What is the recommended layer of shielding used for a radiation-proof darkroom wall?

The recommended layer of shielding for a radiation-proof darkroom wall is 1.5 mm of lead (Pb). Lead is an effective shielding material due to its high atomic number and density, which allows it to significantly attenuate gamma and x-ray radiation. In medical and dental radiography, it is commonly used for shielding walls to protect both patients and staff from unnecessary exposure to radiation. The specific thickness of 1.5 mm is based on guidelines formulated through extensive studies of radiation attenuation properties and safety regulations.

Other materials, such as aluminum (Al) or palladium (Pd), do not provide sufficient protection against the types of radiation typically encountered in darkrooms. Aluminum might be used in certain contexts but is insufficient for serious radiation shielding. Palladium, while having some applications in the production of specialized equipment, is not typically recommended for this type of shielding either. Therefore, the choice of 1.5 mm lead aligns with safety and efficacy standards in radiation protection practices.