Pergamon Radiation Measurements, Vol. 24, No. 4, pp. 375-377, 1995 Copyright © 1995Elsevier ScienceLtd Printed in Great Britain. All rights reserved 1350-4487/95 $9.50+ 0.00 1350-4487(95)00271-5 FAST HEAVY SCINTILLATORS ON THE BASIS OF TUNGSTATE SINGLE CRYSTALS L. L. NAGORNAYA, V. D. RYZHIKOV, U. YA. VOSTRETSOV, I. A. TUPITSINA, S. F. BURACHAS, W. P. MARTYNOV and K. A. KATRUNOV Institute for Single Crystals, Ukrainian Academy of Sciences, Lenin Ave., 60, Kharkov, 310001, Ukraine (Received 27 September 1994; in finalJorm 10 April 1995) Abstract--New very promising heavy fast PbWO4 crystals as radiators for dense high resolution photon calorimeters were studied in this paper. Radiation detector parameters obtained with the real-size calorimeter ceils are presented. It was shown that owing to high density and transparency, quick response (~4 ns), high radiation stability (about 10 mrad) with energy resolution ~ 1% at an energy above 1 GeV, the PbWOa-based scintillators are a most advantageous candidate for the creation of total absorption compact detectors of EM calorimeters. 1. INTRODUCTION Research into a new generation of dense fast and radiation stable scintillators has become very active over the last few years due to an increasing demand for high resolution EM calorimetry. At present a number of scintillators are proposed for this purpose: BGO, GSO(Ce), barium and cerium fluorides, in particular, etc. However, these crystals possess a number of disadvantages. The long luminescence time of BGO and the large radiation length of BaF2 and CeF 3 prevent these from being used for the creation of compact total absorption detectors uti- lized for the study of high energy flows of electrons and gamma quanta. In this respect some heavy tungstate single crystals (MeWO4) seem to be most appropriate. Among them PbWO4 (PWO) is the most promising. Its character- istics as a EM calorimeter are excellent: x0 = 0.87 cm, R m= 2.2cm, d = 8.2g/cm 3. In addition, they are characterized by a short decay time of luminescence (85% for 4 ns). Presented here are the results of the study of growth conditions and properties of large, optically homogeneous, spectrometric PbWO4 single crystals. 2. EXPERIMENTAL For the first time large, highly transparent and optically homogeneous scintillators based on PWO single crystals were obtained by us (Nagornaya and Ryzhikov, 1993). We continued the development of the technological process for the growth of highly transparent and optically homogeneous crystals. They were grown by the Czochralski method using platinum crucibles and in an oxygen-containing atmosphere with high frequency heating. For the automatic control of the crystal diameter a system based on a balance device with computer control of the growth parameters was used. The initial powder of the stoichiometric or preset composition was pre- pared by a high temperature solid phase synthesis of the powdered lead and tungsten oxides (of 99.995% purity). By the said method a series of PWO crystals, 40 mm in diameter and 200-250 mm long were grown. Radiation detectors (20 x 20 x 150- 250mm 3 and 20 x 20 x 5-40mm 3) and samples (10x 10 x 10ram 3) for measuring the absorption and luminescence spectra were made from these crystals. Rectangular blanks, cut from the ingots were polished to the optical grade over the whole surface. The transmission spectra were measured on the spec- trophotometer Hitachi-330, and the luminescence ones were measured on a KSVU-23 (manufactured by St Petersburg Optical-Mechanical Factory). 3. RESULTS 3,1. Optical luminescence characteristics The transmission and emission spectra of PWO single crystals of different impurity and stoichio- metric composition (T= 5, 300K) are shown in Figs 1-3. The emission spectrum of PWO (with composition close to a stoichiometric one) has the form of a wide nonelementary band with the emission maximum at 430-435 nm. With the increase of the lead oxide content in the crystal a displacement of the main maximum is observed. Alongside the main band, a wide band with a maximum at 640nm appears. It was found that when growing crystals from a repeat melt in the oxygen-containing atmos- phere a redistribution of the luminescence band intensity in favour of the green one was observed. The 375