Alpha particles, beta minus particles, positrons and gamma rays are all ionising radiation. This means they can knock electrons off atoms that they pass. When an atom loses an electron it becomes a positive ion, and the electron that was removed is a free negative charge. The radiation is what causes the ionisation.
Each time the radiation ionises an atom it loses some of its energy. It carries on until it has used up all its energy, and then it stops.
Ionising radiation is dangerous to living things. It can damage or kill cells, and it can change the DNA in a cell, which may lead to cancer.
