Gamma radiography detects metal flaws using penetrating radiation

Steps:

• Industrial radiography requires gamma-emitting isotopes to penetrate dense metals and reveal cracks via shadows on film.
• Select isotopes with sufficient half-life for safe, practical handling during inspections.
• Eliminate alpha emitters, as they lack penetration depth for metals.
• Compare half-lives: needs years, not days or minutes, for usability.

Why B is correct:

• Cobalt-60 emits high-energy gamma rays that penetrate metals effectively, per radiation attenuation laws, with a 5.3-year half-life ideal for industrial sources.

Why the others are wrong:

• A: Alpha particles from americium-241 cannot penetrate metal surfaces.
• C: Radium-223's alpha emission and 11-day half-life make it unsuitable for penetration or handling.
• D: Barium-137's 3-minute half-life is too short for preparation and use in testing.

Final answer: B