Monitoring incident beam

It has been stressed [Blostein 2001 Blostein 2003 (a) Blostein 2003 (b) Cowley 2003] that an accurate determination of the incident neutron intensity I Eq) is essential for the determination of cross section ratios on VESU-VIO. I Eq) was measured using the VESUVIO incident beam monitor 1 (see Fig. 1). The incident energy of the neutrons is related to their time of flight measured in the monitor via... 

Figure 8.2 (a) The overflowing cylinder (OFC). (b) Schematic setup of the OFC with neutron reflection. Slits - SI, S2, S3, S4. M -incident beam monitor. D - flnal detector. Reprinted with permission from [16]. (2003) American Chemical Society. 

Figure 10 Schematic diagram of the direct-geometry spectrometer MARI at ISIS. Ml, M2 and M3 are incident beam monitors.

Fixing the incident beam angle and rotating the crystal about tlie surface nonnal while monitoring the... 

An infrared beam is directed through a crystal of refractive index (ni) onto a sample of smaller refractive index (n2). The intensity of the reflected beam is monitored as a function of the wavelength of the incident beam. These absorptions are used to identify the chemical structure. ATR has a sampling depth of about 0.3-3.0 microns. 

Radiation from a xenon or deuterium source is focussed on the flow cell. An interchangeable filter allows different excitation wavelengths to be used. The fluorescent radiation is emitted by the sample in all directions, but is usually measured at 90° to the incident beam. In some types, to increase sensitivity, the fluorescent radiation is reflected and focussed by a parabolic mirror. The second filter isolates a suitable wavelength from the fluorescence spectrum and prevents any scattered light from the source from reaching the photomultiplier detector. The 90° optics allow monitoring of the incident beam as well, so that dual uv absorption and fluorescence... 

Figure 12.9—OpticaI scheme of a spectrofluorimeter having two detectors, one of which is used to control the intensity of the light source. A fraction of the incident beam is reflected by the beam splitter and monitored by a photodiode to control the intensity of the incident beam. Comparison of the signals obtained from both detectors allows the elimination of any drift in the light source. This procedure, for single beam instruments, gives approximately the same stability as with double beam instruments. (Model F4500 reproduced by permission of Shimadzu.)...

The first four mirrors (>99.7% reflectance at 1.06 micron) act as a far field isolator which locates the multipass cavity 15 meters away from the laser and effectively isolates the laser from the potentially damaging retroreflected 1.06 micron radiation from the normal incidence beam splitter. The multipass cavity is aligned by monitoring the retroreflected 1.06 micron pulse which is found to emerge from the Nd YAG laser cavity, 120 nsec after the original pulse, when optimum alignment is achieved. 

The most common mode of chemical analysis presented herein has been the monitoring of elastically/inelastically scattered or recoiled incident beam species, or... 

The principal components of a fluorescence spectrophotometer (fluorimeter) are shown in Fig. 26.4. The instrument contains two monochromators, one to select the excitation wavelength and the other to monitor the light emitted, usually at 90° to the incident beam (though light is actually emitted in aU directions). As an example, the wavelengths used to measure the highly fluorescent compound naphthalene are 270 nm (excitation) and 340 nm (emission). Some examples of molecules with intrinsic fluorescence are given in Table 26.1. 

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