Practise Edexcel A-Level Physics particle conservation laws by analysing decays, collisions, unseen particles and bubble-chamber tracks.
Actinium-225 is a radioactive isotope. It decays to francium by emitting alpha particles. Actinium-225 has a short half-life, which makes it suitable for medical applications.
The francium nucleus and the alpha particle move away from each other after the decay.
Explain why the kinetic energy given to the alpha particle is just less than 5.9 MeV . mass decrease for the decay =6.35×10−3u
Use 1 u = 934 MeV.
The mass of the Fr nucleus is much greater than the mass of the alpha particle.
Momentum is conserved, so the recoil velocity of the Fr nucleus is much less than the velocity of the alpha particle.
Therefore the alpha particle has most of the kinetic energy, just less than 5.9 MeV.