A widely used positron emitter in medical imaging is
PHYSICS · Multi-part · A Level · Physics · Particles and radiation · Particles and radiation
Problem
A widely used positron emitter in medical imaging is 22Na, which decays to an excited state of 22Ne by emitting a positron and a neutrino. The excited neon nucleus subsequently drops to its ground state by emitting a γ photon.
(1) Write the balanced nuclear equation for the decay of 22Na described above, showing all emitted particles. Explain how electric charge is conserved in this process.
(2) Using appropriate lepton number assignments, explain how lepton number conservation is satisfied in the decay you wrote in part (a).
(3) Compare a positron emitted in this decay with an electron emitted in a typical β− decay in terms of (i) charge, (ii) rest mass, and (iii) predominant interaction mechanisms with matter. Discuss how these differences influence their respective stopping distances in tissue.