Radioisotopes in Industry
- Science and industry use radioisotopes in a variety of ways to improve productivity and, in some cases, to gain information that cannot be obtained in any other way.
- Sealed radioactive sources are used in industrial radiography, gauging applications, and mineral analysis.
The attributes of naturally decaying atoms, known as radioisotopes, give rise to their multiple applications across many aspects of modern day life (see also information paper on The Many Uses of Nuclear Technology).
Industrial tracers
Radioisotopes are used by manufacturers as tracers to monitor fluid flow and filtration, detect leaks, and gauge engine wear and corrosion of process equipment. Small concentrations of short-lived isotopes can be detected whilst no residues remain in the environment. By adding small amounts of radioactive substances to materials used in various processes it is possible to study the mixing and flow rates of a wide range of materials, including liquids, powders, and gases and to locate leaks.
Radiotracers are used widely in industry to investigate processes and highlight the causes of inefficiency. They are particularly useful where process optimization can bring material benefits, such as in the transport of sediments. Radiotracers are also used in the oil and gas industry to help determine the extent of oil fields.
Inspection
Radioactive materials are used to inspect metal parts and the integrity of welds across a range of industries. Industrial gamma radiography exploits the ability of various types of radiation to penetrate materials to different extents. Gamma radiography works in much the same way as X-rays screen luggage at airports. Instead of the bulky machine needed to produce X-rays, all that is needed to produce effective gamma rays is a small pellet of radioactive material in a sealed titanium capsule.
The capsule is placed on one side of the object being screened, and photographic film is placed on the other side. The gamma rays, like X-rays, pass through the object and create an image on the film. Just as X-rays show a break in a bone, gamma rays show flaws in metal castings or welded joints. The technique allows critical components to be inspected for internal defects without damage.
X-ray sets can be used when electric power is available and the object to be scanned can be taken to the X-ray source and radiographed. Radioisotopes have the supreme advantage that they can be taken to the site when an examination is required – and no power is needed. However, they cannot be simply turned off, and so must be properly shielded both when in use and at other times.
The process of gamma radiography, a type of non-destructive testing (NDT), is used to validate the integrity of poured concrete and welds on fluid vessels, pipelines, or critical structural elements. The unique characteristics of gamma radiography have resulted in the technique becoming a crucial tool throughout many industries. For example, to inspect new oil or gas pipelines, special film is taped over the weld around the outside of the pipe. A machine called a 'pipe crawler' carries a shielded radioactive source down the inside of the pipe to the position of the weld. There, the radioactive source is remotely exposed and a radiographic image of the weld is produced on the film. This film is later developed and examined for signs of flaws in the weld.
Gamma radiography has found use outside of core industrial applications, with the technique successfully employed following the devastating earthquake in Nepal in April 2015. NDT was used to test the integrity of critical buildings such as schools and hospitals, as well as historical attractions. Both Japan and Malaysia have since backed an IAEA initiative to use NDT for the inspection of civil structures more widely following natural disasters.
Researcher at Myanmar's Department of Atomic Energy testing equipment to be used in non-destructive testing
Gauges
Gauges containing radioactive (usually gamma) sources are in wide use in all industries where levels of gases, liquids, and solids must be checked. The IAEA estimates that several hundred thousand such gauges are operating in industry worldwide. They measure the amount of radiation from a source which has been absorbed in materials. These gauges are most useful where heat, pressure, or corrosive substances, such as molten glass or molten metal, make it impossible or difficult to use direct contact gauges.
The ability to use radioisotopes to accurately measure thickness is widely used in the production of sheet materials, including metal, textiles, paper, plastics, and others. Density gauges are used where automatic control of a liquid, powder, or solid is important, for example as in detergent manufacture.
Radioisotope instruments have three advantages:
- Measurements can be made without physical contact to the material or product being examined, increasing the envelope of operating environments and decreasing inspection time.
- Very little maintenance of the isotope source is necessary.
- The cost/benefit ratio is excellent – many instruments pay for themselves within a few months through the time savings they facilitate.
There are two broad types of nucleonic gauges used in industry: fixed and portable. Fixed gauges are typically used in production facilities – mines, mills, oil and gas platforms – as a means of controlling and monitoring quality from a production process. For example, in the North Sea, fixed nucleonic gauges are sometimes deployed to determine conditions within separator vessels and to monitor residual oil content within separated gas streams.
Nucleonic gauges are also used in the coal industry. The height of the coal in a hopper can be determined by placing high energy gamma sources at various heights along one side with focusing collimators directing beams across the load. Detectors placed opposite the sources register the breaking of the beam and hence the level of coal in the hopper. Such level gauges are among the most common industrial uses of radioisotopes.
Some machines which manufacture plastic film use radioisotope gauging with beta particles to measure the thickness of the plastic film. The film runs at high speed between a radioactive source and a detector. The detector signal strength is used to control the plastic film thickness.
In paper manufacturing, beta gauges are used to monitor the thickness of the paper at speeds of up to 400 m/s.
When the intensity of radiation from a radioisotope is being reduced by matter in the beam, some radiation is scattered back towards the radiation source. The amount of 'backscattered' radiation is related to the amount of material in the beam, and this can be used to measure characteristics of the material. This principle is used to measure different types of coating thicknesses.
Portable gauges have applications in agriculture, construction, and civil engineering. For example, portable gauges may be used to determine the degree of soil compaction on agricultural land, or the density of asphalt in paving mix for a road surface.
Neutron radiography is an NDT technique similar to that of X-ray and gamma ray. Neutrons from a research reactor can interact with atoms in a sample causing the emission of gamma rays which, when analyzed for characteristic energies and intensity, will identify the types and quantities of elements present.
The two main techniques are thermal neutron capture (TNC) and neutron inelastic scattering (NIS). TNC occurs immediately after a low-energy neutron is absorbed by a nucleus; NIS takes place instantly when a fast neutron collides with a nucleus.
Most commercial analyzers use californium-252 neutron sources together with sodium iodide detectors, and are mainly sensitive to TNC reactions. Others use Am-Be-241 sources and bismuth germanate detectors, which register both TNC and NIS. NIS reactions are particularly useful for elements such as carbon, oxygen, aluminium and silicon, which have low neutron capture cross-sections. Such equipment is used for a variety of on-line and on-belt analysis in the cement, mineral, and coal industries.
Carbon dating
Analyzing the relative abundance of particular naturally-occurring radioisotopes is of vital importance in determining the age of rocks and other materials that are of interest to geologists, anthropologists, hydrologists, and archaeologists, among others.
Appendix: Industrial radioisotopes
Naturally-occurring radioisotopes
Carbon-14 (half-life: 5730 yr):
Used to measure the age of wood, other carbon-containing materials (up to 20,000 years), and subterranean water (up to 50,000 years).
Chlorine-36 (301,000 yr):
Used to measure sources of chloride and the age of water (up to 2 million years).
Lead-210 (22.3 yr):
Used to date layers of sand and soil up to 80 years.
Tritium, H-3 (12.3 yr):
Used to measure 'young' groundwater (up to 30 years).
Artificially-produced radioisotopes
Americium-241 (half-life: 432 yr):
Used in backscatter gauges, smoke detectors, fill height detectors, and in measuring ash content of coal.
Caesium-137 (30.17 yr):
Used for radiotracer technique for identification of sources of soil erosion and deposition, as well as in density and fill height level switches. Also for low-intensity gamma sterilization.
Chromium-51 (27.7 yr):
Used to label sand to study coastal erosion, also a tracer in study of blood.
Cobalt-60 (5.27 yr), lanthanum-140 (1.68 d), scandium-46 (83.8 d), silver-110m (250 d), gold-198 (2.7 d):
Used together in blast furnaces to determine resident times and to quantify yields to measure the furnace performance.
Cobalt-60 (5.27 yr):
Widely used for gamma sterilization, industrial radiography, density, and fill height switches.
Gold-198 (2.7 d) & technetium-99m (6 hr):
Used to study sewage and liquid waste movements, as well as tracing factory waste causing ocean pollution, and to trace sand movement in river beds and ocean floors.
Gold-198 (2.7 d):
Used to label sand to study coastal erosion.
Hydrogen-3 (in tritiated water) (12.3 yr):
Used as a tracer to study sewage and liquid wastes.
Iridium-192 (73.8 d):
Used in gamma radiography to locate flaws in metal components.
Krypton-85 (10.756 yr):
Used for industrial gauging.
Manganese-54 (312.5 d):
Used to predict the behaviour of heavy metal components in effluents from mining waste water.
Nickel-63 (100 yr)
Used in light sensors in cameras and plasma display, also electronic discharge prevention and in electron capture detectors for thickness gauges. Also for long-life beta-voltaic batteries. Made from nickel-62 by neutron capture.
Selenium-75 (120 d):
Used in gamma radiography and non-destructive testing.
Strontium-90 (28.8.yr):
Used for industrial gauging.
Thallium-204 (3.78 yr):
Used for industrial gauging.
Ytterbium-169 (32 d):
Used in gamma radiography and non-destructive testing.
Zinc-65 (244 d):
Used to predict the behaviour of heavy metal components in effluents from mining wastewater.