Assuming an Xray source has Xray energy of 100 keV, how much (thickness) of each off each material would you need to cut the Xray intensity by half for: i) lead glass ( ~= is 4.0 g/cm3 ) ii) concrete ( ~ = 2.3 g/cm3 ) iii) bakelite ( ~= 1.3 g/cm 3 )