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1. Oxford Dictionary

   half-life

   • IPA[ˈhɑːflʌɪf]

   英式

   • n.
     the time taken for the radioactivity of a specified isotope to fall to half its original value；the time required for any specified property (e.g. the concentration of a substance in the body) to decrease by half.

   • noun: half-life, plural noun: half-lifes

2. • 釋義

   n.

   名詞

   • 1. the time taken for the radioactivity of a specified isotope to fall to half its original value iodine-131 has a half-life of 8.1 days
   • ▪ the time required for any specified property (e.g. the concentration of a substance in the body) to decrease by half.