What type of radiation is most easily shielded?

Alpha particles are the type of radiation that can be most easily shielded. They have a relatively large mass and a positive charge, which makes them strongly interact with matter. This interaction causes alpha particles to lose their energy quickly and rapidly come to a stop when they encounter even very light materials. In fact, a sheet of paper or the outer layer of human skin is sufficient to block alpha particles effectively.

This characteristic of alpha particles means that they pose minimal risk when external exposure is considered, although they can be harmful if ingested or inhaled. The high interaction rate with matter is why they require such minimal shielding compared to other types of radiation. In contrast, gamma rays and X-rays require denser materials, such as lead, for adequate shielding because of their penetrating power, while beta particles are more penetrating than alpha particles but still can be stopped with relatively moderate barriers like plastic or glass.