What Are Stable Isotope Ratios?

Isotopes

Isotopes differ from normal elements in the number of protons contained in their nucleus. Normally, any given element has the same number of protons and neutrons. An isotope, on the other hand, contains an unequal number of neutrons and protons. An isotope's number of neutrons and protons is recorded using a ratio. For example, a regular carbon atom consists of six electrons, six protons and six neutrons. Carbon-13, an isotope of carbon, has six electrons, six protons and seven neutrons.

Some isotopes are regarded as unstable while others are regarded as stable. An isotope's stability depends on its atomic makeup. If an isotope has too many, or too few, neutrons, it is considered a radioisotope, or an unstable isotope. Radioisotopes always decay into a stable isotope. On the other hand, stable isotopes do not decay. Since their particular combination of protons and neutrons will not cause decay, carbon-13 and carbon-14 are examples of stable isotopes.

Stable isotopes are measured through a process called gas isotope-ratio mass spectroscopy. For the first step, researchers transform the isotopes into gas and ionize them. Ionization is the act of removing electrons from atoms, thus giving them the atom a positive charge. These positively charged gas isotopes are sent through a bent tube. As they travel, a magnet separates these isotopes according to their mass. A tool called a Faraday collector measure the mass of the isotopes at the end of the tube.

Stable isotopes are at the basis of several tools ecologists use to conduct research. One process, for example, is called the natural abundance isotope technique, a technique that uses stable isotopes to measure how efficiently a particular plant uses water. Another technique, the isotope tracer technique, allows ecologists to measure the rate of mineralization that occurs within soil.