Japan Team Succeeds in Muon Reacceleration in Major Breakthrough
Tokyo, June 16 (Jiji Press)--A Japanese research team has succeeded in reaccelerating muons, a type of elementary particle, after artificially cooling them, in the first such breakthrough in the world.
The achievement is expected to help better re-examine the standard theory of physics that explains the movements of elementary particles forming matters and improve the accuracy of internal inspections of giant structures, according to the team of researchers from entities including the High Energy Accelerator Research Organization and the Japan Atomic Energy Agency.
Muons are created in large quantities when cosmic rays collide with the earth's atmosphere. Muons have characteristics similar to those of electrons but have a mass some 200 times greater.
Muons have a very high ability to penetrate materials, even bedrock several kilometers thick, and therefore are used for internal inspections for volcanos and pyramids, as well as for surveys of reactors at Tokyo Electric Power Company Holdings Inc.'s meltdown-stricken Fukushima No. 1 nuclear power station.
If the density of a material is high, the number of muons passing through it decreases, so it is possible to visualize the density distribution inside the ground and giant structures by analyzing the direction to which the muons flew and the number of the particles.
Muons can also be created artificially by colliding protons against graphite in a particle accelerator, but aligning the speed and direction of the created particles had been difficult.
Muons' life span is extremely short, at two millionth of a second.
The research team created muons traveling at a speed about 30 pct of that of light in a particle accelerator at the Japan Proton Accelerator Research Complex, or J-PARC, in the village of Tokai, Ibaraki Prefecture, eastern Japan.
The team then let the muons pass through silica aerogel, a sponge-like insulation material, and cooled the particles by irradiating them with a laser to almost stop their movements.
After that, the team added energy to the muons and successfully reaccelerated them to a speed about 4 pct of that of light.
Muons that are reaccelerated after being stopped travel in the same direction at the same speed, making it possible to understand with higher accuracy the shape and other features of materials through which they pass.
The achievement may enable more detailed surveys of the inside of structures and lead to the development of more precise microscopes.
In addition, it may help researchers understand physical phenomena that cannot be explained by the current standard theory.
The research team is now working to develop by 2028 a technology to reaccelerate muons to a speed some 94 pct of that of light.
KEK professor Tsutomu Mibe, head of the research, said, "(With this achievement), we can say that we have taken a step toward developing a microscope using the world's only muons."
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