half life

• Tempo necessário para que uma quantidade (por exemplo, de uma substância radioativa, de um medicamento no organismo ou de uma reação química) se reduza à metade do valor inicial. Também é usado metaforicamente para descrever a velocidade com que algo diminui ou decai com o tempo.

The time required for a quantity (such as a radioactive substance, a drug in the body, or a chemical reaction) to reduce to half its initial value. Also used metaphorically to describe the rate of decline or decay of something over time.

1. Radioactive decayC1formal

   The time required for a quantity of a radioactive substance to reduce to half of its initial value.

   Meia-vida

   • The half-life of carbon-14 is about 5,730 years.
   • Scientists use half-life to date ancient artifacts.
   • Uranium-238 has a half-life of 4.5 billion years.

2. Chemical eliminationC1formal

   The time it takes for the concentration of a substance (e.g., a drug) in the body to decrease by half.

   Meia-vida

   • The drug has a half-life of approximately 12 hours.
   • Doctors consider the half-life when prescribing medication.
   • The half-life of caffeine in the human body is about 5 hours.