Final answer:
Primary radiation barriers vary in thickness depending on material and type of radiation, with high-density materials like lead providing effective shielding for gamma rays. A typical thickness for lead shielding can be in the millimeter range, such as 0.170 mm, which halves the gamma rays from Technetium-99m.
Step-by-step explanation:
Primary radiation barriers are designed to protect individuals from the harmful effects of different types of radiation, such as alpha particles, beta particles, gamma rays (notated as y rays), and X-rays. Each type of radiation has its own penetration power and therefore requires different materials and thicknesses for shielding.
The thickness of shielding needed to reduce gamma radiation, which is very penetrating, can vary based on the material used. For instance, the reactor vessel in nuclear power plants, which is a steel shell with a thickness of 3-20 centimeters, can absorb much of the radiation produced. Additionally, a main shield made out of 1-3 meters of high-density concrete is used for further protection, while lighter materials may be employed for a personnel shield to protect operators from gamma rays and X-rays.
Lead is a dense, high atomic number element often used for shielding as it can effectively attenuate gamma radiation with thinner material compared to others. For example, one half of the gamma rays from Technetium-99m (99mTc) are absorbed by a 0.170-mm-thick lead shielding. Based on this rate of absorption, calculations can be made to determine the required thickness that will absorb almost all gamma rays, providing effective radiation protection.
In general, high-density materials are significantly more effective for protection against gamma emissions than low-density ones, and the choice of shielding material and its required thickness will greatly depend on the type of radiation and the desired level of protection.