Diffraction slit width

XRD Characterization The powder x-ray diffraction of the mechano-chemically milled complex borohydride has been carried out by the Philips X pert diffractometer with Cu-Koi radiation of X= 5.4060 A. The incident and diffraction slit width used for the measurements are 1° and 2° respectively. The sample holder was covered with Polyethylene tape (foil) with an O-ring seal in an N2 filled glove box in order to avoid or at least minimize the 02/moisture pickup during the XRD measurements. The diffraction from the tape was calibrated without the actual sample and found to be occurring at 29 angles of 22° and 24°, respectively. The XRD phase identification and particle size calculation has been carried out using PANalytical X pert Highscore software, version l.Of. 

With an entrance collimator a quasi parallel beam is produced from the radiation coming through the entrance aperture, which has a width se and a heigth he. The entrance collimator has a focal length and a width W. The diffraction slit width (so) and the diffraction slit heigth (h0) are the half-widths given by ... 

A7Z can be determined by measuring the practical resolution of the monochromator from the deconvolution of the two components of the Hg 313.1 nm line doublet and subtraction of the contributions of the diffraction slit width (so = 7 f/W) and the entrance slit width (se). The contribution of the natural width of the Hg lines can be neglected, as it is very low in the case of a hollow cathode lamp. 

The first factor is technical, related to instrumental parameters such as the entrance slit width, the quality of the optics (e.g. focal distance), and diffraction through narrow orifices. 

Figure 3. Emission spectra obtained from an induction coupled plasma with an ultrasonic nebulizer (for sample introduction). Aim spectrometer, JACO model with a diffraction grating blazed at 250 nm, and a slit width of 20 pm, was used. The spectral resolution was 10.3 nm/500 channels = 0.0206 nm/channel. (a) Emission spectrum of a 1 pg/l bertjlium, 1% HNOj solution, (b) Emission spectrum of a 1% HN03 blank solution, (c) Difference spectrum obtained by subtracting spectrum (b) from (a). Spectra were obtained after an on-target integration for 8 sec.

Figure 3.1-6 The main components of a grating spectrometer N is the number of interfering rays, given by the number of rules so is the half width of the diffraction pattern of the collimator lens with the diameter D and the focal length /, it determines the optimal slit width (Laqua, 1980), h is the slit length.

In principle, the diffraction patterns can be quantitatively understood within the Fraunhofer approximation of Kirchhoff s diffraction theory as described in any optics textbook (e.g., [Hecht 1994]). However, Fraunhofer s optical diffraction theory misses an important point of our experiments with matter waves and material gratings the attractive interaction between the molecule and the wall results in an additional phase of the molecular wavefunction [Grisenti 1999], Although the details of the calculations are somewhat involved2, the qualitative effect of this attractive force on far-field diffraction can be understood as a narrowing of the real slit width to an effective slit width [Briihl 2002], For our fullerene molecules the reduction can be as big as 20 nm for the unselected molecular beam and almost 30 nm for the slower, velocity selected beam. The stronger effect on slower molecules is due to the longer and therefore more influential interaction between the molecules and the wall. 

The beam diffracted by the specimen passes through another Soller slit and the receiving slit F before entering the counter (Fig. 7-8). Since the receiving slit defines the width of the beam admitted to the counter, an increase in its width will increase the maximum intensity of any diffraction line being measured but at the expense of some loss of resolution. On the other hand, the relative integrated intensity of a diffraction line is independent of slit width, which is one reason for its greater fundamental importance. ... 

The spectral range of interest for AAS spans from the near infrared (852.1 nm for Cs) to the vacuum ultra violet (193.6 nm for As). A monochromator is a device which separates, isolates, and controls the intensity of a narrow region of the radiant energy which is transmitted to the detector (characterised by its spectral slit width). It consists of an entrance slit, a dispersing unit (a diffraction grating) and an exit slit. The greater the intensity of the radiation transmitted to the detector the lower the signal amplification required (which contributes to electronic noise). However, the entrance and exit slits must be of similar mechanical widths (aperture size) so that, in practice, a compromise must be chosen (slit width versus narrow... 

If the intensity of the source and the sensitivity of the detector are sufficient, the spectral purity can be improved (the bandpass decreased) by decreasing the slit width. The decrease may not be hnear, however, and a limit is reached due to aberrations in the optics and diffraction effects caused by the slit at very narrow widths. The diffraction effectively increases the spectral slit width. In actual practice, the sensitivity limit of the instrument is usually reached before diffraction effects become too serious. 

Note that the position of the maximum value /Max does not depend on the total number of slits N. The maximum value /Max increases markedly with decreasing slit width, /s, in accordance with the equation shown in Table 1.1. With diffraction gratings, one can obtain light of narrow wavelength distribution without having recourse to a prism system. 

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