Radioactive decay describes the transformation of unstable nuclei into more stable configurations through the emission of particles or electromagnetic radiation. In nuclear medicine, understanding decay modes is essential for predicting imaging characteristics, radiation dose, and biological behaviour of radiopharmaceuticals.

This section explores alpha decay, beta-minus decay, beta-plus (positron) decay, electron capture, isomeric transition, and internal conversion. Each decay pathway produces characteristic emissions that determine suitability for SPECT, PET, or therapeutic applications. For example, positron emission forms the basis of PET imaging, while isomeric transition enables gamma emission in technetium-99m.

Decay mode questions are frequently examined in FRCR and ABR Core physics examinations, particularly in scenarios linking nuclear transformation equations to emitted particles and clinical use.

The questions below test your understanding of decay equations, conservation laws, emitted radiation energies, and clinical implications for imaging and therapy. Mastery of these mechanisms provides a conceptual bridge between nuclear structure and practical radionuclide selection.

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