Isotopes (and Radioactivity)
Many elements have one or more isotopes. Isotopes are of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties. Some isotopes are not stable and ultimately break down or change into other elements. We call such isotopes radioactive. Many elements have both stable and radioactive isotopes. For example, the element carbon has 3 isotopes: 12C and 13C are stable, whereas 14C is unstable and will undergo radioactive decay. All there isotopes have 6 protons, but have 6, 7, and 8 neutrons, respectively.
Figure 1.25. Radioactive elements that occur in rocks and minerals include isotopes of potassium, thorium, radium, and uranium. and may display measurable radioactivity. A geiger counter us used to measure materials for radioactivity.
In the natural environment there are 80 different elements that have one or more isotopes. Of these, at least 254 stable isotopes that have never been observed to decay. Another 50 are radioactive. With the invention of nuclear weapons, and the numerous nuclear bomb test through the 1950s to the present, there are now many more radioactive isotopes loose in the environment. The mixing of these radionuclides in the air, water, and sediments dilute their concentrations, but also disperse them to all regions of the world.
For example, the March 2011 Fukushima Daiichi nuclear disaster associated with the massive earthquake and tsunami in Japan released large amounts of radiation into the marine environment.