settle whether this value of λ is to be given to λ 2 or λ 3 . From other data (see section 226) it will be shown later that it must refer to λ 3 . Thus λ 3 = 4·13 × 10 -4 (sec) -1 .
The experimental curve agrees very closely with theory if λ2 = 5·38 × 10-4 (sec)-1.
The agreement between theory and experiment is shown by the table given below. The maximum value IT (which is taken as 100) is reached at a time T = 36 minutes.
In order to obtain the β-ray curve, the following procedure was adopted. A layer of thin aluminium was placed inside a glass tube, which was then exhausted. A large quantity of radium emanation was then suddenly introduced by opening a stop-cock communicating with the emanation vessel, which was at atmospheric pressure. The emanation was left in the tube for 1·5 minutes and then was rapidly swept out by a current of air. The aluminium was then removed and was placed under an electroscope, such as is shown in Fig. 12. The α rays from the aluminium were cut off by an interposed screen of aluminium ·1 mm. thick. The time was reckoned from a period of 45 seconds after the introduction of the emanation.
| Time in minutes | Theoretical value of activity | Observed value of activity |
|---|---|---|
| 0 | 0 | 0 |
| 10 | 58·1 | 55 |
| 20 | 88·6 | 86 |
| 30 | 97·3 | 97 |