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The Hardware That Searches For Dark Matter (hackaday.com)
szczys writes: Deep in a gold mine in South Dakota, the Large Underground Xenon experiment waits in the darkness for a tiny flash of light that signals that dark matter actually exists. So far we theorize that it does exist, and have gone to great lengths to build hardware to detect dark matter. Very cold, very pure liquid xenon sits waiting for a dark matter particle to strike the nucleus of a xenon molecule, producing a distinct pattern of photons through scintillation. An array of photomultiplier tubes detect the photons, whose pattern is processed by FPGAs on custom boards connected using HDMI. The experiment has generated a list of properties not possessed by dark matter; running for several years no evidence of the particles interacting with the xenon have been found. But when the data collection concludes this year, a much larger version of the impressive hardware will be built.
Neutrinos are light and very fast. Dark matter if it exists as predicted, would be heavy and very slow. Their common property would be rarely interacting with 'normal to us' matter.
I see reference to WIMPs in the article, so in some ways do we consider Dark Matter to be kind of like a neutrino? All around us but not generally interacting with us?
So instead of there being vast tracts of stuff we simply can't figure out where it is, it's spread throughout?
WIMPs, Weakly Interacting Massive Particles is what they suspect dark matter to be. It interacts very weakly, possibly only via gravity which is almost undetectable in the scale of individual particles. Thus it tends to pass right through everything. They are assumed to have some cross section so can possibly interact with themselves and other particles if they hit directly head on which is what this experiment seems to be trying to detect. It's thought when they interact with themselves, they annihilate, so they do not slow each other down and do not form disk shapes such as solar systems or galaxies. Otherwise, they float around, only affected by gravity, so the form a spherical cloud called a halo around other gravitational objects such as solar systems and galaxies in which they fall into orbit.
Dark matter and dark energy have multiple independent lines of supporting empirical evidence. I presume you are willfully ignorant of this. Perhaps you can manage to keep it to yourself next time.
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I see reference to WIMPs in the article, so in some ways do we consider Dark Matter to be kind of like a neutrino? All around us but not generally interacting with us?
Yes. The idea is that Dark Matter particles interact via the same force (the Weak Force) as neutrinos. The difference is that Dark Matter must be a much heavier particle than neutrinos in order to explain the astrophysics, because neutrinos don't clump enough under gravity.
There's a reason why this model is taken seriously: it's possible to calculate how such particles are created very early in the Big Bang. It turns out that if the particle responsible for Dark Matter was created in thermal equilibrium in the very early universe, its abundance today depends only on its interaction strength (not, for example, its mass). If you calculate that interaction strength corresponding the Dark Matter abundance implied by astrophysical measurements, you get exactly the same interaction strength as neutrinos. A pretty amazing coincidence!
Oh dear, Software know-it-alls...
Xenon _can_ bond with itself. It's in a field known as "Plasma Physics". It's not that easy, but I've done it.
First, you need an ECR-IS. Slip in a bit of 4He, ionize it, and set up your initial Cyclotron Resonance spirals of Electrons. Now inject just a sniff of Xenon. (We used 136Xe.) Set up your particle detector downstream of the Analyzer and look for Mass 140- Xenon Helide. Note that this can _only_ exist in the +1 charge state.
Once you've tuned this out, Analyze for Mass 272- +1(136Xe(2)). The best production that I've seen was ~10e2 per second.
Note that various species exist roughly in cylindrical shells within the ECR Plasma, depending on mass and charge state, so very fine adjustments of the ECR Magnetic Fields, RF, and Vacuum can be used to selectively optimize for any given shell. (You'll see a lot of atomic Xenons, all the way up to +54, if you have a good enough ECR.)
We started out with something easier initially- Helium Hydride, on the suggestion of Mike Pryor. One doesn't even need an ECR-IS for this. It's easy to get ~10e14 Helium Hydrides per second with a regular Plasma Source.
Note that all this actually has practical applications, involving Ion Implantation. On the theoretical side, Astrophysicists are delighted; it's rare that they can actually experiment on something, instead of just observe and calculate.
Code Monkeys should stay away from commenting on any Physics more complicated that rolling a ball down an inclined plank, and timing it with a stopwatch.
See also here. Note the comment about a Xe-Xe bond in Xe(2)Sb(2)F(11).
It has been known since 1962 that Xenon can form compounds with other elements. Most of them involve Fluorine, because it is a seriously badass element when it comes to stealing electrons. It can even oxidize Oxygen.
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