Alpha radiation emitted by radioactive substances causes strong ionisation of air particles making air conduct electricity. Alpha radiation is easily absorbed by air and has a range in air of a few centimetres only.Beta radiation has a much weaker ionising effect producing fewer ions and its range in air is about a metre or more.Gamma radiation is electromagnetic radiation and is more weakly ionising than alpha or beta radiation. Photons have no mass or charge so interact less with matter so have an unlimited range in air.