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CsI-based scintillators in γ-detection systems
Nuclear Instruments and Methods in Physics Research A294 (1990) 591-594 North-HOlland
591
CsI-BASED SCINTILLATORS IN y-DETEf-nON SYSTEMS A.V. GEKTIN 1 ), A.I. GORELOV and V.G. VASIL'CHENKO 3)
2) ,
V.I. RYKALIN
3),
V.I . SELIVANOV
2)
,
N .V. SHIRAN')
'All-Union Scientific-Research Institute of Single Crystals, Kharkov, USSR " L V. Kurchatov Institute of Atomic Energy, Moscow 123182, USSR 31 Institute for High-Energy Physics, Serpukhov, USSR
Received 12 June 1989 and in revised form 6 February 1990
Scintillation characteristics of a mixed Csl-CsBr crystal have been studied. The crystal luminescence spectrum is 280-340 nm-, the decay time is 11 ns ; the relative light yield is 0.18 of Nal(TI). The parameters of the -y-quantum hodoscope based on Csi-CsBr and hodoscopic PMTs (HPMTs) have been measured. The hodoscope spatial resolution is shown to be 2a = 2.4 mm . A design of a positron emission tomograph ring on the basis of Csl-CsBr and HPMTs is proposed . It is suggested that the Csl-CsBr scintillator may be used in electromagnetic calorimeters at counting rates greater than 10" s- '.
1. 1"Won In nuclear physics, high-energy physics, nuclear tomography and other fields of science and engineering, much interest has recently been taken in scintillators having a short decay time (10-30 ns), high density and high light yield. Such scintillators allow one to detect fluxes of -y-quanta of high intensity, to improve the time resolution of detectors, etc., which significantly extends the scope of their application . Presently, it is known that at room temperature pure CsI crystals show a decay time of 10 ns [1]. However, their light yield amounts only to 0.05-0.08 of Nal(TI). The fast component of the BaF2-scintillator decay has, approximately, the same light yield. The present work deals with the study of basic characteristics of a fast scintillator based on mixed Csl-CsBr crystals and properties of a scintillator-based y-quantum detector .
2. Scintillation mated s b
on CA crysuds
As known, CsI crystal is an effective scintillator at 0 K, o-exciton. radiation is low temperatures . Below 20 observed in the 290 nin region, which quickly attenuates .Above 20 K, luminescence with increasing temperature takes place with A = 338 nm, specified by rT-exciton relaxation. Due to the temperature quenching, there is no exciton luminescence above 150 K [2]. At the same time, it is noted in some papers that, unlike the classical picture, in Csl crystals ultraviolet luminescence can be observed at room temperature, too [3,4]. Ref. [5] indicates that it is promising to use fast scintillators, in 0168-9002/90/$03 .50 (D 1990 - Elsevier Science Publishers
particular, Csl-CsBr crystals, for positron emission tomography purposes. The physical background of the ultraviolet luminescence in mixed Csl-CsBr crystals under excitation of high-current accelerator electrons (350 keV, 10 A/(s m2 ), 5 ns) by a short-time pulse was considered in ref. [6], where it was presumed that luminescence being stable at high temperatures had an excitonlike character. it is natural to assume that in the case of correctness of the hypothesis proposed in ref. [6], the ultraviolet luminescence should also be observed in excitation induced by other types of particles, in particular -y-quant . The samples of the Csl-CsBr scintillators were grown by the Kyropoulos method in an inert gas atmosphere . The scintillator samples consisted for several percent of r.
3. Scintillation pro
rties of Cs I-CsBr crystals
Fig. I (curve 1) presents a stationary luminescence spectrum of the mixed Csl-CsBr crystals in y-excitation 137CS source . The spectrum is composed of a from the number of overiapping bands in the region of 280-3 nrn. it is c_jo-,e_ to that of the "fast" luminescence in excitation by the electron pulse 161 . The measurements of crystal transparency in a broad range of wavelengths
(curve 2, fig. 1) have shown that in the case of a careful treatment of the surface, optical losses in the ultraviolet
range are, practically, the same as those in the visual range where the luminescence of conventional Csl(TI) and Csl(Na) scintillators is observed . The single-electron method with a resolution of 5 ns was employed to measure the decay time of the Csl-CsBr crystals . The
.V . (North-Holland)
A. V. Gektin et aL / CsI-based scintillators
592
---
00
-n too
cslt-csar
xP - 2020 37 Gs, 660 6ceV 0.3
76
goo
so
40
OA
75
2s
0 250
300
350
WVELRSSSm, NM
400
Fig . 1 . (1) Luminescence spectrum of CsI-CsBr crystal under excitation by -y-quanta of a 137CS source; (2) optical trans parency of CsI-CsBr crystal, 75 mm thick ; (3) quantum efficiency of XP-2020 PMT . results are presented in fig. 2. It is clear from the figure that three decay times are observed . 11, 23 and 36 ns . The basic part of the radiation is de-excited with a decay time of 11 ns. The problem of existence of shorter de-excitation components requires further invesïigation. The amplitude spectrum of Csl-CsBr crystal scintillations is given in fig. 3. A 137Cs 1'-source was used . A
r
190 60 80 cw L R crystal scintillations Fig. 3. Amplitude spectrum of CsI-CsBr 137CS source (integration under excitation by -y-quanta of a time is 0.5 ps). o
40
sample of 25 mm in diameter and 22 mm in height was studied . A crystal polished on all the sides was wrapped up in an a'ß uminium foil and mounted on a photocathode of a PMT XP-2020. To achieve the optical contact, petrolatum oil was used. One can see from fig. 3 that the FWHM of the total-absorption peak is 21% . One should note a "slow" decrease of counting on the right-hand slope of the peak. This suggests that the total reflection of light from the crystal cylinder surfaces was not ensured, and hence the collection of light on the PMT photocathode was insufficiently effective. To deter mine the CsI-CsBr scintillation light yield, the amplitude spectrum of Nal(Tl) (30 in diameter and 25 mm in height) packed in a magnesium-oxide 137CS -y-source was meareflector and excited ny the sured . Taking into account the XP-2020 PMT quantum efficiency in the luminescence region of CsI-CsBr and Nal(TI) (curve 3, fig. 1), the relative light yield of the investigated CsI-CsBr crystal turned out to be 0.18 of Nal(Tl) . Owing to the short decay time and high light yield, the examined CsI-CsBr crystal appears to be highly promising for detection of charged particles and -yquanta at intensities higher than 107 s -1, as well as for the use in positron-emission and X-ray tomography . The crystals under consideration are also promising for . . :ati .8 .. .-. :rwáa sna «a.` acd doses, siáscs: :®At 1S lnIao rwá Llu-c detection oil' avic large rcaea the radiationless energy losses are small in solid solu tions based on a common cation . 's is due to the fact that decomposition of primary Frenkel defects is difficult in the chain of subsequen4 collisions in a haloid sublattice [7] . . Gamma Cs1-Cs r
Fig. 2 . Decay-time curve of CsI-CsBr scintillator .
t0
o intillato
on h
o ic P Ts
n
The hodoscopic PMT (l-1PMT) [8] is a position-sensitive photomultiplier having one channel of data read-
A . V. Gektin et al. / CsI-based scintillators
593
collection will, apparently, allow the number of photoelectrons to be more than doubted . Hence, it follows that there is a possibility of improving the hodoscope spatial resolution by more than a factor of 2. The above-obtained results on the spatial resolution of the -y-quantum hodoscope suggest that it is possible to use the CsI-CsBr scintillator and HPMT in positron emission tomography. 5. CsI-CsBr crystals in tomographs
Fig. 4. Design and scheme of data readout from hodoscopes of y-quanta, using HPMT and CsI-CsBr scintillator: ? - HPMT; 2 - scintillation assembly ; 3 - time PMT; 4 - source of -y-quanta ; t - A - time-to-pulse height converter; A - amplitude analyzer ; 6YD - shaper. out, in which the coordinate of the exposure point on the photocathode is determined by the drift time of photoelectrons in the prolonged cathode chamber . The characteristic delay times are about 25-35 ns/cm. So far, to detect relativistic particles in the HPMT-based scintillation hodoscopes, use was made of fast organic scintillators, since the coordinate accuracy of these hodoscopes is determined by the decay time of the scintillator [8] . "Heavy" inorganic scintillators with short decay times allow hodoscopes of y-quanta with a good spatial and time resolution, based on the HPMT, to be developed. Fig. 4 presents the design of such a hodoscope and the electronic measuring scheme. An element of the assembly (2) was made up of CsI-CsBr scintillator plates of 3 x 7 x 22 mm3 in size, isolated from each other by mylar. The -y-quanta from the &"Co -y-source (4) passed through 7 thick scintillator . Both the HPMT-30 and time PMT-87 were used to detect the lcht he'rct The nutmat rzianals from the PMT were fed to low-threshold 6YD shapers [9] operating in the "con stant-fraction" mode. e chosen threshold of 10 mV corresponded to the level of single-photoelectron detection. The experimentally measured time resolution of the hodoscope amounted to 2,r = 6 ns, the corresponding spatial resolution was 2a = 2.4 Presently, there exist several ways of improving the hodoscope spatial resolution . The estimates show that the UV entrance will raise the quantum efficiency of the PMT in the CsI-CsBr luminescence region by more than a factor of 3. Besides, the more complete li t
-b
positron emission
Presently, in the positron emission tomographs (PETs), use is made of bismuth germanatc (BGO) as a scintillator, which has a density of 7.13 g/cd ; Z = 74, the decay time is 300 ns; the light yield is 4.12 of Nal(Tl) ; the length of 9096 absorption of -y-quanta with 511 keV energy is 25 mm. The scheme of the PET design, in which several (up to 16) scintillation plates are viewed by two PMTs, and the plate which has operated is identified on the basis of the amplitude analysis of signals from the pMT, is most widespread. We consider the possibility of constructing a PET ring with the use of HPMT and Csl-CsBr scintillator which has the following characteristics: the density is
Fig. 5. Design of an elenteiéi of the hodoscoppc PMT-based posit£cn emission tornograph : 1 - scintillation assembly ; - light guides to HPMT ; 3 - solid light guide ; 4 - time PMT ; 5 - HPMT ; 6 - source of -y-quanta.
594
A. V. Gektin et al. / CsI-based seintillators
4.51 g/cm3; Z = 54; the decay time is 11 ns; the light yield is 0.18 of Nâl(TI) ; the length of 90% absorption of y-quanta with 511 keV energy is 55 mm. The proposed design of the PET element on the basis of the HPMT and CsI-CsBr crystals is shown in fig . 5. The PET ring of 600 mm in diameter is assembled of twelve separate -y-quantum hodoscopes positioned immediately adjacent to one another . The 45 CsI-CsBr scintillation plates (1) measuring 4 x 15 x 55 mm3 are connected with the light guides (2). The side faces of the scintillation plates are scanned through the light guide (3) by the time PMT (4) with an extended photocathode. The PMT (4) generates start signals, the HPMT (5) stop signals. The electronic circuit of the tomograph element is analogous to that presented in fig . 4. The use of the HPMT reduces the number of PMTs on the PET ring (540 scintillators) to twenty-four. Since the HP1v1T stability amounts to 0.3 mm [8), no calibration system of the PET ring is required . The PET calculation characteristics are as follows : the electronic resolution is 2 mm, the maximal counting rate on the ring is 106 s-1. 6. Condusion The scintillation characteristics of the mixed CslCsBr crystal have been investigated . The fast "heavy" Csl-CsBr scintiliator allows the HPMT-based hodoscopes of 1t-quanta, positron emission tomographs and position detectors of other types to be developed . It seems promising to use the Csi-CsBr scintillator for the production of electromagnetic and, possibly, hadron calorimeters in high-energy physics . Note that in developing new multichannel position-sensitive PMTS [10,11] with a sensitive region measuring 200 x 60 mm~, coordinate resolution of 3 mm and gain of more than 107,
there appears a possibility of designing CsI-CsBr scintillator-based time-of-flight PETs, as well as that of -y-quantum hodoscopes and electromagnetic calorimeters operating under fluxes of more than 107 s- ' . Acknowledgements The authors would like to express their gratitude to S.T. Belyaev, A.A. Vasil'ev and V .P. Martemyanov for their support of the present work, and to A.I. Peresypkin and IN. Sinitsyn for their help in performing the work. References [1] Sh. Kubota, Sh. Sakuragi, S. Hashimoto et al., Nucl. Instr. and Meth. A268 (1988) 275. [2] H. Lamatsch, J. Rossel and E. Saurer, Phys. Status Solidi 48 (1971) 311. [3] L. Morgenstern, Optika i Spectroscopia 8 (1960) 672. [4] A.N. Panova and N.V. Shiran, Single Crystals and Engineering 3 (1970) 86 (AUSRI of SC, Kharkov), in Russian. [5] E. Tanaka, IEEE Trans. Nucl. Sci . NS-34 (1987) 313. [6] V.V. Gavrilov, A.V. Gektin and N.V. Shiran, Scintillation Materials 20 (1987) 22 (AUSRI of SC. Kharkov), in Russian. [7] P.P. Still and D. Pooley, Phys. Status Solidi 32 (1969) 147 . [8] V .G. Vasil'chenko and V.I. Rykalin, Pribory i Tekhn ka Eksperimenta 1 (1987) 7. [9] B.Yu. Baldin, Pribory i Tekhnika Eksperimenta 5 (1980) 137. [10] J.P. Boutot, P. Lavaute, G . Eschard et al., IEEE Trans. Nucl. Sci. NS-34 (1987) 449 . [11] V.G. Vasil'chenko, A .G. Daykovsky, N.V. Milova et al., Preprint IHEP 88-114 (Serpukhov, 1988) .
591
CsI-BASED SCINTILLATORS IN y-DETEf-nON SYSTEMS A.V. GEKTIN 1 ), A.I. GORELOV and V.G. VASIL'CHENKO 3)
2) ,
V.I. RYKALIN
3),
V.I . SELIVANOV
2)
,
N .V. SHIRAN')
'All-Union Scientific-Research Institute of Single Crystals, Kharkov, USSR " L V. Kurchatov Institute of Atomic Energy, Moscow 123182, USSR 31 Institute for High-Energy Physics, Serpukhov, USSR
Received 12 June 1989 and in revised form 6 February 1990
Scintillation characteristics of a mixed Csl-CsBr crystal have been studied. The crystal luminescence spectrum is 280-340 nm-, the decay time is 11 ns ; the relative light yield is 0.18 of Nal(TI). The parameters of the -y-quantum hodoscope based on Csi-CsBr and hodoscopic PMTs (HPMTs) have been measured. The hodoscope spatial resolution is shown to be 2a = 2.4 mm . A design of a positron emission tomograph ring on the basis of Csl-CsBr and HPMTs is proposed . It is suggested that the Csl-CsBr scintillator may be used in electromagnetic calorimeters at counting rates greater than 10" s- '.
1. 1"Won In nuclear physics, high-energy physics, nuclear tomography and other fields of science and engineering, much interest has recently been taken in scintillators having a short decay time (10-30 ns), high density and high light yield. Such scintillators allow one to detect fluxes of -y-quanta of high intensity, to improve the time resolution of detectors, etc., which significantly extends the scope of their application . Presently, it is known that at room temperature pure CsI crystals show a decay time of 10 ns [1]. However, their light yield amounts only to 0.05-0.08 of Nal(TI). The fast component of the BaF2-scintillator decay has, approximately, the same light yield. The present work deals with the study of basic characteristics of a fast scintillator based on mixed Csl-CsBr crystals and properties of a scintillator-based y-quantum detector .
2. Scintillation mated s b
on CA crysuds
As known, CsI crystal is an effective scintillator at 0 K, o-exciton. radiation is low temperatures . Below 20 observed in the 290 nin region, which quickly attenuates .Above 20 K, luminescence with increasing temperature takes place with A = 338 nm, specified by rT-exciton relaxation. Due to the temperature quenching, there is no exciton luminescence above 150 K [2]. At the same time, it is noted in some papers that, unlike the classical picture, in Csl crystals ultraviolet luminescence can be observed at room temperature, too [3,4]. Ref. [5] indicates that it is promising to use fast scintillators, in 0168-9002/90/$03 .50 (D 1990 - Elsevier Science Publishers
particular, Csl-CsBr crystals, for positron emission tomography purposes. The physical background of the ultraviolet luminescence in mixed Csl-CsBr crystals under excitation of high-current accelerator electrons (350 keV, 10 A/(s m2 ), 5 ns) by a short-time pulse was considered in ref. [6], where it was presumed that luminescence being stable at high temperatures had an excitonlike character. it is natural to assume that in the case of correctness of the hypothesis proposed in ref. [6], the ultraviolet luminescence should also be observed in excitation induced by other types of particles, in particular -y-quant . The samples of the Csl-CsBr scintillators were grown by the Kyropoulos method in an inert gas atmosphere . The scintillator samples consisted for several percent of r.
3. Scintillation pro
rties of Cs I-CsBr crystals
Fig. I (curve 1) presents a stationary luminescence spectrum of the mixed Csl-CsBr crystals in y-excitation 137CS source . The spectrum is composed of a from the number of overiapping bands in the region of 280-3 nrn. it is c_jo-,e_ to that of the "fast" luminescence in excitation by the electron pulse 161 . The measurements of crystal transparency in a broad range of wavelengths
(curve 2, fig. 1) have shown that in the case of a careful treatment of the surface, optical losses in the ultraviolet
range are, practically, the same as those in the visual range where the luminescence of conventional Csl(TI) and Csl(Na) scintillators is observed . The single-electron method with a resolution of 5 ns was employed to measure the decay time of the Csl-CsBr crystals . The
.V . (North-Holland)
A. V. Gektin et aL / CsI-based scintillators
592
---
00
-n too
cslt-csar
xP - 2020 37 Gs, 660 6ceV 0.3
76
goo
so
40
OA
75
2s
0 250
300
350
WVELRSSSm, NM
400
Fig . 1 . (1) Luminescence spectrum of CsI-CsBr crystal under excitation by -y-quanta of a 137CS source; (2) optical trans parency of CsI-CsBr crystal, 75 mm thick ; (3) quantum efficiency of XP-2020 PMT . results are presented in fig. 2. It is clear from the figure that three decay times are observed . 11, 23 and 36 ns . The basic part of the radiation is de-excited with a decay time of 11 ns. The problem of existence of shorter de-excitation components requires further invesïigation. The amplitude spectrum of Csl-CsBr crystal scintillations is given in fig. 3. A 137Cs 1'-source was used . A
r
190 60 80 cw L R crystal scintillations Fig. 3. Amplitude spectrum of CsI-CsBr 137CS source (integration under excitation by -y-quanta of a time is 0.5 ps). o
40
sample of 25 mm in diameter and 22 mm in height was studied . A crystal polished on all the sides was wrapped up in an a'ß uminium foil and mounted on a photocathode of a PMT XP-2020. To achieve the optical contact, petrolatum oil was used. One can see from fig. 3 that the FWHM of the total-absorption peak is 21% . One should note a "slow" decrease of counting on the right-hand slope of the peak. This suggests that the total reflection of light from the crystal cylinder surfaces was not ensured, and hence the collection of light on the PMT photocathode was insufficiently effective. To deter mine the CsI-CsBr scintillation light yield, the amplitude spectrum of Nal(Tl) (30 in diameter and 25 mm in height) packed in a magnesium-oxide 137CS -y-source was meareflector and excited ny the sured . Taking into account the XP-2020 PMT quantum efficiency in the luminescence region of CsI-CsBr and Nal(TI) (curve 3, fig. 1), the relative light yield of the investigated CsI-CsBr crystal turned out to be 0.18 of Nal(Tl) . Owing to the short decay time and high light yield, the examined CsI-CsBr crystal appears to be highly promising for detection of charged particles and -yquanta at intensities higher than 107 s -1, as well as for the use in positron-emission and X-ray tomography . The crystals under consideration are also promising for . . :ati .8 .. .-. :rwáa sna «a.` acd doses, siáscs: :®At 1S lnIao rwá Llu-c detection oil' avic large rcaea the radiationless energy losses are small in solid solu tions based on a common cation . 's is due to the fact that decomposition of primary Frenkel defects is difficult in the chain of subsequen4 collisions in a haloid sublattice [7] . . Gamma Cs1-Cs r
Fig. 2 . Decay-time curve of CsI-CsBr scintillator .
t0
o intillato
on h
o ic P Ts
n
The hodoscopic PMT (l-1PMT) [8] is a position-sensitive photomultiplier having one channel of data read-
A . V. Gektin et al. / CsI-based scintillators
593
collection will, apparently, allow the number of photoelectrons to be more than doubted . Hence, it follows that there is a possibility of improving the hodoscope spatial resolution by more than a factor of 2. The above-obtained results on the spatial resolution of the -y-quantum hodoscope suggest that it is possible to use the CsI-CsBr scintillator and HPMT in positron emission tomography. 5. CsI-CsBr crystals in tomographs
Fig. 4. Design and scheme of data readout from hodoscopes of y-quanta, using HPMT and CsI-CsBr scintillator: ? - HPMT; 2 - scintillation assembly ; 3 - time PMT; 4 - source of -y-quanta ; t - A - time-to-pulse height converter; A - amplitude analyzer ; 6YD - shaper. out, in which the coordinate of the exposure point on the photocathode is determined by the drift time of photoelectrons in the prolonged cathode chamber . The characteristic delay times are about 25-35 ns/cm. So far, to detect relativistic particles in the HPMT-based scintillation hodoscopes, use was made of fast organic scintillators, since the coordinate accuracy of these hodoscopes is determined by the decay time of the scintillator [8] . "Heavy" inorganic scintillators with short decay times allow hodoscopes of y-quanta with a good spatial and time resolution, based on the HPMT, to be developed. Fig. 4 presents the design of such a hodoscope and the electronic measuring scheme. An element of the assembly (2) was made up of CsI-CsBr scintillator plates of 3 x 7 x 22 mm3 in size, isolated from each other by mylar. The -y-quanta from the &"Co -y-source (4) passed through 7 thick scintillator . Both the HPMT-30 and time PMT-87 were used to detect the lcht he'rct The nutmat rzianals from the PMT were fed to low-threshold 6YD shapers [9] operating in the "con stant-fraction" mode. e chosen threshold of 10 mV corresponded to the level of single-photoelectron detection. The experimentally measured time resolution of the hodoscope amounted to 2,r = 6 ns, the corresponding spatial resolution was 2a = 2.4 Presently, there exist several ways of improving the hodoscope spatial resolution . The estimates show that the UV entrance will raise the quantum efficiency of the PMT in the CsI-CsBr luminescence region by more than a factor of 3. Besides, the more complete li t
-b
positron emission
Presently, in the positron emission tomographs (PETs), use is made of bismuth germanatc (BGO) as a scintillator, which has a density of 7.13 g/cd ; Z = 74, the decay time is 300 ns; the light yield is 4.12 of Nal(Tl) ; the length of 9096 absorption of -y-quanta with 511 keV energy is 25 mm. The scheme of the PET design, in which several (up to 16) scintillation plates are viewed by two PMTs, and the plate which has operated is identified on the basis of the amplitude analysis of signals from the pMT, is most widespread. We consider the possibility of constructing a PET ring with the use of HPMT and Csl-CsBr scintillator which has the following characteristics: the density is
Fig. 5. Design of an elenteiéi of the hodoscoppc PMT-based posit£cn emission tornograph : 1 - scintillation assembly ; - light guides to HPMT ; 3 - solid light guide ; 4 - time PMT ; 5 - HPMT ; 6 - source of -y-quanta.
594
A. V. Gektin et al. / CsI-based seintillators
4.51 g/cm3; Z = 54; the decay time is 11 ns; the light yield is 0.18 of Nâl(TI) ; the length of 90% absorption of y-quanta with 511 keV energy is 55 mm. The proposed design of the PET element on the basis of the HPMT and CsI-CsBr crystals is shown in fig . 5. The PET ring of 600 mm in diameter is assembled of twelve separate -y-quantum hodoscopes positioned immediately adjacent to one another . The 45 CsI-CsBr scintillation plates (1) measuring 4 x 15 x 55 mm3 are connected with the light guides (2). The side faces of the scintillation plates are scanned through the light guide (3) by the time PMT (4) with an extended photocathode. The PMT (4) generates start signals, the HPMT (5) stop signals. The electronic circuit of the tomograph element is analogous to that presented in fig . 4. The use of the HPMT reduces the number of PMTs on the PET ring (540 scintillators) to twenty-four. Since the HP1v1T stability amounts to 0.3 mm [8), no calibration system of the PET ring is required . The PET calculation characteristics are as follows : the electronic resolution is 2 mm, the maximal counting rate on the ring is 106 s-1. 6. Condusion The scintillation characteristics of the mixed CslCsBr crystal have been investigated . The fast "heavy" Csl-CsBr scintiliator allows the HPMT-based hodoscopes of 1t-quanta, positron emission tomographs and position detectors of other types to be developed . It seems promising to use the Csi-CsBr scintillator for the production of electromagnetic and, possibly, hadron calorimeters in high-energy physics . Note that in developing new multichannel position-sensitive PMTS [10,11] with a sensitive region measuring 200 x 60 mm~, coordinate resolution of 3 mm and gain of more than 107,
there appears a possibility of designing CsI-CsBr scintillator-based time-of-flight PETs, as well as that of -y-quantum hodoscopes and electromagnetic calorimeters operating under fluxes of more than 107 s- ' . Acknowledgements The authors would like to express their gratitude to S.T. Belyaev, A.A. Vasil'ev and V .P. Martemyanov for their support of the present work, and to A.I. Peresypkin and IN. Sinitsyn for their help in performing the work. References [1] Sh. Kubota, Sh. Sakuragi, S. Hashimoto et al., Nucl. Instr. and Meth. A268 (1988) 275. [2] H. Lamatsch, J. Rossel and E. Saurer, Phys. Status Solidi 48 (1971) 311. [3] L. Morgenstern, Optika i Spectroscopia 8 (1960) 672. [4] A.N. Panova and N.V. Shiran, Single Crystals and Engineering 3 (1970) 86 (AUSRI of SC, Kharkov), in Russian. [5] E. Tanaka, IEEE Trans. Nucl. Sci . NS-34 (1987) 313. [6] V.V. Gavrilov, A.V. Gektin and N.V. Shiran, Scintillation Materials 20 (1987) 22 (AUSRI of SC. Kharkov), in Russian. [7] P.P. Still and D. Pooley, Phys. Status Solidi 32 (1969) 147 . [8] V .G. Vasil'chenko and V.I. Rykalin, Pribory i Tekhn ka Eksperimenta 1 (1987) 7. [9] B.Yu. Baldin, Pribory i Tekhnika Eksperimenta 5 (1980) 137. [10] J.P. Boutot, P. Lavaute, G . Eschard et al., IEEE Trans. Nucl. Sci. NS-34 (1987) 449 . [11] V.G. Vasil'chenko, A .G. Daykovsky, N.V. Milova et al., Preprint IHEP 88-114 (Serpukhov, 1988) .