Approximately 25,000 experimental transition probabilities (gA), or oscillator strengths (gf), for spectral lines of 70 elements have been derived at the National Bureau of Standards. This work t by C. H. Corliss and W. R. Bozman has increased the number of known transition probabilities for these elements by a factor of 10. The wavelength range of the lines included in the study is from 2000 to 9000 A. More than half the lines are from spectra of elements for which there were no previously known transition probabilities. About two-thirds of the lines are from spectra of neutral atoms, and one-third are from spectra of singly ionized atoms.
The results are expressed on a uniform absolute scale, so that in the analysis of stellar atmospheres, for example, absolute quantities of constituents can be determined. To illustrate the utility of these transition probability values in such practical astrophysical work, Mr. Corliss has used them to construct a curve of growth for the second spectrum of yttrium in the sun. Values from the tables have been used in industrial laboratories to measure temperatures of plasma jets. They also are useful in determining temperatures of stellar atmospheres and of laboratory light sources that emit atomic spectra.
Wavelength and intensity are the primary attributes of a spectral line as observed in the laboratory. The wavelength is ordinarily measured to six significant figures, and occasionally to eight or nine. The intensity, on the other hand, is seldom measured accurately to one figure and never to more than two.
About 30 years ago, W. F. Meggers initiated at the Bureau an extensive program of intensity measurements intended to correct this situation. The light source used to produce the spectra that were measured was a 10-amp, 220-v d-c arc between copper electrodes mounted in water-cooled clamps. The electrodes contained one atom of the element under investigation for every 1000 atoms of copper. The results of this program were recently published as Tables of Spectral-Line Intensities. 2 These tables list the principal lines of the 70 elements generally observed under ordinary conditions in arc spectra, together with their relative intensities on a true scale of relat "Experimental Transition Probabilities for Spectral Lines of Seventy Elements", by C. 11. Cortiss and W. R. Bozman, NBS Mono. 53 (1962). For sale by the Superintendent o[ l)ocuments.