Aluminium-26

Aluminium-26 (26Al, Al-26) is a radioactive isotope of aluminium. It decays by either positron emission or electron capture to magnesium-26. The half-life of 26Al is 7.17×105 years. A small amount of aluminium-26 is made when atoms hit cosmic ray protons.
When aluminium-26 decays it also produces gamma rays and x-rays. Because it is radioactive, it is usually kept behind at least 5 centimetres (2 in) of lead. We use special tools to transfer, use, and store aluminium-26.