Wavelength with fillers

The abihty of fillers to improve paper brightness increases with their intrinsic brightness, surface area, and refractive index. According to the Mie theory, this abiUty is maximum at an optimum filler particle size, about 0.25 pm in most cases, where the filler particle size is roughly one-half the wavelength of light used for the observation. 

To uniquely identify the intrinsic feature of the material, one method of sample preparation is to pelletize the explosive powders or crystals [14], It is standard practice in far-infrared (THz) spectroscopy to press samples into pellet form to measure the THz transmission spectra. When the sample is a powder with a grain size comparable to the THz wavelength (about 300 microns), the powder strongly scatters the THz radiation. Another method of sample preparation is to mix the material (e.g., RDX) with an inert matrix or filler material to create a pellet. The filler is typically a material that is transparent in the THz such as polyethylene. This allows dilute concentrations of a highly absorbing agent to be measured. 

A hollow cathode lamp emits an intense line spectrum of the cathode element, of any other element present in the cathode, and of the filler gas (neon or argon). It is therefore necessary to be able to isolate the lines of the determinant element from any other emitted lines. If we do not, the difference between 7t and /0 will be greatly reduced, and the sensitivity unacceptably poor. Moreover, not all lines of the determinant element give equal sensitivity, and it is therefore also desirable to isolate the determinant line at the wavelength which gives the most useful sensitivity from all other lines. This is done with a grating monochromator. Figure 6 illustrates a typical optical layout in the monochromator of an atomic absorption spectrometer. 

Deuterium or tungsten filament sources with interference filters were also used to provide a simple means of detecting absorbing species a.s they eluted from a column. Some instruments were dual wavelength devices, or they were equipped with filter wheels containing several filters that could be rapidly switched to detect various species as they eluted. Today, filler instruments... 

Flow Proportional Counter. The flow proportional counter covers a wide wavelength range and is generally used for wavelengths longer than 2 A (elements with Z < 27). This detector is illustrated in Fig. 8.24(a). The windows are thin (<6 pm) polymer film, coated on the inside surface with aluminum to permit a homogeneous electric field to be established within the detector. The thin windows allow the filler gas to leak out therefore a supply of filler gas is constantly provided to the detector through the inlet as shown in Fig. 8.24(a). The filler gas for a flow proportional counter is often 10% CH4, 90% Ar, a mixture called PIO gas. The pressure, flow, and temperature of the gas must be precisely controlled for accurate detector response. 

As one of the primary reasons for utilising filler is the development of optical properties, it is necessary to establish a cursory understanding of the interaction of various filler types with light of varying wavelengths. 

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