PROCEEDINGS 
OF THE 
NATIONAL ACADEMY OF SCIENCES 
Volume 8 MAY 15. 1922 Number 5 
NOTE ON X^RAY SPECTRA 
By William Duane and R. A. Patterson 
JBPP^RSON Physical Laboratory, Harvard University, and Si^oane Physical 
Laboratory, Yale University 
Communicated March 20, 1922 
In previous papers^ the authors have presented measurements of the 
critical absorption wave-lengths belonging to the L series of nine of the 
heavy elements (27 wave-lengths in all). We have also discussed the 
bearing of these data on theoretical matters, and their relation to other 
available measurements of X-ray spectra. Since these papers were 
published, many accurate measurements have been made of the emission 
spectra in both the L and M series for the heavy elements. 
Coster, 2 working in Siegbahn's laboratory, has accurately measured 
the L series emission lines for eleven heavy elements. He has extended 
the three known M absorption limits to five for uranium and thorium, 
and has measured the first three M limits for bismuth. 
De Broghe and Dauvillier^ have studied in detail the L series emission 
spectra for six heavy elements. 
With these new, accurate data, Smekal,^ Coster, ^ Dauvillier^ and 
WentzeP have constructed atomic systems to explain the source of each 
known emission line. The systems are based on the Bohr-Sommerfeld 
theory of the origin of characteristic X-radiation. In developing and 
discussing their systems, these investigators have used the values of the 
L absorption limits measured by us. Certain criticisms have been made 
of a few of our values. It has therefore seemed desirable to measure 
some of the limits again. 
Coster^ has suggested a possible source of error in our values for the 
absorption limits of tungsten on the ground that we used an X-ray tube 
equipped with a tungsten anticathode, and that therefore we would get 
an effect not due to absorption alone but also to the neighboring emission 
lines. We wish to call attention to the fact (stated on page 534 of our 
paper in the Physical Review, Dec. 1920) that we took^ the precaution 
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