Gamma rays penetrate aluminum foil for accurate thickness measurement

Steps:

• Identify material: Aluminum foil requires a penetrating radiation to measure varying thicknesses without excessive absorption.
• Compare radiation types: Beta particles are easily stopped by metals like aluminum; gamma rays penetrate denser materials effectively.
• Evaluate half-life: System needs stable radiation intensity over factory operation time, favoring long half-lives.
• Select best match: Gamma source with 6-year half-life ensures penetration and reliability.

Why B is correct:

• Gamma rays transmit through aluminum (low absorption per Beer-Lambert law), and 6-year half-life maintains consistent output for industrial use.

Why the others are wrong:

• A: Beta absorbed by aluminum, preventing measurement; short half-life causes rapid intensity drop.
• C: Beta unsuitable for penetration in aluminum; 6-hour half-life too short for stable operation.
• D: Duplicate of B, but question specifies B as correct (likely typo in choices; assumes B's long half-life fits).

Final answer: B