Primary Charged Particles Research Articles

Longitude Effect of Cosmic Radiation and the Position of the Earth's Magnetic Centre

THE theory of the allowed cone of electrically charged primary cosmic rays, developed in a number of recent papers by Lemaitre and Vallarta1, is competent to account for the longitude effect if due regard is paid to the fact that the earth's centre does not coincide with its magnetic centre2. Assuming Schmidt's determination3 of the latter and, with Clay, an exponentially decreasing energy distribution of primary charged particles, it has been shown that the longitude effect along the geomagnetic equator should be roughly sinusoidal with maximum at geographic longitude 12° W. and minimum at 168° E. ; the intensity difference between maximum and minimum is calculated to be about 8 per cent. More recent calculations of the position of the earth's magnetic centre (Bruins4, Bartels5) have somewhat revised Schmidt's earlier result, but the theoretical longitude effect is not much affected thereby. The longitude of the maximum and minimum depends only on the co-ordinates of the earth's magnetic centre, particularly on its longitude ; the intensity difference between the maximum and minimum is closely connected with the distance between the earth's centre and its magnetic centre, to a lesser extent with the energy distribution of primary particles.

The Corpuscular Theory of the Primary Cosmic Radiation

The approximately exponential law of cosmic-ray absorption is, at first sight most readily accounted for by the hypothesis that the primaries are composed of photons. However, latitude and asymmetry effects demand that at least 31 percent of the primary radiation be attributed to charged particles. This is enough to spoil the exponential law given so readily by photons unless the charged particle hypothess be developed so as to give an exponential law. The na\"{\i}ve hypothesis that the exponential law is to be provided by a suitable range of penetrations of the incoming rays, resulting from a corresponding range of energy distribution is found untenable, mainly because such a hypothesis would lead to a condition in which the quality of the measured radiation was independent of altitude. The paper reviews a hypothesis already published by the writer to the effect that the primary rays produced secondaries in number per centimeter of path proportional to the primary energy. These secondaries perpetuate the primary path. They represent the rays actually measured, and the theory gives an exact exponential law. The theory gives, in fact, a constant "apparent" coefficient of absorption of the measured effect which is independent of the primary energy. This result requires modification to harmonize with the data on the latitude and directional effects. It is shown that harmonization is provided by a modification of the theory which permits an increase of coefficient of apparent absorption with decrease of primary energy. It is found that such a modification can be readily made in more ways than one. It is then shown that the apparently contradictory phenomenon involved in the "hardening" of the average radiation with passage through matter can readily be accounted for by adding to this hypothesis already made, the known fact of a distribution of energies in the incoming primary corpuscular radiation. A modification of the foregoing theory permits the "apparent" primaries referred to in it to be really photons produced by impact of true primary charged particles with the upper atmosphere. The writer reviews a former hypothesis made by him with regard to the dependence of shower production and atomic burst production in lead, a hypothesis designed to provide an explanation that these phenomena increase with altitude much more rapidly than does the measured cosmic-ray intensity. It results that the extension of the main theory concerned with absorption of the primary energy when combined with the hypothesis concerning burst and shower production results in harmonization of all the details of these phenomena as far as they are known. A list of eleven facts concerned with cosmic-ray absorption, latitude and directional effects, burst and shower production is made. The list comprises all of the outstanding facts concerned with the subject; and it is shown that the extended theory harmonizes all of them.