The time resolving power of the multiwire spark counter

NUCLEAR INSTRUMENTS AND METHODS

54 (1967) 327--328à CC) NORTH-HOLLAND PUBLISHING CO.

THE TIME RESOLVING POWER OF THE MULTIWIRE SPARK COUNTER L. MARINESCU, M . PETRASCU and G . VOICULESCU Instittetc of Atcrtnic Phvsic.s, Buchut ,vst, 1 ornprriet

Received 28 June 1967 The time resolving power of the multiwire spark counter was measured. 1t was found a standard fluctuation of about 150 nsec

of the delay between the passage of an ionising particle and the appearance of the spark.

The excellent rise time of the pulse of the multiwire spark counter, was reported earlier by Singh and Sahat) and by Bowman and Hill') . However, it remained an open question whether there is not a fluctuating delay between the passage of an ionizing particle and the appearance of the spark, in order that the spark counter might be used in fast coincidence measurements. In this paper, there are described the results ob-

face at a distance of 0.6 cm each other. In the gap between the two counters a fission !foil was placed, consisting of 500 ,ug/(.m' U3 08 layers coated on each side of an 1 mg/cm2, 8 cm in dia. aluminium support. The counters were operating in air at atmospheric pressure . A good electrical shielding was necessary in order to avoid mutual inducing of pulses between the two counters . The system consisting of these two spark counters, viewing the fission target was placed in the

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tained by studying the time resolving power of the multiwire spark counter. The principle of the performed measurements, consisted in studying the time distribution between the sparks in two identical spark counters, detecting the two simultaneous fragments from a fission act. The spark counters of the type described by Bowman and Hill'), were placed face by

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Fig. 1. Block diagram of the measuring system .

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Fig. 2. Electronic scheme of the shaping circuit and discriminator. 32"

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328

L. MARINBSCU et al.

2750V m: - d1

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Fig. 3. Distribution of time intervals between the sparks in the two counters (operating voltage: 2750 V).

neutron beam of a horizontal channel at VVR-S reactor in Bucharest. In fig. I there is represented a block diagram of the electronics used. In fig. 2 there is given the electronic circuit used for the pulse shaping and discrimination . There were used two methods for investigating the time distribution between the two sparks. In one system there were counted the pulses from one of the spark counters in successive 100 nsec intervals on the cathode ray tube of a 30 MHz "Ribet Desjardins" synchroscope, triggered by the pulses from the other spark counter. In the other system, a time-to-pulse height converter working in the range from 0 to 100 nsec together with a delay line variable in steps up to 1 sec were used. The data obtained by the two methods were consistent between themselves . In fig. 3 there is represented the distribution of time intervals between the two sparks, the operating voltage of the counters being 2750 V and in fig. 4 the distribution cbrresponding to an operating voltage of 3000

Fig. 4. Distribution of time intervals between the sparks in the two counters (operating voltage : 3000 V) .

V. It results a slight improvement of the time distribution with the applied voltage for, in the first case the standard deviation a, is 225 nsec and in the second case ar t is 207 nsec. It follows that the time resolving power of the multiwire spark counter is of the order of ad112 =150 nsec and in spite of the excellent rise time of the pulse this kind of detectors cannot be of use in fast coincidence measurements. The authors would like to thank Prof. H. Hulubei for many valuable discussion and A. Ignatenko and M. Ûmelianenko from JINR-Dubna, who participated in the earlier stage of this work. Also we wish to thank A. Butte for his help in performing the measurements . References

1) G. Singh and N. K. Saha, Nucl . Instr. and Meth . 13 (1961) 322. 2) C. D. Bowman and R. W. Hill, Nucl . Instr. and Meth . 24 (1963) 213.