DIURNAL VARIATIONS IN THE FLUX OF HEAVY NUCLEI IN PRIMARY COSMIC RADIATION

Studies of various kinds of periodic and nonperiodic fluctuations in the intensity of cosmic rays are of considerable interest from the standpoint of the problem of their origin. However, the variations found in a number of studies in the intensity of the total radiation do not exceed fractions of a percent and are entirely masked by the influence of meteorological factors (pressure, temperature). In particular, the diurnal variations of the intensity of cosmic rays at sea level do not exceed \(0.2—0.3\%\)^1. It was natural to conclude that fluctuations in the intensity of the primary radiation should also have an amplitude of the same order.

Only quite recently has it become clear that a very different situation exists for a certain (though small) part of the primary radiation, namely for heavy nuclei.

Several reports have appeared in the literature on the results of ascents of thick-layer photographic plates to great altitudes (about \(28\ \text{km}\)) in daytime and nighttime. The most carefully performed are the recent measurements of Schein and Lord^2, in which special measures were taken to reduce temperature fluctuations and to monitor the influence of these fluctuations on the results of the experiment, and all deviations of the flight altitude from the mean flux were also taken into account. The general result of these measurements is that the flux of heavy nuclei with atomic numbers \(Z\)

within the range from 10 to 26 falls at night, as compared with daytime, by a factor of \(2.55 \pm 0.25\). The distribution of the number of observed cases \(N\) as a function of the number \((n)\) of \(\delta\)-electrons per \(100\,\mu\) of track length, which is related to the nuclear charge \(Z\), was also studied. The corresponding curves for the mean height of 28 km, for daytime (curve 1) and nighttime (curve 2) flights, are shown in the figure; analogous data from previous measurements\(^3\) at an altitude of 21 km are also shown there (curves 3 and 4, respectively).

The results obtained apparently indicate a close connection between the origin of heavy nuclei of the primary radiation and the accelerating action of the electromagnetic fields of the Sun.

G. B.

Cited Literature

1. H. Elliot and D. W. N. Dolbear, Proc. Phys. Soc. A 63, 137 (1950).
2. J. J. Lord and M. Schein, Phys. Rev. 80, 304 (1950).
3. J. J. Lord and M. Schein, Phys. Rev. 78, 321 (1950).
4. P. S. Freier, E. P. Ney, J. Naugle and C. Anderson, Phys. Rev. 79, 206 (1950).