Thin iilms of Elements exposed to Rant gen Bays. 135 



We can employ the expressions for the photo-electric 

 equation given in the introduction in order to calculate 

 what should be the theoretical value o£ the energies of the 

 electrons of the K, L, or M type sent out from the various 

 screens when each is subjected, first to silver and second to 

 barium X-rays. In the absence of any definite knowledge 

 of the relative intensities of the a, /3, 7, etc. lines of the 

 K, L, M X-rays we must confine ourselves throughout to 

 the a lines. 











Table I. 















Values 



f 



Incidence of Silver 



Incidence of Barium 









v/n . 





(K) X-rays. 



(K) X-rays. 



Element 



(S). 



At. 

 No. 



iv 



\- 



M . 



a 



■(*). ! (»)■ , (c)- 



{d). 



(«). 



00. 



2368 



As 



33 



783 



94 



15 



741 1524- j 1618 



1491 



2274 



Se 



34 



835 



101 



16 



GS1 1516 ! 1617 



1431 



2266 



2367 



Zr 



40 



1156 



150 



23 



304 14150 



1610 



1054 



2210 



2360 



Ag 



47 



1633 



220 



36 



... 1377 



1597 



494 



2127 



2347 



Sn 



50 



1871 



254 



43 



... 1336 



1590 



215 



2086 



2340 



Sb ...... 



51 



1950 



265 



46 



... 1322 



1587 



122 



2072 



2337 



Ba 



56 



2383 



328 



60 



... 1245 



1573 





1995 



2323 



Au 



79 





7i7 



156 



760 1477 





1510 



2227 



Pb 



82 





777 



173 



... , 683 



1460 





1433 



2210 





83 





797 



180 



656 



1453 





1406 



2203 



Table I. — Columns 3 and 4 give the values of vjn Q for 

 the K a and L a X-ray spectral lines from the various 

 elements S. These values have been obtained by inter- 

 polation from the observed values quoted by Vegard * ; the 

 values for the M a line are interpolated from the formula f 



/V 



m m 



2-37N + 40. 



Column (a) is obtained from the expression 



Ag (W"o) Ka -s[(^o) K(X + (W»o) Ltt +(W*o)ai tt +-..], 



column (b) by omitting the first of the terms within the 

 square brackets, and column (c) the first and second terms 

 from the square brackets. Columns (d), (e), and (/) in a 

 similar manner when Bai {vln ) Ka is substituted for Ag (v/w ) K- 



in the first part of the expression. 



* L. Vegard, Phil 



f Lac. cit. 



Ma j 



>, vol. xxxv. pp. 293, 301, 316 (1918). 



