$5\mathrm{.}3$ We are designing an x$-$ray tube and want to use a lighter filter. Suppose we

have, in addition to copper, a new material with a density of $5,000$ kg$/$m$3$

and a mass attenuation coefficient of $0\mathrm{.}08$ m$2/$kg at $80$ kVp$.$ In order

to satisfy the NCRP recommendation of $2\mathrm{.}5$ mm Al$/$Eq at $80$kVp$,$ what

should we use, copper or the new material? Explain