The London, Edinburgh and Dublin philosophical magazine and journal of science . pes of radiationare added for comparison. The excited radiation due to air has greater penetrating-power than any of the types of radiations, not deviated by amagnetic field, from the radioactive substances uranium,thorium, and radium, and i- also more penetrating than theexcited radiation produced by radium and thorium. No special experiment has been made to determine theabsorption of the excited radiation in its passage through theair, but its approximate amount can be readily deduced fromknown data. In all the
The London, Edinburgh and Dublin philosophical magazine and journal of science . pes of radiationare added for comparison. The excited radiation due to air has greater penetrating-power than any of the types of radiations, not deviated by amagnetic field, from the radioactive substances uranium,thorium, and radium, and i- also more penetrating than theexcited radiation produced by radium and thorium. No special experiment has been made to determine theabsorption of the excited radiation in its passage through theair, but its approximate amount can be readily deduced fromknown data. In all the different types of radiations examined * E. Rutherford and Miss II. T. Brooks, Phil. Mag. July 1902. 712 Prof. E. Rutherford and Mr. S. J. Allen : Excited it has been generally found that if one radiation is moreeasily absorbed than another, in aluminium for example, it isalso more easily absorbed in air. Since the excited radiationfrom the air is slightly less absorbed in aluminium than thatdue to thorium, we can thus conclude that it is slightly lessabsorbed in air. Fig. /- 2 3 4 S 6 Now it is known that the intensity of the excited radiationfrom thorium falls to half value after passing through 1*6 air. It thus follows that the intensity of the excitedradiation from air falls to half value after passing throughabout 2 cms. of air, and is almost completely absorbed in adistance of 10 or 12 cms. From the differences observed for the penetrating powerand ratio of decay wTe can conclude that the excited radiationfrom air cannot be ascribed to the presence of any knownradioactive substance in the atmosphere. Transmission of Excited Activity. We have seen that the excited radiation from the air issimilar in all respects to the known types of excited activityby thorium and radium. In both cases the activity isconfined to the cathode in an electric field, and can be partlyremoved by rubbing with a cloth or by solution in acid. The differences observed in the rate of decay
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