The law expressing the condition under which a crystal will reflect a beam of x-rays with the greatest amount of distinction or resolution and, at the same time, denoting the angle at which the reflection occurs. For x-ray reflection, the angle formed by the incident or the reflected beam and the crystal planes is the one generally used. If this Bragg angle is represented by q
, if d represents the distance between the planes or layers of atoms, and if l
is the wavelength of the x-rays, the law may be expressed by the equation:
assuming that n must be a whole number.