Page:Radio-activity.djvu/489

 electroscope due to the β and γ rays from the radium was observed. When a lead plate 6 mms. in thickness was placed between the radium and the electroscope, the rate of discharge observed was due to the γ rays alone. By slightly tilting the apparatus, the barium solution flowed into the radium tube and dissolved the radium. The tube was well shaken, so as to distribute the radium uniformly throughout the solution. No appreciable change of the activity measured by the γ rays was observed over the period of one month. The activity measured by the β and γ rays was somewhat reduced, but this was not due to a decrease of the radio-activity, but to an increased absorption of the β rays in their passage through the solution. The volume of the solution was at least 1000 times greater than that of the solid radium bromide, and, in consequence, the radium was subjected to the action of a much weaker radiation. I think we may conclude from this experiment that the radiations emitted by radium have little if any influence in causing the disintegration of the radium atoms.

Voller recently published some experiments which appeared to show that the life of radium varied enormously with its concentration. In his experiments, solutions of radium bromide of known strengths were evaporated down in a platinum vessel 1·2 sq. cms. in area, and their activity tested from time to time. The activity of the radium, so deposited, at first showed the normal rise to be expected on account of the production of the emanation, but after reaching a maximum, it rapidly decayed. For a weight of 10^{-6} mgrs. of radium bromide, the activity for example, practically disappeared in 26 days after reaching its maximum. The time taken for the activity to disappear increased rapidly with the amount of radium present. In another set of experiments, he states that the activity observed on the vessel was not proportional to the amount of radium present. For example, the activity only increased 24 times for a millionfold increase of the radium present, from 10^{-9} mgrs. to 10^{-3} mgrs.

These results, however, have not been confirmed by later experiments made by Eve. He found that, over the range examined, the activity was directly proportional to the amount