A new way to discover hidden nuclear weapons

The US National Laboratory Los Alamos has developed a method to detect heavy elements, such as uranium, using subatomic particles from space called muons

The place that gave birth to the nuclear bomb has now found a way to expose illegal nuclear material. The American Los Alamos National Laboratory has developed a method for detecting heavy elements, such as uranium, using subatomic particles from space called muons. It is possible that in 2008 the "muon tomography" method will protect the borders of the USA.
Every minute about 10,000 muons reach every square meter of the earth's surface.
These charged particles are byproducts of cosmic ray collisions with molecules in the upper atmosphere. Muons, moving at relativistic speeds, can penetrate tens of meters deep into rocks and other materials before being absorbed or deflected by other atoms. Materials with a high density, such as uranium and plutonium which are elements with a high atomic number (Z), i.e. many protons in the nucleus, are particularly effective in scattering muons.
"We take advantage of the fact that scattering is sensitive to Z and is particularly sensitive to the materials from which atomic bombs are built or means to shield such bombs," explains Christopher Morris of Los Alamos, who heads the team that created the technology. "We measure the scattering angle of each muon, the angle of entry and the angle of exit, and the change in angle tells us the amount of material through which the particles passed."

A way to identify smuggled materials
After the security alert level was raised following the 11/XNUMX attacks, Morris and his team realized that muons could provide a way to detect smuggled nuclear materials, a way that would be better than existing detectors based on X-rays, neutrons or gamma rays, which could expose humans to stray radiation. .
There is no such problem in the muon-based scan because muons are already everywhere naturally. And while shielding may disrupt other scanning methods, they only facilitate muon detection of nuclear contraband. The shields are also made of high-density materials and are therefore visible in ion tomography, which is not sensitive to the background scattering that obscures the X-ray images.
A prototype Mione tracker, whose construction was completed in 2006, was able to detect test objects such as a 10 cm long cube of lead hidden in an engine block, which would have managed to escape a normal X-ray scan. "The experiment gave us confidence that the technology would work and that it was possible to move to the next stage of development," says Erica Sullivan, spokesperson for Los Alamos' application department.
The software company Decision Sciences from San Diego, which specializes in defense applications, heard about the work being done at Los Alamos and its enthusiasm grew when it realized that muon tomography is also able to identify materials with a medium atomic number, such as iron and copper, which are used as components in improvised explosive devices. This led in the spring of 2007 to the signing of an official agreement between the company and Los Alamos Laboratories to develop a ion tomography system for internal security purposes.
The partners are now busy developing an operational prototype. "It's no longer about lab simulations or small-scale physical simulations, now it's about the real thing and at real scale," says Dave Klug, project manager at Decision Science. A commercial version of the scanner, named Guardian MT, is expected to be released in 2008.
Unlike the laboratory prototype, the commercial muon tomography scanner will be large enough to drive a heavy truck through. Layers of aluminum tubes filled with gas that function as detectors will wrap an enclosed space about 5 meters high and 3.7 to 4.3 meters wide and about 18 meters long. In the center of each tube will pass a thin wire that will identify muons based on the ionized traces left after the muons have passed through the tube.
The scan will produce detailed tomographic images after 20 seconds to a minute, depending on the size and load of the vehicles. After the system "learns" to recognize the common configurations of common vehicle models, it will be able to ignore familiar and harmless items such as the engine and transmission, thus shortening the scanning time even more - and making any unusual detail stand out even more.
Donald Geesman, a senior physicist and one of the acting directors of the Physics Division at the American National Laboratory Argonne, says that the Los Alamos project is "very fascinating". He adds that team members "have made great progress in solving the difficult problem of achieving sufficient imaging resolution for this purpose."
In light of the generous funding now flowing from Decision Sciences, the developers are confident that the muon tomography will be ready for operation in 2008. According to Kellogg's view: "There is definitely a need for such a product, a need that already existed yesterday."

Subatomic assistance against underground threats
Physicist Luis Alvarez was the first to use muons to peer into objects: he was looking for hidden rooms in one of the pyramids of Giza in the 60s. Although he did not find such chambers, his work proved that muon radiography is a viable technology. Muons don't just provide protection against terrorism, they can also warn against natural threats.
Hiroyuki Tanaka from the University of Tokyo and Toshiyuki Nakano from Nagoya University in Japan used special photographic plates to capture muons passing through the Osayama volcano in Japan. Changes in the number and direction of the muons provided images of the interior of the volcano and the movement of magma within it. The method will therefore be able to predict possible upcoming eruptions.

Writer: Mark Wolverton. Published in Scientific American Israel magazine.