Understanding Radiation: Atoms and Isotopes

By Matt Wood April 3, 2011 20:01

Understanding Radiation:  Atoms and Isotopes

About the Understanding Radiation series

Following the recent problems at the Fukushima No.1 Nuclear Power Plant, the news has been teeming with talk of isotopes, radiation, contamination, and health risks. For many of us, all this talk of half lives and microSieverts can be a little confusing. In order to understand what we are being told in the news, we need to know a little about nuclear physics. The following series of articles will introduce a few fundamental concepts to help us better understand recent events (don’t worry, we’re going to keep this simple).

Let’s start at the beginning, with atoms.

We probably all have a rough idea of what an atom looks like. The center, or nucleus, is made up of pieces called protons and neutrons, and this is surrounded by a cloud of electrons. Protons have a positive charge, neutrons have no charge, and electrons have a negative charge. The forces between these charges holds the electrons around the nucleus. Another force, called the strong force, holds the protons and neutrons together.

The number of protons an atom has determines what element, or what kind of atom it is. If it has 1 proton it is hydrogen, if it has 6 it is carbon, and so on all the way up to the larger atoms like uranium which has 92 protons.

A neutral atom, or an atom with no overall charge, has the same number of electrons as protons. So a neutral hydrogen atom has one electron, and a neutral carbon atom has 6 electrons. Atoms are not always neutral, which means the number of electrons is not always the same as the number of protons. This is important for chemical reactions, but we don’t need to worry about it to understand radiation.

What is important is that atoms of the same element can have different numbers of neutrons. These variations of the same element are called isotopes.

For example, ordinary hydrogen (hydrogen-1) has one proton and one electron. But an isotope called hydrogen-2 has one proton, one neutron and one electron. Hydrogen-3 has one proton, two neutrons and one electron. The different isotopes are numbered according to the total number of protons and neutrons (1 proton + 2 neutrons = hydrogen-3).


Isotopes of hydrogen

Isotopes of hydrogen

As another example, carbon has six protons (this is what makes it carbon) and ordinary carbon has six neutrons, this is called carbon-12. The isotope carbon-13 has seven neutrons and carbon-14 has eight neutrons, but they are all carbon because they all have six protons.

In the same way, most elements have a range of isotopes. Many of these isotopes are unstable because the forces between their protons, neutrons and electrons—the forces which hold them together—are unbalanced. This means they are unhappy as they are and want to change into something more stable, often a different element altogether. This change is called decay, and during decay, isotopes emit excess energy as radiation.

For this reason many isotopes are radioactive because they emit radiation as they decay to something more stable. These unstable, radioactive isotopes are called radioisotopes.

In the next installment in this series we will look at what half life means.


By Matt Wood April 3, 2011 20:01