This summer there?s copper, copper everywhere at the Majorana Demonstrator experiment (MJD), which is being assembled 4,850 feet underground in the Sanford Lab.
MJD will look for neutrinoless double-beta decay, one of the rarest forms of radioactive decay. Its detection could help explain why matter?in other words, us and everything else in the universe?exists.
To work properly, MJD requires a radiation free environment. A mile of rock will block particles caused by cosmic radiation. Lead, copper and plastic shielding will block other kinds of radiation. But MJD also must be protected from itself. That?s why the most sensitive parts of the experiment are being made out of copper formed deep underground, where it is shielded from birth from the (slightly) polluting effect of cosmic radiation.
Two years ago the MJD team began manufacturing copper on the 4850 Level, in an electroforming lab near the Ross Shaft. As of this week, the team has electroformed about 75 percent of the 5,000 pounds of copper they will need. ?We have about a year left to go,? said MJD Principal Investigator Steve Elliott, who is a nuclear physicist at Los Alamos National Laboratory.
The MJD parts inventory, meanwhile, is growing fast: copper spring clips, copper hex bolts, copper high-voltage rings, copper cryostats parts and shiny slabs of copper shielding. All those parts and hundreds more are being machined deep underground, in the Davis Campus, from of the purest copper in the world. And even that level of purity is not quite good enough. After the copper parts are machined, the surfaces are etched with dilute nitric acid to remove any surface impurities that could carry with them slight amounts of radioactivity.
?This copper is phenomenally clean,? Elliott pronounced.
As important as it is, copper plays only a supporting role at MJD. The experiment?s detectors will be enriched germanium crystals that will be installed, in strings, inside cryostats made of ultra-pure copper, The cryostats will keep the detectors cool to below 300 degrees F., which improves their performance as semiconductors.
Natural germanium detectors will be installed in a prototype cryostat made of commercial copper later this month to test the technology, Elliott said. And the MJD team has assembled the necessary parts to build the first ultra-pure cryostat.