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Test Your Knowledge
Key Idea 2: Radioactive and Stable Isotopes

7) What happens when a radioisotope undergoes nuclear decay?

  1. The radioisotope loses exactly half of its electrons, transforming it into a different isotope of the same element, or an atom of a new element.
  2. A spontaneous transformation within the nucleus of the radioisotope transforms it into a different isotope of the same element, or an atom of a new element
  3. The nucleus of the radioisotope combines with the nucleus of another radioisotope
  4. The nucleus of the radioisotope decomposes through the action of bacteria or fungi

8) The half-life of carbon-14 is 5,730 years. You discover a sample of carbon-14 atoms and determine that ¾ of the atoms have undergone radioactive decay. How old do you estimate the sample to be? (Hint: how many half-lives would result in a depletion of ¾ of the sample?)

  1. 11,460 years
  2. 5,730 years
  3. 4,297.5 years
  4. 1,432.5 years
Click here to show answer
A.

9) Stable and radioactive isotopes both have many important practical applications in biology, earth/planetary science, forensics and anthropology, geochronology, industry, medicine and in the creation of other radioactive isotopes.

  • Open the IUPAC Periodic Table of the Elements and Isotopes Learning Tool and click on the carbon element tile.
  • Click on “More Information” and consult the table on the first page. List the stable and radioactive isotopes of carbon.
  • Scroll down to “Carbon Isotopes in Forensic Science and Anthropology.”
  • Write down one interesting application of a stable isotope of carbon and one interesting application of a radioactive isotope of carbon.

10) There have been no experimentally detected nuclear decays in carbon-12 atoms. Therefore, carbon-12 atoms are described as______.

Click here to show answer
stable

11) Taking it further: 18F is a radioactive isotope of fluorine that is used in PET scans. This technique uses 18F atoms in a compound that is injected into the body. As the 18F atoms decay, the radiation is detected on the PET camera and helps to create an image of part of the body. Should people having PET scans be worried about the radiation released by the decay of 18F? Why or why not? Conduct research – paying particular attention to the half-life of 18F.

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