http://www.ck12.org Chapter 11. Nuclear Chemistry
Limit on Carbon-14 Dating
Carbon-14 has a relatively short half-life (seeTable11.1). After about 50,000 years, too little carbon-14 is left in a
fossil to be measured. Therefore, carbon-14 dating can only be used to date fossils that are less than 50,000 years
old. Radioisotopes with a longer half-life, such as potassium-40, must be used to date older fossils and rocks.
Lesson Summary
- Radioactive decay is the process in which unstable nuclei become stable by emitting particles and energy and
changing to different elements. There are three types of radioactive decay: alpha, beta, and gamma decay.
Each differs in what is emitted, how far it can travel, and what it can penetrate. - The rate of radioactive decay varies from one radioisotope to another. The rate is measured by the half-life.
This is the length of time it takes for half of a given amount of a radioisotope to decay. - Radioactive dating is the use of radioactive decay to estimate the ages of fossils and rocks. An example is
carbon-14 dating.
Lesson Review Questions
Recall
- What is radioactive decay?
- Define half-life.
- Which type of radioactive decay is represented by each of the following nuclear equations?
a.^6027 Co→^6028 Ni+−^01 e+Energy
b.^263106 Sg→^259104 Rf+^42 He+Energy
Apply Concepts
- Complete the following nuclear equation. First add the missing subscript. Then use the periodic table in
Figure11.2 to identify the unknown element(X).^21185 At→^207? X+^42 He+Energy - Create a model to demonstrate the concept of the half-life of a radioisotope.
- Assume that a fossil contains one-eighth of the carbon-14 that was present in the organism when it was alive.
How long has it been since the organism died?
Think Critically
- Compare and contrast alpha, beta, and gamma decay.
Points to Consider
Radioactive decay releases energy. Other types of nuclear reactions also release energy.