Y TIE interest in microwave-escitecl electrodelcss discharge tubes has largely centred on their use as Iiigh-intensity line sources for USC in atomic fluorescence spectroscopy
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In this technique, the profile of the atomic line and the nature of the spectral region surrounding it arc of considerably less importance than in atomic absorption spectroscopy because the source is not directly viewed by the detector. However, the "purity" of the emission from these discharge tubes, l~ecausc of the absence of carrier gas spectrum, tlie suppression of ion lines and the elimination of lines of extraneous elements present in electrode materials, appears to make such sources very suitable for atomic absorption measurcment9.
Previously, these electrodeless tubes have been used in conjunction with d.c. amplification systems or their radiation has been mechanically chopped to match the a-c. amplification of the flame spectrometer for both atomic absorption and atomic fluorescence spectroscopy".
Obviously, electronic modulation, tuned to the frequency of the a.c. detecting system, greatly simplifies the experimental arrangement, especially in atomic fluorescence spectroscopy where mechanical choppers physically prevent radiation from reaching the atom reservoir, and greatly facilitates their application to atomic absorption measurements.
In this paper, electronic modulation of electrodeless clischarge tubes is discussed, and the spectra emitted from several modulated sources and the sensitivity attainable by using them in atomic absorption spectroscopy are described. The clischarge tubes used (lead, mercury, silver, thallium and tin) were operated in resonant cavities with microwaves of frequency 2450 f 25 MHz and with superimposed electronic modulation at 50 Hz. Their properties were compared with those of the correspondingly modulate-d hollow-cathocle lamps. Special attention was given to features liable to affect the precision of absorption measurements made with electrodeless discharge tubes as line sources. In all cases, their performance, modulated and unmodulated, was found to be comparable with, or better than, the respective hollow-cathode lamp under optimised running conditions.
Quantitative comparisons of spectral intensities, stabilities, warm-up times and LIlaal. Claim.
Ac~n, 45 (IgGg) 163-170