. Radioactive transformations . nations. Twoor three hundred volts is sufficient tocharge the electroscope, and this insuressaturation over the greater part of therange provided that the active materialdoes not cause the electroscope to loseits charge in less than two or threeminutes. In this way measurements can bemade with rapidity and certainty. Anaccuracy of one per cent can readily beobtained, and with care the precision ofmeasurement may be made still great advantages of this type of instrument are its simplic-ity, portability, and comparative ease of construction. Such anins
. Radioactive transformations . nations. Twoor three hundred volts is sufficient tocharge the electroscope, and this insuressaturation over the greater part of therange provided that the active materialdoes not cause the electroscope to loseits charge in less than two or threeminutes. In this way measurements can bemade with rapidity and certainty. Anaccuracy of one per cent can readily beobtained, and with care the precision ofmeasurement may be made still great advantages of this type of instrument are its simplic-ity, portability, and comparative ease of construction. Such aninstrument, if standardized by a constant source of radiationlike uranium, is very suitable for determining the variation ofactivity of substances, which change very slowly with time. A modification of this electroscope, first used by C. T. , can be utilized to measure extraordinarily minuteionization currents. The construction of the apparatus is seenin Fig. 6. A clean metal vessel, preferably of brass, of about one litre. Fig. Electroscope for compar-ing £ and y ray activitiesand for measurement of veryweak activities. 30 RADIOACTIVE TRANSFORMATIONS capacity, has a gold leaf, L, attached to a rod, R, insulated bya sulphur or amber bead, S, inside the vessel. This is chargedby a movable rod, C, or by a magnetic device. After charg-ing, the upper rod, P, is connected to the case of the instrumentand to earth. In special cases, if extremely minute currentsare to be measured, the rod P is kept connected with a source ofpotential slightly greater than the potential of the electroscopesystem. This insures that there is no leak of the charge acrossthe sulphur support. The movement of the gold leaf is observed as before with amicroscope having a micrometer eyepiece. The great advan-tage of this instrument lies in the fact that the apparatus canbe hermetically closed. The rate of leak observed must thenbe entirely due to the ionization in the interior of the vesseland be indepen
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Keywords: ., bookauthorrutherfo, bookcentury1900, bookdecade1900, bookyear1906
