Source characteristic line

Coherently scattered tube or secondary source characteristic lines. 

Incoherently scattered tube or source characteristic lines. 

For quantitative analysis, the resolution of the spectral analyzer must be significantly narrower than the absorption lines, which are - 0.002 nm at 400 nm for Af = 50 amu at 2500°C (eq. 4). This is unachievable with most spectrophotometers. Instead, narrow-line sources specific for each element are employed. These are usually hoUow-cathode lamps, in which a cylindrical cathode composed of (or lined with) the element of interest is bombarded with inert gas cations produced in a discharge. Atoms sputtered from the cathode are excited by coUisions in the lamp atmosphere and then decay, emitting very narrow characteristic lines. More recendy semiconductor diode arrays have been used for AAS (168) (see Semiconductors). 

Consider individual atoms of an element deposited on a thin substrate highly transparent to x-rays—say atoms of molybdenum upon paper. Let a characteristic line (say molybdenum K ) be excited by a polychromatic beam, x-ray source and detector both being located above the sample. So long as the number of molybdenum atoms is small, they will not noticeably attenuate the incident beam, nor will an x-ray quantum radiated by any molybdenum atom be absorbed by any other. Under these conditions, the intensity of the characteristic line will be proportional to the number of molybdenum atoms and hence to the thickness of the molybdenum film. 

The preceding oversimplified mathematical treatment really amounts to an evaluation of the absorption effect (6.1). The exponential term in Equation 6-4 is obviously a product of two exponential terms, each deriving from Beerks Law. One term governs the attenuation of the beam incident upon the volume element in question, and the other governs the attenuation of the characteristic line emerging frcJm this element. The films are so thin that the use of one value each for 6 and for 02 over the entire film thickness is justified. Finally, one must assume that the intensity measured by the detector remains proportional to the intensity of the source. An exact treatment of the problem would be so complicated that one is justified in seeing what can be done with the simple relationships obtained above. 

CHARACTERISTIC LINES FOUND IN THE VACUUM UV OUTPUT OF HNU SOURCES... 

The basic function of the spectrometer is to separate the polychromatic beam of radiation coming from the specimen in order that the intensities of each individual characteristic line can be measured. In principle, the wide variety of instruments (WDXRF and EDXRF types) differ only in the type of source used for excitation, the number of elements which they are able to measure at one time and the speed of data collection. Detectors commonly employed in X-ray spectrometers are usually either a gas-flow proportional counter for heavier elements/soft X-rays (useful range E < 6keV 1.5-50 A), a scintillation counter for lighter elements/hard X-rays (E > 6keV 0.2-2 A) or a solid-state detector (0.5-8 A). 

A 0.4 m thick SPP layer was exposed to X-rays followed by a flood exposure using near UV radiation. The resist was then dip-developed in a 0.8 wt% TMAH solution for 60 s at 25 °C. We used two x-ray exposure systems to evaluate the characteristics of the SPP resist. One is SR-114 which has a source composed of a molybdenum rotating anode with a 0.54 nm Mo-La characteristic line. The exposure was carried out in air. The other has a synchrotron radiation source with a central wavelength of 0.7 nm (KEK Photon Factory Beam Line, BL-1B). The exposure was carried out in vacuum (<10-4 Pa). A positive resist, FBM-G,15) was used as a standard, because its sensitivity only weakly depends on the ambient. 

It is important to select the best laser source. For practical applications the first harmonic of Nd-YAG (1,064 nm) is preferential, because such a laser is powerful and exists in ruggedized industrial versions. It was foimd that the spectra are principally the same as under Aex = 355 nm (Fig. 8.15), but the characteristic line of F is much weaker and clearly seen only after a delay time of several microseconds when the overall intensity is already low. The characteristic Une of P at 254 nm is very weak and the strongest Unes in the spectra belong to Ca ions. 

Table 1 Photon energies of characteristic lines from low energy resonance sources and X-ray sources...

Meroney, R.N., Pavageau, M Rafailidis, S., and Schatzmann, M. (1996) Study of Line Source Characteristics for 2-d Physical Modelling of Pollutant Dispersion in Street Canyons,./. Wind Engineering Industrial Aerodynamics Vol. 62, 37-56. 

Boumans, P.W.XM . and Vrakking, J.J.A.M. (1987). Detection limits of about 350 prominent lines of 65 elements observed in 50 and 27 MHz inductively coupled plasma (ICP) Effects of source characteristics, noise and spectral bandwidth-"standard" values for the 50 MHz ICP, Spectrochim. Acta 42B, 553-579. 

One of the problems of using the X-ray tube illustrated in Fig. 8.9 is that both continuum and characteristic line radiation is generated at certain operating voltages, as seen in Fig. 8.3. For many analytical uses, only one type of radiation is desired. Filters of various materials can be used to absorb unwanted radiation but permit radiation of the desired wavelength to pass by placing the filter between the X-ray source and the sample. 

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