Beam attenuation

ATR Attenuated total reflection Reflected beam attenuated Similar to IR... 

In most ultrasonic tests, the significant echo signal often is the one having the maximum ampHtude. This ampHtude is affected by the selection of the beam angle, and the position and direction from which it interrogates the flaw. The depth of flaws is often deterrnined to considerable precision by the transit time of the pulses within the test material. The relative reflecting power of discontinuities is deterrnined by comparison of the test signal with echoes from artificial discontinuities such as flat-bottomed holes, side-drilled holes, and notches in reference test blocks. This technique provides some standardized tests for sound beam attenuation and ultrasonic equipment beam spread. 

Reference beam aperture. This is where nothing goes. Or, in extreme cases, you use a reference beam attenuator to cut down the amount of light reaching the detector. 

Gently slide reference beam attenuator and watch pen — stop when pen points to 80 90% T... 

Fig. 129 Using a reference beam attenuator with a KBr window.

Remove your sample, and replace it with the standard polystyrene film sample. You will have to remove any reference beam attenuator and turn the 100% control to set the pen at about 90%, when the chart is at 4000 cm-1. 

The photoablation behaviour of a number of polymers has been described with the aid of the moving interface model. The kinetics of ablation is characterized by the rate constant k and a laser beam attenuation by the desorbing products is quantified by the screening coefficient 6. The polymer structure strongly influences the ablation parameters and some general trends are inferred. The deposition rates and yields of the ablation products can also be precisely measured with the quartz crystal microbalance. The yields usually depend on fluence, wavelength, polymer structure and background pressure. 

The general setup of LDI/MALDI ion sources is comparatively simple (Fig. 10.2). [27] The pulse of laser light is focused onto a small spot which is typically 0.05-0.2 mm in diameter. [28] As laser irradiance is a critical parameter in MALDI, a variable beam attenuator in the laser optical path is employed to adjust... 

Absorption effects combine with this to make the beam attenuate more rapidly. In the absence of extinction, the absorption depth t is given by... 

Figure 2 The photoabsorption (c), photoionization (o-,-), and photodissociation (cr

Because of the complexity of the Ni-58(p,3p4n)Fe-52 reaction, the excitation function is expected to show a monotonical rise from the threshold energy and then remain relatively flat once the maximum is reached. Consequently, an increase in nickel target thickness should raise the yield proportionately. The concentrations of Fe-55 and Fe-59 impurities in the product are also expected to remain unchanged for the same reason. This has been qualitatively checked by simultaneously bombarding 4 Ni foils (.023 g/cm each) placed in our target stack such that the incident proton energies were 192, 127, 80 and 61 MeV, respectively. After correction for beam attenuation the yields were essentially constant. 

Figure 15.11 Decadic beam attenuation coefficients calculated per milligram of DOC as a function of wavelength for a series of water samples from various Swiss lakes and rivers (data from Haag and Hoigne, 1986).

Consider a well-mixed, nonturbid water body with a dissolved organic carbon concentration (DOC) of 4 mg C L-1. The decadic beam attenuation coefficients, a(A), determined for a water sample at five wavelengths are the following (see other examples given in Fig. 15.11) ... 

Decadal beam attenuation coefficients a.(k) of the water at various wavelengths (X) ... 

Spectra were run on a Perkin-Elmer model 125 grating spectrophotometer at room temperature, ignoring the heating effect of the IR beam. Reference beam attenuation was used. The spectral slit width was less than 3 cm-1 in the region 1600-1400 cm-1. Optical density measurements were carried out as previously described (19). 

What do we typically measure when we study a nuclear reaction We might measure aR, the total reaction cross section. This might be measured by a beam attenuation method ( transmitted vs- incident) or by measuring all possible exit channels for a reaction where... 

After filtering, radiation from the monochrometer is focused onto a thermocouple detector. The alternating signal at the detector is amplified and fed to a servo-motor which moves a reference beam attenuator to equalize the intensity of the sample and reference beams. The alternating signal is thereby reduced, producing a state of equilibrium. The absorbance of a sample placed in the sample beam is determined by the extent of movement of the reference beam attenuator. 

The X-ray beam attenuation depends naturally on the range of photon energies, E, with which the XDI investigation is to be conducted. In practice, the choice of optimum photon energy is derived from a judicious compromise of several factors as detailed in Sections 2.4.1.1.-2.4.1.4. 

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