. Radio-activity . and the openings of the cylinder closed, the currentsteadily diminishes with time. The following numbers illustratethe variation with time of the saturation current, due to theemanation in a closed vessel. The observations were taken suc-cessively, and as rapidly as possible after the current of air wasstopped. Time in seconds Current 0 100 28 69 62 51 118 25 155 14 210 6-7 272 4-1 360 1-8 Curve A, Fig. 52, shows the relation existing between thecurrent through the gas and the time. The current just beforethe flow of air was stopped is taken as unity. The current through R.
. Radio-activity . and the openings of the cylinder closed, the currentsteadily diminishes with time. The following numbers illustratethe variation with time of the saturation current, due to theemanation in a closed vessel. The observations were taken suc-cessively, and as rapidly as possible after the current of air wasstopped. Time in seconds Current 0 100 28 69 62 51 118 25 155 14 210 6-7 272 4-1 360 1-8 Curve A, Fig. 52, shows the relation existing between thecurrent through the gas and the time. The current just beforethe flow of air was stopped is taken as unity. The current through R. 16 242 EADIO-ACTIVE EMANATIONS [CH, the gas, which is a measure of the activity of the emanation,diminishes according to an exponential law with the time like theactivity of the products Ur X and Th X. The rate of decay is,however, much more rapid, the activity of the emanation decreas-ing to half value in about one minute. According to the viewdeveloped in section 136, this implies that half of the emanation. 4 5 Time in Minutes Fig. 52. particles have undergone change in one minute. After an intervalof 10 minutes the current due to the emanation is very small,showing that practically all the emanation particles present haveundergone change. The rate of decay has been more accurately determined byBossignol and Gimingham* who found that the activity fell to halfvalue in about 51 seconds. Bronsonf, using the steady deflectionmethod described in section 69, found the corresponding time54 seconds. The decrease of the current with the time is an actual measureof the decrease of the activity of the emanation, and is not in any * Eossignol and Gimingham, Phil. Mag. July, Bronson, Amer. Journ. Science, Feb. 1905. VIl] EADIO-ACTIVE EMANATIONS 243 way influenced by the time that the ions produced take to reachthe electrodes. If the ions had been produced from a uraniumcompound the duration of the conductivity for a saturation voltagewould only have been a fraction of a seco
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