What is the origin of two close and sharp peaks (of kind of equal intensity- doublet) in powder x-ray diffraction?

Basically for Ag nanoparticles. 111 is sharp and single but 200 (44.29 and 44.41), 220 (64.45 and 64.62), 311 (77.37 and 77.60) are showing sharp, kind of equal intensity doublets.

19 October 2021 9,510 10 View