Radioactive Isotopes
Radioactive isotopes are radioactive atoms of ordinary elements such as carbon, cobalt, sodium, or phosphorus. Some radioisotopes are found in the atomic ash that remains after uranium atoms are split in a nuclear pile. Others are created by exposing normal elements to intense radiation inside a nuclear reactor while fission is taking place.
Radioactive isotopes emit radiation in the form of beta and gamma rays. The intensity of the radiation is proportional to the rate at which the radioactive material decays. Thus the different radioisotopes can be used for special purposes and processes.
Tools of research and industry. Tracers, as radioactive isotopes are sometimes called, have been described as the most useful research tool since the invention of the microscope in the 17th century. Physiologists using tracers, for instance, are learning where and at what speed physical and chemical processes occur in the human body.
An example of this technique is an experiment with radioactive sodium 24. A very small amount of the isotope is added to a salt solution that is injected into the body. Instruments that are sensitive to radioactivity follow the tracer in the salt as it travels through the body. Scientists have learned that it passes through the walls of the veins, is carried to the sweat glands, changes into sweat, and appears on the surface of the body in less than a minute. Tracers are also being used to study the flying habits and travel patterns of insects.
Agricultural and botanical research has benefited from the use of radioactive isotopes. Scientists have determined how plants absorb chemicals as they grow. With radioactive cobalt, botanists can produce new types of plants. Structural variations that normally take years of selective breeding to develop can be made to occur in a few months.
Industrial operations often use radioactive tracers instead of X rays or radium in the detection of flaws in cast or welded metal. A few dollars' worth of cobalt can replace thousands of dollars' worth of radium in such work. The petroleum industry employs radioelements in checking almost every kind of operation, from the drilling of wells to the distribution and use of finished products.
Aid to medicine. The field of medicine has benefited greatly from nuclear energy in the form of radioisotopes. Physicians use radioisotopes to locate tumors, to diagnose and treat patients suffering from thyroid irregularities, and to study and treat cancer. The element cobalt has been adapted for many medical needs. A small quantity of the natural element becomes strongly radioactive after it has undergone prolonged exposure to radiation in a nuclear pile. It is placed in a thick lead case with a tiny opening that is covered by a shutter, and it is then shipped to hospitals. Patients suffering from cancer can then be exposed to the healing effects of the radiation under controlled conditions. Radioactive material in this form is much less costly than radium, and it is far simpler to use than X-ray radiation.
The radioisotope of phosphorus is another important diagnostic aid. If a solution containing radiophosphorus is injected into the veins of a patient, it concentrates in the cells of certain brain tumors. A specially designed Geiger counter is then passed over the surface of the head. It accurately locates the tumor by recording the radiation that is emitted from the radiophosphorus lodged in the tumor.
The thyroid gland strongly attracts iodine. Hence radioactive iodine is used both in diagnosing and in treating diseases of the thyroid.
Harnessing Fusion for Peaceful Use
A beginning has been made toward harnessing the most powerful release of nuclear energy, that of the thermonuclear reaction (nuclear fusion, using light elements). The heat needed to start the reaction is at least 50 million degrees Centigrade (122 million degrees Fahrenheit). The fission bomb yields such heat; for peaceful application, however, the heat must be produced without destroying the apparatus.
In present experiments a magnetic field instead of a container is used to hold the material. Ionized deuterium (heavy water) is placed inside the coil of a powerful electromagnet. The magnetic field of the coil confines the material, called plasma in this state, to the axis of the coil. This arrangement is often called a "magnetic bottle." The plasma is heated by shooting a tremendous electric charge through it.
Experiments with laboratory-size "bottles" have generated heats of from 20 to 30 million degrees Centigrade (70 to 85 million degrees Fahrenheit) and perhaps some fusion. Further development is retarded by the enormous amount of power needed for the coils and the charge. This obstacle may be overcome by chilling the apparatus to almost absolute zero (-273 C, or -460 F). The metal in the coils and circuits then offers almost no resistance to the flow of current, and the power requirement might be reduced enough to make the method practical.
Another method being explored is inertial confinement, or, more specifically, laser fusion. In this method small pellets of fusion material (deuterium or tritium) are compressed to extremely high density for a short period of time by very powerful laser (focused light) beams. Other inertial confinement methods involve beams of electrons or heavy ions instead of beams of light. At present scientists do not expect that a workable reactor that uses these fusion methods to generate electricity will be realized before the year 2000.
In 1989 two research chemists announced that they had triggered a nuclear fusion reaction at room temperature using relatively common materials heavy water (in which the hydrogen atoms have been replaced with deuterium), a platinum electrode, and a palladium electrode. However, attempts by other scientists to duplicate the reaction, which was dubbed "cold fusion," produced conflicting results.