Coincidence Counter Studies of the Corpuscular Component of the Cosmic Radiation

Abstract

The directional distribution of the cosmic radiation has been investigated in Peru, geomagnetic latitude X0°, atmospheric depths ft = 6, 6.8, and 10 meters of equivalent water; in Panama, \20°, & = 10 meters; in Mexico, \29°, & = 6.8, 7.2, and 10 meters; and in Pennsylvania and Colorado, \50°, h =10, and 7.2 meters. At each location the west intensity exceeded the east and the percent asymmetry was maximum near zenith-angles of 45 °, falling off towards the horizon. At &=10 meters the maximum asymmetry varied from 2 or 3 percent at X50° to 8 or 10 percent at the equator and at h = 6 meters it attained 16 percent at the equator. It is shown that the observations cannot be accounted for as an effect of secondary rays, and from the Lemaitre-Vallarta theory expressions have been derived which relate both asymmetry and latitudeintensity-variations to a primary corpuscular component. The discovery of the asymmetry therefore establishes beyond doubt the existence of this component, already indicated by the latitude effect. Consistency between magnitudes of the two effects can be established only if the corpuscular component is exclusively positive. The magnitude and the absorption coefficient of this component associate it with the intense soft component of the absorption curve analyses of Millikan and Regener, with coefficient 0.55 per meter of water and containing some 98 percent of the radiation incident at the top of the atmosphere. Although the corpuscular radiation is widely distributed in energy, close analysis shows a band of greater-than-average intensity in the range of positron or proton energies from 1 to 1.8 X10 10 volts. Independent determinations of energy and absorption coefficient show disagreement in order of magnitude with the theory of energy loss by ionization, and the atmospheric range of the asymmetrical radiation is anomalously independent of primary energy. Both characteristics point to some other process for dissipation of energy. Studies have been made of the shower-producing radiation, and it is found that its absorption coefficient in the atmosphere agrees with that of the corpuscular component. The directions of showerproducing rays are likewise asymmetrically distributed showing them to be of positive corpuscular origin. Hence it is suggested that shower-production possibly accounts for the absorption anomalies. Studies of the showerproducing mechanism at high elevations have shown the existence of relatively soft intermediary rays which are also ionizing corpuscles. Studies of the zenith-angle distributions at high and low elevations have shown that the ratio of counts to electroscope ionization is less for the soft than for the harder components and a correction for this effect, probably arising from shower production, brings zenith-angle distributions into fair agreement with the absorption curve analysis of Bowen, Millikan and Neher. Difficulties in accounting for exclusively positive radiation by radioactive and secondary processes are enumerated and the existence of a radial cosmic e...

Domenico Pacini, uncredited pioneer of the discovery of cosmic rays

“…Millikan attacked strongly Compton, but after repeating his experiment in 1933 he admitted that there was a latitude effect and that the cosmic rays must be (mostly) charged particles. In 1933, three independent experiments by Alvarez & Compton [53], Johnson [54], Rossi [55] discovered that more cosmic rays were coming from West than from East close to the Equator: this is due to the interaction with the magnetic field of the Earth, and it demonstrates that cosmic rays are mostly positively charged particles. However, it would take until 1941 before it was established in an experiment by Schein [56] that cosmic rays were mostly protons.…”