Problem 12: Calculate the structurefactor expression for an elemental crystal having a base-centered lattice (with one atom per lattice point). What is the general extinction rule in this case? Problem 13: In 1913, the British physicist Henry Moseley found that the frequency of K\" Xrays is proportional to (Z O')2, where Z is the atomic number of the target material, and a is a shielding constant. Today, this formula is typically written as 1 / A = C (Z (1)2, Where A is the wavelength of the radiation and C is a proportionality constant. (6) Given that A = 1.54 A for copper K ,1 X-rays and 0.71 A for molybdenum K a X- rays, calculate approximate values for C and 0'. (b) Does the value for a make physical sense? Why or why not? (c) What value for 0' would you expect for an X-ray emission line from the L-series? Why? Problem 14: Calculate the velocity and kinetic energy with which electrons strike the target of an xray tube operated at 50,000 volts. What is the short-wavelength limit of the continuous spectrum emitted and the maximum energy per quantum (in joules) of radiation? Problem 15: Refer to the attached patterns and associated lists of peak positions for three unknows (labeled \"unknown 1\