Geologists can determine the ages of rocks and fossils by analyzing the isotopes found in them.
Radiation from certain isotopes can be used to treat cancer and to kill bacteria that cause food to spoil.
See related questions below I'm no professional on this, but I think I can contribute to something.
Isotopes, (I hope you already know this), are types of the same element, but with different mass, usually due to different numbers of neutrons.
Human remains, fossils and organic materials from archaeological sites are all dated using carbon-14.
Books, clothing and food remains are all archaeological artifacts that can be carbon dated.
To answer your question, they are both stable isotopes and between the two of them make up all the carbon on the planet. Carbon 6 and Carbon 7 I think this is mixing up atomic number (number of protons) and atomic mass number (number of protons neutrons). The 2 isotopes of carbon mentioned are carbon 12 and carbon 14.
- Isotopes are used as sources of radiation in medicine, sterilization, nondestructive control, etc.
Carbon-based rocks, such as bitumen and tephra, can also be dated in this manner.
Carbon dating is most effective on material that predates the 1940s; this is due to above-ground nuclear tests increasing the amount of carbon-14 in the environment.
Two of the most common include carbon dating to discover how old fossils and other historical organic (including carbon) artifacts are and uses of radioactive isotopes in medicine.
Radioactive isotopes in medicine are used to help diagnose certain disease states and isolate regions in the body.
A radioactive isotope is a chemical element that has an unstable nucleus subject to decay.