Problem 5.220

How many times will the intensity of a narrow X-ray beam of wavelength 20 pm decrease after passing through a lead plate of thickness $d=1.0 \mathrm{~mm}$ if the mass absorption coefficient for the given radiation wavelength is equal to $\mu / \rho=3.6 \mathrm{~cm}^{2} / \mathrm{g}$ ?