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To test further the relative sensitiveness of the three types of instruments
9
as exemplified by the net drift per microgram, we measured the drift produced in
each by a standard sample of radium. The instruments were paired and readings
of drift were made simultaneously, the radium standard of 4.94 milligrams being
placed 50 centimeters from the central axis of each instrumente The net drifts
thus observed are given in the following table.
TABLE III. RELATIVE DRIFTS OF DIFFERENT TYPES OF ELECTROSCOPES
Type of Instrument
:
Net Drift (divisions per second)
1. Wulf Quartz Fiber
se
0.409
2. Schmidt
:
0.213
3. Lind (Large Chamber)
:
0.430
4. Lind (Small Chamber)
:
0.098
The relative drifts of the three instruments stand in practically the 3ame ratios
as the drifts per microgram recorded in Table II, and this fact has materially
strengthened our confidence in the gama-ray method for detecting radium in living
persons
The decided difference in the sensitiveness of the two Lind electroscopes is
due entirely to the difference in volume of the ionization chambers. The same elec-
troscope head was used, but the large chamber had a volume of three liters as against
a
half liter for the small chamber. This result suggests an easy way of increasing
the sensitiveness of the ordinary type of electroscope when it is desired to use it
as a gamm--ray instrument: Enlarge the ionization chamber.
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"ocrText": "-7-\nTo test further the relative sensitiveness of the three types of instruments\n9\nas exemplified by the net drift per microgram, we measured the drift produced in\neach by a standard sample of radium. The instruments were paired and readings\nof drift were made simultaneously, the radium standard of 4.94 milligrams being\nplaced 50 centimeters from the central axis of each instrumente The net drifts\nthus observed are given in the following table.\nTABLE III. RELATIVE DRIFTS OF DIFFERENT TYPES OF ELECTROSCOPES\nType of Instrument\n:\nNet Drift (divisions per second)\n1. Wulf Quartz Fiber\nse\n0.409\n2. Schmidt\n:\n0.213\n3. Lind (Large Chamber)\n:\n0.430\n4. Lind (Small Chamber)\n:\n0.098\nThe relative drifts of the three instruments stand in practically the 3ame ratios\nas the drifts per microgram recorded in Table II, and this fact has materially\nstrengthened our confidence in the gama-ray method for detecting radium in living\npersons\nThe decided difference in the sensitiveness of the two Lind electroscopes is\ndue entirely to the difference in volume of the ionization chambers. The same elec-\ntroscope head was used, but the large chamber had a volume of three liters as against\na\nhalf liter for the small chamber. This result suggests an easy way of increasing\nthe sensitiveness of the ordinary type of electroscope when it is desired to use it\nas a gamm--ray instrument: Enlarge the ionization chamber."
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