LEAD | If you happen to have some extra xenon lying around – say about 1.8 million liters – officials at the Sanford Underground Research Facility would like to talk to you.
That’s the amount of the colorless, odorless element that makes up only 0.0000087 percent of the Earth’s atmosphere that scientists say will be needed for the deep underground laboratory’s $50 million to $60 million LUX-ZEPLIN experiment, so the Sanford Lab is going to start stockpiling it soon.
At its annual meeting Thursday, the South Dakota Science and Technology Authority unanimously approved a loan from the University of South Dakota Foundation and authorization for its executive director to procure up to 500,000 liters of xenon.
“The SDSTA truly appreciates the USD Foundation’s investment in the LUX-ZEPLIN experiment,” said Mike Headley, the Science Authority’s executive director. “Their investment along with similar investments by the South Dakota State University Foundation and the South Dakota Community Foundation, along with tremendous support from Gov. Daugaard, will help keep the U.S. in a leadership role in the global search for dark matter.”
Two years ago, xenon was priced at nearly $25 per liter, meaning the necessary gaseous element of atomic number 54, obtained through the distillation of liquid air, would have set the Science Authority back a cool $45 million. Fortunately, the price has dropped significantly since then.
“We will pay $5.50 per liter and this is not a discount; it’s the current market price,” said Sanford Lab spokeswoman Constance Walter. “Basically, the increased use of LED lights in vehicles, etc., has decreased the demand for xenon lighting. So, the price has dropped dramatically from a couple of years ago when they were in excess of $20 per liter.”
Headley said late Thursday that the Science Authority had secured the first 500,000 liters at a cost of $6.25 per liter and the remaining 1.3 million liters would cost $5.50 per liter. Consequently, even with the price reduction, the xenon will likely cost the Science Authority nearly $10.3 million.
Initially, the Science Authority will purchase 1.5 million liters, or about 80 percent of the 1.8 million liters the experiment will require, Walters said. The xenon will be delivered over the next two-plus years and when it is purchased, it will first go to the U.S. Department of Energy’s SLAC National Accelerator Laboratory in Menlo Park, Calif., where it will be purified. Then it will be shipped to the Sanford Lab to be placed in the detector sometime in 2018, she explained.
Discovered in 1898 by Sir William Ramsay, a Scottish chemist, and Morris M. Travers, an English chemist, shortly after their discovery of the elements krypton and neon, xenon was used in the Sanford Lab’s original Large Underground Xenon experiment known as LUX.
In October 2013, more than 100 science enthusiasts and government officials gathered at the Sanford Lab to receive initial findings of the LUX, while hundreds more from around the world joined via webcam. In that complex three-month trial involving particle physics, scientists sought to detect mysterious dark matter particles previously observed only through their gravitational effects on galaxies.
Nearly a mile deep in the bedrock of the Black Hills and shielded from vast amounts of cosmic radiation that constantly bombard the earth’s atmosphere, the LUX was comprised of a phone booth-sized titanium tank filled with nearly a third of a metric-ton (370 kilograms) of liquid xenon cooled to minus 150 degrees, scientists explained. The detector was further buffered from background radiation by its immersion in a 72,000-gallon tank of ultra-pure water.
Now, scientists around the globe are awaiting the start-up of the much larger 60-ton particle detector known as the LUX-ZEPLIN or LZ, which will be approximately 30 times larger (10 metric tons or 10,000 kilograms of xenon) and 100 times more sensitive than the LUX.
And, it’s going to take quite a bit of xenon to make that happen.