9702 · 23.2
Radioactive decay flashcards
Revision flashcards for Cambridge 9702 Radioactive decay (syllabus 23.2). Flip, recall, then mark a real past-paper question.
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What are the two fundamental characteristics of radioactive decay?
It is **spontaneous** (independent of external conditions) and **random** (unpredictable for individual nuclei).
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Define activity (A) and state its SI unit.
Activity is the rate at which radioactive nuclei decay in a sample. Its SI unit is the **Becquerel (Bq)**, where 1 Bq = 1 decay per second.
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How is the activity (A) of a sample related to its decay constant (\lambda) and the number of undecayed nuclei (N)?
$A = \lambda N$
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What does the term 'half-life' ($t_{1/2}$) mean for a radioactive isotope?
It is the time taken for half of the radioactive nuclei in a sample to undergo decay.
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Write the formula that connects half-life ($t_{1/2}$) and the decay constant (\lambda).
$t_{1/2} = \frac{\ln 2}{\lambda}$
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What does the decay constant (\lambda) represent?
It quantifies the probability that a single nucleus will decay per unit of time.
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How do external conditions like temperature or pressure affect radioactive decay?
They do not. Radioactive decay is entirely independent of external physical conditions.
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Write the exponential decay equation for the number of undecayed nuclei.
$N = N_0 e^{-\lambda t}$
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If a sample undergoes 3 half-lives, what fraction of its initial activity remains?
$(1/2)^3 = 1/8$ or 12.5\% remains.
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What are the typical units for the decay constant (\lambda)?
Per second (s^{-1}) or per year (year^{-1}) depending on the half-life duration.