungstate crystals grown by a new technology at the Bogoroditsk Technochemical Plant for the PANDA experiment has been measured. The optical properties of the crystals have been investigated at temperatures ranging from +20 to −20°C under irradiation with a 137Cs radionuclide source. The light yield in the crystal is seen to considerably increase with a decrease in its temperature. In addition, the loss of the crystal transparency under irradiation at low temperatures is higher than under irradiation at room temperature. As a result, at a fixed dose rate, the signal from the crystal at a negative temperature may be considerably greater than the signal at room temperature even if the accumulated dose is high.

A highly stable monitoring system based on blue and red light emitting diodes coupled to a distribution network comprised of optical fibers has been developed for an electromagnetic calorimeter that uses lead tungstate crystals readout with photomultiplier tubes. We report of the system prototype design and on the results of laboratory tests. Stability better than 0.1% (r.m.s.) has been achieved during one week of prototype operation., 10 pages, 6 figures, LaTeX2e

We employed two independent methods to study possible damage to the scintillation mechanism in lead tungstate crystals due to irradiation by a 34 V pion beam. Firstly 10 crystals were irradiated simultaneously over 30 h by a narrow beam, so that only a small region of each crystal was affected. We studied the effect of the irradiation on the light output non-uniformity. If a localized degradation was observed, it would indicate damage to the scintillation mechanism. Secondly, we detected light output using two phototubes attached to the sides of a crystal. Since these phototubes detect scintillation light only from a small localized region, the effect of transmission loss should be minimal. We did not see any statistically significant evidence for scintillation mechanism damage with either method. The effect is consistent with zero, and the upper limit is 0.5% at 95% C.L.

We report on the performance of a monitoring system for a prototype calorimeter for the BTeV experiment that uses Lead Tungstate crystals coupled with photomultiplier tubes. The tests were carried out at the 70 GeV accelerator complex at Protvino, Russia., Comment: 12 pages, 8 figures, LaTeX2e, revised version

The electromagnetic calorimeter of PANDA at the FAIR facility will rely on an operation of lead tungstate (PWO) scintillation crystals at temperatures near -25 deg.C to provide sufficient resolution for photons in the energy range from 8 GeV down to 10 MeV. Radiation hardness of PWO crystals was studied at the IHEP (Protvino) irradiation facility in the temperature range from room temperature down to -25 deg.C. These studies have indicated a significantly different behaviour in the time evolution of the damaging processes well below room temperature. Different signal loss levels at the same dose rate, but at different temperatures were observed. The effect of a deep suppression of the crystal recovery process at temperatures below 0 deg.C has been seen., Comment: 10 pages 7 figures

Radiation damage in lead tungstate crystals reduces their transparency. The calibration that relates the amount of light detected in such crystals to incident energy of photons or electrons is of paramount importance to maintaining the energy resolution the detection system. We report on tests of lead tungstate crystals, read out by photomultiplier tubes, exposed to irradiation by monoenergetic electron or pion beams. The beam electrons themselves were used to measure the scintillation light output, and a blue light emitting diode (LED) was used to track variations of crystals transparency. We report on the correlation of the LED measurement with radiation damage by the beams and also show that it can accurately monitor the crystals recovery from such damage., Comment: 9 pages, 6 figures, LaTeX2e

Studies of the radiation hardness of lead tungstate crystals produced by the Bogoroditsk Techno-Chemical Plant in Russia and the Shanghai Institute of Ceramics in China have been carried out at IHEP, Protvino. The crystals were irradiated by a 40-GeV pion beam. After full recovery, the same crystals were irradiated using a $^{137}Cs$ $\gamma$-ray source. The dose rate profiles along the crystal length were observed to be quite similar. We compare the effects of the two types of radiation on the crystals light output., Comment: 10 pages, 8 figures, Latex 2e, 28.04.04 - minor grammatical changes