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Located 350 feet below the surface on the Fermilab site, the MINOS underground hall is a familiar place to many neutrino enthusiasts. Shielded from cosmic rays that bombard Earth’s surface, this underground area provides a quiet place to observe elusive neutrinos and test sensitive particle detector technology.

During the past two decades, the hall was home for two of Fermilab’s flagship neutrino experiments: MINOS and MINERvA. After collecting neutrino events for many years, the experiments were shut down in 2019, but their detectors remained.

Now this valuable underground space is available for new experiments. This summer, the decommissioning team removed the last of approximately 400 detector planes from the area. Scientists have already plans to use the space for new research endeavors, from neutrino research and dark matter searches to quantum science. In particular, the ArgonCube collaboration is eager to test its detector technology for the near detector of the Deep Underground Neutrino Experiment.

Decommissioning the detectors

The first step, however, was to decommission and remove the two large detectors that were still in the hall: MINERvA in the front and MINOS in the back. About 40 people participated in this project at one time or another. We worked on tasks, such as saving equipment for future use or transferring heavy detector planes for recycling.

We began the detector decommissioning project in early 2020. We expected it would take at least a year to disassemble the two detectors and remove the detector planes, each up to 20 feet wide, 13 feet high and as heavy as a few tons.

Our number one goal was to do this heavy-lifting job safely. Careful planning and diligent coordination were the key for keeping everybody safe, and we completed the project without a single accident. We also faced the additional challenge from the pandemic, which arrived in Illinois right after we started the decommissioning. We took extra steps to ensure social distancing and personnel health protection.

Part of our job was to preserve valuable detector items for future use. We had to dis-cable all electronics and carefully pack and store all items. This was a challenging task as some of the electronics were installed at the top of the tall detector planes and connected with very long cables to electronics racks located on the side of the detector hall.

We also had to dismount the heavy detector planes from their support structures, one by one, using a special lifting platform. We then placed each plane on a very sturdy cart and rolled them one at a time to the 350-feet deep MINOS shaft to lift them to the surface building.

On Wednesday morning, June 30, the team took the last detector plane — a 4-ton steel plate with its face covered by scintillator panels — to the surface. It marked the completion of the decommissioning, which stands as a great accomplishment achieved under difficult conditions.

Ready to remove the final detector plane from the MINOS underground hall (from left to right): Steve Hahn, ND, decommissioning field manager; Jon Thebe, PPD, experiment installation; Dean Beckner, PPD, detector fabrication; Tom Wicks II, PPD, experiment installation; Tom Olszanowski, PPD, experiment installation; and Joe “Skippy” Brown, ND, electrical group. Photo: Ryan Postel, Fermilab

Meet the team

The decommissioning team comprised physicists, engineers and technicians from the Neutrino Division, Particle Physics Division as well as universities collaborating on ArgonCube and MINERvA.

A tall gentleman with the biggest smile stands out among this group, literally and figuratively. Steve Hahn is the field manager for the decommissioning project. He also serves as the Neutrino Division liaison to the first new experiment soon to take residence in the underground hall: ArgonCube2x2.

Since the planning stage of the decommissioning work, Steve has been a fixed figure in the MINOS underground area. He literally lives there, people say. His smiling face and gentle manner are guaranteed to lift your spirit. And he smiles all the time – even when his face is covered by a mask.

Steve is the one who communicated with everyone to make sure things were being done smoothly and safely. He helped develop and write down detailed procedures. He made sure that before the start of a task, crews were briefed and reminded of the importance to work safely.

“Steve [Hahn] and the entire team did such an excellent job in preparation and in carrying out the mission safely,” said Steve Brice, head of the Neutrino Division. “Communication is key, and Steve is always there for things small and big.”

Congratulations to the decommissioning team for the great accomplishment. With your dedicated effort and hard work, the MINOS underground hall is again ready to welcome another round of exciting experiments. The foundation for new science ventures has been laid.

Ting Miao is a senior scientist in the Neutrino Division and serves as the project manager for the installation and testing of the ArgonCube2x2 prototype detector for DUNE.