Which of the following radiation types is considered non-ionizing?

Ultraviolet radiation is considered non-ionizing because it does not carry enough energy to ionize atoms or molecules, which is a process that involves the removal of tightly bound electrons. Non-ionizing radiation can cause other types of damage, such as thermal effects, but it does not have sufficient energy to produce ionization directly.

In contrast, gamma radiation, X-ray radiation, and alpha radiation are forms of ionizing radiation. These types of radiation have higher energy levels, enabling them to displace electrons from atoms, leading to ionization. This property of ionizing radiation means it has the potential to cause significant biological damage, which is a critical consideration in radiation safety protocols.

Thus, ultraviolet radiation stands out as the correct choice when identifying non-ionizing radiation among the options presented.