Resolution spectrometry

The stability of the wavelength setting of a monochromator can be a problem in high resolution spectrometry. This difficulty has been overcome by the use of the resonance monochromator (S24), consisting of a hollow cathode lamp modified to produce only an atomic vapor. The vapor is irradiated with the light to be analyzed and fluorescence occurs at the resonant wavelength of the cathode element. The intensity of the fluorescence is proportional to the component of that wavelength in the primary radiation. 

Large aperture, high resolution spectrometry can be achieved using interferometers. A scanning system used in conjunction with Fourier transform spectroscopy (see Section 3.4) would facilitate the rapid measurement of complex spectra. As computer facilities are essential, the technique lends itself to automated analysis. 

Reednick J. (1979) A unique approach to atomic spectroscopy high energy plasma excitation and high resolution spectrometry, Am Lab May 127-133. 

High resolution spectrometry is practicable with some of the emission spectra produced by Ar impact, although the low intensities observed... 

Analogue stabilization is only suitable for low-resolution spectrometry. Scintillation detectors are particularly prone to drift because of the temperature sensitivity of the electronics and to instabUity of tbe high voltage. This form of... 

For high-resolution spectrometry systems, it is essential to use preamplifiers and amplifiers with alow noise specification. 

As with the preamplifier, the scintillation amphfier need not be of such a demanding low noise specification as would be needed for semiconductor systems. In the manufacturers catalogues, a distinction is commonly made between amplifier , suitable for low-resolution spectrometry, and spectroscopy amplifier intended for high-resolution spectrometry using semiconductor detectors. Typical simple amplifier modules provide pole-zero cancellation and automatic base line restoration. The pulse shaping time options provided are often limited on such instruments and may need to be selected internally. Because of the faster rise time of scintillation pulses, the time constants provided are usually within the range 0.2 to 2 or 3 (its. 

Scintillation spectrometry, of necessity, is restricted to simple measurements of few nuchdes. Very often, it wUl be sufficient to use the limited peak area measurement facilities of the MCA system (be it hardwired or software emulator) based upon manually set regions-of-interest. One should be cautious about attempting to use spectrum analysis programs for the analysis of scintillation spectra. Most programs will have been developed with semiconductor spectra in mind and may not be suitable, although ORTEC do provide ScintiVision-32, specifically aimed at low resolution spectrometry. If in doubt, the software supplier will be able to advise. 

The reason hes in the fact that the counts in a germanium spectrum, even though fewer in number, are concentrated within a few channels, whereas the counts in the sodium iodide spectrum are spread over many channels. This means that peaks are easier to detect in the germanium spectrum and ultimately the limit of measurement is lower. The huge difference in resolution between the two detectors cannot be compensated by the increase in the count rate from the sodium iodide detector. That being said, there are low count rate situations where the need for high-resolution spectrometry is not paramount and the higher cost of a semiconductor detector is not justified. 

Itoh, Y Kasuya, A. and Hasegawa, T. (2009) Analytical understanding of multiple-angle incidence resolution spectrometry based on classical electromagnetic theory. J. Phys. Chem. A, 113, 7810-7817. 

F1g.7.5. Schematic diagram of a tunable diode laser instrument for high-resolution spectrometry (Courtesy Spectra Physics)... 

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