Page:Radio-activity.djvu/245

 where λ is a constant and e the natural base of logarithms. The experimental curve of the rise of activity from a minimum to a maximum value is therefore expressed by the equation

I_{t}/I_{0} = 1 - e^{-λt},

where I_{0} is the amount of activity recovered when the state of constant activity is reached, I_{t} the activity recovered after a time t, and λ is the same constant as before.

129. Uranium X. Similar results were obtained when uranium was examined. The Ur X was separated by Becquerel's method of successive precipitations with barium. The decay of the separated activity and the recovery of the lost activity are shown graphically in Fig. 49. A more detailed discussion of this experiment is given in section 205.

Fig. 49.

The curves of decay and recovery exhibit the same peculiarities and can be expressed by the same equations as in the case of thorium. The time-rate of decay and recovery is, however, much slower than for thorium, the activity of the Ur X falling to half its value in about 22 days.