Radio-Activity

by Ernest Rutherford

Fig. 57.

Let p be the partial pressure of the emanation at a distance x from the source C. This will be approximately uniform over the cross section of the cylinder. From the general principles of diffusion we get the equation

d²p dp

K ---- = – ---- .

dx² dt

The emanation is continuously breaking up and expelling α particles. The emanation-residue gains a positive charge, and, in an electric field, is removed at once from the gas to the negative electrode.

Since the activity of the emanation at any time is always proportional to the number of particles which have not broken up, and since the activity decays with the time according to an exponential law,

where p₁ is the value of p when t = 0 and λ is the radio-active constant of the emanation.