Consider that a monoenergetic point source of gamma radiation \((800 \mathrm{keV})\) with strength of \(10^{5}\) gammas \(/ \mathrm{s}\) is located at a point in air. At a distance of \(5 \mathrm{~cm}\), a composite shield of lead (thickness \(0.5 \mathrm{~cm}\) ) and iron (thickness \(2.5 \mathrm{~cm}\) ) is kept. Find the gamma flux at a distance of \(30 \mathrm{~cm}\) from the shield (mass attenuation coefficient for air, lead, and iron are \(7.074 \mathrm{E}-02,8.870 \mathrm{E}-02\), and \(6.699 \mathrm{E}-02 \mathrm{~g} / \mathrm{cm}^{2}\), respectively).