Symbol N
N is part of the quantity the equation computes from the expression on the right.
Read this term in its guide →Published equation contexts
Why this formula appears here
The property that makes radioactive decay useful as a clock is not that it happens on a convenient timescale — some isotopes decay in fractions of a second, others over timescales longer than the universe’s age — but that it happens with no memory. An atom of uranium-238 that has existed, undecayed, for four billion years is exactly as likely to decay in the next second as one formed a microsecond ago. There is no wear, no fatigue, no accumulated probability of failure the way there is in a mechanical clock’s escapement or a living organism’s senescence. This absence of memory is what makes decay first-order: the number of decays in a short interval is proportional only to the number of…
Read the representative guide
Symbol t
t is an argument of the function-like quantity on the left; its role is set by that function’s stated inputs.
Read this term in its guide →Symbol e^-λ t
λ t is one of the signed contributions combined to compute the quantity on the left.
Read this term in its guide →How to interpret it
With a fixed numerator, increasing a nonzero denominator reduces the fraction. Read it with the definitions, units, and assumptions supplied by the article.
Research cited beside this formula
Published contexts (1)
A symbol can carry a different meaning in another article. Each occurrence keeps its own guide and term definitions.
Equation 1 · Evolutionary Nuclear Physics
Radioactive Clocks: How Nuclear Physics Gave Evolution Its Time
This equation states an equality: the expressions on both sides have the same value under the article’s assumptions.
The property that makes radioactive decay useful as a clock is not that it happens on a convenient timescale — some isotopes decay in fractions of a second, others over timescales longer than the universe’s age — but that it happens with no memory. An atom of uranium-238 that has existed, undecayed, for four billion years is exactly as likely to decay in the next second as one formed a microsecond ago. There is no wear, no fatigue, no accumulated probability of failure the way there is in a mechanical clock’s escapement or a living organism’s senescence. This absence of memory is what makes decay first-order: the number of decays in a short interval is proportional only to the number of…
Meanings in this article
- : the initial population.
- : the half-life derived from it.
- : the decay constant characteristic of the isotope.