PROCEEDINGS
OF THE TOMSK POLYTECHNIC INSTITUTE
OF THE ORDER OF THE OCTOBER REVOLUTION AND THE ORDER
OF THE RED BANNER OF LABOR
named after S. M. Kirov

Volume 278　　　　　　　　　　　　　　　　　　　　　　　　　　　　1975

VIEWING A NARROW-GAP SHOWER SPARK CHAMBER THROUGH A TRANSPARENT ELECTRODE

P. S. ANAN’IN, V. I. KRYSHKIN, A. G. STERLIGOV, Yu. P. USOV

(Presented by the scientific-technical seminar of the High-Energy Laboratory, Research Institute of Nuclear Physics)

Introduction

In the traditional viewing of an image in a spark chamber (SC) with a small gap (two orthogonal projections), a difficulty arises that is associated with recording the large number of particles characteristic of any track detector: the number of particles in an electromagnetic or nuclear shower increases as the energy of the primary particle increases, while the shower core contracts; therefore, when a shower is recorded by a track detector, the probability of undercounting the number of particles in the shower because of track overlap increases. Thus, for a diffusion chamber having a spatial resolution of \(\sim 0.1\) mm, better than in an SC, the correction for undercounting particles in a shower with 10 tracks reaches 10% [1]. Viewing through a transparent electrode of an SC makes it possible practically to eliminate this error in measuring the number of particles in a shower; on the other hand, with a small interelectrode gap there is no need to record a second projection, which simplifies the processing of the results.

The main purpose of the present work is to investigate the experimental capabilities of a narrow-gap SC with high shower efficiency and viewing through one of the transparent electrodes. For this purpose, the spatial distribution of electron-photon showers formed in lead was studied, as was the change in the number of particles in a shower due to the presence of a thin layer of material whose properties differ from those of the main absorber.

The characteristics of cascade curves have been measured by various methods: track detectors [1—5], scintillation and Cherenkov counters [6, 7], etc. In each case, different results are obtained depending on whether ionization losses or the number of particles in the shower are recorded. And even for the same methods, the results depend on the design features of the detectors. Thus, when cosmic-ray showers are recorded by an SC or by ionization calorimeters, the presence of a metal with small \(Z\) leads to a decrease in the number of particles in the shower due to the transition effect [9—11]. This phenomenon has been studied mainly by measuring ionization losses with scintillation counters and photoemulsions [12, 13]. However, these results cannot be used directly in work with an SC, since the recording of showers by an SC has several special features: the registration efficiency depends on the number of particles in the SC gap, on their angle of entry relative to the plane of the electrodes, on the SC power-supply system [14, 15], etc.

The results obtained are of interest both from the standpoint of SC technique and may also prove useful in the design of shower detectors for high-energy photons and electrons based on determining the energy of the primary particle by measuring the number of particles at the shower maximum [16].

Experimental arrangement and apparatus

The experiment was carried out at the 1.5 GeV electron synchrotron “Sirius.” The photon beam of the synchrotron was incident on the aluminum target of an analyzing magnet. Electrons with momentum \(1\ \mathrm{GeV}/c\) were deflected, passed through two scintillation counters (Fig. 1), and coincidences from these triggered the high-voltage supply of the SC. The SC consisted of a single discharge gap formed by two brass meshes (cell \(0.2 \times 0.2\ \mathrm{mm}^2\)), spaced 12 cm apart and stretched over a glass frame. Glass plates 1.5 mm thick were glued onto the meshes; through these the SC image was photographed and viewed by a television system. The diameter of the SC electrodes was 120 mm; the chamber was filled with technically pure neon. The SC was powered by a generator with wave impedance \(0.4\ \Omega\), assembled on artificial lines based on K 15-4 capacitors (470 pF, 30 kV) according to a series-connection circuit (Blumlein). The voltage-pulse amplitude was 16 kV, the duration 60 ns, and the rise and fall times 22 ns. Reducing the wave impedance of the generator and supplying the chamber with pulses of fixed

Fig. 1.

duration was used as a means of increasing the shower efficiency [17]. The latter was studied by two methods. In the first, the SC was placed in the bremsstrahlung beam in series with a wide-aperture SC having high shower efficiency [15]. However, under the stated conditions this method does not provide reliable quantitative estimates of the shower efficiency because of the substantial difference in the memory time of the chambers being investigated. In addition, when viewing the image in the wide-aperture SC through the side walls, counting losses arise because of track overlap, which become significant when the number of particles is greater than 10. However, up to this value it can be stated reliably that the shower efficiency of the narrow-aperture SC is close to 100%.

In the second method, the shower in the SC was simulated by means of ultraviolet illumination [19]. In this case up to 195 sparks were recorded simultaneously in the SC. We note that the maximum number of particles recorded in a shower was 24.

Measurement Results

A lead converter was placed in front of the spark chamber (SC); its thickness \(t\) was varied from 5 to 20 mm, and after the lead there were plexiglass plates of thickness 5, 15, and 20 mm. The distribution of the number of particles in the SC was recorded as a function of the thickness of the lead converter, both in the absence and in the presence of the plexiglass plates.

First, the distribution of the primary-electron beam without a converter was studied. The diameter of the scintillator of counter \(C_2\), Fig. 1, was 5 mm; however, because of beam divergence and multiple scattering on the path to the SC, the beam size in the SC was 8 mm (the width of the distribution at half-height).

Fig. 2.

When working with the converter, the number of tracks and their distance from the center of the beam were counted. The probability function for the simultaneous appearance of \(N\) particles, \(W(N)\), was then constructed. Figure 2 shows this distribution for a lead-converter thickness of 25 mm. The statistical errors plotted are one standard deviation. The distribution is described by a Poisson law only qualitatively. Similar distributions were constructed for each thickness of lead and plexiglass. The mean value of \(N\) and the distribution of the number of particles as a function of distance from the center of the electron beam were then found.

Figure 3 shows the radial distributions of the number of particles in the shower for three lead thicknesses. A rapid broadening of the shower is observed as the thickness increases. Similar distributions constructed for the lead + plexiglass system practically do not differ from those shown in Fig. 3; however, the mean number of particles in the shower in this case decreases noticeably (Fig. 4).

Figure 5 shows the ratio \(K\) of the number of particles at the shower maximum in lead without plexiglass to the number of particles under the same conditions with plexiglass, as a function of plexiglass thickness. The curve is taken from [18].

From the analysis of the data obtained it follows that: 1) the distribution of the number of particles in the shower is only in qualitative agreement with a Poisson distribution; 2) the radial distribution of the shower depends strongly on the thickness of the lead converter, i.e., the error in determining the shower center when the lead thickness is changed from 5 to 25 cm increases from \(\pm 5\) to \(\pm 10\) mm (one standard deviation); 3) the presence of a material with small \(Z\) leads to a decrease in the number of particles in the shower in the same ratio as the ionization losses, although the SC effectively registers

Fig. 3. The thickness of the lead converter corresponds to: 1 — 0.5 cm, 2 — 1.5 cm, 3 — 2.0 cm.

Fig. 4. a — no Plexiglas plate; b — between the lead converter and the SC a Plexiglas plate 5 mm thick was installed.

Fig. 5. 1 — data of work [12]; 2 — our data.

particles traveling perpendicular to the electrodes, and, as the angle \(\varphi\) to the direction of the electric field increases, the efficiency falls as \(\cos \varphi\) [14, 17], while the main contribution to the transition effect is made by particles moving isotropically.

In conclusion, it should be noted that a narrow-gap SC with high shower efficiency and viewing through one of the transparent electrodes may in a number of cases have certain advantages over ordinary SCs, for example, when determining the energy of shower particles from the number of electrons at the shower maximum.

References

1. H. Thom. Phys. Rev. 1964, 136, B447.

2. A. Bauer, B. Brocking, H. Faissner, H. Karl, H. Kohmstedt and J. Stein. Proceedings of the International Symposium on Electron and Photon Interactions at High Energies. Hamburg, 1965, 401.

3. J. Cronin, E. Engels, M. Pyka and K. Roth. RSI, 1962, 33, 946.

4. R. Kajikawa. Journ. Phys. Soc. Japan. 1963, 18, 1365.

5. A. G. Gapotchenko, B. B. Govorkov, S. P. Denisov, N. G. Kotelnikov, D. A. Stoyanova. PTE, 1965, 5, 60.

6. O. A. Zaimidoroga, V. M. Kutin, Yu. D. Prokoshkin, V. M. Tsupko-Sitnikov. OIYaI, Preprint R 1-3976, 1968.

7. C. A. Heusch and C. Y. Prescott. Phys. Rev. 1964, 135, B772.

8. S. Z. Belen’kii. Avalanche Processes in Cosmic Rays. OGIZ, Gostekhizdat, 1948.

9. K. Pinkau. Phys. Rev. 1965, 139, B1548.

10. V. A. Dmitriev. ZhETF, 1958, 35, 553.

11. A. D. Erlykin, A. K. Kulichenko. Izv. AN SSSR, Ser. fiz., 32, 502 (1968).

12. Carol Jo Crannell et al. Phys. Rev. 1965, 182, 1435.

13. T. Yuda. Nuclear Instruments and Methods. 1969, 73, 301.

14. A. G. Gapotchenko, B. B. Govorkov, S. P. Denisov, S. S. Starostin. PTE, 1968, 6, 58.

15. M. I. Daion, B. A. Dolgoshein, V. I. Efremenko, G. A. Leksin, V. A. Lyubimov. Spark Chamber. Moscow, Atomizdat, 1967.

16. A. A. Tuarkin. Nuclear Instruments and Methods. 1970, 85, 277.

17. Yu. P. Usov, P. S. Anan’in, A. G. Sterligov, V. G. Tolmacheva. PTE, 1970, 4, 42.

18. Carol Jo Crannell. Phys. Rev. 1969, 182, 1441.

19. A. G. Sterligov, Yu. P. Usov. PTE, 1972, 3, 53.