January 17, 2021 / by Kimberly Hickok, SLAC National Accelerator Laboratory

The trick, Akerib said, is getting pure xenon, without which all the benefits of the noble gas are moot. However, purified noble gases aren’t readily available—the fact that they don’t interact with much of anything also means they are generally pretty difficult to separate from one another. And, “unfortunately you can’t just buy a purifier off the shelf that will purify noble gases,” Akerib said.

Akerib and his colleagues at SLAC therefore had to figure out a way to purify all of the liquid xenon they needed for the detector.

The biggest contaminant in xenon is krypton, which is the next lightest noble gas and has a radioactive isotope, which could mask the interactions researchers are actually looking for. To prevent krypton from becoming the particle detector’s kryptonite, Akerib and his colleagues spent several years perfecting a xenon purifying technique using what’s called gas charcoal chromatography. The basic idea is to separate ingredients in a mixture based on their chemical properties as the mixture is carried through some kind of medium. Gas charcoal chromatography uses helium as the carrier gas for the mixture, and charcoal as the separation medium.

by by William Schultz, Lawrence Berkeley National Laboratory

The heart of the LZ dark matter detector is comprised of two nested titanium tanks filled with ten tons of very pure liquid xenon and viewed by two arrays of photomultiplier tubes (PMTs) able to detect faint sources of light. The titanium tanks reside in a larger detector system to catch particles that might mimic a dark matter signal.

“I’m thrilled to see this complex detector ready to address the long-standing issue of what dark matter is made of,” said Berkeley Lab Physics Division Director Nathalie Palanque-Delabrouille. “The LZ team now has in hand the most ambitious instrument to do so.”

The design, manufacturing, and installation phases of the LZ detector were led by Berkeley Lab project director Gil Gilchriese in conjunction with an international team of 250 scientists and engineers from over 35 institutions from the US, UK, Portugal, and South Korea. The LZ operations manager is Berkeley Lab’s Simon Fiorucci. Together, the collaboration is hoping to use the instrument to record the first direct evidence of dark matter, the so-called missing mass of the cosmos.

Henrique Araújo, from Imperial College London, leads the UK groups and previously the last phase of the UK-based ZEPLIN-III program. He worked very closely with the Berkeley team and other colleagues to integrate the international contributions. “We started out with two groups with different outlooks and ended up with a highly tuned orchestra working seamlessly together to deliver a great experiment,” Araújo said.