The Center for Ultra-Low Background Experiments in Dakota (CUBED) could be measuring trace amounts of radioactivity this week in the Davis Campus on the 4850 Level.
University of South Dakota physicist Jason Goon, a visiting professor from Malaysia, spent the last few weeks setting up a CUBED low-background counter on the first floor of the Davis Chamber. It?s in a room near the large water tank that protects the Large Underground Xenon (LUX) dark matter detector. Goon had help from Lab Supervisor Dana Byram, who was a member of the CUBED collaboration when he was a graduate student at USD.
The CUBED detector uses 1.2 kilograms of germanium, kept cool in a stainless steel cryostat and protected from outside radiation by a wall of copper bricks, a stainless steel box and an outer layer of lead bricks. Outside the instrument, a small Dewar filled with liquid nitrogen slowly feeds nitrogen gas into the device. ?The nitrogen pushes all the air out of the detector,? Byram says. That?s important because air contains trace amounts of radon.
Germanium detectors can measure very small amounts of gamma radiation emanating from materials placed inside the device?s small enclosure ?This is an extremely valuable resource for experiments trying to detect rare processes,? Sanford Lab Science Director Jaret Heise says. Experiments like LUX and the Majorana Demonstrator, which is looking for neutrinoless double-beta decay, are installed deep underground to escape cosmic radiation. Experiments are protected from radiation from the surrounding rock by water tanks?the LUX strategy?or enclosures made of lead?Majorana?s method. But researchers also must determine how much radiation is generated by materials used to build the experiments themselves. Most materials contain at least some radiation, and CUBED can provide tools to measure it.
But first the CUBED detector will count background radiation in the Davis Cavern itself, including radiation coming from the local rock. That data will be useful to both LUX and Majorana. ?We will have the most precise background measurements taken at the Davis Cavern,? says Goon.
CUBED Principal Investigator Dongming Mei, an associate professor of physics at USD, hopes to install a second detector in the Davis Campus next year. ?We want to build up assay and screening capacity for the dark matter and neutrinoless double-decay experiments,? Mei says. The CUBED team also has demonstrated a new method to grow detector-grade germanium crystals. Mei plans to test crystals grown at USD next year. Someday low-background counters could be using ultra-pure crystals grown deep underground at the Sanford Lab.
CUBED has been designated a Governor?s Research Center. The experiment is a collaboration of 11 research universities from throughout the nation, led by USD, and funded by South Dakota, the National Science Foundation and the Department of Energy EPSCoR program.