Majorana builds on experience

For the past year, the Majorana Demonstrator experiment has been collecting valuable information in its search for a rare form of radioactive decay using a prototype. Researchers believe neutrinoless double-beta decay occurs inside enriched germanium detectors and need to be sure everything that will be used in the actual experiment works the way it should. 

"The prototype was a complete shakedown of everything for the actual experiment," said Vince Guiseppe, Assistant Professor of Physics at the University of South Carolina. 

The prototype is a cryostat that contains natural germanium detectors. The actual experiment uses enriched and natural detectors. While the prototype ran inside the shield, the team evaluated the detectors and the design. "Much of what we learned was incorporated into the design of Module 1," Guiseppe said. 

For two weeks, the prototype and Module 1 sat side by side inside the shield. But last week, the prototype was removed and put into the glove box for decommissioning. Many of the parts, with the exception of the cryostat, will be used to build a second module. 

The cryostat used in Module 1 is made of ultra-pure copper electroformed on the 4850L. It contains 20 enriched germanium detectors (16.8 kg) and nine natural germanium detectors (5.7 kg). There?s a good reason for that, Guiseppe said. "If we see double-beta decay in the enriched detectors, it should not be seen as often in the natural detectors." In addition, the natural detectors act as extra shielding from radiation.

The detectors for Module 1 were built into seven strings over a period of about 10 months. "It's very delicate and challenging work. And there's a lot at stake," Guiseppe said. 

First, researchers build each unit that encapsulates each detector. That includes copper parts, electronics and connectors. And because the enriched detectors are different sizes, some parts must be custom made. Next, the detectors are "stacked" into strings (both natural and enriched) and tied together along with a careful routing of cables. Finally, the strings are attached to the cryostat—a complicated process that involves over 100 electronic connections. 

With Module 1 inside the shield, researchers are focusing on the next phase: building Module 2. "We anticipate having it built this fall so we can commission it by the end of the year," Guiseppe said.