Complex sentence: Bismuth-213 is one of the isotopes which has been used: this is made by the alpha decay of Ac-225, which in turn is made by the irradiation of radium-226 with a cyclotron.
Split into simpler sentences: Bismuth-213 is one of the isotopes which has been used: this is made by the alpha decay of Ac-225. The actinium-225 is made by the irradiation of radium-226 with a cyclotron.