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Time resolution of a large area planar spark counter
Nuclear Instruments and Methods in Physics Research A263 (1988) 381-386 North-Holland, Amsterdam
381
TIME RESOLUTION OF A LARGE AREA PLANAR SPARK COUNTER Noboru FUJIWARA, Naoko IIDA and Seishi NOGUCHI Department of Physics, Nara Women's University, Kita-Uoya Nishi-machi, Nara, 630, Japan
Ryuhei SUGAHARA, Tsuyoshi SUWADA, Taro OHAMA and Kasuke TAKAHASHI
National Laboratory for High Energy Physics, Oho-machi. Tsukuba-gun, Ibaragi, 305, Japan
Received 7 May 1987 and in revised form 17 August 1987 A planar spark counter of size 1 .0 m x 0.1 m has been developed and tested . The constituent elements are a semiconductive glass anode and a window float-cast glass cathode coated by vacuum-deposited copper. The distance between electrodes is 200 Wm . A single counter time resolution of 61 ps was achieved with cosmic rays . 1. Introduction For most investigations of the final states in high energy experiments the identification of the outgoing particles is highly desirable over the whole momentum range . For high momenta, aerogel and the Cherenkov counter can be used, whereas in the low momentum region energy deposition measurements (dE/dx) of the particles together with the measured momentum are available. In the momentum region between 800 MeV/c and 2.0 GeV/c a measurement of the time of flight (TOF) of the particles can play an important role. Planar spark counters (PSCs) are detecting devices designed mainly for a very good time resolution . A time resolution of about 50 ps has been obtained with a small area (100-200 cm2) PSC [1-6]. However, the construction of a large area PSC with fine time resolution must solve some problems : (1) The effect of the transmission properties of the counter on the time resolution . (2) Manufacturing turned out to be difficult, especially to prepare a high quality cathode. The first problem was simulated using an inner spark pulser and an electric design for a large area PSC was presented with electrical properties as revealed [7]. Essentially, it was presented that a large area PSC should be designed as a transmission line . Regarding the second problem, it was tried to make a large area metallic cathode by gluing a thin copper foil onto a window float-cast glass and polishing it with fine alumina powder . By this technique a time resolution of about 100 ps was achieved [8]. This is the best time resolution for a large area PSC already developed but the resolution was about twice that of the small area PSC. Another method is to use window float-cast glass cathodes of 0168-9002/88/$03 .50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
arbitrary size coated by vacuum-deposited metal and joint them as a cathode plate. In the following, we describe the counter design of a large area PSC using a semiconductive glass as an anode and window float-cast glasses as cathodes coated by vacuum-deposited copper and chromium, details of construction and operation, the setup of the experiment and the results of our measurements with cosmic rays .
2. Counter design and construction The basic parts of the spark counter (fig . 1) were two parallel planar electrodes at high voltage separated by gas. The size of electrodes was 10 x 100 cm2. The width of the space gap, - 200 Am, was set by indium-plated copper washers between the electrodes . A 3 mm thick semiconductive glass made by Ohara Ltd. was used as the anode. The volume resistivity of the anode was 3 x 10 1° 0 cm . On the outer surface of the anode, eight copper strip lines as signal transmission lines were attached with conductive glue . The width of the strips was 8 mm and the gap between strips was 4 mm . The cathode plate was made of two 10 x 51 cm2 window float-cast glasses coated by vacuum-deposited copper and chromium. A chromium layer of 0.2 Am thickness under the copper layer of 4 Am thickness provided better adherence of the copper to the glass. Moreover, the copper layer was covered with a chromium layer of 1 Ant thickness and electron emissions from the surface of the cathode were suppressed to some extent in comparison with copper. Two pieces of cathode plate were jointed with indium as shown in fig. 2.
382
N. Fujiwara et al. / Time resolution of a large area planar spark counter Socket
Inner Chamber
Hi-K
100 cm
ivvaiiauaiuiuniiii wouua umiurn-rriiauiiifiuuuauiiiiiioiiannuiini ~a~aaar
Signal Pin
Anode (Semiconductor Glass)
Pressure Vessel
Gap Cathode (High Voltage)
Pressure Vessel
r- Inner Chamber
10 cm
riiairiic hail oiiiiiiiariirniiiniinadibiirrir in' i ® lMEM I 111 Rubber
Strip Line
Cathode Gap Spacer
Anode (Semiconductive Grass) Fig. 1. Structure of a planar spark counter (PSC).
L Cathode 2 Cathode 1 Fig. 2. Structure of cathode jointed with indium .
The assembly was carried out in a clean bench according to the following order. First the spacer washers of 3 mm in diameter were cleaned with an ultrasonic cleaner. Daiflon S3, a solvent of Daikin Co ., and acetone were used as a solvent. These spacer washers were dipped in 5% diluted chloric acid, rinsed with ethanol one by one and placed on the top of teflon pins aligned on a fixing table. The distances between spacer washers were all 5.0 cm, to suppress a sag of the electrodes within 2 pm at a high voltage of 6 kV . Secondly the semiconductive glass anode was cleaned with acetone and polished slightly with fine-grain cerium oxide. Finally, this anode glass was rinsed with pure water and dried. The anode glass was placed over the spacer washer on the teflon pins on the fixing table. A weight of 40 kg was placed on the anode glass (1 .0 kg for each spacer) for about an hour . Two cathode glasses were cleaned one by one in the same way as the anode. The anode glass with spacer washers was turned upside down and placed on the fixing table. An indium strip of 0.03 x 0.5 x 10 cm3 was placed on the surface of the
N. Fujiwara et al. / Time resolution
gap side of the anode, corresponding to the junction position of the two cathode plates as shown in fig. 2. Two cathodes were set on the spacer washers and the indium strip, along guide pins on the fixing table. This set was brought into an inner vessel made of plastic. The anode and the cathode were fixed by screws on the vessel as shown in fig. 1. The inner vessel was set into the pressure vessel for final assembly. 3. Gas circulation and initial operation The counter was set in a gas circulation system. The mixing ratio of argon was 80% and the balance was a quencher. The component and the mixing ratio of the gas are listed in table 1 . The gas pressure was 10 atm, leading to about 10 primary ion pairs released by a minimum ionizing particle. Under this condition, the counter efficiency was very close to 100% [8]. The gas flow rate was 10 cm/s through the spark gap. Table 1 Gas component for the PSC Gas
Argon Isobutane Ethylene 1, 3 Butadiene Hydrogen
Mixing ratio [%] 80 10 2 2 6
of a
large area planar spark counter
383
Using four 100 PCi'Co sources, the virgin counter was operated just above the threshold voltage. Over a period of about one week the operating voltage was gradually raised . The counting rate with 'Co sources was monitored during the initial operation (burn-in) period and was kept not to exceed 2 Hz/cm2. By this initial operation, the counter was stabilized [8]. 4. Experimental setup and data analysis The experimental setup and the block diagram for the data acquisition system are shown in fig. 3. A coincidence of the scintillation counters Sl and S2 defined a cosmic ray trigger . The counters Sl, 3 .2 cm thick, and S2, 0.5 cm thick, had areas of 4 .8 x 8.5 cm' and 10 .0 x 10 .0 cm2, respectively . The S1 counter had been made specially as a timing counter and the signal from the counter was used as a start signal for a TDC. The timing resolution of the Sl counter was 60 ps after correction by the pulse amplitude from the Sl . Signals were picked up from both ends, A and B, of Sl and the strip lines of the PSC. The signals were time and pulse height analyzed . The electronics used in this experiment were commercially available NIM and CAMAC units. Data from the TDC and ADC modules were analyzed by a DEC P.-PDP-11 microcomputer. The TOF of a cosmic ray between Sl and the PSC was defined as follows:
Cosmic Rays S1
Gate Fig. 3. Experimental setup and block diagram for the data acquisition system.
384
N. Fujiwara et al. / Time resolution of a large area planar spark counter
20
m
F z
w
10
N 0
0
100
r.
200
300
400
500
ADC(Q) Fig. 4. Typical pulse height spectrum at a applied voltage of 6.0 kV for cosmic ray triggers. 5 4
w
2
0 ADC (Q)
POSITION
5' PSC
4 3 2
~~nal!!iloln .
0 POSITION ADC (Q) Fig. 5. Dependence of TOF` defined in the text on (a) the pulse height of the plastic scintillator Sl, (b) the pulse height of the PSC, (c) the position of a cosmic ray trajectory in the Sl and (d) the position on the strip line of the PSC.
N. Fujiwara et al. / Time resolution
where to and tB are TDC values for the signal from the end A and B respectively, and the superscript i stands for the strip line number . A cosmic ray induced the signal on the plural strip lines of the PSC. Comparing the pulse height in neighboring strips, the strip line number i stands for the strip line which gives maximum pulse height . Two kinds of correction were made on TOF' defined above to obtain the time resolution of the PSC. The first was the correction (AT),, for the pulse height dependence of the measured time using a discriminator of the leading edge type. The pulse height dependence of (AT),, was assumed to be: ( 4 T)PH -
C, Q_C2
where Q is the pulse height of the signal from the scintillator S1 or the PSC . Actually, the correction for the PSC was almost negligible . The second was the correction for a difference of flight path of a cosmic ray trajectory. This difference was approximately corrected using the position of the particle's trajectory along the line AB of S1 and the PSC . The direction AB of S1 was perpendicular to the direction AB of the PSC and the TOFs were corrected for Sl and the PSC independently . The position dependence of the correction (4T)Pos was assumed to be: (AT) Pos = C(X - C4) 2,
of a
large area planar spark counter
where X is the position along the line AB of S1 or the PSC and defined as: X=t,4 -t a. The correction parameters C,, C2, C and C4 for each counter were determined so as to minimize the pulse height dependence and the position dependence of the TOF . 5. Results The threshold voltage of the PSC was about 3.4 kV at a gas pressure of 10 atm. The following results were obtained at a gas pressure of 10 atm and an operational voltage of 6.0 kV using cosmic rays. Fig. 4 shows the typical pulse height spectrum for the PSC. The average integrated charge induced on the strip line was calculated to be about 3000 pC, and each spark discharges an area of about 40 mmz, i.e. about 7 mm in diameter . Fig. 5 shows the scatter plots for the dependence of TOF' defined in section 4 on (a) the pulse height of S1, (b) the pulse height of the PSC, (c) the position of a cosmic ray trajectory in S1 and (d) the position of the strip line on the PSC respectively. In the figures, for example (b), the dependences of TOP on the parameters except the pulse height of the PSC were already corrected to show explicitly the dependence on the pulse height of the PSC . The PSC pulse height depen-
100
SIGMA(TOTAL) = 85 ± 4 ps SIGMA(PSC) = 61 ± 4 ps
0
Fig. 6.
38 5
TOF (ns) Distribution of TOFs at an applied voltage of 6.0
kV
for cosmic ray triggers.
386
N. Fujiwara et al. / Time resolution of a large area planar spark counter
dence of TOF' was very small in comparison with the S1 pulse height dependence . This means that the rise time of the PSC pulse was exceedingly rapid in comparison with the rise time for the plastic scintillator . The rise time of the pulse for the PSC was obtained from the scatter plot and was about 250 ps . The correction for the difference of flight path of a cosmic ray was a small correction and within 100 ps . The distribution of TOFs which were corrected as described above is shown in fig. 6. The time resolution was obtained by fitting with a Gaussian curve. The width of the observed distribution was the combined resolution of the S1 and the PSC and was 85 ± 4 ps. Taking into account the time resolution of 60 ps for S1, a time resolution of 61 ± 4 ps was obtained for the PSC. 6. Conclusion For the large area PSC designed as a transmission line, almost the same time resolution of 61 ± 4 ps as for the small area PSC was achieved using two float-cast glasses coated by vacuum-deposited copper and chromium, and jointed with indium as a cathode. (1) The electrical design as a transmission line gives a size-independent time resolution. (2) High quality cathodes of large area are prepared by the joint method using economic size cathodes. A realistic size PSC will be available to separate pions and kaons up to 2.5 GeV/c. During this experiment the counter was operated for
about 190 h, accumulating about 540 sparks/cm2. The life time of the counter is a subject for further investigation . Acknowledgements The authors are indebted to director T. Nishikawa of National Laboratory for High Energy Physics for financial support of this R&D work. We wish to acknowledge the assistance of students of Nara Women's University. This work was supported by a Grand-in-Aid for Fundamental Scientific Research of the Ministry of Education. References [1] Yu .N . Pestov and G.V. Fedotovich, SLAC Trans. 184
(1978) . [2] I.B . Vasserman et al ., SLAC Trans. 196 (1981). [3] V.D . Laptev, Yu. N. Pestov and N .V. Petrovykh, UDC 539.1 .074.27 (1975) p . 1698 . [4] A.D . Afanas'ev, V.D . Laptev, Yu .N . Pestov and B.P. Sannikov, UDC 539 . 1 .074.27 (1975) p . 1701 . [5] V.D . Laptev and Yu .N . Pestov, UDC 539 .1 .074 .27 (1975) p . 1703 . [6] W.B. Atwood, G.B . Bowden, G.R. Bonneaud, D.E . Klem, A. Ogawa, Yu . N. Pestov, R. Pitthan and R. Sugahara, Nucl . Instr. and Meth . 206 (1983) 99. [71 N . Fujiwara, A. Ogawa, Yu .N . Pestov and R. Sugahara, Nucl . Instr. and Meth . A240 (1985) 275 . [81 A. Ogawa, W.B . Atwood, N. Fujiwara, Yu.N . Pestov and R. Sugahara, Proc. IEEE 1983 Nss, San Francisco (1983) IEEE Trans. Nucl . Sci . NS-31 (1984) 121 .
381
TIME RESOLUTION OF A LARGE AREA PLANAR SPARK COUNTER Noboru FUJIWARA, Naoko IIDA and Seishi NOGUCHI Department of Physics, Nara Women's University, Kita-Uoya Nishi-machi, Nara, 630, Japan
Ryuhei SUGAHARA, Tsuyoshi SUWADA, Taro OHAMA and Kasuke TAKAHASHI
National Laboratory for High Energy Physics, Oho-machi. Tsukuba-gun, Ibaragi, 305, Japan
Received 7 May 1987 and in revised form 17 August 1987 A planar spark counter of size 1 .0 m x 0.1 m has been developed and tested . The constituent elements are a semiconductive glass anode and a window float-cast glass cathode coated by vacuum-deposited copper. The distance between electrodes is 200 Wm . A single counter time resolution of 61 ps was achieved with cosmic rays . 1. Introduction For most investigations of the final states in high energy experiments the identification of the outgoing particles is highly desirable over the whole momentum range . For high momenta, aerogel and the Cherenkov counter can be used, whereas in the low momentum region energy deposition measurements (dE/dx) of the particles together with the measured momentum are available. In the momentum region between 800 MeV/c and 2.0 GeV/c a measurement of the time of flight (TOF) of the particles can play an important role. Planar spark counters (PSCs) are detecting devices designed mainly for a very good time resolution . A time resolution of about 50 ps has been obtained with a small area (100-200 cm2) PSC [1-6]. However, the construction of a large area PSC with fine time resolution must solve some problems : (1) The effect of the transmission properties of the counter on the time resolution . (2) Manufacturing turned out to be difficult, especially to prepare a high quality cathode. The first problem was simulated using an inner spark pulser and an electric design for a large area PSC was presented with electrical properties as revealed [7]. Essentially, it was presented that a large area PSC should be designed as a transmission line . Regarding the second problem, it was tried to make a large area metallic cathode by gluing a thin copper foil onto a window float-cast glass and polishing it with fine alumina powder . By this technique a time resolution of about 100 ps was achieved [8]. This is the best time resolution for a large area PSC already developed but the resolution was about twice that of the small area PSC. Another method is to use window float-cast glass cathodes of 0168-9002/88/$03 .50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
arbitrary size coated by vacuum-deposited metal and joint them as a cathode plate. In the following, we describe the counter design of a large area PSC using a semiconductive glass as an anode and window float-cast glasses as cathodes coated by vacuum-deposited copper and chromium, details of construction and operation, the setup of the experiment and the results of our measurements with cosmic rays .
2. Counter design and construction The basic parts of the spark counter (fig . 1) were two parallel planar electrodes at high voltage separated by gas. The size of electrodes was 10 x 100 cm2. The width of the space gap, - 200 Am, was set by indium-plated copper washers between the electrodes . A 3 mm thick semiconductive glass made by Ohara Ltd. was used as the anode. The volume resistivity of the anode was 3 x 10 1° 0 cm . On the outer surface of the anode, eight copper strip lines as signal transmission lines were attached with conductive glue . The width of the strips was 8 mm and the gap between strips was 4 mm . The cathode plate was made of two 10 x 51 cm2 window float-cast glasses coated by vacuum-deposited copper and chromium. A chromium layer of 0.2 Am thickness under the copper layer of 4 Am thickness provided better adherence of the copper to the glass. Moreover, the copper layer was covered with a chromium layer of 1 Ant thickness and electron emissions from the surface of the cathode were suppressed to some extent in comparison with copper. Two pieces of cathode plate were jointed with indium as shown in fig. 2.
382
N. Fujiwara et al. / Time resolution of a large area planar spark counter Socket
Inner Chamber
Hi-K
100 cm
ivvaiiauaiuiuniiii wouua umiurn-rriiauiiifiuuuauiiiiiioiiannuiini ~a~aaar
Signal Pin
Anode (Semiconductor Glass)
Pressure Vessel
Gap Cathode (High Voltage)
Pressure Vessel
r- Inner Chamber
10 cm
riiairiic hail oiiiiiiiariirniiiniinadibiirrir in' i ® lMEM I 111 Rubber
Strip Line
Cathode Gap Spacer
Anode (Semiconductive Grass) Fig. 1. Structure of a planar spark counter (PSC).
L Cathode 2 Cathode 1 Fig. 2. Structure of cathode jointed with indium .
The assembly was carried out in a clean bench according to the following order. First the spacer washers of 3 mm in diameter were cleaned with an ultrasonic cleaner. Daiflon S3, a solvent of Daikin Co ., and acetone were used as a solvent. These spacer washers were dipped in 5% diluted chloric acid, rinsed with ethanol one by one and placed on the top of teflon pins aligned on a fixing table. The distances between spacer washers were all 5.0 cm, to suppress a sag of the electrodes within 2 pm at a high voltage of 6 kV . Secondly the semiconductive glass anode was cleaned with acetone and polished slightly with fine-grain cerium oxide. Finally, this anode glass was rinsed with pure water and dried. The anode glass was placed over the spacer washer on the teflon pins on the fixing table. A weight of 40 kg was placed on the anode glass (1 .0 kg for each spacer) for about an hour . Two cathode glasses were cleaned one by one in the same way as the anode. The anode glass with spacer washers was turned upside down and placed on the fixing table. An indium strip of 0.03 x 0.5 x 10 cm3 was placed on the surface of the
N. Fujiwara et al. / Time resolution
gap side of the anode, corresponding to the junction position of the two cathode plates as shown in fig. 2. Two cathodes were set on the spacer washers and the indium strip, along guide pins on the fixing table. This set was brought into an inner vessel made of plastic. The anode and the cathode were fixed by screws on the vessel as shown in fig. 1. The inner vessel was set into the pressure vessel for final assembly. 3. Gas circulation and initial operation The counter was set in a gas circulation system. The mixing ratio of argon was 80% and the balance was a quencher. The component and the mixing ratio of the gas are listed in table 1 . The gas pressure was 10 atm, leading to about 10 primary ion pairs released by a minimum ionizing particle. Under this condition, the counter efficiency was very close to 100% [8]. The gas flow rate was 10 cm/s through the spark gap. Table 1 Gas component for the PSC Gas
Argon Isobutane Ethylene 1, 3 Butadiene Hydrogen
Mixing ratio [%] 80 10 2 2 6
of a
large area planar spark counter
383
Using four 100 PCi'Co sources, the virgin counter was operated just above the threshold voltage. Over a period of about one week the operating voltage was gradually raised . The counting rate with 'Co sources was monitored during the initial operation (burn-in) period and was kept not to exceed 2 Hz/cm2. By this initial operation, the counter was stabilized [8]. 4. Experimental setup and data analysis The experimental setup and the block diagram for the data acquisition system are shown in fig. 3. A coincidence of the scintillation counters Sl and S2 defined a cosmic ray trigger . The counters Sl, 3 .2 cm thick, and S2, 0.5 cm thick, had areas of 4 .8 x 8.5 cm' and 10 .0 x 10 .0 cm2, respectively . The S1 counter had been made specially as a timing counter and the signal from the counter was used as a start signal for a TDC. The timing resolution of the Sl counter was 60 ps after correction by the pulse amplitude from the Sl . Signals were picked up from both ends, A and B, of Sl and the strip lines of the PSC. The signals were time and pulse height analyzed . The electronics used in this experiment were commercially available NIM and CAMAC units. Data from the TDC and ADC modules were analyzed by a DEC P.-PDP-11 microcomputer. The TOF of a cosmic ray between Sl and the PSC was defined as follows:
Cosmic Rays S1
Gate Fig. 3. Experimental setup and block diagram for the data acquisition system.
384
N. Fujiwara et al. / Time resolution of a large area planar spark counter
20
m
F z
w
10
N 0
0
100
r.
200
300
400
500
ADC(Q) Fig. 4. Typical pulse height spectrum at a applied voltage of 6.0 kV for cosmic ray triggers. 5 4
w
2
0 ADC (Q)
POSITION
5' PSC
4 3 2
~~nal!!iloln .
0 POSITION ADC (Q) Fig. 5. Dependence of TOF` defined in the text on (a) the pulse height of the plastic scintillator Sl, (b) the pulse height of the PSC, (c) the position of a cosmic ray trajectory in the Sl and (d) the position on the strip line of the PSC.
N. Fujiwara et al. / Time resolution
where to and tB are TDC values for the signal from the end A and B respectively, and the superscript i stands for the strip line number . A cosmic ray induced the signal on the plural strip lines of the PSC. Comparing the pulse height in neighboring strips, the strip line number i stands for the strip line which gives maximum pulse height . Two kinds of correction were made on TOF' defined above to obtain the time resolution of the PSC. The first was the correction (AT),, for the pulse height dependence of the measured time using a discriminator of the leading edge type. The pulse height dependence of (AT),, was assumed to be: ( 4 T)PH -
C, Q_C2
where Q is the pulse height of the signal from the scintillator S1 or the PSC . Actually, the correction for the PSC was almost negligible . The second was the correction for a difference of flight path of a cosmic ray trajectory. This difference was approximately corrected using the position of the particle's trajectory along the line AB of S1 and the PSC . The direction AB of S1 was perpendicular to the direction AB of the PSC and the TOFs were corrected for Sl and the PSC independently . The position dependence of the correction (4T)Pos was assumed to be: (AT) Pos = C(X - C4) 2,
of a
large area planar spark counter
where X is the position along the line AB of S1 or the PSC and defined as: X=t,4 -t a. The correction parameters C,, C2, C and C4 for each counter were determined so as to minimize the pulse height dependence and the position dependence of the TOF . 5. Results The threshold voltage of the PSC was about 3.4 kV at a gas pressure of 10 atm. The following results were obtained at a gas pressure of 10 atm and an operational voltage of 6.0 kV using cosmic rays. Fig. 4 shows the typical pulse height spectrum for the PSC. The average integrated charge induced on the strip line was calculated to be about 3000 pC, and each spark discharges an area of about 40 mmz, i.e. about 7 mm in diameter . Fig. 5 shows the scatter plots for the dependence of TOF' defined in section 4 on (a) the pulse height of S1, (b) the pulse height of the PSC, (c) the position of a cosmic ray trajectory in S1 and (d) the position of the strip line on the PSC respectively. In the figures, for example (b), the dependences of TOP on the parameters except the pulse height of the PSC were already corrected to show explicitly the dependence on the pulse height of the PSC . The PSC pulse height depen-
100
SIGMA(TOTAL) = 85 ± 4 ps SIGMA(PSC) = 61 ± 4 ps
0
Fig. 6.
38 5
TOF (ns) Distribution of TOFs at an applied voltage of 6.0
kV
for cosmic ray triggers.
386
N. Fujiwara et al. / Time resolution of a large area planar spark counter
dence of TOF' was very small in comparison with the S1 pulse height dependence . This means that the rise time of the PSC pulse was exceedingly rapid in comparison with the rise time for the plastic scintillator . The rise time of the pulse for the PSC was obtained from the scatter plot and was about 250 ps . The correction for the difference of flight path of a cosmic ray was a small correction and within 100 ps . The distribution of TOFs which were corrected as described above is shown in fig. 6. The time resolution was obtained by fitting with a Gaussian curve. The width of the observed distribution was the combined resolution of the S1 and the PSC and was 85 ± 4 ps. Taking into account the time resolution of 60 ps for S1, a time resolution of 61 ± 4 ps was obtained for the PSC. 6. Conclusion For the large area PSC designed as a transmission line, almost the same time resolution of 61 ± 4 ps as for the small area PSC was achieved using two float-cast glasses coated by vacuum-deposited copper and chromium, and jointed with indium as a cathode. (1) The electrical design as a transmission line gives a size-independent time resolution. (2) High quality cathodes of large area are prepared by the joint method using economic size cathodes. A realistic size PSC will be available to separate pions and kaons up to 2.5 GeV/c. During this experiment the counter was operated for
about 190 h, accumulating about 540 sparks/cm2. The life time of the counter is a subject for further investigation . Acknowledgements The authors are indebted to director T. Nishikawa of National Laboratory for High Energy Physics for financial support of this R&D work. We wish to acknowledge the assistance of students of Nara Women's University. This work was supported by a Grand-in-Aid for Fundamental Scientific Research of the Ministry of Education. References [1] Yu .N . Pestov and G.V. Fedotovich, SLAC Trans. 184
(1978) . [2] I.B . Vasserman et al ., SLAC Trans. 196 (1981). [3] V.D . Laptev, Yu. N. Pestov and N .V. Petrovykh, UDC 539.1 .074.27 (1975) p . 1698 . [4] A.D . Afanas'ev, V.D . Laptev, Yu .N . Pestov and B.P. Sannikov, UDC 539 . 1 .074.27 (1975) p . 1701 . [5] V.D . Laptev and Yu .N . Pestov, UDC 539 .1 .074 .27 (1975) p . 1703 . [6] W.B. Atwood, G.B . Bowden, G.R. Bonneaud, D.E . Klem, A. Ogawa, Yu . N. Pestov, R. Pitthan and R. Sugahara, Nucl . Instr. and Meth . 206 (1983) 99. [71 N . Fujiwara, A. Ogawa, Yu .N . Pestov and R. Sugahara, Nucl . Instr. and Meth . A240 (1985) 275 . [81 A. Ogawa, W.B . Atwood, N. Fujiwara, Yu.N . Pestov and R. Sugahara, Proc. IEEE 1983 Nss, San Francisco (1983) IEEE Trans. Nucl . Sci . NS-31 (1984) 121 .