Have you ever noticed how often you hear the words "nuclear" and "radioactive"? For example, if you live in Apex, North Carolina, you only live a few miles away from the Shearon Harris nuclear power plant, so you probably hear about nuclear power all the time. There are dozens of nuclear power plants all over the United States. You hear about nuclear bombs and nuclear submarines constantly on the news. People are worried about radioactive waste and radioactive radon gas in their homes. You may even have a nuclear device in your bedroom!

Why are there so many nuclear things in our world? It's because certain atoms give off a special kind of energy called nuclear radiation. In this article, we will look at five different ways that people harness this energy, both for good and for evil. But first, let's understand what "radioactive" means.

What does "radioactive" mean?
Let's start by understanding where words like "nuclear radiation" and "radioactive" come from. You know that everything is made of atoms. There are 92 different types of atoms in nature. Most of those atoms are stable. For example, gold is a stable atom. If you take an atom of gold and put it in a bottle, and then come back in several million years, it will still be an atom of gold. But not all atoms are stable. Some atoms change over time. We say that these elements are radioactive. Uranium is a good example of a radioactive element.

Image courtesy/credit Jupiter Images/Steve Allen Control rods are insterted into the core of a nuclear reactor.

How does a radioactive element change?
We say that it decays. When it decays, an amazing thing happens -- it changes to a different element. A radioactive atom can decay in three ways: Alpha decay, beta decay or spontaneous fission. When an atom decays, it creates nuclear radiation. We use the term radiation because particles radiate from the decaying atom. For example, when an element undergoes alpha decay, it throws off an alpha particle. An alpha particle is made up of two protons and two neutrons bound together. The alpha particle flies off at about 10,000 miles per second.

Why is nuclear radiation dangerous?
Because these high-speed flying particles (like alpha particles) can damage cells. If enough cells are damaged, you die. If a lot of cells are damaged, you get radiation sickness from all the damage. If you are hit by a small amount of radiation, it seems harmless at first. But the damaged cells can turn cancerous over time, and you get cancer tumors in different parts of your body. Even though nuclear radiation is dangerous, it turns out that you can do lots of useful things with nuclear radiation. You just have to be careful with radioactive material because of all of the harmful effects of radiation exposure.

Nuclear Spacecraft One of the ways NASA uses radioactivity is to produce electricity. Probes that fly toward planets like Jupiter and Saturn are far away from the sun. They can't use solar panels to generate electricity. Instead, they have RTGs (radioisotope thermoelectric generators - try saying that three times fast). An RTG uses radioactive material (like plutonium) to create heat. Then thermocouples convert the heat to electricity. Thermocouples generate electricity directly from heat. They use a really interesting electrical effect that happens when you join two different metals together. For example, take two iron wires and one copper wire. Twist one end of the copper wire and one end of one of the iron wires together. Do the same with the other end of the copper wire and the other iron wire. If you heat one of the twisted joints with a flame, the heat will create electricity in the wires. An RTG uses thousands of thermocouples, with the plutonium providing the heat. RTGs have no moving parts, so they are very reliable. The radioactive material makes heat for many years.