Yes, the way I like to think of it as a double condition, the > reflection‐in‐a‐mirror condition *plus* the special condition imposed > by Bragg’s Law. This is why I often prefer the unfashionable spelling > “reflexion”. > > -- > Ian ◎ >
Me too. Actually "reflexion" (but the verb is "reflect") is the original correct spelling (from Latin reflectere & reflexio); apparently at some point in its history it became misspelt due to a false analogy with "correct" & "correction" (Latin corrigere & correctio). Now back to the science! It's important to understand that a "powder" is not amorphous which would indeed give a continuous pattern: it's a bunch of micro-crystals in random orientations. Therefore a powder diffraction pattern is a single crystal pattern averaged over all orientations. Rotating the crystal does not change the Bragg angles of the spots, however it does change their angular positions so each diffracted beam is smeared out over conical surface. Each of these cones then projects as a circle on a flat area detector (of course in powder diffraction one would use a linear detector since it's not necessary to measure a complete circle). Cheers -- Ian
