12 storey crystal ball force ghost particles appeared

-- approaching the national science and engineering Jiangmen neutrino experiment device

2019 03 20 April 08:58 source: Science Daily

Between the two nuclear power plants, more than 700 meters deep granite, it dug a huge hole to accommodate a 12 storey high crystal ball. The crystal ball, will be immersed in a filled with 30 thousand tons of pure water in the pool, was tied steel. The cylinder pool, 43.5 meters in diameter, 44 meters deep. The pool above is a variety of measurement facilities.

IHEP for map

Between the two nuclear power plants, more than 700 meters deep granite, it dug a huge hole to accommodate a 12 storey "crystal ball". A ball from a flicker in the past will reveal the secret of neutrino.

Jiangmen neutrino experiment device is under construction in Guangdong, is a high energy physics experiment device the most complex China hitherto unknown. Compared with the current best international similar device, its size is 20 times larger, precision nearly doubled.

The world's largest organic glass ball

Neutrino is called ghost particles, to detect it, humans have to struggle. Today, the Jiangmen underground Neutrino Experiment Station (JUNO) by physicists have high hopes: some basic characteristics of accurate measurement of neutrino.

The universe is filled with neutrinos. Every 3 seconds billion from the sun penetrate everyone's body. The neutrinos are difficult with other substances, such as through the universe into nothingness. The modern neutrino experiment will use the target material as huge trap, improve the chances of neutrino capture.

The core of JUNO, is a 35.4 meters in diameter, the hollow ball 12 cm thick organic glass. Made so big, because there should be filled with 20 thousand tons of liquid (called liquid scintillation) as target material.

This is the largest human made of organic glass ball. Institute of High Energy Physics Institute Wang Yifang told Technology Daily reporter, currently the world for particle physics of organic glass ball, it is smaller than 20 times; the organic glass aquarium tank is much smaller than it.

The crystal ball meaning, is made of transparent medium, separate flash and liquid water inside outside. IHEP researcher Cao Jun said, the organic glass ball must be very transparent, and strong.

"Empty ball 12 storey, like houses might collapse. Other materials made out, it is difficult to use organic glass. Because the organic glass is easy to crack." Cao Jun said, "did not make this kind of national standard ball. We built a mechanical laboratory, make a set of standard."

The crystal ball preparations have been completed. When the experiment hall after digging, it will be built on site, because tens of meters of the ball cannot pass through the tunnel.

The largest underground artificial cave

JUNO is senior Dayawan neutrino experiment device. They are using a massive neutrino release fission reaction. Is different, Dayawan is a neutrino detection of nuclear power plants; while JUNO is the use of two nuclear power plants, 10 neutrino reactor.

Located in the Guangdong Yangjiang nuclear power plant will be built in 6 reactors, the Taishan nuclear power plant will be built in 4 reactors. Both JUNO distance is 53 kilometers.

Cao Jun told reporters that if the detector is not equal to a reactor distance, small neutrino spectrum structure will cancel each other (like the peaks and troughs of sinusoidal signal offset). According to the calculation, should be at a distance of two nuclear power plants are a 53 kilometers wide and 200 meters long 2 kilometers of the rectangular area setting detector.

53 kilometers far away from the neutrino reactor to the flow will become weak. So, compared with the Dayawan JUNO detector, target material weight one thousand times. JUNO large glass ball, soaked in a filled with 30 thousand tons of pure water in the pool, was tied steel (to overcome the buoyancy of 3000 tons). The cylinder pool, 43.5 meters in diameter, 44 meters deep. The pool above is a variety of measurement facilities.

For all of this requires a diameter of 50 meters, 70 meters high giant hall. JUNO was designed in more than 700 meters of granite mountain, to shield the cosmic ray interference.

Therefore, JUNO is the largest mountain carved underground caves. It also brings a lot of trouble, a tunnel excavation and hall are touched on the water gushing, civil engineering delay problem. Project group of side grouting water plugging, side pumped. They are not all through the water, to avoid too much pressure outside the cave collapse brought risk.

The deployment of well liquid

This is the neutrinos detected: a neutrino hit a proton, it turned into a neutron and a positron. Positron annihilation then let out a light. Add a neutron nucleus, unstable atomic nuclei quickly split and emit gamma photons. Therefore, one after the two dynasty, is the sign of neutrino collision.

The scientists prepared by liquid scintillation, it has three properties: proton (especially to create opportunities for neutrino hit); particularly transparent (light fired); try not radioactive (avoid signal useless).

Dayawan Chinese experiment, scientists created the world's best liquid scintillation. In JUNO, they improved the formula, reached a new high quality liquid scintillation.

This subject is liquid scintillation alkylbenzene, plus some special ingredients. It is pure swimming pool but also more transparent, light through tens of meters, little attenuation.

Cao Jun said, in order to reduce radioactive impurities (such as liquid natural gas argon, krypton, radon, or solid uranium), through aluminum oxide filtration, vacuum distillation, water extraction, steam stripping a series of processes, equivalent to tens of thousands of tons of liquid wash, steamed again".

In fact, organic glass ball material JUNO, and various other materials and equipment, but also through the treatment to eliminate radioactive.

See the light

JUNO in the measurement of the neutrino at the same time, will also received a lot of useless signal. Some pool and pool at the top of the detector, is used to detect cosmic rays, the related signal out.

Cao Jun said, 2 million tons of liquid scintillation every day can only capture to 60 4, an atmospheric neutrino neutrino reactor, 1, and 90 earth solar neutrino neutrino. In contrast, although the mountain block let cosmic ray intensity reduce 20 million times, there are 10 million cosmic ray interference signal every day.

JUNO more than 40000 the world's most sensitive eyes - 18000 20 inch and 26000 3 inch photomultiplier tube. The photomultiplier tube can be faint light into electrical signals. Because JUNO requires high energy resolution, before the commercial product is not up to the standard. For a few domestic enterprises and joint research institute, has developed the highest detection and cheap product efficiency of the world.

The photomultiplier tube shaped like a bulb, inside is vacuum, years of soaking in the pool there is a risk. Scientists consider: if a "bulb" crack a little water instantaneous suction vacuum rebound in space center, will form a shock. This wave of great damage, will trigger a chain reaction, destroy other photomultiplier tube.

To this end, they give the photomultiplier tube made a protective cover, if damaged, the water can not be rushed into the formation of shock wave.

"To solve these problems, love physical scientists may feel less fun, more complicated. But to make important scientific achievements, must bear the trouble." Cao Jun said.

In the standard model of particle physics, neutrinos are massless neutrino oscillation, and show that it has the quality, this is a beyond the standard model of experimental phenomena (dark matter is another standard model can not explain the puzzle). So the neutrino research is a breakthrough in the existing theory.

JUNO may be running in 2021. It will be to make sure that a very high degree of the answer, the crucial "neutrino mass order", and more accurate measurement of neutrino parameters, a brick building on the important physics tim. (Gao Bo)

(commissioning editor: Wen Jiaqi (Intern), Xiong Xu)

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