Fluctuations in Cosmic-Ray Ionization as Given by Several Recording Meters Located at the Same Station

Abstract

A graphical comparison is given of the intensity variations of cosmic rays as registered on several different recording meters located in the same room during a period of ten weeks. As one might expect, the agreement is statistical rather than coincident. The barometer effect as calculated from the data of the individual meters ranges from 1 to 2 percent per cm Hg. A diurnal analysis carried out for a ten-day period during which barometric changes were small indicates a maximum of intensity at about 9:00 A.M. having a magnitude about 0.19 percent greater than the average. A pronounced increase in ionization has been observed during rainfall when the meters were operated with top shield removed. This has been ascribed to $\gamma$-radiation from active deposits brought down from the upper atmosphere with the raindrops. The average number of cosmic-ray ionizing particles traversing unit area of the ionization chamber in unit time, as estimated from statistical fluctuation data, is shown to compare favorably with counter observations. As regards ionization bursts: Analysis of distribution-in-time of the bursts shows that they occur in a purely random manner. Size frequency distributions covering a period of several weeks on eight different meters can be represented for the most part by a single exponential function. An analysis of nearly 700 bursts occurring over a 25 mm Hg range of pressure gives no evidence of a barometer effect on burst frequency, although the consistency of the data is not sufficient to rule out the possibility of an effect as large as 8 percent per cm Hg. The frequency is a function of shield thickness, being much greater for a reduced top shield than for the full 12 cm of lead.