Scientists have shown that helicopters can locate hidden radioactive sources to within 2 meters (about 6.5 feet) and estimate their strength within 2 percentage points, using analysis that runs in microseconds instead of hours or days. The method was tested by military helicopters flying about 30 meters (roughly 100 feet) above known sources in Switzerland, including areas near the Mühleberg and Gösgen nuclear plants, according to the American Nuclear Society.

The work, by researchers at the University of Michigan and Switzerland's Paul Scherrer Institute, is a monitoring tool, not an energy technology. Its value is speed. After a reactor accident, a transport mishap or the loss of an industrial radioactive source, responders need to know quickly where contamination is and how strong it is.

For people living near nuclear facilities, that speed translates into decisions about evacuation zones, sheltering, protective equipment and whether to distribute potassium iodide pills. Faster, more precise maps could help officials target those actions rather than applying them broadly.

Turning a Blurry Signal Into a Map

Airborne radiation surveys face a basic problem. Gamma rays scatter off air molecules and off the aircraft itself before reaching the detector, blurring the signal, and a single pass captures only a small fraction of the radiation emitted. Standard full-spectrum analysis tries to match that blurred data against simulated templates, a process that can take hours or days.

The new approach, described in Nature Communications as quantitative mobile gamma-ray spectrometry through Bayesian inference, splits the problem in two. One part models scattering in the air, accounting for temperature and humidity. The other uses precomputed factors for scattering inside each specific aircraft type. With those pieces ready, simulations run in microseconds, so thousands of predicted spectra can be compared with in-flight data.

Lead author David Breitenmoser, a postdoctoral research fellow in nuclear engineering at the University of Michigan, said: "Better measurements could help emergency responders make faster, better-informed decisions." In the field tests, detectors rode in the helicopters' cargo bays, and the team reported locating sources within 2 meters even when signals were weak and distorted.

Test Sites Near Two Swiss Reactors

The Mühleberg plant near Bern was shut down in 2019 and is being decommissioned, while Gösgen remains in operation. Flying near such sites lets researchers test the method against real-world background radiation, terrain and buildings rather than only in laboratory conditions.

The sources used were known and placed for testing, which means the team could check its estimates against true values. That is the right first step, but it is not the same as finding an unknown, shielded or mixed source during an actual emergency, where multiple radioactive isotopes, wind-carried contamination and rough terrain complicate measurements.

The researchers also suggested broader uses. The same approach could improve routine monitoring around nuclear facilities, mineral exploration, environmental surveys and geological mapping. In the paper, they noted it could even sharpen estimates of radioactive elements on other planets.

How the U.S. Already Flies Radiation Patrols

The United States runs its own airborne radiation teams. The National Nuclear Security Administration's Aerial Measuring System, part of its Nuclear Emergency Support Team, flies Leonardo AW139 helicopters fitted with radiation sensors to map natural background levels before major events, according to an NNSA notice about surveys over Las Vegas.

Those baseline maps help responders spot anything unusual during an emergency. Mike Toland, an Aerial Measuring System pilot and aviation manager, said "Collecting real-world background information adds even more value to the flights." NNSA has said low-flying survey helicopters are routine and announces flights so residents are not alarmed.

Airborne surveys have proven their value in real disasters. After Japan's Fukushima Daiichi accident in 2011, U.S. and Japanese teams flew radiation-mapping missions over affected areas to help guide evacuation and cleanup decisions — work that relied on slower, less precise analysis than the new method promises.

Lost sources are a quieter but recurring problem. Radioactive materials used in medical devices, industrial radiography and oil-well logging are occasionally lost or stolen, and searching for a small source across a wide area by ground teams can take days. A fast airborne scan that estimates both location and strength could shorten those searches and reduce the time people might unknowingly be exposed.

Nothing in the new study indicates that U.S. agencies have adopted the Michigan-Swiss method. Whether it could be integrated into existing American systems would depend on aircraft-specific calibration, testing, and agency decisions.

Limits Before It Reaches the Field

The study is peer-reviewed, but it is a demonstration with known sources at low altitude. The summaries did not report performance at higher altitudes, in dense cities or with several overlapping sources. Each aircraft type also needs its own precomputed scattering factors, which adds setup work before deployment.

Residents near nuclear plants do not need to take any action because of this research. The practical steps remain the same: know whether you live within your plant's emergency planning zone, sign up for local alerts, and follow instructions from state and county emergency managers if an incident occurs. Unexplained low-flying helicopters are usually scheduled surveys — check your state or local emergency management agency rather than social media for confirmation.

The next steps are likely to include tests with more complex sources and integration with emergency agencies' workflows. The bottom line is that a new analysis method turns a quick helicopter pass into a precise radiation map almost instantly, a potentially valuable upgrade for nuclear emergencies that still needs testing under messier, real-world conditions.

What Readers Want to Know

What did the researchers develop?

A method that analyzes airborne gamma-ray measurements in microseconds to locate radioactive sources and estimate their strength.

How accurate was it?

In Swiss tests, it located sources within 2 meters and estimated their activity within 2 percentage points of actual values.

Where was it tested?

From military helicopters flying about 30 meters above known sources in Switzerland, including near the Mühleberg and Gösgen nuclear plants.

Is this a new kind of nuclear power?

No. It is a monitoring and emergency-response tool.

Does the U.S. use similar helicopters?

Yes. NNSA's Aerial Measuring System flies radiation-sensing helicopters, though it has not announced adopting this method.

What should people near nuclear plants do?

Know your emergency planning zone, sign up for local alerts, and follow official instructions during any incident.