Figure 3-15b shows the K a and K characteristic x rays emitted by a molybdenum (Mo) target in an x-ray tube whose accelerating potential

Figure 3-15b shows the K_a and K_β characteristic x rays emitted by a molybdenum (Mo) target in an x-ray tube whose accelerating potential is 35 kV. The wavelengths are K_a = 0.071 nm and K_β = 0.063 nm.

(a) Compute the corresponding energies of these photons. 

(b) Suppose we wish to prepare a beam consisting primarily of K_a x rays by passing the molybdenum x rays through a material that absorbs K_β x rays more strongly than K_a x rays by photoelectric effect on K-shell electrons of the material. Which of the materials listed in the accompanying table with their K-shell binding energies would you choose? Explain your answer.

Figure 3-15b

Element Zr Z Ex (keV) Nb Mo 40 41 42 18.00 18.99 20.00 Tc 43 21.04 Ru 44 22.12