The study of radiation from an atomic and molecular perspective, encompassing elemental transformation and reaction effects, as well as physical, physiological, and medical aspects, is known as radiochemistry or nuclear chemistry. The use of radioactivity to examine ordinary chemical reactions is a big part of radiochemistry. This is in stark contrast to radiation chemistry, in which the radiation levels are kept too low to have any effect on the chemistry. Radiochemistry is the study of radioisotopes, both natural and man-made.
Nuclear chemistry is defined as "the branch of chemistry concerned with the chemical study of nuclei and nuclear processes."