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Half-life
The half-life of a radioactive isotope is the time taken for the number of undecayed radioactive nuclei, or the activity of a sample, to fall to half its initial value.
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Half-life
Half-life tells us how long it takes for a radioactive sample's activity to fall to half.
Recommended for Class 10
Half-life
The half-life of a radioactive isotope is the time taken for the number of undecayed radioactive nuclei, or the activity of a sample, to fall to half its initial value.
Example
Suppose the initial activity is:
800 Bq
After one half-life:
400 Bq
After two half-lives:
200 Bq
After three half-lives:
100 Bq
General Pattern
After `n` half-lives:
**Remaining fraction = (12)ⁿ**
Important Idea
Half-life does not mean every nucleus survives for exactly half that time.
It is a statistical property of a large population.
Uses of Half-life
Half-life helps scientists:
estimate how quickly radioactive materials decay; select isotopes for medical and industrial applications; * estimate the age of certain materials using suitable radioactive dating methods.
Half-life — Advanced
Half-life is a characteristic statistical timescale for an isotope and is related to exponential decay.
Common Mistakes
Common Mistakes
- Mistake
Half-life is not the time until all nuclei disappear.
- Mistake
After each half-life, half of the remaining undecayed nuclei are expected to decay.
Revision Zone
60-Second Revision
Quick cues from this topic — use them for last-minute revision.
1 half-life → 12 remains.
2 → 14.
3 → 18.
- Definition
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Practice
PQ
Q1. Define half-life.
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Q2. 1000 Bq after one half-life →
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Q3. After two →
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Q4. After three →
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Q5. Explain why half-life does not predict one nucleus.
Exam Practice
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Q1. Define half-life.
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Q2. Explain successive halving.
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Q3. Solve a half-life numerical.
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Q4. Explain statistical meaning.
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Q5. State one application.
School-standard facts for Matric and Intermediate. Original explanations — not copied from textbooks.