. The American journal of roentgenology, radium therapy and nuclear medicine . reflects •Read at the Midwinter Meeting. Eastern Section of The American Roentgen Ray Society, Atlantic City, January 26-2S. 1922. 167 [68 Roentgen Rays of Short Wave-Lengths and Their Measurement only rays of certain definite wave-lengths,X given by equation (i) X = 2d sin 0, (1) where the angle, theta, is the angle betweenthe roentgen-ray beam coming throughthe tube and the planes in the crystalcontaining its molecules. By measuringthis angle, theta, we can determine fromequation (1) the wave-length of the roent-g
. The American journal of roentgenology, radium therapy and nuclear medicine . reflects •Read at the Midwinter Meeting. Eastern Section of The American Roentgen Ray Society, Atlantic City, January 26-2S. 1922. 167 [68 Roentgen Rays of Short Wave-Lengths and Their Measurement only rays of certain definite wave-lengths,X given by equation (i) X = 2d sin 0, (1) where the angle, theta, is the angle betweenthe roentgen-ray beam coming throughthe tube and the planes in the crystalcontaining its molecules. By measuringthis angle, theta, we can determine fromequation (1) the wave-length of the roent-gen rays entering the ionization chamber. length spectra of roentgen rays that havepassed through filters of 1 mm. of copper,and of 12 mm. curves of Figure 2 represent thedata obtained in these experiments. Thevertical coordinates give the ionizationcurrents (expressed in arbitrary units)measured with the crystal in differentpositions, and the horizontal coordinatesgive the wave-lengths of the roentgen Absorber Quadrant Electrometer x LeadSheet. Mill ammeter1 === Larth Fig. 1. In making measurements with an x-rayspectrometer care must be taken toprotect the instrument from stray radia-tion. It was for this purpose that the tubeand generating plant were placed in oneroom and the spectrometer in another. Inmaking measurements on the absorptionof roentgen rays extreme care must beused in correcting for the natural ioniza-tion of the gas in the ionization chamberand for the ionization current due to anyslight residual radiation. This correctionhas been made in all the experimentsdescribed below. 4. Before passing on to the methods ofmeasuring the effective wave-lengthof a roentgen-ray beam, I shall give theresults of experiments on the short wave- rays as calculated by equation (1) fromthe angles made by the beam of roentgenrays with the crystal planes. It must be pointed out that the ioniza-tion currents represented by curves of thiskind do not give t
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