Question

The effective atomic numbers of tissue and air are both about 7.5. Compared to a gram of tissue, about how many interactions would occur in a gram of aluminum exposed to a beam of low energy photons? to medium energy photons? to high energy photons

Answer 1

When exposed to low energy photons, the photon ionizes aluminium creating one fast moving electron and a low energy photon, this fast moving electron again interacts with aluminium hence a total of two interactions occur.

When exposed to a medium energy photons, it ionizes aluminium and gives one fast moving electron, one slow moving electron and a low energy photon. The fast moving electron results in another interactions, hence a total of three interactions occur.

When exposed to high energy electrons, it ionizes aluminium and gives two fast moving electrons and a positive ion. These two fast moving electrons results in two more interactions, hence a total of four interactions occur.