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    "title": "Report, no date",
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        "Safety Light Collection",
        "Records Related to Radium Dial Painters"
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    "seq": 18,
    "pageIndex": 0,
    "type": "photo",
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    "ocrText": "- 3 -\nX\n14.3 X 106 X .05 - 7.15 X 105 atoms of radon will be present in the ionization\nchamber, and of this number, the fraction, 2.1 X 10-6 disintegrates per second.\n-6\nCarrying out the multiplication of 7.15 X 105 x 2.1 X 10-6 we obtain 1.5 for the\nnumber of atoms of radon disintegrating per second. As we have shown, a net drift of\n1 division per second.of the leaf requires a transformation of approximately 250 atoms of\nradon per second, including its short-lived products. Hence the expected net drift will\nbe very small indeed, namely,\n1.5 = 0.006 divisions per second,\n250\na\nvalue\nof the same order of magnitude as the natural drift of the instrument used in our\nexperiments. An increase in drift of this magnitude when identified as produced by radon\ncan safely be made the basis for approximate quantitative determinations. In this connec-\ntion it should be emphasized that observed increase in drift will be only one-sixth the\nthe\nabove value, or 0.001 divisions per second when standard sized ionization chamber of one-\nhalf liter volume is used for testing expired air for the presence of radon.\nDETECTION OF RADON---SCINTILLATION METHOD. The lens used in commercial spinthariscopes\nhas a magnification of 7 times, and covers a field of 20 mm diameter at best. Hence the\narea of the luminous zinc sulfide soreen on which the scintillations can be observed is\nlimited to 3.1 square centimeters. By means of the special mounting and lens which we\nhave employed in our experimental arrangement, a screen area of 6 sq. eme may come under\nobservation. This screen area will still be slightly less than 2 per cent of the surface\narea of a cylindrical chamber 8 centimeters in diameter and 10 centimeters high, whose\nvolume is approximately 500 cubic centimeters. Now the total number of alpha particles\nexpelled per second from the emanation contained in 500 00 of expired air exhaled\nby\na\nsubject bearing 20 micrograms of r adium will be only 0.25, or in one minute not more than\n15 alpha particles will strike the walls of the counting chamber. At best but 2 per cent\nof the alpha particles will fall on the screen, which is equivalent to saying that one\nwould expect to observe a single scintillation at intervals of about three minutes.\nSince the natural number of scintillations observed by us on samples of phosphorescent"
}