A mass of lead is embedded in a block ofaluminium 2mm thick.radiations from a radioactive substance incident on the side of block produce aa shadow on a dlourescent screen placed beyond the block.the shadow of block of aluminium is fainter than the shadow of lead .

Give reason for the difference in detail and simple language

Aluminium is low density material. Lead is high density material. Attenuation of  γ-radiation from low density materials is less and more radiation will reach flourescent screen. Hence the shadow of aluminium part is fainter.  Attenuation of  γ-radiation from high density materials is more and less radiation will reach flourescent screen. Hence the shadow of lead part is darker.