Answer to Question #9776 Submitted to "Ask the Experts"
Category: Radiation Basics
The following question was answered by an expert in the appropriate field:
If a radioactive lightning rod (which has high activity) will be standing on a pile of different metals for a long time, is it possible for the other materials near it to become radioactive?
This is an interesting question for me since I have not been involved with the use or past evaluation of radioactive lightning rods, and I had to do a bit of searching to learn something about how they were fabricated. I’ll give some introduction to their characteristics and use, but if you don’t care about that you can skip ahead to the last two paragraphs, which give my conclusions regarding your question.
Radioactive lightning rods were somewhat popular during the 1970s and later. Many countries have now disallowed the manufacture and sale of these devices. Some countries have instituted programs to remove the radioactive sources from the lightning rods that have already been installed, but there are still numerous such lightning attractors in use throughout the world.
The devices use radioactive material, often in the form of multiple alpha-emitting sources of either 241Am or 226Ra, positioned around the rod close to the tip (other radionuclides have also been used). The amount of radioactivity in such a device has varied, often from somewhat less than 37 MBq to perhaps 370 MBq. The radioactive material was usually deposited or held on a steel substrate and covered with a thin metallic coating, often gold. The covering was thin to allow the alpha radiation to penetrate and ionize the air. The argument was that producing air ionization around the rod provided enhanced conductivity that would encourage the streaming of ions from the rod to the descending and developing lightning bolt, thus increasing the likelihood that the lightning would strike the rod rather than some other “target" in the vicinity. It is my understanding that studies done to evaluate the effectiveness of these radioactive rods have shown that they are no more effective than standard nonradioactive lightning rods.
Because lightning rods spend their lives outside in all types of weather, it is possible that the radioactive sources could be affected by wind, rain, snow, hail, sleet, heat, and/or lightning in such a way that one or more sources could have its covering damaged or disrupted sufficiently to expose the source material, which could then leach or otherwise migrate from the source to the surroundings. Similarly, persons installing, moving, or maintaining lightning rods, or otherwise being involved in activities where the lightning-rod assembly had to be handled, could inadvertently damage one or more of the sources, making such vulnerable to possible leakage of radioactive material. The physical and chemical characteristics of the radionuclide used may affect the degree of leakage from a damaged source—e.g., an electroplated 241Am source may be more stable than a 226Ra source in which the radium is in the form of a radium salt bound in some other matrix.
I guess the bottom line is that, yes, it is possible for sources on a radioactive lightning rod to get damaged and either leak or possibly get dispersed in some catastrophic event, and such escaped material could contaminate other material in the vicinity. Such contamination could be detected and measured using appropriate investigative and analytical techniques.
We should finally note that, if the sources have remained intact so that leakage of the radioactive material, itself, is not a consideration, material in the vicinity will not become radioactive. The sources do emit their radiations, such as alpha particles and other possible ionizing radiation, depending on what radionuclides are present. These radiations lose their energies by interacting with air and possibly other material in the vicinity, but they do not result in the production of any radioactive material. The radiations themselves could be detected by holding an appropriate detector close to the sources.
George Chabot, PhD, CHP