Geiger counter
There are a few properties of radioisotopes which make them useful. One of them is the fact that they give off radiation and so they can always be found with a Geiger (GUY-ger) counter. This is an instrument which ticks when it is struck by an atomic ray. With the help of a counter, radioisotopes can be used as tracers, or tags.
Tracers are used in dozens of interesting ways. One is to find leaks in pipes. Sometimes there is a leaky pipe buried in the floors or walls of a building. How can you find out where the leak is without tearing the building apart? It is very simple. Just add a tiny bit of a radioisotope to the water in the pipe. Then move a Geiger counter along the floor or wall in which the pipe is enclosed. When the ticks stop—or continue, but spread out over a large area—you have found the leak.
A similar trick is often used in the oil industry. Sometimes the same pipeline is used for oil and for gasoline. A worker at the far end of the pipeline has the job of turning off a valve when the oil stops coming through, and turning on a different valve to send the gasoline to the proper tank. But how does he know when the oil is finished and the gasoline is about to start? There's nothing to it. A dash of radioisotope is mixed with the last gallon of oil. The worker keeps his Geiger counter on the pipe. When it begins to tick, it's time to make the change.
If you had a tire factory, how would you find out which kind of rubber gave the best wear? You could make four different kinds of tires and add a bit of radioisotope to the rubber of each. With the tires on a car, instead of driving thousands of miles, as in the past, you could drive just a short distance. As the tires turned, tiny bits of rubber would wear off. A Geiger counter moved over the tire tracks would tell you right away which tire lost the least rubber. Tire companies use this test widely.
Radioisotopes mixed with wax or polish tell how much is left on a car after washing. Radioactive dirt smeared on cloth tells which detergent does the best washing job. If radioisotopes are mixed with the liquid in a tank, a Geiger counter on the outside of the tank can tell where the top of the liquid is. This is much easier than sending a man all the way to the top of the tank to measure the contents with a dip stick.
Scientists have made great use of the radioisotope carbon-14. Carbon-14 occurs naturally in the air and is taken in by all living plants. It is also taken in by all people or animals who eat plants. Once a living thing dies, however, it does not take in any more carbon-14. Now it happens that carbon-14 has a very long half-life—about 5,000 years. So even if a plant or an animal has been dead for 25,000 years, there are still slight traces of carbon-14 left. By measuring the quantity with a counter and comparing it to the quantity in a living plant or animal of the same kind, scientists can tell the age of very old things.
dating with Carbon-14
When ancient writings about Biblical times, called the Dead Sea Scrolls, were found, they were wrapped in linen. The linen, made from the fibers of the flax plant, was tested for carbon-14. It was found to be about 2,000 years old. The same method has been used to find the age of ancient wood, leather, cloth, bones—and even mummies!
Radioisotope tracers have been of great benefit to farmers. Mixed with fertilizers, they can be followed with a Geiger counter to see just how the plant uses the fertilizer and how fast. Tracers have shown how certain feeds make animals grow fatter. They help in the study of milk production by cows, egg production by chickens, and growth of wool on sheep.
Perhaps the most important of all tracer uses is in medicine. Radioactive iodine, or iodine-131, is used to find diseases of the thyroid gland. The patient swallows a small dose of the tracer and a counter shows how fast it is taken in by the thyroid gland. This shows how active the gland is. Tracers also help to find brain tumors. And they can be used to follow the circulation of the blood. If an artery is blocked, a person may die because his blood can't circulate. A counter can find the trouble spot and help save a life.
Radioisotopes which are used as medical tracers are not harmful to the body. They are carefully selected to have a very short half-life. Their radioactivity is gone before it can do damage. Also, they are used in tiny quantities.
While radioisotopes do wonderful jobs as tracers, they can do some other very interesting things, too. Let's see what some of them are.
10
ATOMS TO CHANGE ATOMS
When the rays of a radioactive substance strike the atoms of another substance, they may cause changes. We call the exposure to rays irradiation (ir-rade-ee-AY-shun). One of the changes caused by irradiation is called ionization (eye-on-i-ZAY-shun).
Radioisotopes do many important jobs for us by irradiation. In industry, certain petroleum and other materials are changed by irradiation into special fuels, oils, and even synthetic rubber.
Irradiation is used to improve the quality of plastics and to vulcanize rubber. It used to take several hours to vulcanize with heat. A few minutes of irradiation does the same job.
The food industry has begun to experiment with irradiation as a new way to sterilize food. Items which normally spoil quickly, such as hamburger, sausage, cheese, and bread, are exposed to radiation. The rays destroy all of the bacteria that cause food to spoil. The food is immediately sealed in airtight plastic bags. It will remain perfectly fresh for months—or even years. This process may make the canning or freezing of food completely unnecessary.
irradiation prevents sprouting
Even foods which generally keep well, such as onions or potatoes, can be helped by irradiation. The treatment kills any insects that might be in the sack, and also keeps the vegetables from sprouting. A treated potato will keep for a very long time. A number of experiments have been done with potatoes. Before long you will probably see irradiated potatoes for sale in your market.
Irradiation can even improve food crops and other plants while they are still being grown. Changes caused by the rays have already created new and better varieties of corn, peanuts, and oats. The same dose of irradiation works in another way, too—it kills the insects which damage the crops.
Irradiation used in certain medicines can destroy a patient's diseased tissue. Many forms of cancer are treated by this method. In some cases, the patient is injected with a radioisotope. In other cases, he is just exposed to its rays, which are projected from a special machine. Sometimes, tiny bits of isotope, called seeds, are actually placed directly in the cancer. Other patients are asked to drink the isotope in a special preparation called a "radioactive cocktail."
Besides their many uses as tracers and irradiators, isotopes have great value as substitutes for expensive X-ray machines. The rays can pass through many materials and, by making a picture on a film underneath, can show differences in thickness or other flaws. Some of the materials that are inspected this way are sheet metal, paper, rubber, and plastics. Also, piston rings for auto engines, and airplane engine valves.
Doctors, too, can use radioisotopes instead of X rays. An X-ray machine is a huge piece of equipment which needs a special room and costs thousands of dollars. A radioisotope machine is about the size of a large can of fruit juice and weighs only ten pounds. It can be carried about easily and is most valuable in an emergency or at a place where there is no X ray available.
These are only some of the things that atoms can do for us. Atomic energy is still young. In the years to come, there will be many changes. During your lifetime, the peaceful atom should make the world an easier, healthier, happier place!
radioisotope machine
APPENDIX
Some other important atomic pioneers:
Chadwick, James: Discovered the neutron in 1932.
Joliot-Curie, Irene and Frederic: Daughter of Marie and Pierre Curie, and her husband. Were the first to make artificial radioisotopes in 1933.
Rutherford, Ernest: Worked out the nature of radioactivity in 1902, discovered the nucleus of the atom in 1911, and split the first atom in 1919.
Soddy, Frederic: Discovered isotopes in 1910.
Urey, Harold: Discovered hydrogen's heavy isotope, deuterium, in 1932.
GLOSSARY
| AEC | Atomic Energy Commission (U.S.) All atomic energy in the United States is under the control of the AEC. The Commission is in charge of the sources, manufacture, and uses of all fissionable materials. It has important programs of research, building, training, and information. |
| artificial element |
A chemical element that does not exist in nature but which can be made in an atomic reactor. |
| atomic furnace |
An atomic reactor. |
| canal | A tank of water which is used to hold dangerously radioactive materials in order to protect workers. |
| coffin | A thick metal box which is used to hold very radioactive material. |
| contaminated | Anything that has accidentally become radioactive. |
| cool off | To stop being radioactive. Some materials have to cool off before they can be handled safely. |
| critical size | The smallest amount of atomic fuel that will allow a chain reaction to take place. |
| curie | The unit used to measure radiation. It is equal to the amount of radiation given off by one gram of radium in one second. |
| Einstein, Albert | (1879-1955), born in Germany, fled under Hitler, and became an American citizen in 1940. In 1955 he published a brilliant theory which became the basis for the discovery of atomic energy. The theory stated that neither matter nor energy can ever be destroyed, but that matter can be changed into energy. Einstein expressed this in the equation E = mc^2. It means that energy (E) is equal to mass (m) multiplied by the speed of light (c), multiplied by itself. Mass is the amount of material or matter in anything. The speed of light is 186,000 miles a second. |
| emit | To give off. Radioactive substances emit rays. |
| enriched uranium |
Ordinary uranium which has fissionable uranium added to it. |
| fissionable | Usable as an atomic fuel. A material whose atoms will split. |
| fusion | A source of atomic energy which is the opposite of fission. Instead of nuclei being split, they are forced together. The energy of the sun is released by fusion. |
| hot | Radioactive. |
| moderator | A material which is used in an atomic reactor to slow down the speed of the neutrons. Graphite and water are common moderators. |
| nuclear energy |
The correct name for energy produced by changes in atomic nuclei. Atomic energy is the common name for nuclear energy. |
| pig | Heavy metal container for radioactive material. Similar to coffin. |
| pitchblende | The ore richest in uranium. |
| remote manipulator |
A device that can handle radioactive materials mechanically while the operator remains safe behind a shield. (Also called a master slave manipulator.) |
| scram | To stop an atomic reactor. An emergency stop is called a fast scram. |
| transmute | To change one kind of atom into another kind. |
INDEX
alpha particle, 30
atomic energy, 8
atomic number, 27
atomic pile, 36
atomic power, 42
atomic theory, 15
Becquerel, Antoine Henri, 20
beta particles, 30
boiling water reactor, 44
breeder reactor, 46
cadmium, 38
carbon-14, 56
chain reaction, 35, 36, 44
chemical compound, 15
Compton. Arthur H., 40
Conant, James B., 40
control rod, 38
Curie, Marie, 22
Curie, Pierre, 22
Dalton, John, 15
Dead Sea Scrolls, 57
decay, 30
Democritus, 13
electron, 26, 29
element, 15
energy, 32
Fermi, Enrico, 36
fission, 34
fossil fuels, 9, 46
gamma rays, 30
Geiger counter, 53
graphite, 36, 44
Iodine-131, 57
ionization, 60
irradiation, 60
isotopes, 28
neutron, 26, 28
nucleus, 27, 29
pitchblende, 23
plutonium, 46
power plant, 42
pressurized water reactor, 43
proton, 26
radioactivity, 22
radioactive cocktail, 64
radioactive iodine, 57
radioisotope, 52, 64
radium, 23, 30, 32
Roentgen, Wilhelm K., 18
uranium-234, 29
uranium-235, 29, 46
uranium-238, 29, 46