Gamma rays penetrate for detection; short half-life ensures safety

Steps:

• Radiation must penetrate body tissues to reach external detectors.
• Alpha and beta particles are stopped by skin or shallow tissues, while gamma rays pass through.
• Half-life should be short (hours) for quick imaging and low patient dose, not years.
• Match properties: penetrating radiation with brief activity.

Why C is correct:

• Gamma rays, being high-energy electromagnetic radiation, have low ionization and high tissue penetration (defined by minimal absorption in matter), enabling external detection; few hours half-life balances test duration with radiation safety per ALARA principle.

Why the others are wrong:

• A: Alpha particles, highly ionizing helium nuclei, are stopped by outer skin layers and cannot exit the body.
• B: Beta particles, electrons/positrons, penetrate only a few mm/cm and are absorbed internally; years-long half-life causes excessive exposure.
• D: Gamma rays penetrate well, but years-long half-life prolongs unnecessary radiation dose to patient.

Final answer: C