China’s neutrino facility reaches final stage before scientists hunt for ghost particles

The Juno facility in Guangdong has started filling with ultrapure water at 100 tonnes per hour, on track to collect data from August: IHEP

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Staff seal the bottom of a water tank with Tyvek material at the Juno construction site in southern China. Juno is expected to operate for at least 30 years. Photo: Xinhua

Published: 6:05pm, 19 Dec 2024

A mega scientific facility in south China designed to measure neutrinos, the elusive “ghost particles”, has started filling with ultrapure water, marking the final critical milestone before research begins.

The ultrapure water – which has been filtered through multiple stages of the water purification system – began filling the detector at the Jiangmen Underground Neutrino Observatory (Juno) in Guangdong province on Wednesday at a rate of about 100 tonnes per hour, according to the Institute of High Energy Physics (IHEP) of the Chinese Academy of Sciences, the project’s lead institution.

To try to measure the mass of different types of neutrinos produced by two nearby nuclear power plants, Juno’s key component is a massive subterranean sphere detector. It will be filled with 20,000 tonnes of a “liquid scintillator” and suspended in 35,000 tonnes of pure water 700 metres (2,300 feet) below ground.

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The liquid filling process will be carried out in two stages and will take eight months, according to IHEP.

In the first two months, ultrapure water will fill both the interior and exterior of the giant sphere. During the following six months, the ultrapure water inside the sphere will be replaced by liquid scintillator.

Neutrinos – the smallest and lightest of the 12 elementary particles that make up the material world – are difficult to detect because they have no electrical charge, very little mass and travel at near light speed.

Although almost all the particles will pass through the detection liquid without a trace, some will interact with the liquid, triggering two flashes of light which will then be recorded by thousands of light-detecting phototubes.