Average Lifespan

Being given a whole of elements of which the number decrease towards zero, the average lifespan (also called lifespan) is a number which characterizes the reduction ratio (Décroissance) of the unit. In particular, if the individual lifespan of an element of the unit is the time spent between one moment of reference and the disappearance of this element, the average lifespan is the arithmetic mean of the individual lifespans.

Average lifespan, exponential decay and half-life

The average lifespan τ of the elements of a unit decreasing in an exponential, equal way contrary to the constant of noted decrease λ (cf exponential Decay), is connected to the noted Demi-vie $t\_\; \{1/2\}$ by the relation:

$t\_\; \{1/2\}\; =\; \backslash \; tau\; \backslash \; cdot\; \backslash \; ln\; 2\; =\; \backslash \; frac\; \{\backslash \; ln\; 2\}\; \{\backslash \; lambda\}$

Use

The half-life is the parameter generally employed to characterize a Isotope Radioactif or a unstable Elementary particle. Typically, the dating with the Carbon-14 requires to know beforehand only the proportion of carbon-14 at the living organisms and the half-life of the isotope 14 of carbon.

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