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What is the Radioactive Disintegration Series?
Grade Level:
Class 12
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Definition
What is it?
The Radioactive Disintegration Series is a sequence of nuclear reactions where an unstable parent radioactive nucleus decays step-by-step into a stable non-radioactive daughter nucleus. Each step involves the emission of alpha (α) or beta (β) particles, changing the atomic number and mass number until stability is reached.
Simple Example
Quick Example
Imagine a big family tree where the oldest member (parent) passes on a quality to their child, who then passes a slightly changed quality to their child, and so on, until the very last child has a completely stable quality. Here, the 'quality' changing is like the nucleus decaying, step by step, until it becomes stable and stops changing.
Worked Example
Step-by-Step
Let's track a decay series starting from Thorium-232 (atomic number 90).
Step 1: Thorium-232 (90Th232) undergoes alpha decay.
Alpha decay means emitting an alpha particle (2He4). So, the mass number decreases by 4, and the atomic number decreases by 2.
90Th232 -> 88Ra228 + 2He4 (Radium-228 is formed)
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Step 2: Radium-228 (88Ra228) undergoes beta decay.
Beta decay means emitting a beta particle (-1e0). So, the mass number remains the same, and the atomic number increases by 1.
88Ra228 -> 89Ac228 + -1e0 (Actinium-228 is formed)
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Step 3: Actinium-228 (89Ac228) undergoes beta decay.
89Ac228 -> 90Th228 + -1e0 (Thorium-228 is formed)
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Step 4: Thorium-228 (90Th228) undergoes alpha decay.
90Th228 -> 88Ra224 + 2He4 (Radium-224 is formed)
This series continues through many more alpha and beta decays until it finally reaches a stable lead isotope, Lead-208 (82Pb208).
Answer: The Thorium-232 series is a long chain of alpha and beta decays that ends with stable Lead-208.
Why It Matters
Understanding radioactive disintegration series is crucial in nuclear physics and medicine. Doctors use this knowledge in cancer treatment (radiotherapy) and medical imaging, helping to save lives. Engineers in nuclear power plants also rely on it for safe energy production, ensuring our homes get electricity.
Common Mistakes
MISTAKE: Thinking that a radioactive series involves only one type of decay (e.g., only alpha or only beta). | CORRECTION: A series usually involves a mix of both alpha and beta decays, alternating until a stable nucleus is formed.
MISTAKE: Confusing the effect of alpha and beta decay on mass and atomic numbers. | CORRECTION: Alpha decay reduces mass number by 4 and atomic number by 2. Beta decay keeps mass number same but increases atomic number by 1.
MISTAKE: Believing that all radioactive elements decay directly into a stable element in one step. | CORRECTION: Most heavy radioactive elements decay through a series of intermediate radioactive elements before finally becoming stable.
Practice Questions
Try It Yourself
QUESTION: If an element X (92X238) undergoes one alpha decay, what are the mass number and atomic number of the new element Y? | ANSWER: Mass number = 234, Atomic number = 90
QUESTION: An element Z (83Z210) undergoes one beta decay. What is the atomic number of the resulting element? Does its mass number change? | ANSWER: The atomic number increases to 84. No, its mass number does not change.
QUESTION: A radioactive nucleus has an atomic number of 90 and a mass number of 230. It undergoes one alpha decay followed by one beta decay. What are the final atomic number and mass number? | ANSWER: Final atomic number = 89, Final mass number = 226
MCQ
Quick Quiz
Which type of decay increases the atomic number by 1 while keeping the mass number unchanged?
Alpha decay
Beta decay
Gamma decay
Neutron emission
The Correct Answer Is:
B
Beta decay involves the emission of an electron, which effectively converts a neutron into a proton, thus increasing the atomic number by 1. Alpha decay changes both mass and atomic numbers, while gamma decay and neutron emission have different effects.
Real World Connection
In the Real World
In India, the use of radioactive isotopes from disintegration series is vital in various fields. For example, hospitals use Technetium-99m, which is formed from the decay of Molybdenum-99, for medical diagnostic scans like detecting heart problems or bone diseases. This helps doctors see inside the body without surgery.
Key Vocabulary
Key Terms
RADIOACTIVE DECAY: The process by which an unstable atomic nucleus loses energy by emitting radiation | ALPHA PARTICLE: A particle consisting of two protons and two neutrons, identical to a helium nucleus | BETA PARTICLE: An electron or positron emitted from an atomic nucleus during radioactive decay | PARENT NUCLEUS: The original unstable nucleus that undergoes radioactive decay | DAUGHTER NUCLEUS: The nucleus formed as a result of the radioactive decay of a parent nucleus
What's Next
What to Learn Next
Now that you understand disintegration series, you can explore 'Half-Life of Radioactive Elements'. This concept will teach you how to calculate the time it takes for half of a radioactive sample to decay, which is super important for dating ancient artifacts and understanding nuclear waste management.
