Final answer:
Radioactivity is nuclear in origin as it involves the emission of particles or energy from an atomic nucleus during radioactive decay, leading to transmutation of elements. This stands in contrast to chemical reactions, which involve changes in electron configurations and are of a lower energy scale. The fact that radioactivity primarily involves elements with high atomic numbers and results in vastly different atomic structures underscores its nuclear nature.
Step-by-step explanation:
The characteristics of radioactivity that show it is nuclear in origin and not atomic include the nature of radioactive decay, where unstable atomic nuclei emit particles or energy to gain stability. Rather than involving the electrons that orbit the nucleus (which would be an atomic process), radioactivity involves changes to the protons and neutrons within the nucleus itself. This process can result in the transformation of one element into another, known as transmutation, which is a clear indication that the phenomenon is nuclear. The energy released during radioactive decay is the result of changes in the nucleus and is significantly greater than energies typically involved in chemical reactions, which are atomic in scale.
Additionally, radioactivity is most commonly associated with elements that have high atomic numbers, and particularly with isotopes that are neutron-rich. The spontaneous emission occurs as a means to achieve a more stable nuclear configuration, releasing energy and particles such as alpha particles, beta particles, and gamma rays, all of which originate from changes to the nucleus.