Sealed Sources and Tracers: Multiple Applications
2026 Editorial Revision
Sealed sources
The structure and packaging of sealed sources are designed to prevent the dispersion of radioactive materials and any contact with them. When not in use, the sources are stored in containers or shielded storage units to avoid any unnecessary exposure to radiation. Small sealed source on the left and, on the right, a container for the storage and transport of a powerful radioactive source.
© ANDRA/IAEA
Tiny quantities of radioactive atoms are used to meet the needs of medicine, industry or research, in the form of radioactive sources or tracers. These radionuclides, most of which do not exist naturally, are generally produced in specialized facilities: small reactors designed for this purpose or, in the case of certain very short-lived isotopes used in medicine in large hospitals, small accelerators (cyclotrons) installed permanently on site.
Their uses include cancer treatment, medical diagnosis, industrial irradiation, non-destructive testing, level and thickness gauges, parameter monitoring and numerous laboratory applications. For industrial irradiation and cancer treatment (Gamma Knife), some sources are powerful.
These radionuclides can be a source of non-natural exposure to radioactivity if precautions are not taken. The dispersion of radioactive elements must be prevented when they present a hazard due to their activity, the harmful nature of their radiation or their half-life.
Small laboratory sources
Samples of small commercially available laboratory sources used to test the operation of Geiger counters. A quantity of radionuclide with the required activity is placed in a hollow plastic disc 3 mm deep, filled with epoxy glue that immobilizes the radioactivity. The activity of the three sources shown in the figure (alpha, beta and gamma) is on the order of tens of kilobecquerels (or microcuries, millionths of a curie), activities comparable to the natural activity of the human body, that is, very low.
© Imagesco
This is why radioactive sources are generally sealed to prevent the dispersion of radioactive materials. When not in use, they are stored in a container or shielded storage unit to avoid any unnecessary exposure to radiation.
The main radiation protection issue associated with radioactive sources is their very large number, a consequence of their many applications. Thus, the French Nuclear Safety and Radiation Protection Authority (ASNR) has to manage some 17,500 sealed radioactive sources used in industry, research and medicine.
Another issue concerns the end of life of these sources, which become waste managed by the National Agency for Radioactive Waste. At the end of 2002, the number of spent sealed sources was estimated at approximately 140,000.
Tracers can be considered radioactive sources that are not sealed. The quantities of radioactive elements involved are much smaller and their lifetimes are short, which allows their dispersion. They are widely used in medical diagnosis.
The use of radioactive tracers incorporated into molecules is very common in biological research. They are therefore a powerful investigative tool in cellular and molecular biology. The main radioactive elements used as tracers are phosphorus-32 or phosphorus-33, carbon-14, sulfur-35, chromium-51, iodine-125 and tritium. They are used as tracers and for calibration or teaching purposes.
A wide variety of radioactive tracers are used in industrial processes to investigate the causes of problems or losses in efficiency, measure flows, monitor the mixing of materials, and locate leaks in heat exchangers and pipelines. For example, the oil industry uses radioisotopes to identify leaks in its oil and gas pipelines.
The use of radioactive tracers in industrial processes affecting the environment is no longer considered desirable by the ASNR.