Page:Popular Science Monthly Volume 67.djvu/22

16 of the atom, after the a particle is expelled, is the atom of the emanation, so that each atom of radium gives rise to one atom of the emanation. Let q be the number of atoms in each gram of radium breaking up per second. When a state of radioactive equilibrium is reached the number N of emanation particles present is given by $$N = q/\lambda$$ where λ is the constant of change of the emanation. Now Ramsay and Soddy deduced from experiment that the volume of the emanation released from 1 gram of radium was about one cubic millimeter at atmospheric pressure and temperature. It has been experimentally deduced that there are $$3.6 \times 10^{19}$$ molecules in one cubic centimeter of gas at ordinary pressure and temperature. The emanation obeys Boyle's law and behaves, in all respects, like a heavy gas, and we may in consequence deduce, since $$N = 3.6 \times 10^{16}$$ and $$\lambda = 2.0 \times 10^{-6}$$, the value $$q = 7.2 \times 10^{10}$$.-Now the particles expelled from radium in a state of radioactive equilibrium are about equally divided between four substances, viz., the radium itself, the emanation, radium A and radium C. We may thus conclude that the number of α particles expelled per second from 1 gram of radium in radioactive equilibrium is $$2.9 \times 10^{11}$$. The value deduced by this method is intermediate between the values previously obtained (see previous table), on the assumption that the heating effect is entirely due to the a particles.

I think we may conclude from the agreement of these two methods of calculation that the greater portion of the heating effect of radium is a direct result of the bombardment of the expelled a particles, and that, in all probability, about $$5 \times 10^{10}$$ atoms of radium break up per second.

The energy carried off in the form of β and γ rays is small compared with that emitted in the form of α rays. By calculation it can be shown that the average kinetic energy of the β particle is small in comparison with that of the a particle. This is confirmed by comparative measurements of the total ionization produced by the α and β rays, when the energy of the rays is all used up in ionizing the gas, for the total ionization produced by the β rays is small compared with that due to the γ rays. The total ionization produced by the γ rays is about the same as that produced by the β rays, showing that, in all probability, the energy emitted in the form of these two types of radiation is about the same. From the point of view of the energy radiated and of the changes which occur in the radioactive bodies, the α rays thus play a far more important rôle in radioactivity than the β or γ rays. Most of the products which arise from radium and thorium emit only α rays, while the β and γ rays appear only in the last of the series of rapid changes which take place in these bodies.