Single-beam measurements

Now, we are not particular experts in X-ray and gamma-ray spectroscopy (nor mass spectroscopy, for that matter), but our understanding of those technologies is that they are used mainly in emission mode. Even when the exciting source is a continuum source, such as is found when an X-ray tube is used to produce the exciting X-rays for an X-ray Fluorescence (XRF) measurement, the measurement itself consists of counting the X-rays emitted from the sample after the sample absorbs an X-ray from the source. These measurements are themselves the equivalent of single-beam measurements and will thus also be Poisson-distributed in accordance with the basic physics of the phenomenon. 

Obviously, single-beam measurements cannot characterize collective particle motions because gi2)(q. r) does not depend on v. Dual-beam (heterodyne) techniques (Section III.A.2) measure the real part of g<1)([Pg.231]

A circular dichroism detector (CD) can differentiate between enantiomers by measuring the difference in absorbance of right and left-handed circularly polarized light. Unlike single beam measurements made by optical rotation based detectors, the CD measurements of differential... 

In principle, the maximum water depth that can be detected with echo-soimding techniques is unlimited. If a variety of highly efficient transducers are available, single beam measurements can be carried out from extreme shallow water to the deepest trench of 11,000 metres. 

This paper deals with the control of weld depth penetration for cylinders in gold-nickel alloy and tantalum. After introducing the experimental set-up and the samples description, the study and the optimization of the testing are presented for single-sided measurements either in a pulse-echo configuration or when the pump and the probe laser beams are shifted (influence of a thermal phenomenon), and for different kind of laser impact (a line or a circular spot). First, the ultrasonic system is used to detect and to size a flat bottom hole in an aluminium plate. Indeed, when the width of the hole is reduced, its shape is nearly similar to the one of a slot. Then, the optimization is accomplished for... 

In the process of performing a spectrophotometric determination of Ee, an analyst prepares a calibration curve using a single-beam spectrometer, such as a Spec-20. After preparing the calibration curve, the analyst drops the cuvette used for the method blank and the standards. The analyst acquires a new cuvette, measures the absorbance of the sample, and determines the %w/w Ee in the sample. Will the change in cuvette lead to a determinate error in the analysis Explain. 

Because a FIXE spectrum represents the int al of all the X rays created along the particle s path, a single FIXE measurement does not provide any depth profile information. All attempts to obtain general depth profiles using FIXE have involved multiple measurements that varied either the beam energy or the angle between the beam and the target, and have compared the results to those calculated for assumed elemental distributions. Frofiles measured in a few special cases surest that the depth resolution by nondestructive FIXE is only about 100 nm and that the absolute concentration values can have errors of 10-50%. 

Sheik-Bahae, M., Said, A. A. and Van Stryland, E. W. (1989) High-sensitivity, single-beam ri2 measurements. Opt. Lett., 14, 955-957. 

Unac, R. O., Bustos, V., Wilson, J. et al. (2006) Molecular beam measurements and Monte Carlo simulations of the kinetics of N20 decomposition on Rh(l 11) single-crystal surfaces , J. Chem. Phys., 125, 074705-1. 

FTIR spectra were collected with a Nicolet 740 spectrometer and a custom built in situ gas flow cell. The spectrometer was equipped with a MCT-B detector cooled by liquid nitrogen. Approximately 15 mg of the MgO catalyst sample was pressed into a self-supported disc and placed in a sample holder located at the center of the cell. The temperature in the cell was measured with a thermocouple placed close to the catalyst sample. Transmission spectra were collected in a single beam mode with a resolution of 2 cm 1. Prior to introduction... 

The Z-scan technique, first introduced in 1989 [64, 65], is a sensitive single-beam technique to determine the nonlinear absorption and nonlinear refraction of materials independently from their fluorescence properties. The simplicity of separating the real and imaginary parts of the nonlinearity, corresponding to nonlinear refraction and absorption processes, makes the Z-scan the most widely used technique to measure these nonlinear properties however, it does not automatically differentiate the physical processes leading to the nonlinear responses. 

Sheik Bahae M, Said AA, Van Stryland EW (1989) High-sensitivity, single beam n2 measurements. Opt Lett 14 955-957... 

When using a single-beam spectrometer, I0 is measured when a reagent blank is used to zero the absorbance scale. The value of I is then measured when the sample is inserted into the spectrometer. On the other hand, when using a double-beam instrument both the reagent blank, 70, and the sample, I, are measured continuously and the appropriate ratio is determined electronically. 

In practical situations the absorbance of a sample is determined by making two measurements, the first to determine 70 and the second to determine I. The determination of I0 is used to cancel a large number of experimental factors that could affect the result. When measuring I0 the sample container must closely match the unknown container in all ways except for the analyte content. The cuvettes should be a matched pair if a double beam instrument is used and the same cuvette can be used for both the blank and sample with a single beam instrument. The blank solution filling the cuvette should be identical to the solvent that the sample is dissolved in, except for the sample itself. If done correctly, the least-squares line for the calibration graph will come very close to the 0,0 point on the graph. 

The single beam instrument measures directly the amount of energy transmitted by the sample. They give the most accurate transmittance measurements and is particularly helpful for quantitative analysis. It has simpler and more reliable systems than double beam. 

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