We must therefore conclude that the β and γ rays together do not supply more than a small percentage of the total heat emission of radium—a result which is in accordance with the calculations based on the total ionization produced by the different types of rays.
248. Source of the energy. It has been shown that the
heating effect of radium is closely proportional to the activity
measured by the α rays. Since the activity is generally measured
between parallel plates such a distance apart that most of the α
particles are absorbed in the gas, this result shows that the heating
effect is proportional to the energy of the emitted α particles.
The rapid heat emission of radium follows naturally from the disintegration
theory of radio-activity. The heat is supposed to be
derived not from external sources, but from the internal energy of
the radium atom. The atom is supposed to be a complex system
consisting of charged parts in very rapid motion, and in consequence
contains a large store of latent energy, which can only be manifested
when the atom breaks up. For some reason, the atomic
system becomes unstable, and an α particle, of mass about twice
that of the hydrogen atom, escapes, carrying with it its energy of
motion. Since the α particles would be practically absorbed in a
thickness of radium of less than ·001 cm., the greater proportion
of the α particles, expelled from a mass of radium, would be stopped
in the radium itself and their energy of motion would be manifested
in the form of heat. The radium would thus be heated by its own
bombardment above the temperature of the surrounding air. The
energy of the expelled α particles probably does not account for
the whole emission of heat by radium. It is evident that the
violent expulsion of a part of the atom must result in intense
electrical disturbances in the atom. At the same time, the residual
parts of the disintegrated atom rearrange themselves to form a
permanently or temporarily stable system. During this process
also some energy is probably emitted, which is manifested in the
form of heat in the radium itself.
The view that the heat emission of radium is due very largely to the kinetic energy possessed by the expelled α particles is strongly confirmed by calculations of the magnitude of the heating effect to be expected on such an hypothesis. It has been shown
