166 



BELL SYSTEM TECILMCAL JOVRSAL 



although by itself it merely shows that particular transformations of 

 X-ray energy- become possible at particular fretjuencies. The elec- 

 tronic spectra, although much less accurate for purposes of measure- 

 ment, are neetled to show how this absorbed X-ra>' energy is used. 



These absorption-sijectra show that the levels in the atom are much 

 more numerous than the electronic s|)ectra with their lower "resoK- 

 ing power'" can re\eal: lor example, ilurr are tiiree /,-!e\eIs ,iiid live 





U Nil, -+7 



'KtMor^OtaKlyv I 



^■ntL-»«x>«^ Tyl • SI 



Bo.Ti.u.iitv yi'Sfo 



^.bsofl|vti»>\iK. 



Fig. 7 



..^/-levels. 'Pile ti\e .l/-le\els of tiioriuni (iispla\- iheniseKes (Hot 

 as clearly as might be desired) in Fig. S, wiiicii consists of absorption- 

 spectra photographed by P. A. Ross at I. eland .Stanford I iiixersitv-. 

 I'.acli spectrum extends from low fre(|ucn(ies ,it the left to a niax- 

 inunn iimiting-fre<|uen(\- at (lie riiiht. the limit dt|)endiiii.; on tile 

 \ollage applied to tlii^ X-r,i\- tube and nut on the properties of the 

 absorbing atoms. .\s the limit ing-rri(|niiu\- is increased b\' increas- 

 ing the xoltage. the absorption-edges resulting from electrons being 

 extracted Irnm the li\e .l/-le\-els succe.ssi\el\' ajipear. Along with 

 each new absorption-edge tluri' appear oni' or two new emission- 

 lines, emitted by the thorium atoms during the rearrangements 

 which follow upon the extraction of an electron.'" These correspond 



' .Nctualiy these lines were not cniitled liy the same atoms as absorbed the A'-rays, 

 hut by thorium atoms in the target of the .V-ra>- tube whence the primary .V-rays 

 came; the preliminary elcrlron-exiractions were performed in most cases by swift 

 electrons. There is no reason to supposi- that the agency ctTectinR the electron- 

 extraction has anything to do with ihe subse(|uenl rearr.ingenients of the atom. 



