GENERAL KNOWLEDGE

Detailed explanation-1: -Beta particles: Beta particles can be stopped by a layer of clothing or by a few millimeters of a substance such as aluminum. Beta particles are capable of penetrating the skin and causing radiation damage, such as skin burns.

Detailed explanation-2: -However, only a thin sheet of aluminum is required to stop beta radiation because the metalloid properties of aluminum cause an electrostatic interaction with the charged beta particle, which is usually an electron but can be a positron in the case of beta plus decay.

Detailed explanation-3: -Beta particles travel appreciable distances in air, but can be reduced or stopped by a layer of clothing, thin sheet of plastic or a thin sheet of aluminum foil. Several feet of concrete or a thin sheet of a few inches of lead may be required to stop the more energetic gamma rays.

Detailed explanation-4: -Thus with an aluminum shield with thickness more than 0.5 mm we should be able to stop all the beta particles coming from the Sr90 decay while most of the particles coming from Y90 should have enough energy to pass the shield and reach the detector.