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![[Figure 3]](ge5117fig3mag.jpg)
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Figure 3
Intensity patterns (left-hand column) and the real parts of the diffraction amplitudes (right-hand column) from slit apertures corresponding to two of the examples listed in Table 1 ![[link]](../../../../../../logos/arrows/j_arr.gif){kind=small} . The neutron wavelength is taken to be 5 Å. The intensity patterns are plotted at a point of observation a distance S (0.5 m) away from the aperture along the y axis, perpendicular to the direction of propagation of the wave incident on the slit. For the amplitude plots, the y axis is also perpendicular to the incident beam direction, whereas the x axis extends a distance of five neutron wavelengths along the direction of propagation back from the farthest observation point at a distance S (0.5 m). One measure of the distance ΔrT over which a given wavefront is uniform in phase to within one wavelength can be determined by examining two consecutive wavefronts propagating along the x axis, as pictured in the upper right-hand plot. Choose an arbitrary leading wavefront. Draw a curve (shown as blue) along that wavefront's ridge of relative maximum amplitude. Next, construct a straight line (shown as red) parallel to the transverse y axis through the central maximum (at y = 0.0) of the wavefront immediately following (to the left). The x coordinates of either of the intersections of the blue curve and red line differ from that of the central maximum of the leading wavefront by one wavelength. For the 10 µm slit, this measure corresponds roughly to that obtained from the first minimum of the intensity on either side of the central maximum. The 10 µm-wide slit produces a pattern at 0.5 m that is in the far-field limit, while that of the 100 µm aperture is well within the near-field region. |
![[Figure 3]](ge5117fig3.jpg)
 | JOURNAL OF APPLIED CRYSTALLOGRAPHY |
ISSN: 1600-5767
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