The purest crystals ever seen in Australia set to arrive in Stawell
The purest sodium iodide crystals ever seen in Australia, and in any dark matter physics experiment currently underway anywhere in the world, will arrive in the Victorian town of Stawell in coming months.
The sodium iodide crystals will form the heart of the SABRE South dark matter experiment that will be located in the Stawell Underground Physics Laboratory (SUPL).
Particle physicists from across Australia and Italy, led by the ARC Centre of Excellence for Dark Matter Particle Physics (CDM) are collaborating on the project that aims to detect dark matter and confirm or refute results achieved by scientists in Italy.
The experiment will comprise a large steel vessel filled with 12,000 litres of liquid scintillator and photomultiplier tubes holding the seven crystals, which will each weigh seven kgs and measure 10 inches long, at its centre.
If dark matter hits the crystals, they will glow and that activity will be detected by the photomultiplier tubes.
The seven crystals are grown in a platinum crucible that reaches nearly 1,000 degrees Celsius at the Shanghai Institute of Ceramics, Chinese Academy of Sciences in China.
They are incredibly fragile and cannot be exposed to air or handled without special equipment as moisture can cause them to degrade. They are stored within ultrapure metal cylinders and will be placed in a special low-humidity cabinet when they arrive in SUPL.
The underground location of the laboratory was chosen to reduce the cosmic radiation that reaches the experiment. Within SUPL, scientists will use a purpose-built glovebox to handle the crystals when they are constructing the experiment.
They will arrive in Australia by sea rather than sky as air travel would expose the crystals to too much cosmic radiation, which would create additional radioactive backgrounds and make them unusable. The first crystal is expected to arrive in a few weeks, with all seven due by the end of the year.
CDM lecturer Suerfu Burkhant of the University of Melbourne is leading the growth of the crystals and says the project required pristine conditions to ensure they remained suitable for the experiment.
“It took us years of research and development to reach this level of high-purity, and it will be the first time that physicists will commission crystals of such high-purity in an underground experiment worldwide,” Dr Burkhant said.
“The ultrapure crystals are a crucial part of the SABRE South dark matter experiment so we have to ensure we are protecting them from contamination at every stage of their production and transport.
If the crystals are exposed to air or any other contaminants, they will quickly start to degrade and we would not be able to use them in this experiment, which is also very sensitive to contamination.”
CDM researcher and Senior Lecturer at the University of Sydney, Theresa Fruth, says the SABRE South experiment has the potential to provide crucial data to scientists, as this will be the first underground dark matter search in the Southern Hemisphere.
“Scientists from around the world have been working together for more than a decade to make the SABRE South experiment happen and so it is exciting to see that we are starting to put all the pieces together,” Dr Fruth said.
“These crystals are one of the final elements of the experiment that we need before we start the installation of the detector in the Stawell Underground Physics Laboratory.
“Building an experiment sensitive to something as difficult to detect as dark matter requires careful design and manufacturing. Not only the production of the crystals, but also every component of the experiment needs to be designed, selected, and installed with great care. And you need the right place – deep underground- to run your experiment! So, it is very exciting to be the first experiment hosted in Australia’s very own underground lab, SUPL.”
CDM Director Elisabetta Barberio of the University of Melbourne says the search for dark matter could be a defining project for science in Australia.
“If we can provide essential clues about the nature of dark matter, we will transform our understanding of the universe and all that surrounds us,” Professor Barberio said.
“Dark matter comprises 85 per cent of the matter of the universe and is considered the greatest mystery of the universe. We can only imagine the potential of understanding what it is.
“We are very proud to be conducting this world-leading research in regional Victoria, in collaboration with researchers from many different scientists from across the globe.”For interviews, contact: Fleur Morrison | 0421 118 233 | fleur.morrison@unimelb.edu.auThe National