Problem $1(10$ points$).$ Calculate the geometric efficiencies of$...($a$)$ A PET scanner whose ring of detectors is diameter $700$ mm and width $100$ mm with radioactive source placed in its center. $($b$)$ An Anger camera of area $1$ m $1$ m with a point source of radioactivity placed $0\mathrm{.}5$ m away from the center of the camera.