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Message: <blockquote data-quote="freyar" data-source="post: 6688231" data-attributes="member: 40227">These I can answer pretty quickly before I get to the other stuff....It isn't an energy issue but a "what type of force" issue.  We say we know of 4 fundamental forces: electromagnetic, strong nuclear, weak nuclear, and gravitational (technically, we can now add a 5th, the Higgs force, though it hasn't yet been observed in all the same ways the others have).  For particle physics experiments, gravity is so feeble as to be non-existent, so let's not count that.  While electrons feel the electromagnetic and weak forces, neutrons feel the strong and weak forces, and protons feel all three, neutrinos only feel the weak force.  As you might guess from the name, the weak force  doesn't affect things very strongly, which is due to the fact that it is very short range.  So neutrinos just don't have the capability to interact with other particles easily.Here's another way to put it.  Imagine you are a fundamental particle.  If you look around, other particles appear to be carrying targets sized according how easy they are for you to hit.  If you're an electron or neutron, a proton looks really big.  However, if you're a neutrino, other particles look super-tiny.  To give you some perspective, if you had a beam of neutrinos, half of them would make it through a wall of lead more than a light year thick.  This means neutrino detectors have to be very big to catch a very few out of a fantastical number of neutrinos.In addition to interacting very weakly, neutrinos have a very small mass, no more than one-millionth that of electrons, which are the next lightest massive particles.  At the energies we've ever observed neutrinos, they are so relativistic to be moving at a speed indistinguishable from c, the speed of light in vacuum.  And most any neutrino produced has enough energy to be moving that fast.  (Since neutrinos do have mass, it is technically possible to have one moving slowly, but I don't know of a way, for example, you could easily produce them in an experiment or astrophysical event and have them come out slowly.)That blue light in the reactor is called Cherenkov radiation and deserves a bit of explanation.  Light moves at c, "light speed," only in vacuum.  In air, light moves a bit more slowly and even more slowly in water.  What's happening in that reactor is production of a bunch of neutrinos with a lot of energy.  A small fraction of these neutrinos hit electrons in the water so hard that the electrons start moving very close to c and even faster than light moves in water.  Just like an object moving faster than sound in air creates a sonic boom, those electrons create a "light boom," which is the Cherenkov radiation.Bear with me, mini-lecture ahead.  There are two basic types of fundamental particles, force-carriers like photons (called bosons), and matter particles like electrons (fermions).  The fundamental matter particles are 6 types of quarks, electrons, muons (heavier version of electrons), taus (even heavier versions of electrons), and neutrinos.  Now, as far as the weak nuclear force is concerned, these matter particles come in pairs: 3 pairs of quarks, electrons and electron neutrinos, muons and muon neutrinos, taus and tau neutrinos (yes, imaginative naming, I know).  So there are actually 3 types of neutrino.As for other properties of the neutrinos (all 3 types), we've already covered that they only interact through the weak force and that they have a very small mass.  The other very important thing about neutrinos is that they can change type as they fly along.  In other words, you could create a whole bunch of electron neutrinos and send them off to a detector.  But by the time they reach the detector, some will have changed into muon neutrinos or tau neutrinos.  This is what the big neutrino experiments are trying to understand, for the most part --- what is the precise physics that causes neutrinos to change type.  This is one of the things we know about particle physics that tells us the Standard Model is incomplete, and it might be telling us that there are even other types of neutrinos that don't even feel the weak nuclear force (called "sterile" neutrinos), and these might be the dark matter we observe in astrophysics (or a part of it).  Anyway, one of my colleagues at my university works on one of these neutrino experiments.  I assume you're asking about technological uses.  Neutrino technology is in very early stages since they're very slippery particles, but there are some ideas. As you've noticed, nuclear reactors produce lots of neutrinos, so a sophisticated neutrino detector could act like an "x-ray machine" to look inside of nuclear reactors where you can't send equipment due to the high radiation.  This could help with monitoring non-proliferation agreements or the Fukushima accident site.  There have also apparently been some experiments using neutrinos for communication purposes, but I don't know details.Yup, there are anti-neutrinos.  Certainly, neutrinos and anti-neutrinos can annihilate and could even produce gamma rays or at least photons of some energy.  But the odds of that happening are astronomically slim, so I'm pretty certain no one's ever seen that happen.Another fun fact about neutrinos and anti-neutrinos: we talked a bit earlier about the spin of particles.  Most matter particles, like electrons, can spin in two basic ways.  However, neutrinos can only spin one way --- we call them left-handed.  Anti-neutrinos can only spin the other way --- they are right-handed.  This is another complicating feature for neutrino theory.  Where are the right-handed neutrinos?  Are they the sterile neutrinos?  Do they exist at all?  There are lots of models to explain this fact along with the way neutrinos change type, but we just don't have the data yet to say what's right.</blockquote>

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