http://www.ck12.org Chapter 3. Chemical Interactions
3.57 Radioisotopes
- Describe radioisotopes, and give an example of a radioisotope.
- Explain why radioisotopes have unstable nuclei.
- Identify radioactive elements.
This fossil skull came from an ancient human ancestor. Scientists used carbon-14 dating to estimate its age. Carbon-
14 is one of several radioisotopes that scientists use to estimate the ages of fossils and other ancient materials.
What Are Radioisotopes?
All the atoms of a given element have the same number of protons in their nucleus, but they may have different
numbers of neutrons. Atoms of the same element with different numbers of neutrons are called isotopes. Many
elements have one or more isotopes that are radioactive. These isotopes are calledradioisotopes. Their nuclei are
unstable, so they break down, or decay, and emit radiation.
Q:What makes the nucleus of a radioisotope unstable?
A:The nucleus may be unstable because it has too many protons or an unstable ratio of protons to neutrons. For a
nucleus with a small number of protons to be stable, the ratio of protons to neutrons should be 1:1. For a nucleus
with a large number of protons to be stable, the ratio should be about 1:1.5.
An Example: Carbon-14
Find carbon in theFigure3.106, and you’ll see that its atomic number is 6. This means that all carbon atoms have
6 protons per nucleus. Almost all carbon atoms also have 6 neutrons per nucleus. These carbon atoms are called