What does the term “criticality” refer to in radiation safety?

The term "criticality" in radiation safety specifically refers to the condition under which a nuclear chain reaction becomes self-sustaining. When a sufficient amount of fissile material—such as uranium-235 or plutonium-239—is present and in the right configuration, the reactions caused by the splitting of these atoms can achieve a balance that maintains the reaction without any external neutron sources. This is a crucial concept in nuclear safety, as uncontrolled criticality can lead to a dangerous increase in radiation levels and pose significant risks to safety.

Understanding criticality is vital for radiation safety personnel since it influences protocols related to the handling and storage of radioactive materials. Personnel must be trained to recognize the conditions that can lead to criticality accidents and how to prevent them.

The other terms mentioned, while related to nuclear physics or radiation, do not accurately define criticality. For instance, the core of a nuclear reactor refers to the physical structure containing nuclear fuel, and radiation levels refer to the amounts of radiation present in an environment or emitted by materials. The process by which radiation is absorbed does not capture the essence of criticality within the context of nuclear chain reactions.