X$-$ray diffraction is used to study the structure of crystallized proteins, nucleic acids, and other biological macromolecules. It was actually the technique used to study the structure of DNA in the early $1950$s$.$ X$-$rays of wavelength $0\mathrm{.}19$ nmnm $$are to used to study the structure of a protein. One of the maxima in intensity is located at $0\mathrm{.}8$ radrad from the crystal planes responsible for this maximum.