The EXO Project
The Enriched Xenon Observatory 200, or EXO-200, is designed to look for an ultra-rare phenomenon that could reveal key secrets about the nature of the neutrino. Neutrinos – meaning “small neutral ones” – are subatomic particles lacking an electric charge.
Double beta decay is the radioactive decay of the nucleus of an atom — such as xenon. Typically, two electrons or positrons (beta particles) and two antineutrinos —— are emitted from the nucleus when two neutrons become protons. This was first observed in 1986.
Neutrinoless double beta decay has not yet been seen but is thought to exist. In neutrinoless double beta decay, no neutrinos would be emitted from the nucleus. In order for this to occur, the neutrino must be its own antiparticle. Most particles have an antimatter partner with the opposite electric charge. Because neutrinos and antineutrinos are both neutral, they could be identical.
The EXO-200 takes advantage of the shielding against cosmic rays by the WIPP overburden for conducting its search for neutrinoless double beta decay in the salt beds of the underground repository.
Stanford University leads a consortium of scientists involved in the EXO Project. Many of EXO's scientists are also affiliated with the SLAC National Accelerator Laboratory.
Substantial space in the northern section of the repository has been set aside for EXO and other experiments. Stanford University leads a host of academic institutions in the experiment, which essentially involves cycling enriched xenon through an ultra-sensitive detector that could pick out a single atom produced by neutrinoless double beta decay.
Scientists involved with the project say they believe in starting small when it comes to understanding the nature of the universe. But understanding the nature of the neutrino, they say, will ultimately help them understand more about the nature of stars and galaxies.
EXO's detector, pictured here, was assembled at Stanford University. It was shipped to WIPP in a thick shield to protect it from exposure to natural radiation.
What’s especially interesting about the project is that it is an experiment which demands that it not be exposed to any avoidable amount of radiation – and it is taking place in an underground repository for nuclear waste.
An EXO technician takes a reading inside one of the site's cleanrooms.
The final component of the EXO observatory, called the Time Projection Chamber, arrived at WIPP in November 2009. Scientists began collecting data in the fall of 2010.