In 2011, the Majorana team began electroforming copper in a clean room near the Ross Shaft on the 4850 Level. Two weeks ago, Cabot-Ann Christofferson, Liaison for the Majorana Demonstrator Project to Sanford Lab, and Anne-Marie Suriano, a Ph.D. candidate at the School of Mines, set one of the last mandrels (stainless steel cylinders) onto which copper will be grown for MJD.
"The copper will be used as an infrared shield around the detectors when they are inside the cryostat," Christofferson said.
To date more than 6,600 pounds of copper have been electroformed on 33 mandrels for the experiment at SURF, Christofferson said. Not all parts within the Majorana Demonstrator need the highest purity material, so in those cases copper was electroformed at a shallow facility at Pacific Northwest National Laboratory.
The process works like this:
Mandrels weighing up to 60 pounds each are lowered into the center a sulfuric acid bath and surrounded by nearly one ton of copper nuggets that have been triple-etched in nitric acid. Dilute sulfuric acid breaks down the copper, freeing uranium, thorium and radioisotopes like Cobalt-60, which will stay in solution and not be included into the electroformed copper.
Finally, an electrical current is run through the mandrel, which attracts the copper ions, causing the copper to accumulate on the surface of the mandrel at a rate of about 33 millionths of a meter per day. Most mandrels stay in the solution for over a year, depending on the thickness required. It's a process that requires constant upkeep, Christofferson said.
"The copper has to be kept as the same height as the mandrel. But as the nuggets dissolve they sink to the bottom so we have to constantly add more nuggets. We also have to maintain the chemistry of the baths."
Christofferson said the past four years with Majorana have been an adventure. "I have learned so much about science outside my field. I've also learned a lot about people. Proper management of a workforce can be just as important as the systems we are building."