Which of these types of ionizing radiation is most penetrating?

Gamma rays are the most penetrating type of ionizing radiation. This high level of penetration can be attributed to their electromagnetic nature and lack of mass and charge. Gamma rays are a form of photon radiation and have very high energy, which allows them to pass through various materials, including human tissue, concrete, and even lead, to some extent.

In contrast, alpha particles, being composed of two protons and two neutrons, are heavy and positively charged, which limits their ability to penetrate materials. They can be stopped by just a sheet of paper or the outer layer of skin. Beta particles, which are high-energy, high-speed electrons or positrons, have greater penetration abilities than alpha particles but are still significantly less penetrating than gamma rays; they can be stopped by plastics or a few millimeters of aluminum. Neutrons have variable penetration power depending on their energy and the material they are interacting with, but generally, they are less penetrating than gamma rays. Thus, gamma rays stand out as the most penetrating type of ionizing radiation among the options provided.