Nuclear Medicine and Nuclear Submarines

Doctors have found many ways to use radioactivity to cure diseases. Doctors can also use radioactivity to form images of the body. With an X-ray, you pass radiation through the body and take a picture when the radiation comes out on the other side. Another way is to put radioactive liquids inside the body and then measure the radiation as it flows out of the body. Doctors either inject a radioactive liquid, or have you swallow a radioactive drink. Then they use computers and special detectors and scanners to measure the radiation that comes out. For example, bones like to absorb phosphorus. So if you inject radioactive phosphorus into the body, the bones will absorb it. If you have bone cancer, any tumors will absorb a lot more of the phosphorus than normal bones will. Doctors can measure the radioactive hot spots that the tumors create and then treat them.

Another way to use radiation is to kill cancerous cells. Doctors place a radioactive pellet or wire near a tumor, and the radiation kills the tumor cells. It is not perfect, because the radiation may kill some healthy cells as well. But radiation therapy is helpful when it is impossible to remove a tumor through surgery.

Nuclear Submarines
If you take a nuclear power plant, and you shrink it, and you put it inside a submarine, you get a nuclear submarine. Nuclear subs have two big advantages over "normal" submarines. A normal submarine has either a diesel or a gasoline engine. It also has a huge bank of batteries. The sub can't run its engine underwater – the engine needs air to run. So when it is underwater, the sub uses its batteries to power an electric motor. Once the batteries get low, the sub has to come up to the surface. It runs its engines long enough to recharge the batteries, and then goes underwater again. This is a big problem, because it’s hard to hide a sub when it’s up on the surface running a big diesel engine. The other problem is that the big diesel engine needs thousands and thousands of gallons of fuel, and the fuel takes up lots of space in the sub. Since a nuclear power plant doesn't "burn" anything, it doesn't need a supply of air like a diesel engine does. That means that the nuclear reactor in a nuclear sub can run constantly. Now the sub can stay underwater for months at a time if it wants to. It never has to come to the surface for air. This is a huge advantage, because the sub can go all over the world undetected.

Image courtesy U.S. Navy/ General Dynamics Electric Boat The Seawolf-class nuclear-powered attack submarine Jimmy Carter (SSN 23), underway during sea trials

The other advantage of nuclear power is that the uranium fuel is long lasting. A nuclear sub can go for a decade or more without refueling. The only reason it needs ever come to port is to replace the crew and load up a new supply of food for them. For this same reason, modern aircraft carriers use nuclear power. They can stay at sea without having to worry about refueling.

Nuclear Power in Your Bedroom Most of the smoke detectors used in America today are radioactive. They use a little pellet of Americium-241 to detect smoke. They use Americium-241 because it gives off alpha rays. Here's what happens. An Americium atom is sitting around, and for some reason it decides it is time to change. Scientists don't really know why this happens, but it happens all the time and it happens consistently. When it changes, two protons and two neutrons in the Americium atom fly out of the nucleus as an alpha particle. An alpha particle travels at about 10,000 miles per second, or 36,000,000 miles per hour. So there are these alpha particles streaming out of the Americium pellet. They hit oxygen and nitrogen atoms in the air. When the alpha particles hit the atoms, they knock electrons off the atoms. These atoms, because they are missing electrons, now have a positive charge. The smoke detector has an electrical circuit that can count these positive atoms. The number of positive atoms will be very consistent until there is smoke in the air. The smoke particles attach to the positive atoms and neutralize them. Since the smoke detector is counting the number of positive atoms, it can see the change in the number of positive atoms. That tells the smoke detector that there must be smoke in the air, and the smoke detector sounds the alarm! Why isn't the Americium inside the smoke detector dangerous? Because alpha rays can only travel a few inches through air. Even a sheet of paper can block alpha rays. So the alpha rays never get outside of the smoke detector and they cannot hurt you. Now, if you were to open up the smoke detector, dig out the pellet of Americium and either breathe the dust or eat the pellet -- that COULD hurt you. So don't try it.