New shield design improves CUBED detector

Sensitive physics experiments like the Large Underground Xenon (LUX) and Majorana Demonstrator (MJD) experiments seek significant events that help them better understand the universe. Deep underground they escape most of the cosmic rays that bombard Earth?s surface. But radiation exists everywhere: in the materials used, in the rocks, and in the air. That?s where low background detectors come in. 

The Center for Ultra-Low Background Experiments in Dakota (CUBED) began collecting data on the 4850 Level in 2013. When researchers realized the level of radon gas within the detector was too high, they looked first at the shielding.

 ?CUBED has very good shielding,? said Kevin Lesko, Operations Office Head at Lawrence Berkley National Lab (LBNL). ?It?s got 6 inches of lead, 4 inches of copper, and a stainless steel box around the detector. That?s quite a bit.?

So how was the radon getting in? The culprit was a gap between the lead and stainless steel?or radon exclusion?shields, said Vic Gehman, a project scientist from LBNL. ?We reconfigured the lead shielding to eliminate the gap and added gaskets to the radon exclusion shield.?

Last week, Gehman and Chris Chiller, a graduate student at the University of South Dakota, disassembled the shield then, carefully following the new design, put it back together. 

Finally, they ?wrapped the lead like a fancy Christmas present in Mylar? and purged the area with nitrogen gas to push out the radon, Lesko said. 

Since then, backgrounds have dropped by 25 percent, Lesko added. ?That?s important because CUBED will be used to test materials for the next generation of experiments at Sanford Lab.?