Acceptance monochromator

Procedures for determining the spectral responslvlty or correction factors In equation 2 are based on radiance or Irradlance standards, calibrated source-monochromator combinations, and an accepted standard. The easiest measurement procedure for determining corrected emission spectra Is to use a well-characterized standard and obtain an Instrumental response function, as described by equation 3 (17). In this case, quinine sulfate dlhydrate has been extensively studied and Issued as a National Bureau of Standards (NBS) Standard Reference Material (SRM). 

The irradiating X-ray beam cannot be focussed upon and scanned across the specimen surface as is possible with an electron beam. Practical methods of small-spot XPS imaging rely on restriction of the source size or the analysed area. By using a focussing crystal monochromator for the X-rays, beam sizes of less than 10 pm may be achieved. This must in turn correspond with the acceptance area and alignment on the sample of the electron spectrometer, which involves the use of an electron lens of low aberration. The practically achievable spatial resolution is rarely better than 100 pm. A spatial resolution value of 200 pm might be regarded as typical, and it must also be remembered that areas of up to several millimetres in diameter can readily be analysed. 

For a comparison of the intensities achievable after monochromatization, one has, however, to take into account that - depending on the design - monochromators can accept an appreciable amount of radiation in the horizontal direction. For radiation from a bending magnet this increases the accepted radiation proportionally, but this is not so for undulator radiation due to its strong confinement in the vertical and horizontal directions. 

After an investigation of several years with the same type of algae and approximately the same intensity of monochromatic light as used by Warburg we are forced to conclude that the photosynthetic process is considerably less efficient than the 0.2 or 0.3 which is now accepted.63 With the monochromator already described and with direct, microchemical analysis of the gas or by titration for oxygen we find a quantum yield of about 0.05 changing somewhat with the conditions. Under our conditions ten to twenty quanta instead of the classical four seem to be necessary to convert one molecule of carbon dioxide into plant material. 

The number of devices required to multiplex a monochromic television display of moderate resolution is enormous, about 100,000, and color schemes triple this number (see, e.g., Uchida etal., 1982,1983). To succeed, therefore, a specific technology must demonstrate not only that individual elements meet the (very modest) electrical requirements but also that active matrices, with gate counts comparable to the largest intergrated circuits produced, can be fabricated with acceptable yields. 

Wavelength repeatability is a measure of the precision of wavelength measured. The bandwidth refers to the width of an emission band (from the monochromator) at half peak height. This value, normally provided by the manufacturer is accepted. Using a mercury vapor lamp one can also check the spectral width. A number of well defined emission lines at 243.7, 364.9, 404.5, 435.8, 546.1, 576.9, and 579 nm can be used to check spectral bandwidth. However, the accuracy of the absorbance measured is dependent on the ratio of spectral bandwidth to the normal bandwidth (NEW) of the absorbing species. Most active pharmaceutical compounds have a normal bandwidth of approximately... 

An electric beam chopper and a tuned amplifier are incorporated into most AA instrument. Operationally, the power to the hoUow-cathode lamp is pulsed so that the light is emitted by the lamp at a certain number of pulses per second. On the other hand, aU of the light coming from the flame is continuous. When light leaves the flame, it is composed of pulsed, unabsorbed light from the lamp and a small amount of unpulsed flame spectrum and sample emission. The detector senses all light, but the amplifier is electrically tuned to accept only pulsed signals. In this way, the electronics in conjunction with the monochromator discriminate between the flame spectrum and sample emission. 

Figure 2.10 Bragg Brentano geometry with a diffracted beam monochromator. The crystal is usually graphite, which has a low degree of crystalline perfection, and hence a large acceptance angle (tenths of a degree). Thus a flat crystal is adequate.

The convenhonal spectrometer consisted of a Coderg double monochromator equipped with a cooled PMT and was described in detail by Brooker et al. (1994). A 1 W laser was required to obtain spectra with adequate signal to noise ratio. A half-wave plate controlled the polarization of the incident beam. The 90° scattered light was analyzed with Polaroid films with accepted parallel or perpendicular polarized light. A quarter wave-plate in front of the entrance slit served to compensate for grating polarization preference. 

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