Bragg reflections, occurrence

That the bond density is also of significance for heavier atoms is evident from the occurrence of the spherical-atom forbidden (222) reflection of diamond and silicon, even at low temperatures where anharmonic thermal effects (see chapter 2) are negligible. The historical importance of the nonzero intensity of the diamond (222) reflection is illustrated by the following comment made by W. H. Bragg, in 1921 ... 

The curve in Fig. 56b shows entirely different conditions. The first maximum is displaced much nearer to the point of penetration. This indicates the very frequent occurrence of some distance in the liquid which exceeds the intramolecular distances of the individual atoms for according to Bragg s reflection law... 

---