Nuclear Energy

Two important concepts in physics explain how massive amounts of energy can come from very small particles -- Einstein's famous equation E = MC² and nuclear radiation.

E = mc²
An atom's nucleus and the structure of certain isotopes make it possible to release incredible amounts of energy when the atom splits. You can understand how much energy this process releases by looking at Einstein's equation E = mc², where E is energy, m is mass and c is the speed of light (approximately 300,000 kilometers per second). Although you may have heard of this equation without knowing what it really means, the concept behind it is pretty simple. Matter and energy are essentially interchangeable -- matter can be converted into energy, and energy can be converted into matter, and the numbers involved are enormous. The speed of light is a huge number -- if you multiply a large amount of mass by the speed of light, you get an extreme amount of energy. And even though atoms are small -- they don't have a lot of mass -- it takes a vast number of them to make a substance.

Substances like uranium, which are commonly used in nuclear bombs, have a very high atomic number -- the atoms themselves are larger and contain more particles than the atoms of other naturally-occurring substances. Because of this additional nuclear material, uranium has the power to release a lot of energy. If you multiplied 7 kilograms of uranium by the speed of light squared, you would get about 2.1 billion Joules of energy. By comparison, a 60-watt light bulb uses 60 joules of energy per second. The energy found in a pound of highly enriched uranium is equal to something on the order of a million gallons of gasoline. When you consider that a pound of uranium is smaller than a baseball and a million gallons of gasoline would fill a cube that is 50 feet per side (50 feet is as tall as a five-story building), you can get an idea of the amount of energy available in just a little bit of U-235.

Radioactive decay
Radioactive decay involves atoms splitting or shedding their parts, and these parts leave the atom at high speeds, becoming rays. There are three types of radioactive decay:

• Alpha decay: A nucleus ejects two protons and two neutrons bound together, known as an alpha particle.
• Beta decay: A neutron becomes a proton, an electron and an antineutrino. The ejected electron is a beta particle.
• Spontaneous fission: A nucleus splits into two pieces. In the process, it can eject neutrons, which can become neutron rays. The nucleus can also emit a burst of electromagnetic energy known as a gamma ray. Gamma rays are the only type of nuclear radiation that comes from energy instead of fast-moving particles.

You can learn more about exactly what happens in these types of decay in How Nuclear Radiation Works.

On the next page we'll look at the first important step in making nuclear bombs -- nuclear fission.