Bragg condition

Also known as Bragg's formula, this is the basic formula that describes the conditions for diffraction of X-rays by crystals, and was derived by Bragg father and son in 1912. Considering a group of parallel atomic planes with interplanar spacing in a crystal, as is clear from the diagram,

2d sin θ ＝ n λ

(where n is a positive integer and λ is the wavelength of the X-rays) is satisfied, the path difference is an integer multiple of the wavelength, resulting in a strong diffracted beam. This formula is called the Bragg formula, and θ is the Bragg angle. When this formula holds true, the incident X-rays can be thought of as being specularly reflected by the atomic lattice surface, so diffraction that satisfies the Bragg condition is called Bragg reflection. This formula also applies to electron beams and neutron beams. It is equivalent to the Laue condition.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

ブラッグの式(Bragg's formula)ともいう．結晶によるX線の回折条件を表す基本式で，1912年，Bragg(ブラッグ)父子により導かれた．結晶中に面間隔をもつ平行な原子網面群を考えると，図から明らかなように，

2d sin θ ＝ nλ

(ここで，nは正の整数，λはX線の波長)を満足するとき，行路差が波長の整数倍になるので強い回折線が生じる．この式をブラッグの式，θをブラッグ角という．この式が成り立つとき，入射X線は原子網面によって鏡面反射されたと考えてもよいので，ブラッグ条件を満たす回折をブラッグ反射という．この式は電子線，中性子線にも適用される．これはラウエ条件と同等である．

出典　森北出版「化学辞典（第2版）」化学辞典 第2版について　情報