Beta particles penetrate paper variably for thickness detection

Steps:

• Beta particles from a source pass through the paper sheet to a detector, with absorption increasing as thickness grows.
• Thicker paper reduces beta particle count at the detector, allowing real-time thickness monitoring.
• Alpha particles lack sufficient penetration power for this application.
• Gamma rays penetrate too readily, providing minimal absorption variation.

Why A is correct:

• Alpha particles, being helium nuclei, have low penetration due to high ionization and are stopped by thin materials like paper, per radiation interaction principles.

Why the others are wrong:

• B: Alpha particles do not induce radioactivity in paper; they cause ionization without nuclear activation.
• C: Gamma radiation is emitted by many isotopes, regardless of half-life, including long-lived sources like cobalt-60.
• D: Gamma rays, being electromagnetic, penetrate paper easily and require dense materials like lead for stopping.

Final answer: A