demivie

Demivie is a term used to describe the time required for a quantity to fall to half of its initial amount. The term is derived from the French demi-vie, meaning half-life, and in many contexts the English equivalent is half-life. In practice, demivie is used in physics, chemistry, and pharmacology to describe exponential decay processes.

In physics, the demivie (half-life) of a radioactive substance is the time over which its activity decreases by a factor of two. If the activity decays as A(t) = A0 e^{-λt}, then t1/2 = ln(2)/λ. For example, carbon-14 has a physical half-life of about 5730 years.

In pharmacology, demivie can refer to either the biological half-life (time for a drug’s concentration to reduce by half in the body) or the effective half-life (which combines physical decay and elimination). The effective half-life is given by 1/t1/2,eff = 1/t1/2,phys + 1/t1/2,biol.

Measurement and usage: Demivie is estimated by monitoring relevant quantities over time and fitting exponential decay models. It is a key parameter for dating in archaeology and for dosing regimens in medicine.

Etymology and usage notes: The term is most common in French-language contexts; English-language literature typically uses “half-life.” When encountered as demivie in English texts, it usually reflects a direct translation or citation of French sources.

Related concepts: half-life, decay constant, exponential decay, biological half-life, pharmacokinetics.