Energy, mass and antimatterEdexcel A-Level Physics: Mind map

Exam questions on Energy, mass and antimatter

1. In a positron emission tomography (PET) scanner, a positron emitted by a radioactive tracer in a patient annihilates with an electron in the surrounding tissue. Both particles can be taken to be at rest when they annihilate. The rest mass of an electron is 0.511 MeV/c².
   Calculate the energy, in MeV, of each photon produced.2 marks
2. A gamma ray photon of energy 3.0 MeV, which leaves no track in a bubble chamber, converts into an electron and a positron close to an atomic nucleus. The chamber is in a uniform magnetic field and the two particles leave tracks that start at the same point. The rest mass of an electron is 0.511 MeV/c².
   Calculate the total kinetic energy of the electron and the positron, in MeV, immediately after the pair is created. Assume the nucleus takes negligible energy.2 marks
3. Physicists fire a beam of electrons at liquid hydrogen to investigate the structure of the proton, which has a radius of about 1 × 10⁻¹⁵ m. At low beam energies the electrons scatter as if the proton were a single point. At very high beam energies some electrons are scattered through large angles, showing that the proton has internal structure.
   Explain why electrons of very high energy are needed to investigate the internal structure of the proton.3 marks