Physics
Decay constant
The probability per unit time that an atom decays. It is inversely proportional to the half life.
The Formula
lambda = ln(2) / t1/2
The probability per unit time that an atom decays. It is inversely proportional to the half life.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| lambda | Decay constant | per unit time | Fraction of the sample decaying per unit time. |
| ln 2 | Natural logarithm of two | dimensionless | The constant 0.6931471805599453. |
| t_1/2 | Half life | time | The time for half the sample to decay. |
What Each Symbol Means
lambdaper unit time
Decay constant
Fraction of the sample decaying per unit time.
ln 2dimensionless
Natural logarithm of two
The constant 0.6931471805599453.
t_1/2time
Half life
The time for half the sample to decay.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate half life page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Calculate Half Life, filed under Science. Every number the guide produces comes from substituting into this one line.