If the gamma rays are at 662 keV [1], you'd need about 8cm of rock [2] to block 50%. For comparison, sunglasses typically block 70%-80% of visible light. [1] h

If the gamma rays are at 662 keV [1], you'd need about 8cm of rock [2] to block 50%. For comparison, sunglasses typically block 70%-80% of visible light. [1] https://en.wikipedia.org/wiki/Caesium-137 https://en.wikipedia.org/wiki/Caesium-137 [2] https://pdfs.semanticscholar.org/7248/4e8995c811d31837199d7c629e51a882e3e0.pdf https://pdfs.semanticscholar.org/7248/4e8995c811d31837199d7c...