Using Braggs law

A reflection from the (111) planes of a cubic crystal was observed at a glancing angle of 11.2° when Cu K , X-rays of wavelength 154 pm were used. What is the length of the side of the unit cell  

Strategy We can find the separation, d, of the lattice planes from eqn 11.11 and the data. Then we find the length of the side of the imit cell by using eqn 11.10. Because the unit cell is cubic, a = b = c,so eqn 11.10 simplifies to 

Solution According to Bragg s law, the separation of the (111) planes responsible for the diffraction is 

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Since every Kai/Ka2 double peak is caused by scattering from a single reciprocal lattice point, the rf-spacing remains constant and the scattered intensity is proportional to the intensities of the two components in the characteristic spectrum. Using Braggs law the following equation reflects the relationship between the positions of the diffraction peaks in the doublet ... 

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