The spread of radioactive isotopes from the Fukushima Daiichi Nuclear Power Plant in Japan in 2011 and the continuing threat of a possible release of radiation from the Zaporizhzhia nuclear complex within the Ukrainian war zone have underscored the necessity for effective and reliable ways of detecting and monitoring radioactive isotopes. Less dramatically, on a regular basis operations of nuclear reactors, mining and processing of uranium into fuel rods, and the disposal of spent nuclear fuel also require monitoring of radioisotope release.
Now, researchers at MIT and the Lawrence Berkeley National Laboratory (LBNL) have provide you with a computational basis for designing quite simple, streamlined versions of sensor setups that may pinpoint the direction of a distributed source of radiation. Additionally they demonstrated that by moving that sensor around to get multiple readings, they will pinpoint the physical location of the source. The inspiration for his or her clever innovation got here from a surprising source: the favored computer game “Tetris.”
The team’s findings, which could likely be generalized to detectors for different kinds of radiation, are described in a paper published in Nature Communications, by MIT professors Mingda Li, Lin-Wen Hu, Benoit Forget, and Gordon Kohse; graduate students Ryotaro Okabe and Shangjie Xue; research scientist Jayson Vavrek SM ’16, PhD ’19 at LBNL; and plenty of others at MIT and Lawrence Berkeley.
Radiation is normally detected using semiconductor materials, comparable to cadmium zinc telluride, that produce an electrical response when struck by high-energy radiation comparable to gamma rays. But because radiation penetrates so readily through matter, it’s difficult to find out the direction that signal got here from with easy counting. Geiger counters, for instance, simply provide a click sound when receiving radiation, without resolving the energy or type, so finding a source requires moving around to try to seek out the utmost sound, similarly to how handheld metal detectors work. The method requires the user to maneuver closer to the source of radiation, which may add risk.
To offer directional information from a stationary device without getting too close, researchers use an array of detector grids together with one other grid called a mask, which imprints a pattern on the array that differs depending on the direction of the source. An algorithm interprets the several timings and intensities of signals received by each separate detector or pixel. This often results in a posh design of detectors.
Typical detector arrays for sensing the direction of radiation sources are large and expensive and include not less than 100 pixels in a ten by 10 array. Nonetheless, the group found that using as few as 4 pixels arranged within the tetromino shapes of the figures within the “Tetris” game can come near matching the accuracy of the big, expensive systems. The hot button is proper computerized reconstruction of the angles of arrival of the rays, based on the times each sensor detects the signal and the relative intensity each detects, as reconstructed through an AI-guided study of simulated systems.
Of the several configurations of 4 pixels the researchers tried — square, or S-, J- or T-shaped — they found through repeated experiments that essentially the most precise results were provided by the S-shaped array. This array gave directional readings that were accurate to inside about 1 degree, but all three of the irregular shapes performed higher than the square. This approach, Li says, “was literally inspired by ‘Tetris.'”
Key to creating the system work is placing an insulating material comparable to a lead sheet between the pixels to extend the contrast between radiation readings coming into the detector from different directions. The lead between the pixels in these simplified arrays serves the identical function because the more elaborate shadow masks utilized in the larger-array systems. Less symmetrical arrangements, the team found, provide more useful information from a small array, explains Okabe, who’s the lead writer of the work.
“The merit of using a small detector is when it comes to engineering costs,” he says. Not only are the person detector elements expensive, typically made from cadmium-zinc-telluride, or CZT, but the entire interconnections carrying information from those pixels also turn out to be far more complex. “The smaller and simpler the detector is, the higher it’s when it comes to applications,” adds Li.
While there have been other versions of simplified arrays for radiation detection, many are only effective if the radiation is coming from a single localized source. They will be confused by multiple sources or those which can be opened up in space, while the “Tetris”-based version can handle these situations well, adds Xue, co-lead writer of the work.
In a single-blind field test on the Berkeley Lab with an actual cesium radiation source, led by Vavrek, where the researchers at MIT didn’t know the ground-truth source location, a test device was performed with high accuracy to find the direction and distance to the source.
“Radiation mapping is of utmost importance to the nuclear industry, as it might help rapidly locate sources of radiation and keep everyone protected,” says co-author Forget, an MIT professor of nuclear engineering and head of the Department of Nuclear Science and Engineering.
Vavrek, one other co-lead-author, says that while of their study they focused on gamma-ray sources, he believes the computational tools they developed to extract directional information from the limited variety of pixels are “much, far more general.” It’s not restricted to certain wavelengths, it might even be used for neutrons, and even other forms of sunshine, ultraviolet light, adds Hu, a senior scientist at MIT Nuclear Reactor Lab.
Additional research team members include Ryan Pavlovsky, Victor Negut, Brian Quiter, and Joshua Cates at Lawrence Berkely National Laboratory, and Jiankai Yu, Tongtong Liu, Stephanie Jegelka at MIT. The work was supported by the U.S. Department of Energy.
