half-life
half-life — 名詞
1. the time it takes a radioactive element to lose half its radioactivity through n
半衰期
放射性物質強度減半所需的時間
the time it takes a radioactive element to lose half its radioactivity through natural atomic change
The half-life of uranium-238 is about 4.5 billion years, making it useful for dating ancient rocks.
鈾-238 的半衰期約為 45 億年，因此可用來測定古老岩石的年齡。
half-life of [isotope] + is + duration
Students in the lab measured the half-life of a small sample of radioactive cobalt over three weeks.
學生在實驗室花了三週測量一小塊放射性鈷樣本的半衰期。
Carbon-14 has a half-life of roughly 5,700 years, so archaeologists rely on it to date old bones and wooden tools.
碳-14 的半衰期大約是 5，700 年，因此考古學家靠它來判定古代骨頭和木器的年代。
After one half-life, a sample of radioactive iodine will contain only half of its original atoms.
經過一個半衰期後，放射性碘的樣本中只剩下原本一半的原子。
A short half-life means the radioactive material loses its danger more quickly after use.
半衰期短表示放射性物質在使用後會更快失去危險性。
- decay period
a less common, more technical term used in physics textbooks
- half-value period
an older or more formal term for the same concept, rarely used in everyday speech
文法句型
the half-life of [substance]
[substance] + has/ have + a half-life of [duration]
用法筆記
Can be followed by 'of' to specify which substance (e.g. 'the half-life of carbon-14'). Frequently used as a countable noun, though the singular form is far more common.
常見錯誤
2. the time a living body needs to process a chemical substance until its level in
藥物半衰期
藥物在體內濃度減半所需時間
the time a living body needs to process a chemical substance until its level in the blood reaches fifty percent of the starting amount
The drug's half-life in the blood is about six hours, so patients take it twice a day.
這種藥在血液中的半衰期大約是六小時，因此患者一天服用兩次。
drug's half-life determines dosing schedule
Caffeine has a half-life of roughly five hours in most adults, though the exact time varies from person to person.
咖啡因在多數成人體內約有五小時的半衰期，但確切時間因人而異。
Because the medication has a long half-life, Elena only needs to take one pill every morning.
因為這種藥物的半衰期很長，Elena 每天早上只需要吃一顆藥。
Nala's blood test showed the half-life of the antibiotic was shorter than expected, so the doctor increased the dose.
Nala 的血液檢查顯示抗生素的半衰期比預期短，因此醫生增加了劑量。
A drug with a very short half-life must be given through a steady drip rather than a single injection.
半衰期很短的藥物必須透過持續點滴給藥，而非一次注射。
- elimination half-life
the precise technical term used in pharmacology, broader than just breakdown
- biological half-life
emphasises that the process occurs inside a living organism
文法句型
the half-life of [drug/substance]
[substance] + has/ have + a half-life of [duration]
[possessive] + half-life
用法筆記
Commonly used with a possessive noun ('the drug's half-life') or with 'of' ('the half-life of the medication'). The context is almost always medical or pharmaceutical.
常見錯誤
3. a way of describing how quickly a feeling, popular idea, or memory loses about h
消退期
感覺或流行消退一半所需的時間
a way of describing how quickly a feeling, popular idea, or memory loses about half of its original strength and begins to fade away
The public outrage over the scandal had a surprisingly short half-life and faded within a week.
公眾對醜聞的憤怒消退期短得驚人，不到一週就平息了。
figurative: half-life of an emotional reaction
Online trends now have such a brief half-life that a viral video can be forgotten in just a few days.
現今網路熱潮的消退期非常短，一支爆紅影片可能幾天內就被遺忘。
Lucía felt that the half-life of her sadness grew longer each year, never quite disappearing completely.
Lucía 覺得她的悲傷消退期一年比一年長，始終無法完全消散。
Political promises seem to have a half-life of about six months before voters stop believing them.
政治承諾的消退期大約是六個月，過了這個時間選民就不再相信了。
- shelf life
more common for physical products but also used figuratively; implies usefulness before something expires rather than fading gradually
- fade rate
less common; used informally to describe how fast something loses its impact
文法句型
a + [adjective] + half-life
the half-life of [feeling/trend/idea]
用法筆記
A figurative extension of the scientific term. Often modified by adjectives ('short half-life', 'long half-life') and found in informal journalism, opinion writing, or casual conversation about cultural phenomena.