4.3 Radioactive series and branching

Radioactive decay series and branching are key concepts in understanding nuclear transformations. These processes involve chains of radioactive decays, from unstable parent nuclides to stable end products, with multiple intermediate steps and decay modes.

Branching in radioactive decay adds complexity, as some nuclides can decay through different pathways. This affects decay rates, half-lives, and daughter nuclide production. Understanding these processes is crucial for applications in geology, nuclear medicine, and waste management.

Radioactive Decay Series

Characteristics and Types of Decay Series

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• Decay series represents a sequence of radioactive decays from an initial parent nuclide to a stable end product
• Uranium series begins with uranium-238 and ends with lead-206 after 14 decay steps
• Thorium series starts with thorium-232 and concludes with lead-208 through 10 decay steps
• Actinium series initiates with uranium-235 and terminates at lead-207 after 11 decay steps
• Neptune series commences with plutonium-241 and finishes with bismuth-209 via 9 decay steps

Decay Processes and Intermediate Nuclides

• Decay series involve multiple types of radioactive decay (alpha, beta, gamma)
• Uranium series includes intermediate nuclides such as thorium-234, protactinium-234, and radium-226
• Thorium series features intermediate elements like radium-228, actinium-228, and lead-212
• Actinium series encompasses intermediate nuclides including thorium-231, protactinium-231, and francium-223
• Neptune series contains intermediate elements such as americium-241, neptunium-237, and thallium-209

Significance and Applications of Decay Series

• Decay series provide insights into the age and composition of geological formations
• Uranium series dating helps determine the age of carbonate materials (coral reefs, cave deposits)
• Thorium series analysis aids in studying ocean circulation patterns and sediment transport
• Actinium series contributes to understanding nuclear fuel cycles and radioactive waste management
• Neptune series plays a role in the production of certain medical isotopes for diagnostic imaging

Branching in Radioactive Decay

Branching Ratio and Its Implications

• Branching ratio defines the probability of a particular decay mode occurring for a radioactive nuclide
• Expressed as a fraction or percentage of the total decay events
• Influences the overall decay rate and half-life of the radioactive nuclide
• Branching ratios can vary from nearly 0% to 100% for different decay modes
• Impacts the production and abundance of daughter nuclides in decay chains

Types of Branching Decay

• Branching decay occurs when a radioactive nuclide can decay through multiple pathways
• Isobaric decay involves the decay of a nuclide to different daughter nuclides with the same mass number
• Beta decay branching can produce different elements with the same mass number (potassium-40 to calcium-40 or argon-40)
• Alpha decay branching may result in different daughter nuclides with varying energy levels
• Electron capture branching competes with positron emission in some nuclides (beryllium-7 to lithium-7)

Isomeric Transitions and Nuclear Energy States

• Isomeric transition involves the decay of a metastable nuclear state to a lower energy state of the same nuclide
• Occurs through the emission of a gamma-ray photon or internal conversion electron
• Metastable states have longer half-lives compared to typical excited nuclear states
• Technetium-99m, widely used in nuclear medicine, undergoes isomeric transition to technetium-99
• Isomeric transitions contribute to the complexity of nuclear decay schemes and energy level diagrams