Use of Radioactive Isotopes. Naturally occurring radium has been used for some time in radiotherapy, particularly in the treatment of cancer, and the y-rays from radium or radon have been used in taking radiographs. They present commercial availability of artificial radioactive isotopes has, however, greatly increased the research and industrial application of radio techniques. The following selection of examples will illustrate the range of usage.
1. Used as Tracer Techniques: An object with a very small amount of a radioactive isotope attached to it, or incorporated in it, can readily be detected by picking up the radiation from it. A joint in a buried pipe or cable can be marked, for example, in this way, or the efficiency of a mixing process can be followed by adding a radioactive isotope to one of the ingredients before mixing and then observing how even the level of radiation is throughout the final mixture.
The wear inside an engine can be measured by making the various moving parts radioactive and measuring the resulting radioactivity in the circulating oil. The flow of a material, e.g. molten glass through a furnace, fertilizer through a drier, or gases in ventilation system, can all, also, be controlled by tracer techniques.
There are, too, many biological and medical uses.
3. The uptake of phosphorus by a plant from a phosphate fertilizer: This can be traced by using a fertilizer containing 32P, and radioactive tracer studies, using 14C, have been very valuable in elucidating the nature of photosynthesis.
4. Study of Iron (II) Ion In Blood Stream: Introduction of radioactive 59Fe into the blood stream has enabled the part played by iron in blood formation and use to be studied, and blood circulation is followed by injecting a saline solution containing a little 24Na.
5. Diagnosis of Thyroid Disease Using Iodine: 131I has been used both in the diagnosis of thyroid disease and in research on the functioning of the thyroid gland.
6. Detections of the diffusion of a metal containing radioactive isotopes into another metal
7. The solubility of water (made from tritium) in hydrocarbons.
8. The solubility of very sparingly soluble salts (made radioactive) in a solvent, can be measured. Moreover, chemical reaction of the type,
AB+B’ AB’ + B
Where B and B are the same element can be followed if non-radioactive B and radioactive B’ are used. In this way exchange rates can be measured. The detailed behaviour of any element in other chemical reactions can be investigated, too, by using a radioactive isotope of the element.
9. Measuring Thickness of Materials: The β- and y-rays emitted by radioactive isotopes can be very useful, particularly in measuring or controlling thicknesses of materials. The amount of radiation passing through a material will decrease as the material gets thicker. If a source of β or y-rays is placed on one side of the material and the detector on the other side, the scale reading on the detector will give a measure of the thickness of the material and can, infact, be calibrated directly in thickness units. Such measurements can be made without touching the material concerned so that they can be applied, for example, to sheet steel coming through a high speed rolling mill.
Typical uses are in controlling the thickness of paper, plastic sheeting and sheet metal, in checking the packing of tobacco in cigarettes, in measuring or monitoring the thickness of coating of one metal on another, and in checking the level to which a container is filled with a liquid or solid. β-rays can be used for material thicknesses up to about 1.5 mm of steel.
10. y-rays Are Used in Radiography Instead of X-rays: A radioactive isotope which gives y-rays is much cheaper, much smaller, and more portable and manoeuvrable than X-rays. A typical use is provided by the standard method of testing welds when laying a pipeline. 60Co or 192Ir are used to provide y-rays which enable a radiograph of the weld to be taken.