Later in his life in 1900, Becquerel measured the properties of beta particles, and he realized that they had the same measurements as high speed electrons leaving the nucleus.  In 1901 Becquerel made the discovery that radioactivity could be used for medicine. Henri made this discovery when he left a piece of radium in his vest pocket and noticed that he had been burnt by it. This discovery led to the development of radiotherapy which is now used to treat cancer. In 1908 Becquerel was elected president of Académie des Sciences, but he died on 25 August 1908, at the age of 55, in Le Croisic, France. He died of a heart attack, but it was reported that "he had developed serious burns on his skin, likely from the handling of radioactive materials."