China has started constructing a $330-million underground neutrino detector this week which, upon completion, will have similar goals as the Indian Neutrino Observatory (INO) coming up in Theni, Tamil Nadu. Situated at a site 150 km west of Hong Kong, the Jiangmen Underground Neutrino Observatory (JUNO) is being built underground by the Institute of High Energy Physics (IHEP), Beijing.

It will supplement the Daya Bay Reactor Neutrino Experiment, a China-based multinational neutrino physics centre located 52 km northeast of Hong Kong that has been operating since 2011. In fact, as Daya Bay studies neutrinos coming through space toward Earth, JUNO will study those from two nuclear reactors being constructed at locations some 50 km away.

If all goes well, the lab will open in 2020 and operate well beyond 2040. “It will be a big challenge to build such a large underground lab and a detector in five years,” Ifang Wang, Director, IHEP, told physicsworld. Neutrinos are colloquially called “ghost particles” because they travel at almost the speed of light, hardly interact with matter, and are very light. Therefore, trapping and measuring a neutrino requires extremely sensitive equipment shielded from interfering radiation.

The JUNO detector will be situated in a dome of diameter 50 m and height 80 m, about 700 m underground. Its detector comprises 20,000 tonnes of a liquid scintillator surrounded by more than 15,000 photomultiplier tubes. The liquid will produce a scintillation, or flash of light, when a neutrino strikes a hydrogen atom. The flash will be picked up by the tubes as an electric signal.

There are three kinds, or flavours, of neutrinos, designated 1, 2 and 3. Each flavour is known to spontaneously transform into the other, a process called oscillation that is characteristic of particles that have mass. However, physicists have been unable to measure their masses. What they have been able to accomplish is find their difference. Of late, interest has grown in the mass of neutrino-3 with respected to the other two, which is what INO and JUNO will study. Together, these detectors will join the already operating Hyper-Kamiokande in Japan and the NOvA in the U.S.

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