Chinese scientists’ pursuit of cosmic rays opens windows to the universe

Source:Xinhua Published: 2019/10/24 17:58:40

An aerial view of the Large High-Altitude Air Shower Observatory in Daocheng, Southwest China's Sichuan Province Photo: IC

In the wilderness of Daocheng, Southwest China's Sichuan Province, Chinese scientists are constructing an observatory to study cosmic rays, which have blasted huge rocks from the Ice Age. Scientists are installing different detectors to form a "net" that can catch particles generated by cosmic rays. This can help scientists study both micro and macro worlds in the universe.

Three huge underground pools, more than triple the size of the Water Cube, the National Aquatic Center in Beijing, will hold detectors collecting high-energy photons generated by remote celestial bodies. Surrounding the pools, 12 telescopes will be erected to collect high-precision measurement of high-energy cosmic rays.

Construction of the first half of the observation station, known as Large High-Altitude Air Shower Observatory (LHAASO), is set for completion by the end of this year and the entire project by the end of 2020, said Cao Zhen, chief scientist of LHAASO and a researcher at the Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences.

Century-long enigma

Discovered in 1912, cosmic rays are still an enigma. They are direct samples of matter from outside the solar system. Physicists are still pondering where they come from and how they can accelerate to ultra-high energies.

Scientists have found most cosmic rays are atomic nuclei. All the natural elements in the periodic table are present in cosmic rays. About 90 percent of them are the nuclei of hydrogen (protons); about 9 percent are helium nuclei (alpha particles); and the other heavier elements, electrons, gamma rays, neutrinos and antimatter particles make up 1 percent.

Since most cosmic rays are charged, their paths through space are deflected by magnetic fields. 

On their journey to Earth, the magnetic fields of the galaxy, the solar system, and the Earth itself scramble their flight paths, making it difficult to discern their origin. 

Many countries have invested in the study of cosmic rays. China, the US, Russia, Japan, Germany and other countries have established observation stations.

China's exploration path

China's cosmic ray detection began in the early 1950s. Chinese scientists built the country's first cosmic ray observatory on a 3,200-meter-high mountain in Southwest China's Yunnan Province. Its scientific equipment was advanced by international standards at the time.

After China's reform and opening-up, Tan Youheng, a researcher with the IHEP, went to study in Japan. He was inspired by the air shower array technology for cosmic ray detection, and wanted to conduct similar work in China. In 1989, under the leadership of Tan and other scientists, China began to build an cosmic ray observatory in Yangbajing, Southwest China's Tibet Autonomous Region.

"Without national development, we would not have the funds to develop the technology," said Huang Jing, a researcher at IHEP and a spokesperson for the project.

World-leading observatory

When Cao Zhen worked in Yangbajing, he started drawing up a plan for a new-generation cosmic ray observation base that would be a world-leading observatory. His team spent five years investigating potential sites throughout China. Daocheng was chosen due to its high altitude, convenient transportation, stable power supply, sufficient water resources and local government support.

Infrastructure construction started in July 2016, and the building of the observatory began in June 2018.

The main objective of LHAASO is to discover the origin of cosmic rays, and study their acceleration and transmission mechanisms, said Cao.

In the second huge pool of LHAASO, water detectors have been installed to form an array. They will be submerged in 100,000 tons of the purest water in the world.

"The water comes from nearby lakes and rivers and has gone through strict purification. Only transparent pure water can make the detectors catch the signals generated by high-energy particles clearly," said Chen Mingjun, deputy director of the Cherenkov detector array.

 The speed of LHASSO's construction is not only a result of the scientists' efforts, but also of China's industrial production capacity, said Cao.

The LHASSO project has drawn world attention as scientists from European countries hope to bring their scientific equipment to the observatory. Research teams from Australia and Thailand will directly participate, too. "After completing the LHASSO project, China is expected to lead the world in the field of cosmic ray research," Cao said.
Newspaper headline: Cosmic construction


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