Bragg Diffraction: Calculate 1st & 2nd Order Angles

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    Bragg Diffraction
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The discussion centers on calculating the first and second-order diffraction angles for X-rays diffracted by a crystal with atomic plane spacing of 0.120 nm and energy of 15.0 keV. It highlights the use of the formula 2dcosΘ = mλ instead of the more commonly known 2dsinΘ = mλ, emphasizing that the angle in question is between the crystal surface and the diffracted beams rather than the normal to the surface. This distinction is crucial because Bragg diffraction involves reflection of X-rays from the crystal surface, unlike typical light diffraction that involves transmission. The manual's approach is clarified as being appropriate for the specific context of Bragg diffraction. Understanding these angles and the correct formula is essential for accurate calculations in crystallography.
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The spacing between atomic planes in a crystal is 0.120 nm . 15.0 keV x rays are diffracted by this crystal What is the angle of first-order diffraction?What is the angle of second-order diffraction?My question is that the manual says to use 2dcosΘ=mλ instead of 2dsinΘ=mλ( bragg diffraction condition). Why?
 
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Can you illustrate with a diagram?
 
Mohammed Shoaib said:
The spacing between atomic planes in a crystal is 0.120 nm . 15.0 keV x rays are diffracted by this crystal What is the angle of first-order diffraction?What is the angle of second-order diffraction?My question is that the manual says to use 2dcosΘ=mλ instead of 2dsinΘ=mλ( bragg diffraction condition). Why?
With Bragg diffraction the angle used in the analysis is the angle between the crystal surface and the diffracted beams,...NOT the angle between the normal and the diffracted beams (you are probably more familiar with that one...Sin theta)
The diffraction is caused by reflection of X rays from the surface of the crystal not transmission (which is usually the case with light and transmission gratings)
 
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