Enter the 2019 R&D 100 Awards!
Silicon Strip Cosmic Muon Detectors were a 2018 R&D 100 Award winner. All of the R&D 100 Awardees were announced at the R&D 100 Awards Gala held in Orlando, Florida on Nov. 16, 2018.
The R&D 100 Awards have served as the most prestigious innovation awards program for the past 57 years, honoring R&D pioneers and their revolutionary ideas in science and technology.
Submissions for the 2019 R&D 100 Awards are now being accepted. Any new technical product or process that was first available for purchase or licensing between January 1, 2018 and March 31, 2019, is eligible for entry in the 2019 awards. The 2019 R&D 100 Awards will be held Nov. 22, 2019 in New Orleans, LA.
Detecting muons—unstable subatomic particles that rain down from the atmosphere—could help the U.S. Department of Homeland Security identify where nuclear materials like plutonium and uranium are hidden, such as in a vehicle or shipping container.
Researchers from the Nevada National Security Site (NNSS) Mission Support and Test Services and the U.S. Department of Energy’s Fermi National Accelerator Laboratory have developed the Silicon Strip Cosmic Muon Detector, which can be placed underground and in the walls and ceilings of locations like toll stops, border crossings and seaports to try to identify potentially dangerous materials.
In an exclusive interview with R&D Magazine, Jesse Andrew Green, the principal scientist for NNSS, explained that while muons easily pass through most materials, including humans, when they pass through materials with a high atomic number—such as uranium and plutonium—they scatter and can be picked up with the 2018 R&D 100 Award-winning detector. “It does not require a big truck to move these things around, you can conceivably move the contents of a nuclear weapon in the back of a car,” Green said. “The idea is to be able to find such a thing because they are made of very high density, very high atomic materials—plutonium and uranium.
“Muons can scatter through them more than other materials,” he added. “So as they are coming from outer space through Earth’s atmosphere and through such a material, if you have a tracking system you can potentially look at the pattern of scattering of muons as they are going through this material and you can identify based on how much scattering you see whether something of interest is there or not.”
High-energy protons and nuclei constantly bombard Earth’s atmosphere from many different sources and much of the Sun’s low-energy flux is captured by Earth’s magnetic field. However, higher-energy flux enters from outside the solar system and this flux of high-energy particles interacts with the upper atmosphere to create short-lived mesons that then decay into many different particles, principally muons/anti-muons, photons, and electrons/positrons. Muons are similar to electrons with approximately 200 times the mass.
Originally, researchers from Los Alamos National Laboratory developed the idea of scanning muons in an effort to detect special nuclear materials.
Currently, gas-filled drift tubes are used for position-sensitive charged particle detection and tracking. However, these systems are extremely large and take up a significant amount of space. They are also associated with high development and maintenance costs and feature high voltage and potentially flammable gas.
Muon trackers use planes of muon detectors to identify the path of a muon before it enters the region to be evaluated and as the muon exits the region. Software then compiles the data to calculate the trajectories of the muons, resulting in a tomographic image and the identification of the material contained within the region. Muons can pass relatively unimpeded through most materials, but scatter when they interact with materials with a high atomic number. Materials with a high atomic number produce a unique signature that is different from other materials like lead, steel or concrete.
“If you have something in that vehicle that causes a lot of deflection of that muon path and that keeps happening in one place then you are going to stop that vehicle and you are going to look at it a lot more closely,” Green said. “It might not be totally definitive but you would have a lot of motivation to stop that vehicle and look at it.”
The new detector strips are fabricated with several aluminum microstrips on top to locate muons passing through the silicon below it. The detection medium is the silicon depletion layer, which is created by reverse biasing the sensors with a voltage of 200 volts.
The detectors have an extremely slim profile, enabling muon trackers to detect shielded nuclear materials, explosives and other items the government would be interested in tracking.
According to Green, for the trackers to work, the vehicle must be relatively stationary with the detectors both underneath and above the subject.
One of the areas these lightweight strips can be particularly effective is at the seaports, which see nearly seven million cargo containers arriving and offloaded annually in the U.S, making them a prime delivery method for nuclear weapons or special nuclear material. While these cargo ships are regularly scanned, concrete, lead and other materials can block these materials from conventional radiation detectors and X-ray scanners.
According to Green, companies such as Decision Sciences, are exploring the use of drift-tube muon scanners to scan containers at seaports.
This work was done by Mission Support and Test Services, LLC, under Contract No. DE-NA0003624 with the U.S. Department of Energy and supported by the Site-Directed Research and Development Program. DOE/NV/03624–0518.