UMich, PSI researchers report new airborne radiation-detection method

Researchers from the University of Michigan College of Engineering and Switzerland's Paul Scherrer Institute are reporting the development of a new airborne method of radiation detection that accurately identifies single or mixed source identity, activity, and location. Their research has been published in Nature Communications under the title "Quantitative Mobile Gamma-Ray Spectrometry through Bayesian Inference."

The research is expected to improve the work of emergency responders by enabling them to more quickly and precisely determine where people in radiologically hazardous situations-such as a nuclear reactor meltdown or a nuclear weapon detonation-should evacuate for safe shelter. The research also should help responders better determine what other types of protective measures should be implemented for such people, including distribution of protective equipment and potassium iodide pills (which protect the thyroid gland from radiation).

Blurred radiation signals: One problem in radiological emergencies that the research team sought to address is that sources of radiation often become "blurred" as radiation signals make their way to airborne detectors-the types of detectors that are typically used in such emergencies. This blurring is caused by the scattering of gamma rays as the rays collide with particles in the air and with the aircraft containing the detectors.

Another problem is that airborne detectors typically capture only a small fraction of emitted gamma rays during one-pass flyovers. Those limited signals then have to be processed through full-spectrum analyses in which the blurred data are matched against predicted templates derived from computer simulations. This processing usually requires several hours or even days to complete.

Gamma-ray mapping and Bayesian analysis: The radiation-detection method involves the application of highly accurate quantitative mapping of gamma-ray emitters, which was "achieved by combining mobile gamma-ray spectrometry with high-fidelity Monte Carlo simulations and full-spectrum Bayesian inference." The method also involves the separation of the gamma ray analysis into two parts: scattering in the air (which considers such factors as air temperature and humidity) and scattering inside the aircraft (which considers precomputed mathematical factors specific to the kinds of aircraft used in the detection flyovers).

The method was field tested with military helicopter flyovers about 30 meters above multiple known radiation sources in Switzerland, including in the vicinities of the Mühleberg and Gösgen nuclear power plants. (Mühleberg was shut down in 2019 and currently is being decommissioned.) The helicopters contained radiation detectors in their cargo bays.

Rapid pinpoint analysis: Results showed that the radiation sources were pinpointed within two meters-even when the signals were weak and distorted-and the radiation activities of these sources were estimated within two percentage points of their actual values. The researchers described that latter accomplishment as "an unprecedented level of detail compared to previous methods."

Furthermore, the simulation analyses required only microseconds to perform rather than hours or days. This speed allowed for a detailed Bayesian analysis, in which thousands of simulation-predicted spectral templates were compared against the blurred in-flight data to continuously update the statistical information for the precise detection of the radiation sources.

Critical advance in quantitative sensing: According to the paper's abstract, "The developed method marks a critical advance in quantitative gamma-ray sensing, enabling improved radiological situational awareness, enhanced terrestrial geophysical and geochemical mapping." Potential terrestrial applications of the new method, aside from emergency response, include routine radiological monitoring of areas surrounding nuclear facilities, mineral-exploration surveys, and other environmental monitoring.

The paper further notes that the method could provide "more robust constraints on radionuclide abundances" in the analyses of other planets and extraterrestrial bodies in the solar system.

Exciting potential: UMich postdoctoral research fellow of nuclear engineering and radiological sciences David Breitenmoser, who was the lead author on the paper, said that the "better measurements could help emergency responders make faster, better-informed decisions, and ultimately protect or even save lives." He added, "What excites me most is the combination of speed and quantitative detail could make airborne measurements substantially more useful in both emergency response and routine monitoring."