Concerning the Experiment
EXO is definitely an experiment searching for neutrinoless double beta decay within the 136 isotope of xenon. The experiment presently includes two facets:

1. EXO-200. a 200-kilogram prototype experiment presently operating at WIPP. It’s measured the very first time the 2-neutrino mode of double beta decay of Xenon 136. It’s also set probably the most stringent limit around the rate of neutrinoless double beta decay. It is constantly on the collect data to be able to enhance this limit or potentially uncover the decay.
2. nEXO, (“next EXO”), a tonne scale experiment using Xenon 136 to look for neutrinoless double beta decay. The collaboration is undergoing extensive RD to create the xenon detector and a method to “tag” the barium daughter ion created through the decay to be able to eliminate all backgrounds.

There are lots of benefits of utilizing a noble element, particularly xenon. It’s relatively simple to purify the LXe, which enables so that it is reused in numerous detectors. The 136 isotope could be enriched utilizing the same centrifuge techniques employed for fissile nuclear isotopes, making processing vast amounts achievable, while putting the centrifuges to peaceful use. The xenon 136 Q-value the power from the decay is 2.48 MeV, that is sufficient to become above most of the uranium gamma lines. Gamma sun rays from naturally-occurring radioactive isotopes really are a background which will make the decay we are thinking about difficult or impossible to identify. Nobel fluids like LXe are natural radiation detectors, and thus we avoid the requirement for excess materials that may generate extra radioactive backgrounds. In addition, we could achieve great energy resolution through collecting both ion technology electrons and scintillation light in the xenon.

Finally, xenon potentially enables for complete background rejection through tagging from the daughter Barium ion. This excellent property motivates a lot of the job made by our collaboration.

Neutrinoless Double Beta Decay
Neutrinoless double beta decay is really a special situation of beta decay. Beta decay is a very common type of nuclear decay which takes place when a neutron within an unstable nucleus emits an electron as well as an antineutrino and turns into a proton.

Double beta decay takes place when a nucleus is energetically or spin forbidden to decay through single beta decay. While it’s been predicted to exists for a lengthy time, the lengthy half-existence causes it to be hard to observe. Double beta decay was just first noticed in 1986. Many isotopes undergo double beta decay, including xenon 136. EXO-200 was the very first experiment to look at this decay in xenon. In normal double beta decay, two electrons and 2 antineutrinos are ejected in the nucleus when two neutrons become protons. The half-lives of double beta decay isotopes are extremely lengthy, above 10 two decades. This really is greater than a billion occasions more than age the world! If you began with 8 billion atoms that may undergo double beta decay at the outset of the world, you realized about 1 to possess decayed right now.

Neutrinoless double beta decay hasn’t yet been seen, however, many theories predict it. It is just like normal double beta decay, speculate of special qualities from the neutrino, no neutrinos could be released in the nucleus.

The electrons would carry all of the energy from the decay, unlike normal double beta decay, where the antineutrinos carry away energy. Thus, neutrinoless double beta decay includes a unique, observable signature. To ensure that this to happen, the neutrino would need to be its very own antiparticle. If neutrinos are their very own antiparticles, which are classified as “Majorana” particles, this admits many elegant theories to describe how neutrinos acquire mass and why their mass is really much smaller sized than every other particle we all know.

You want to see neutrinoless double beta decay for 2 reasons. First, we do not determine if the neutrino is its very own antiparticle or otherwise, to see it might answer this without a doubt. Second, we do not be aware of exact mass from the neutrino along with a measurement from the neutrinoless double beta decay half existence would let us appraise the neutrino mass. Even when we do not see neutrinoless double beta decay, a restriction around the half existence places a restriction around the neutrino mass.

If you are still curious, Physics World includes a nice article on neutrinoless double beta decay that’s more in depth, but nonetheless available to a lay person.

EXO-200
EXO-200 is really a prototype to build up approaches for dealing with liquid xenon currently projection chamber (TPC). One possibility for tonne-scale EXO is really a liquid TPC, so knowledge of EXO-200 technologies will lead to the style of tonne-scale EXO. Furthermore, EXO-200 supplies a testing ground for developing and procuring very radiopure materials and removing backgrounds. EXO-200 provides fundamental measurement from the double beta decay of xenon 136 and can provide improved limits around the rate of (or possibly observation of) neutrinoless double beta decay.

We’re using 200 kg of liquid xenon (LXe) enriched to 80% from the 136 isotope for EXO-200. The LXe fills our TPC vessel. Whenever a particle deposits energy within the liquid xenon, it ionizes the xenon atoms, knocking electrons off. We apply an electrical field towards the xenon, which pushes most of the electrons to wire grids where they’re collected. The grid position supplies a 2D location, and the amount of electrons relates to the event’s energy. However, many xenon ions recombine using the electrons before they are able to drift away. This puts the xenon atoms into excited states. Once the excited atoms relax, they release ultraviolet light, referred to as scintillation, which we collect on avalanche photodiodes (APDs). Time between your light signal (which will come nearly immediately) and also the ion technology signal (which must drift and takes microsecond to reach) enables us to rebuild the entire 3D location from the event when combined with 2D position in the wire grids. In addition, the quantity of light can also be associated with the event’s energy. Mixing the ion technology and lightweight signals enables a much better energy menasurement than using either signal by itself.

The TPC vessel is contained inside a cryostat system to keep the xenon at liquid temperature. The vessel is found in a amount of HFE-7000, an artificial fluid that’s liquid from 70 degrees lower to LXe temperatures. The HFE is at a sizable copper cryostat, that is then inside another coper cryostat having a vacuum gap among for insulation. The cryostat is shielded with lead and found in a category-100 cleanroom located 2150 foot subterranean in the Department of Energy’s Waste Isolation Pilot Plant. All this is essential to defend from radioactive backgrounds and cosmic sun rays. On the top of this, materials contained inside the lead happen to be extensively counted for radiopurity. The types of materials are lower in radioactive isotopes and contamination. A lot of the materials are ultrapur, copper, teflon, phosphorbronze, and acrylic.

Owner: EXO-200 Maintained By: EXO-200 Updated: Friday September 16, 2016