Inspecting reinforced concrete or underground pipes is an essential but surprisingly challenging job, requiring special training and potentially dangerous X-ray equipment. Now, researchers from Los Alamos National Laboratory think they have an easier way: cosmic rays.
They aren’t joking around. In 2010, a failure to inspect buried natural gas pipes resulted in a massive explosion in a residential neighborhood south of San Francisco that killed eight people. While Pacific Gas and Electric was later found to have ignored warnings indicating the pipes might not be in great shape, direct inspection remains difficult—often, it means shutting down and digging up pipes, stripping off insulation, then taking X-rays to identify thin or otherwise worn parts that need to be replaced. The equipment itself comes with an additional challenge: Just like a hospital X-ray machine, radiation from X-ray inspection equipment can be very dangerous in the hands of an inexperienced or unlicensed operator.
It took four hours to get a sufficiently detailed picture—cosmic rays don’t shine brightly—but the valve position showed up clearly in the team’s images.
The alternative, suggest a research team led by LANL’s Matt Durham, is to use cosmic rays, which originate in outer space and actually rain down on us all the time. Cosmic rays include particles called muons, electrons’ much heavier cousins, which it turns out make pretty good inspectors. Unlike X-rays, they pass easily through dirt, foam insulation, and other potential barriers, meaning it doesn’t take that many muons, relatively speaking, to locate cracks in a pipe or thin spots in concrete. In turn, inspectors don’t need to lug around specialized and potentially hazardous equipment to produce muons—as long as there are enough muons laying around.
To see if the idea of using naturally occurring muons to inspect infrastructure would work, Durham and his team placed samples of concrete and metal pipe between two muon detectors, which are really just a bunch of criss-crossing wires that shoot off an electrical current when muons strike them. The first detector determines how many muons are falling and where—how bright the light is, so to speak, and where it’s pointed—while the second detects how many muons pass through cracks and thin spots in test materials.
Using that relatively simple and, compared to an X-ray machine, safe set-up, the researchers tested whether they could see if a valve in a section of pipe was open or closed. It took four hours to get a sufficiently detailed picture—cosmic rays don’t shine brightly—but the valve position showed up clearly in the team’s images. Their detector also made easy work of detecting thin pipes and concrete slabs, they found.
Durham and his team write in AIP Advances that, while their method can’t beat X-rays for resolution, it is safer and simpler. “For example, it may be feasible to use muon radiography over lengths of pipe that are in use, and only resort to more invasive and precise methods of corrosion inspection when possible problem areas are found,” they write.
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