Half-life

Radioactive substances give out radiation from the nuclei

Radiation can be measured with a GEIGER-MULLER TUBE AND COUNTER - this records the count-rate (the number of radiation counts per minute).

Radioactive decay is entirely random- unpredictable. HOWEVER:

You can find out the time it takes for the amount of radiation emitted by a source to half- this is the HALF-LIFE. This may be used to predict even though it's random.

Half-life can be used to find the rate of a source's activity. Activity is measured in BECQUERELS (Bq) - 1Bq is 1 decay per second.

The half-life is the time taken for the number of radioactive nuclei in an isotope to half.