ON THE DISTRIBUTION OF NUCLEAR DISINTEGRATIONS NEAR LARGE SHOWERS OF HEAVY PARTICLES

A. P. Zhdanov was the first to describe a case of the complete disintegration of a heavy nucleus under the action of very energetic particles forming part of cosmic radiation[^1]. Subsequently, he also described many different nuclear disintegrations occurring under the action of cosmic rays[^2].

In a recently published paper[^3], A. P. Zhdanov presents a photograph of a new case of disintegration in which a shower consisting of 70–80 particles was formed, flying predominantly in one direction. This time the author pays special attention not to the character of the shower itself, but to the simpler disintegrations accompanying it. It turns out that the number of such disintegrations in the immediate vicinity of the shower is exceptionally large: on a portion of the plate measuring only \(0.06\ \mathrm{mm}^2\), 16 disintegrations were found, which is approximately 4500 times greater than the number of disintegrations falling on the same area under ordinary conditions. As the distance from the center of the shower increases, the number of disintegrations rapidly decreases; the disintegrations themselves are located predominantly in the direction of motion of the shower particles. All these data make it possible to suppose that a genetic connection exists between the shower and the simpler nuclear disintegrations.

To prove this supposition, a map was made of the disintegrations found over an area of \(1.44\ \mathrm{mm}^2\), which made it possible to study in more detail the angular distribution and the dependence of their number on the distance from the center of the shower. The disintegrations were divided into “stars,” “showers,” and single tracks, and, in addition, were grouped according to the ranges of the particles entering into them. In all cases a predominance was found in the number of disintegrations in the direction of emission of the particles of the main shower; a particularly distinct asymmetry of the angular distribution was observed for disintegrations with the longest-range particles and for the “shower.” In studying the dependence on distance, in all cases a sharp decrease was found in the concentration of disintegrations in the direction of motion of the particles of the main shower, and a very weak decrease in the opposite direction.

The concentration of disintegrations in the direction of emission of the particles of the main shower and the sharp decrease in their number with increasing distance from its center confirm the supposition that these disintegrations have a secondary origin, and do not arise simultaneously with the shower under the action of a powerful narrow beam of cosmic particles. The disintegrations are produced by some particles which are emitted together with the particles of the shower itself, are not recorded by the photographic plate, and have ano-

minimal cross section for interaction with nuclei. The author estimates for these particles \(\sigma \sim 10^{-21} - 6\cdot 10^{-23}\ \mathrm{cm}^2\). Since most secondary disintegrations are “stars,” it is natural to suppose that the particles producing them are slow negative mesotrons (P. I. Lukirskii and N. A. Perfilov have recently shown that such mesotrons interact especially effectively with nuclei, producing disintegrations of the “star” type, owing to the smallness of their own momentum\(^{4}\)) or varytrons discovered by A. I. Alikhanov and A. I. Alikhanyan\(^{5}\). The asymmetry of the angular distribution of the lines in secondary disintegrations indicates that the energy of the cosmic particle that produced the shower is \(\sim 10^{10} - 10^{11}\ \mathrm{eV}\).

Thus, in this work A. P. Zhdanov showed that, in the disintegration of nuclei by cosmic particles, not only are various particles emitted that enter into the composition of the nucleus itself, but new particles of the varytron type are also formed.

V. Leshkovtsev.

CITED LITERATURE

1. A. P. Zhdanov, DAN, XXIII, No. 1 (1939).
2. A. P. Zhdanov, Phys. Rev. 65, 202 (1944); Physics in School No. 2 (1946).
3. A. P. Zhdanov, DAN, LXIV, No. 5 (1949).
4. P. I. Lukirskii and N. A. Perfilov, DAN LIV, 219 (1948); LXI, 257, 259 (1948).
5. A. I. Alikhanov and A. I. Alikhanyan, Journ. of Phys. 11, 97 (1947).