Topic 8: Nuclear and Particle Physics

Question 1

Proton beam therapy is being introduced in the UK as a new cancer treatment.
A beam of protons is accelerated by a cyclotron to an energy of 23 MeV and is then
focused onto a tumour.

Explain how the cyclotron produces the high‑energy proton beam. (6 marks)

Answer 1

• There is an alternating p.d./E-field
• P.d./E-field accelerates protons between dees
• Magnetic field perpendicular to the plane of dees
• Proton path curved by magnetic field
• As the velocity of protons increases, radius of path in dees increases
• The time for which a proton is in a dee remains constant Or the frequency of p.d./E-field is constant