The Matter of Things

Understanding the metamorphosis of neutrinos — neutral subatomic particles — as they pass through the earth could be the key that unlocks many of the mysteries of our world and solar system.

Fermilab National Accelerator Laboratory in Batavia, Ill., is home to the Tevatron, the world’s most powerful operating particle accelerator, which produces a neutrino beam for analysis. Fermilab and the University of Minnesota are collaborating to build the NOvA Far Detector Building to house a neutrino detector for studying these elusive pieces of matter.

Burns & McDonnell was initially hired by Fermilab to design and construct a three-mile access road to the detector site in Ash River, Minn. Successfully maneuvering through various historical preservation and environmentally sensitive areas, Burns & McDonnell earned the job as engineer and architectural design firm for the remainder of the project.

The NOvA Far Detector will detect neutrino interactions with matter utilizing the neutrino beam from Fermilab approximately 500 miles away. The nature of neutrinos makes them difficult to detect. Traveling at nearly the speed of light, they mostly pass through the 500 miles of the earth’s crust between Fermilab and Ash River with ease. Consequently, the neutrino detector must be very large — 14,000 tons — to see a small fraction of the neutrinos interact. “The distance increases the detector’s sensitivity to the neutrino mass ordering, so the farther from Fermilab, the better,” says Steve Dixon, Fermilab Level 2 manager for sites and buildings.

To alleviate confusion with other particles misidentified as neutrinos, the detector needs to be built underground, and the rocky terrain of northern Minnesota, dense with granite, makes shielding it challenging. “We are using a combination of concrete and barite aggregate. Barite is denser than granite, so we could use less of it while still accomplishing the same amount of shielding,” says Jack Steenken, Burns & McDonnell project manager. “Still, the span and weight of the shielding precluded conventional reinforced concrete design, so the final design incorporates a composite roof consisting of pre-stressed beams tied to a reinforced concrete deck.”

Adding to the complexity, various air exchanges are needed to cool, heat and pressurize the space around the detector equipment, making strict temperature and moisture control critical. “Outside air temperatures could go as low as minus 40 degrees Fahrenheit, while the detector could reach 105 degrees,” Steenken says. To meet heating and cooling needs, Burns & McDonnell recommended using a unit with multiple refrigeration circuits, multiple-speed scroll compressors and modulating hot gas reheat.

As the first Department of Energy project using American Recovery and Reinvestment Act funds, Steenken says extra care was taken in all aspects of the design and architecture to meet federal requirements.

For more information, contact Jack Steenken, 630-724-3200.

Download Article