The material used for safety from nuclear radiation is:

Lead ($\text{Pb}$) is heavily used as a protective shield against harmful ionizing nuclear radiation (such as gamma rays and X-rays). Lead has a very high density ($\rho \approx 11.34{\text{g/cm}}^3$) and a high atomic number ($Z=82$). These properties give it a high electron density per unit volume, allowing it to efficiently absorb and attenuate high-energy photons through the photoelectric effect and Compton scattering.