Nuclear isomers are nuclei that exist in excited energy states for a measurable duration before decaying to their ground state or another lower energy state. Unlike typical nuclear excitations that last for fractions of a second, nuclear isomers can persist for microseconds to years, depending on the energy barrier and quantum transition rules involved.
Key Characteristics:
- Nuclear isomers have the same number of protons and neutrons as the ground state nucleus, but differ in internal energy and often spin configuration.
- The transition from the isomeric state to the ground state is typically hindered by quantum selection rules (such as spin or parity changes), making the decay process slow.
- They usually decay via gamma emission or internal conversion (where the energy is transferred to an orbital electron).
Types of Isomers:
- Metastable isomers (m-states): These are the most well-known and long-lived types. Example: Technetium-99m, widely used in medical imaging.
- Spin isomers: Arise due to high spin differences between the isomeric and ground states, making gamma decay highly forbidden.
- K-isomers: Found in deformed nuclei where the quantum number “K” (related to spin projection) causes decay suppression.
Applications:
- Used in nuclear medicine, radiation therapy, and nuclear batteries.
- Studied for potential in isomer-based energy storage or controlled release systems.
In summary, nuclear isomers represent trapped high-energy configurations of atomic nuclei, offering insight into nuclear structure and transitions, and providing useful tools in science and technology.