A quality control system in a metal processing plant uses a radioactive source and a detector to monitor the thickness of manufactured copper foil of thickness 0.2 mm as it rolls off the press.
Which radiation type and half-life characteristics are most appropriate for this system?
Alpha radiation with a short half-life; alpha particles are highly ionizing, ensuring high detector sensitivity, and a short half-life prevents the copper foil from becoming radioactive.
Beta radiation with a long half-life; beta particles are partially absorbed by the thin copper foil, and a long half-life ensures the source activity remains stable without requiring frequent recalibration.
Gamma radiation with a short half-life; gamma photons are needed to penetrate metal sheets, and a short half-life minimizes the long-term radiation hazard to factory workers.
Gamma radiation with a long half-life; gamma photons are highly penetrating and can pass through metals, while a long half-life ensures that the detector measures a constant count rate over many years.