sci_phy
Half-Life
Chapter summary, hard words and model exam answers for ICSE Class 10 Hindi.
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Physics · CBSE 10 · ICSE 10 · GCSE (AQA, Edexcel, OCR)
Summary
Decay is random for a single nucleus, but with millions the pattern is exact. The half-life is a fixed property of each isotope.
After n half-lives the fraction remaining is (1/2) to the power n. The activity (decays per second) halves over the same interval.
The same interval halves it again wherever you measure on the curve. The curve never quite reaches zero.
Carbon-14 dates dead plants and animals. A medical isotope needs a half-life long enough to scan but short enough to clear from the body.
Hard words & meanings
| half-life | the time for half of the undecayed nuclei in a sample to decay |
| activity | the number of nuclei that decay each second, measured in becquerel |
| isotope | atoms of an element with the same protons but different numbers of neutrons |
| radioactive decay | the random breakdown of an unstable nucleus, releasing radiation |
| becquerel (Bq) | the SI unit of activity; one becquerel is one decay per second |
| carbon-14 | a radioactive form of carbon with half-life 5730 years, used for dating |
| random | happening with no fixed order; you cannot predict which nucleus decays next |
| count rate | the number of radiation counts a detector records each second or minute |
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