the Absorjjtion of Rontgen Rays. 



749 



value of \ varies as the density o£ the absorbing element, the 

 values of the more fundamental quantity are tabulated, 

 p being the density of the absorbing element. The quantity 

 - may be called the mass coefficient of absorption. 



Table I. 

 Mass absorption coefficients ( ) 



Eadiator. 



*_ 



C 



Mg. 



Al. 



Fo.. 



Ni. 



Cu. 



Zn. 



Ag. 



Sn. 



Pt. 



Au. 



Cr 



Fe 



Co 



Ni 



Cu 



Zn 



As 



Se 



Ag 



15-3 



101 

 7-96 

 6-58 

 5-22 

 4-26 

 2-49 

 204 

 •41 



126-5 

 80 

 63-5 

 51-8 

 41-4 

 347 

 19-3 

 15-7 

 2-2 



136 



88-5 

 716 

 59-1 

 47-7 

 39-4 

 225 

 189 

 25 



1038 

 661 

 672 



314 



268 



221 



134 



116-3 

 17-4 



129 

 83-8 

 67-2 

 56-3 

 62-7 



265 



166 



141-3 

 22-7 



143 



95-1 

 75-3 

 61-8 

 53-0 

 55-5 



176 



1498 

 24-3 



170-5 



112-5 



915 



74-4 



609 



501 



203-5 



174-6 



271 



580-5 



381 



314 



262 



214 



175 



105-3 

 87-5 

 13-3 



713-7 

 472 

 392 

 328 

 272 

 225 

 131-5 

 112 

 16-5 



[51(r8] 



340 



281 



236 



194 



162-5 



1057 

 93-0 

 56-5 



[507+]? 

 367 

 306 

 253 

 210 

 178-2 

 106-1 

 1000 

 61-4 





Fig. 3 (p. 750) exhibits the relation between the mass 

 coefficients of absorption in a number of elements and the mass 

 coefficient of absorption in Al — the former being plotted as 

 ordinates and the latter as abscissae. 



Discussion of Results. 



In studying these results it is necessary to know something 

 of the secondary rays emitted by the various absorbing- 

 substances. 



C, Mg, and Al are elements from which a characteristic 

 secondary radiation has not yet been observed. They cer- 

 tainly do not emit such a radiation in appreciable intensity 

 when subject to ordinary beams of X-rays, unless it be in the 

 form of exceedingly soft radiation, much softer than that of 

 chromium, and such as would be absorbed in a thin layer 

 of air. There is, however, the possibility, if not the proba- 

 bility, of the emission of such a radiation from all elements. 



