What is meant by “radiation decay”?

Radiation decay refers to the transformation of a radioactive substance over time. This process occurs because unstable atomic nuclei lose energy and change to more stable forms. During decay, an atom emits radiation, which can include alpha particles, beta particles, or gamma rays. As this transformation takes place, the original radioactive substance decreases in quantity, ultimately leading to a reduction in radioactivity. This foundational concept is crucial in understanding the behavior of radioactive materials, including their half-lives and how they eventually turn into stable isotopes.

The other choices touch on relevant concepts but do not accurately describe radiation decay. For instance, while the decrease of radiation levels in the environment can result from decay, it does not define the decay process itself. Shielding radiation is a protective measure against radiation, and measuring radiation doses is a method of assessing exposure, neither of which pertains to the concept of decay directly.