PROCEEDINGS 
OF THE 
NATIONAL ACADEMY OF SCIENCES 
Volume 2 
MAY 15. 1916 
Number 5 
THE HIGH FREQUENCY SPECTRUM OF TUNGSTEN 
By Albert W. Hull and Marion Rice 
RESEARCH LABORATORY, GENERAL ELECTRIC COMPANY 
Received by the Academy. March 20. 1916 
Mosely^ has shown that the high frequency spectrum given out by 
the target of an X-ray tube consists of two series of lines superimposed 
upon a continuous spectrum. The lines, which are known as the K 
and L series, respectively, are characteristic of the material of the target. 
Mosely measured the wave lengths of most of the K lines for elements 
having atomic weights between aluminum and silver, and of the L 
lines for elements from calcium to gold, and showed that for all the 
Hues measured the square roots of the frequencies of corresponding lines 
are proportional to the atomic numbers of the elements emitting them. 
Maimer^ has added to this list the lines of six more elements between 
silver and lanthanum, and W. H. Bragg^ and others have studied in 
great detail the hues of a few of these elements, especially rhodium and 
platinum. 
The continuous or band spectrum was observed qualitatively by 
Mosely (I.e.), and its short wave-length limit at different voltages meas- 
ured by Duane and Hunt,^ who found this limiting frequency, i^^ax, 
to be exactly proportional to the voltage on the tube, and given accu- 
rately by the quantum relation hv^^y, = eV, where V is the voltage on 
the tube, e the charge of an electron, and h Planck's constant. 
The spectrum of tungsten is of special interest on account of its use 
as target material in X-ray tubes, and it has been the subject of several 
recent investigations. Barnes^ measured the L lines, but was unable 
to find any K lines, although his voltage, 96,000, was sufficiently high 
for their excitation. Gorton^ also measured the L Hues. Rutherford, 
Barnes and Richardson,^ using the coefficient of absorption method, 
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