What are nuclear isomers?

Nuclear isomers refer to specific excited states of a radioactive nucleus that possess the same number of protons and neutrons but differ in energy levels. These excited states arise when a nucleus absorbs energy, moving to a higher energy configuration while retaining its identity as a particular element. This difference in energy levels allows the isomers to have unique properties, such as varying half-lives or transition pathways.

When the nucleus transitions from the excited state back to a lower energy state or a ground state, it may emit radiation, which can include gamma rays. This process has implications in the study of nuclear reactions, radioactive decay, and applications in nuclear medicine.

In contrast to this correct definition, the other options do not accurately describe nuclear isomers. For instance, isotopes pertain to variations of elements with different neutron counts, not specifically relating to energy levels or excited states. Additionally, nuclei that cannot undergo decay are not characteristic of isomers, as all isotopes—whether stable or unstable—can be subjected to changes under certain conditions. Lastly, stable isotopes do not reflect the concept of isomers, as stability implies no excited states that would lead to radiation emissions.