The high density and atomic number of lead make it effective at blocking or attenuating gamma rays. Here are a few reasons why lead is particularly effective in this regard:
Density: Lead is a dense material, which means it has a large mass per unit volume. Gamma rays are high-energy electromagnetic radiation that consists of photons. When gamma rays interact with matter, they undergo a process called Compton scattering, where they collide with electrons in the material. The likelihood of scattering increases with the number of atoms the gamma rays encounter. With its high density, lead provides a higher number of atoms per unit volume, increasing the chance of interaction and scattering.
Atomic number: The atomic number of lead is 82, which indicates the number of protons in its nucleus. Gamma rays can interact with atomic nuclei through a process known as the photoelectric effect. In this process, gamma ray photons transfer their energy to an atomic electron, causing it to be ejected from the atom. The probability of the photoelectric effect occurring depends on the atomic number of the material. Materials with higher atomic numbers, like lead, have a greater likelihood of absorbing gamma rays through this process.
Pair production: At extremely high energies, gamma rays can interact with the electric field near the nucleus of an atom and convert their energy into the creation of an electron and a positron (the antimatter counterpart of an electron). This process is called pair production. The likelihood of pair production occurring also increases with the atomic number of the material. Lead, with its high atomic number, provides a greater chance for pair production to take place, effectively absorbing the gamma rays.
Due to its density and high atomic number, lead is often used as shielding in various applications involving radiation, such as in radiation therapy, nuclear power plants, and industrial settings where gamma rays are present.