The Emission and Transmission of Rontgen Rays . 0 y > where I0 is the initial intensity of the beam as it leaves the aluminium window, and I its intensity aftertransmission through a screen. The slope of the tangent to the curve at any pointgives (when multiplied by 2*3) the value of the coefficient of absorption (X) at thatregion. A. is defined by the relation I = I0e~A^, where d is the thickness of screen atthe point. If the relation is homogeneous over any region, the graph will, of course,be a straight line. VOL. CCIX.—A. T 138 MR. G. W. 0. KAYE ON THE Aluminium Screens.—Turning to fig.
The Emission and Transmission of Rontgen Rays . 0 y > where I0 is the initial intensity of the beam as it leaves the aluminium window, and I its intensity aftertransmission through a screen. The slope of the tangent to the curve at any pointgives (when multiplied by 2*3) the value of the coefficient of absorption (X) at thatregion. A. is defined by the relation I = I0e~A^, where d is the thickness of screen atthe point. If the relation is homogeneous over any region, the graph will, of course,be a straight line. VOL. CCIX.—A. T 138 MR. G. W. 0. KAYE ON THE Aluminium Screens.—Turning to fig. 7 (aluminium screens), we notice a generalresemblance between the curves for platinum, copper, nickel and iron radiators. Theyindicate the kind of absorption usual with Rontgen rays—that is, the coefficient ofabsorption steadily diminishes with increasing thickness of screen. The four curvesbecome practically parallel with the thickest screens. The proximity of the earlyportions of the nickel and copper radiation curves will be LOG. •01 C M. THICKNESS of ALSCR££/V Fig. 7. Al screen, 20,000 volts. It is the aluminium radiation that presents interest. The curve consists of anearlier steeper portion (A. = 120) which merges, when the screen attains a thickness ofabout 0*01 cm., into a straight line for the rest of its path (X = 40). Throughout thislatter region, then, the absorption is exponential, and the aluminium radiation behavesas if it were homogeneous. Copper Screens.—If we inspect fig. 8, which embodies the results obtained withcopper screens, we no longer see this indication of homogeneity on the part of thealuminium radiation. Instead, the curve presents the gradual diminution in gradientwith increasing thickness of screen that is typical of Rontgen rays. It is now thecopper radiation that appears homogeneous—its graph for screens thicker than about0*0015 cm. is a straight line (X = 470). For thinner screens the curve is a littlesteeper (X = 620).
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