半減期
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定義
試料中の放射性原子の正確に半分が原子核崩壊するのに要する時間。
解説
Half-lives span an enormous range: polonium-214 decays in 164 microseconds, while uranium-238 has a half-life of 4.47 billion years—comparable to Earth's age. Carbon-14, with a half-life of 5,730 years, is the basis of radiocarbon dating used in archaeology. After 10 half-lives, less than 0.1% of the original material remains.
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