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New Underground Lab to Shed Light on Dark Matter

One kilometer underground in Stawell, in the Northern Grampians in Victoria, a team of Australian scientists has put the final touches on an underground lab that will help us understand the nature of our universe.

Stage 1 of the Stawell Underground Physics Laboratory was officially opened today. It will be home of multi-disciplinary scientists from five research partners who help us understand dark matter.

In the ultra-low radiation deep underground environment, scientists will use the state-of-the-art SABRE Dark Matter Detector to ‘see’ dark matter, and answer some of the biggest questions in physics.

Dark matter is theorized to be an invisible and unknown substance that makes up about 85 percent of the universe's mass.

Amongst many puzzles, humankind’s first detection of dark matter would confirm the theory that dark matter particles provided the gravitational seeds for the formation of galaxies.

The challenge is that dark matter has remained undetected while its effects have been observed, meaning much about its nature is unknown. That is where the Australia team of scientists and the new lab come in.

Delivery of the underground laboratory has involved partners from the Universities of Melbourne, Adelaide and Swinburne, ANU, ANSTO and Stawell Gold Mines.

The lab, located in a disused gold mine, includes a research hall that is 33 meters long, 10 meters wide and 12.3 meters high. Around 4,700 cubic meters of rock were excavated in its construction.

The Federal and Victorian Governments contributed $5 million each to the project.

The dark matter research will be coordinated by the Centre of Excellence for Dark Matter Particle Physics, headquartered at the University of Melbourne, established with a $35 million grant from the Australian Research Council.

Professor Elisabetta Barberio is the head of the Head Centre of Excellence. “We know there is much more matter in the universe than we can see,” Professor Barberio said.

With the Stawell Underground Physics Laboratory, we have the tools and location to detect this dark matter. Proving the existence of dark matter will help us understand its nature and forever change how we see the universe.

Professor James McCluskey, Deputy Vice-Chancellor (Research) at the University of Melbourne, said universities are places of deep discovery supported by global partnerships in advancing the frontiers of knowledge.

“Research which is needed to address the great unanswered questions – such as ‘what is dark matter?’ – is nearly always done in collaboration.

“Working with our partners and sharing our collective knowledge and expertise, the Stawell Underground Physics Laboratory will facilitate experiments which are critical in the global search for dark matter.’’

ANSTO’s Senior Advisor, Synchrotron Science, was among the delegation at the lab's official opening today.

Scientists from ANSTO, which operates highly sensitive radiation detectors at Lucas Heights, advised on the extremely low background radiation environment to operate the SABRE Dark Matter Detector.

“The ultra-sensitive precision detectors that are being used to search for particles of dark matter require very low levels of background radiation, which is where ANSTO assisted,” Dr Richard Garrett said.

“We contributed to the design of the laboratory, and to the specifications and selection of materials used in its construction to ensure minimal background radiation and maximum research accuracy.

“For too long, our understanding of dark matter has been in the dark. Our elimination of background radiation will give the chief investigators confidence that any particles they detect are not something else.”

In addition to understanding dark matter, ANSTO researchers will use the lab for very sensitive measurements of environmental samples, and to investigate development of biological systems like cell cultures, in the absence of background radiation.

Technical Background: The SABRE Dark Matter Detector

SABRE stands for Sodium iodide with Active Background Rejection. 

The detector consists of approximately 100 tons of steel and polyethylene shielding, surrounding a 2.6m by 3.1m vessel made from radioactive-free pure steel containing the liquid scintillator.

Immersed in the 12 tons of liquid scintillator are the ultra-pure sodium iodide detector crystals instrumented to observe dark matter interactions.

Photomultiplier tubes (PMTs), light detectors capable of observing single photons, are independently coupled to sodium iodide crystals and the liquid scintillator to sense the light emitted when different types of radiation interact with these detector elements.

Since dark matter rarely interacts with ordinary matter, any events where the liquid scintillator and sodium iodide simultaneously observe radiation can be rejected, as this will not be an actual dark matter event.

The scintillation liquid provides an ‘active veto’ to eliminate background radiation, significantly reducing the background count rate over SABRE’s predecessor, the DAMA/LIBRA lab in Italy.

To potentially detect dark matter particles, the detector must be protected from all other radiation sources as far as possible.

In the underground lab, the SABRE detector has three layers of protection:

  • An underground location situated over 1km underground in the Stawell Gold Mine, where almost all cosmic ray radiation will be eliminated
  • The detector itself will be heavily shielded by around 100 tonnes of steel and polymer shielding
  • The liquid scintillator “veto” system detects and eliminate false signals

The scintillator is based on an organic solvent, Linear Alkyl Benzene (LAB), mixed with fluorescent chemicals.

The supplier has specially manufactured the ultra-pure LAB to the JUNO neutrino experiment through a collaboration with the Institute of High Energy Physics in Beijing.

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