Solid-state detectors advantage

Transmission spectroscopy offers two significant advantages over photoacoustic spectroscopy of powders. First, transmission spectroscopy is not susceotible to external acoustic disturbances. Commercial spectrometers must be modified for vibrational isolation in order to obtain good photoacoustic spectra. Secondly, transmission spectroscopy can use solid state detectors with very fast response times, whereas photoacoustic spectroscopy is much slower, with spectra taking a few minutes to collect as compared to a few seconds for transmission spectra when both are taken with an FTIR. 

The first detectors to be used in OMA systems were standard TV image tubes. These were silicon vidicons or the more sensitive Silicon Intensified Target (SIT) detectors, which both employed silicon targets to convert optical information into electronic form. More recently, the use of solid state detectors in the form of a diode array (Reticon) has been found to have some advantages over the vidicons and SIT tubes. Current developments in the field of charge coupled devices (CCD) will probably soon provide an even better multielement detector for use in OMA systems. 

In energy dispersive instruments, all the characteristic X-rays from the specimen are first detected by a high resolution solid state detector. The detector output consists of electrical pulses of amplitude proportional to the energy of the detected photons. These pulses, once linearly amplified, are electronically sorted according to their amplitude by means of a pulse height analyzer. An advantageous consequence of this detection mode is that analysis of all chemical elements can be performed simultaneously. Since it eliminates the use of crystal goniometers and the X-rays are not spatially dispersed, this type of spectrometer is also sometimes referred to as nondis-persive. 

The energy dispersive spectrometer (Solid State Detector) fitted to a chamber which includes the sample and a Y tay source is the dominant instrument in the high momentum transfer regime for the electron momentum distribution measurements. Two such systems are sho n in fig. 3b and 3c. Recently,instead of the Y ray source in Compton spectrometers,there have been employed x-ray spectrometry tubes with heavy metal anodes operated at 100 kV, with the obvious advantages (fig.3d). Table (1) presents a... 

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