does anyone know any uses of isotopes?

Answer 1

Do you mean isotopes that undergo radioactive decay?

There are quite a few of these. Some are used as medical tracers, Tc-99 is one see the applications section of

some radioisotopes are used in the oil industry as tracers.

C-14 is used in radiodating materials.
K-40 is used to date rocks.

As for stable isotpoes....

The ratio of some isotopes are characteristic of where a plant grows or some one has lived. An example here is the ratio of H:Deuterium is different for morphine from different sources.
The isotopes in lead are also characteristic of the source. Thus it is possible to distinguish between lead in artic (from petrol) that has come from USA produced tetraethyl lead and that produced in Russia.

Answer 2

yes, i do mean isotopes that undergo radioactive decay. However i do not really understand what this radioactive thing have to do with isotopes or unstable or stable.