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of rays always occur together and in the same proportion. The curves measured by the β rays are very different, especially for the case of a short exposure to the emanation. This is clearly shown in Fig. 68, which gives the β and γ ray curves for exposures of 10 minutes, 40 minutes, and 1 hour, and also the limiting case of an exposure of 24 hours.
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Fig. 67.
About 25 minutes after removal, the activity decays approximately at the same rate in each case. For convenience of repre-
