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Particle Physics Questions

Q4.

(a) Pair production can occur when a photon interacts with matter. Explain the process of pair production.

When a photon interacts with an orbital electron or a nucleon within the nucleus, the energy of the photon is used to create a particle-antiparticle pair. In order to conserve momentum, the photon needs to interact with interacting particle

(2 marks)

(b) Explain why pair production cannot take place if the frequency of the photon is below a certain value.

E = hf so the energy of photon is proprtional to its frequency. When pair production occurs the energy is converted to mass according to the equation E = mc2. If the energy/frequency is below the conversion to the mass/rest energy of the particle and antiparticle pair the event will not occur.

(3 marks)

(c) Energy and momentum are conserved during pair production. State two other quantities that must also be conserved.

Any two of: charge, lepton number, baryon number or strangeness.

(2 marks)

(Total 7 marks)