Copper-64 (64Cu^{64}\text{Cu}64Cu) is a radioactive isotope that undergoes positron decay and is increasingly used in diagnostic PET scans.
Explain the physics of electron-positron annihilation that occurs inside the patient's body and how it allows the PET scanner to locate areas of high tracer concentration.
The half-life of copper-64 is 12.7 hours12.7\text{ hours}12.7 hours. Calculate the time ttt, in hours, required for the activity of the copper-64 radiopharmaceutical to decrease to 8.5%8.5\%8.5% of its initial value.
Unlike oxygen-15 (half-life 122 s122\text{ s}122 s), a hospital performing PET scans with copper-64 does not need an on-site cyclotron. Suggest why regional distribution of copper-64 is feasible.
