Which type of radiation is emitted during radioactive decay and has the least penetrating power?

Alpha particles are the type of radiation emitted during radioactive decay that possess the least penetrating power. Composed of two protons and two neutrons, alpha particles are relatively heavy and carry a positive charge. Due to their size, they interact strongly with matter, which limits their ability to penetrate through materials.

For example, alpha particles can be stopped by a sheet of paper or even the outer layer of human skin, making them less hazardous when external exposure is considered. However, if alpha-emitting materials are ingested or inhaled, they can pose significant health risks due to their high energy and localized damage potential.

In contrast, gamma rays and X-rays, being electromagnetic waves, have much greater penetrating abilities and can pass through several centimeters of lead or concrete. Beta particles, being lighter and charged particles, can penetrate further than alpha particles but are still less penetrating than gamma rays or X-rays. Understanding these characteristics is crucial in both radiation safety and the application of radioactive materials in various fields.