Nuclear Half-Life

Half-life#card §

The time it takes for half of a radioactive sample to decay (generally in seconds or years). It can also be defined as the time after which there is a 50% chance that an individual nucleus has decayed.

If the mass is 100g, after one half life it would be 50g, After another it would be 25g, and 12.5g, 6.25g, etc. This is a logarithmic relationship.

You cannot speed up or slow down half-lives.

Half Life Formula#card §

$$N=N_0(\frac{1}{2}{)}^n$$

$N$ = remaining nuclei $N_0$ = initial no. nuclei $n$ = no. half lives since $N_0$ calculated

Activity#card §

The number of decays per second of a sample, also called the decay rate. As more nuclei have decayed (time has passed), the activity of the substance will decrease (the rate decreases).

$$A=A_0(\frac{1}{2}{)}^n$$

$A$ = the activity at a given time (Bq) $A_0$ = the initial activity (Bq) $n$ = no. half-lives since the initial measurement (no units)

Rate: the number of nuclei decaying per unit of time ∴ 1 Bq = 1 decay/disintegration per second (becquerel)