How much water shielding do you require, if you want to reduce the intensity of a $100$ keV monoenergetic X$-$ray beam $($narrow beam$)$ to $1\%$ of its incident intensity? The half value layer for $100$ keV X$-$rays in water is $4\mathrm{.}15$cm and the linear attenuation coefficient for $100$keV X$-$rays in water is $0\mathrm{.}167$ cm$^-$¹.