Читать книгу Patty's Industrial Hygiene, Physical and Biological Agents - Группа авторов - Страница 45

Shielding a radiation source decreases the gamma ray dose rate to a level given by

(10)

where I₀ is the dose rate incident on the shield, I is the emergent dose rate, μ is the attenuation coefficient for the shielding material and for the gamma ray energy (μ is a function of the shielding material and of the gamma ray energy), and t is the shield thickness. (Values for μ may be found in appropriate handbooks and textbooks 4,5.) For example, if one wishes to use a lead shield to reduce the dose rate from 100 to 2.5 mrem h⁻¹ at a certain distance from a ¹³⁷Cs source (0.661 MeV gamma), calculate the shield thickness after finding that μ (Pb, 0.662 MeV) = 0.058 cm⁻¹: