Which type of radiation has the least penetrating ability?

Alpha radiation has the least penetrating ability of all the types of radiation listed. This is primarily due to the nature of alpha particles, which are composed of two protons and two neutrons (essentially helium nuclei). Because of their relatively large mass and positive charge, alpha particles interact strongly with matter. They have a limited range and can typically be stopped by a sheet of paper or even the outer layer of human skin.

Alpha particles lose their energy quickly as they collide with other atoms, which means they do not penetrate deeply into materials. This limited penetration is contrasted with the other types of radiation mentioned. Gamma radiation, being electromagnetic and having no mass or charge, can penetrate through materials with greater ease. Similarly, beta radiation, which consists of high-energy, high-speed electrons or positrons, has greater penetration capabilities than alpha particles but is still less penetrating than gamma and x-ray radiation.

Understanding the penetration abilities of these types of radiation is critical for radiation safety and protection measures, as it dictates the materials needed for shielding and the precautions to be taken when working with different sources of radiation.