Thunder-storms and the penetrating radiation

Abstract

The possibility of a connection between thunder-storms and the penetrating radiation was first suggested by C. T. R. Wilson, who pointed out that the powerful fields within thunder-storms should exert an important accelerating effect upon β-particles produced by the disintegration of the radioactive material carried in the air. He showed that many of these particles should gain far more energy from the field in traversing a given distance than they lost in ionisation, and that they might thus acquire a very considerable fraction of the energy corresponding to the fall of potential, of the order of 10 9 volts, between the poles of the cloud. He examined the effect of close encounters of these accelerated particles with atomic electrons, resulting in the ejection of fast secondary particles, and also the action of ordinary nuclear scattering, and found that neither of these would seriously interfere with the accelerating process. The secondary electrons, indeed, would often be emitted with sufficient energy and in a suitable direction to be accelerated themselves. An occasional encounter with an atomic nucleus at a distance at which the inverse square law of force failed to hold would be the only possible manner in which the process might be stopped, but such an encounter would be so rare that the β-particle would have acquired a very considerable amount of energy before it occurred and this might be radiated as a penetrating γ-ray quantum. "The general effect of an accelerating field is that a β-particle, instead of dying as it were a natural death by gradual loss of energy, is continually acquiring more and more energy and increasing its chance of surviving all accidents other than direct encounters with the nuclei of atoms." In this paper these accelerated particles will be referred to as runaway electrons, a description first applied to them by Eddington. Interest in this suggestion, which, as Wilson pointed out, might bear on the question of the origin of part at least of the penetrating radiation, is heightened by the fact that recent estimates of the energy of this radiation considered either as γ- or β-rays give results of the order of 10 9 e.-volts.