Complex sentence: Beta can be cut off by an aluminium sheet just a few millimetres thick and are electrons.Gamma this is the most penetrating of the three and is a massles chargeless high energy photon.
Split into simpler sentences: Beta can be cut off by an aluminium sheet just a few millimetres thick and are electrons. Gamma is the most penetrating of the three and is a massless chargeless high energy photon.