EXO on the Road
On a small side street on Stanford's main campus, just across from a bustling construction site, a transport company loaded four shipping containers onto trucks yesterday. The activity may well have blended into the background for a casual observer, but for Giorgio Gratta and a handful of others, it marked a milestone in the search for knowledge about neutrinos.
"Today, we completed an integral step in the complex process that will take the prototype Enriched Xenon Observatory [EXO] to the bottom of a mine shaft in New Mexico," said Gratta, the EXO project leader. "But we're not done yet; there are still two other truck journeys, a mine shaft, and shifting salt to think about."
EXO is an underground observatory that will search for something never before seen: a neutrinoless double beta decay, which would prove that neutrinos are their own anti-particle, and will tell scientists more about the mass of these nearly massless particles.
Before EXO can start taking data, the very sensitive equipment must first be transported into the New Mexican mine piece by piece. This is no trivial matter, for the experimental equipment must be shielded from all radioactive sources—even the slight radioactivity found in a sneeze would cause a problem. It must also be kept from cosmic rays, which would transmute stable atoms of the equipment into unstable ones, causing false signals in the detector.
The entire experiment was built in a transportable clean room, which itself was protected within a bunker-like building with 7-foot-thick ceilings. The clean room is modular, and disassembles into six truck-sized pieces. Two of these modular containers are now speeding along on the back of a truck on their way to New Mexico. The other modulesas well as support equipmentwill follow later.
The very last module to undertake the journey will contain the detector itself. This component will make the trip only after researchers and transporters have gained experience with the first two loads, and it will be transported as quickly as possible to minimize the time it is above ground, susceptible to cosmic rays. With this in mind, the detector will be ferried by not one but two truck drivers who can make the trip from Stanford to New Mexico without stopping to sleep.
Once the modules arrive at the salt mine, their journey will be far from over. Built one inch smaller than the mine shaft, each container, dangling from a few ropes, must be carefully lowered down to the mine floor 700 meters below. What's more, the shaft only has rail guides at the top and the bottom; in between, the load must be perfectly balanced under the ropes so that it doesn't tilt, dig its corners in the mine shaft and get stuck.
"We've done tests and calculations—it will be difficult, but it will work," said Gratta.
Once all the containers make it to the bottom of the mine shaft, a 41-ton forklift will transport them through several hundred meters of tunnel to an experimental area. There crews will reassemble the components upon hydraulically adjustable stilts that will stabilize the experiment even if the salt bed shifts beneath it.
After this long journey, the observatory will rest here for several years, taking data that may redefine our understanding of neutrinos.
"We hope to be up and running by the end of the year," said Gratta. "It's a huge undertaking, but EXO will offer us a glimpse into neutrinos never before seen."
Kelen Tuttle, SLAC Today, July 6, 2007