1The time taken for the radioactivity of a specified isotope to fall to half its original value.
半衰期（某种同位素的放射性衰变为原来的一半所用的时间）
iodine-131 has a half-life of 8.1 days
Example sentencesExamples
The small, lead-shielded canisters contain pellets or a fine powder of caesium 137, which emits powerful gamma radiation with a half-life of 30 years.
Tritium is radioactive, with a half-life of 12.26 years.
Radioactive depleted uranium has a half-life of 4500 million years.
In addition, the plants would produce 7,313 tonnes of highly radioactive waste with a half-life of 24,000 years.
The FDA recommends keeping a fourteen-day supply on hand; radioactive iodine has a half-life of eight days.
1.1The time required for any specified property (e.g. the concentration of a substance in the body) to decrease by half.
半存留期（某种特性，如体内某种物质的浓度，减少为原来的一半所需的时间）
Example sentencesExamples
It stays in the body for a lifetime, it has a half-life of 28, 29 years and it gets into the bone, it's taken up just like calcium.
This constitutes the main long-term threat in the area as the chemical has a half-life of 30 years.
Frova may represent an important advancement in the treatment of migraine headache as no other currently marketed treatment has a half-life of more than six hours.
Prealbumin, also known as transthyretin, has a half-life of only 1 to 2 days.
At age 18, caffeine has a half-life of 4.5 hours, which increases with age.
Definition of half-life in US English:
half-life
nounˈhæf ˌlaɪfˈhaf ˌlīf
1The time taken for the radioactivity of a specified isotope to fall to half its original value.
半衰期（某种同位素的放射性衰变为原来的一半所用的时间）
iodine-131 has a half-life of 8.1 days
Example sentencesExamples
Radioactive depleted uranium has a half-life of 4500 million years.
The FDA recommends keeping a fourteen-day supply on hand; radioactive iodine has a half-life of eight days.
In addition, the plants would produce 7,313 tonnes of highly radioactive waste with a half-life of 24,000 years.
Tritium is radioactive, with a half-life of 12.26 years.
The small, lead-shielded canisters contain pellets or a fine powder of caesium 137, which emits powerful gamma radiation with a half-life of 30 years.
1.1The time required for any specified property (e.g. the concentration of a substance in the body) to decrease by half.
半存留期（某种特性，如体内某种物质的浓度，减少为原来的一半所需的时间）
Example sentencesExamples
It stays in the body for a lifetime, it has a half-life of 28, 29 years and it gets into the bone, it's taken up just like calcium.
At age 18, caffeine has a half-life of 4.5 hours, which increases with age.
Prealbumin, also known as transthyretin, has a half-life of only 1 to 2 days.
Frova may represent an important advancement in the treatment of migraine headache as no other currently marketed treatment has a half-life of more than six hours.
This constitutes the main long-term threat in the area as the chemical has a half-life of 30 years.