What is the primary mode of decay for Tc-99m?

• A. Beta decay
• B. Alpha decay
• C. Isomeric transition
• D. Spontaneous fission

Answer: (C)

The primary mode of decay for Technetium-99m (Tc-99m) is isomeric transition. This decay process involves the transition of the nucleus from a higher energy state to a lower energy state without the emission of particles such as alpha or beta particles. In the case of Tc-99m, it has a metastable state that allows it to exist in a higher energy form, which then releases energy in the form of gamma radiation when it transitions to the more stable Tc-99 state.

Isomeric transition is a common decay mode for many radionuclides, especially those used in medical imaging, due to the ability to emit gamma rays. Gamma radiation can penetrate tissues effectively, making Tc-99m an ideal choice for diagnostic imaging in nuclear medicine. The efficiency and utility of gamma emission in imaging applications underscore the significance of isomeric transition as the dominant decay mechanism for Tc-99m.