Thursday, October 18, 2018

Neutrinos - The Little Neutral Ones



-  2131  - -  Neutrinos - The Little Neutral Ones.  The neutrino is a tiny elementary particle that is a billion times more abundant than protons and electrons that make up our normal atoms.  Neutrinos are produced in the fusion reactions of our Sun and in the natural radioactive decay of elements in the Earth’s crust.
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----------------------------------  2131  -  Neutrinos - The Little Neutral Ones
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-  The neutrino is a tiny elementary particle that is a billion times more abundant than protons and electrons that make up our normal atoms.  Neutrinos are produced in the fusion reactions of our Sun and in the natural radioactive decay of elements in the Earth’s crust.
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-  This may surprise you but your body contains about 20 milligrams of Potassium 40.  This is one of these natural radioactive elements.  During normal radioactive decay inside your body you are emitting 340,000,000 neutrinos each day.  These neutrinos leave your body at light speed and travel to the farthest ends of the Universe.
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-  Neutrinos are invisible, they carry no electric charge, and have almost no mass.  Consequently, they pass through most everything with no interactions at all.  In fact, from all the various sources there are 1,000,000,000,000 neutrinos (trillions) passing through your body every second.
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-  Before describing where neutrinos come from I first need to define how we measure them and how we can tell them apart.  We know that energy is equal to mass times the speed of light squared (E = mc^2).  So, mass can be describe as Energy divided by the speed of light squared (m = E/c^2).  One convenient way to measure mass in small particles is in electron volts.
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-   One electron volt, one eV, equals the energy of one electron falling through an electrostatic potential difference of one volt.  This is a very small amount of energy.  1 ev = 1.6 * 10^-19 joules of energy.  One electron volt is the energy needed to lift a grain of sand one centimeter off the surface of Earth.  One eV is the energy used in the blink of an eye.
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------------------------   There are 18,750,000,000,000,000 eV in an uncontrollable sneeze.
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------------------------   A Sneeze = 3*10^-3 joules / 1.6*10^-19 joules/eV = 1.875 * 10^16 eV
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 -  An electron has a rest mass of 511,000 eV.  If the electron disintegrates into pure energy it would yield 1,022,000 eV of energy. 
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-   A proton has a mass of 938,000,000 eV.  One kilogram of mass = 90*10^15 joules.  1 eV/cm^2 = 1.783*10^-36 kilograms.  Charged particles in a nuclear bomb explosion range from 300,000 to 3,000,000 eV.  A molecule in the air has an average energy of .03 eV.
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-   Hopefully, these numbers give you some flavor of energy in electron volts.  Now we will use this measure to describe the sources of neutrinos:
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-   (1)  Neutrinos from stars, and from our Sun:
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--------------------------------------  .000006 neutrinos / cm^3  at 20,000,000 eV
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-  The sun emits 2*10^38 neutrinos per second.  The Earth’s surface receives 40,000,000,000 neutrinos per second per square centimeter.  The Sun generates these neutrinos through the fusion of hydrogen into helium.  85% of the Sun’s neutrinos come from two protons combining to form Deuterium nuclei plus a positron and plus an electron neutrino.  Deutrium is heavy hydrogen, it is a proton combined with a neutron.
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-  (2)  Neutrinos from high energy particle accelerators and from nuclear reactors, or from nuclear bombs:
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----------------------------------------  5*10^20 neutrons per second  at  4,000,000 eV
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-  A nuclear reactor core will radiate 500,000,000,000,000,000,000 neutrinos each second.  Neutrinos from particle accelerators today very with mean energies from 30,000,000 eV to 30,000,000,000 eV.
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-  (3)  Neutrinos from natural radioactivity in Earth’s crust:
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----------------------------------------  6,000,000 neutrino / second / centimeter^2
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Natural radioactivity occurs from beta decay of Uranium, Thorium, and Potassium 40.  It is equivalent to about 20,000 nuclear plants.
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-  (4)  Neutrinos from the Big Bang:
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------------------------  330 neutrinos /cm^3 over the whole Universe at .0004 eV
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-  This is very similar to the Cosmic Microwave Background Radiation that was caused by the decoupling of photons from electrons, 300,000 years after the Big Bang that started out as light and now comes to us as microwave energy, 1.4 Ghz at 2.73 degrees Kelvin. ( You can convert energy in electron volts to temperature in Kelvin multiplying by 11,605). 
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-  The Neutrino Cosmic Background comes from decoupling of neutrinos emitted by neutrons about one second after the Big Bang.  Before the decoupling neutrinos were absorbed by protons as fast as emitted by neutrons.
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-   After one second of cooling the lower temperature prevented the protons from absorbing neutrinos and the neutron emitted neutrinos were free.  Today, they are very low energy, only .0004 eV.  By comparison, on average, there are 330,000,000 neutrinos, 0.5 protons, and 1,000,000,000 photons in each cubic meter of the Universe
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-  (5)  Neutrinos from Supernova explosions:
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---------------------------------------------  0.0002 neutrino / cm^3
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-  These were first detected in the Supernova 1987a in the Magellan Cloud exploding 150,000 lightyears from Earth.
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-  (6)  Neutrinos from Cosmic Rays:
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-  When a Cosmic Ray penetrates Earth’s atmosphere hitting a gas molecule it shatters and generates a shower of elementary particles.  Cosmic Rays are hydrogen nuclei (protons) traveling at nearly the speed of light.  Among the particles are atmospheric neutrinos.
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-  The sum of all of these sources create trillions of neutrinos traveling through your body, and everything else, every second at the speed of light.  400,000,000,000 from the Sun, 50,000,000 from natural radioactivity, 100,000,000 from nuclear plants all around the world.
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-  These neutrinos are very difficult to detect and to measure.  The most successful experiment in detecting the very high energy neutrinos is occurring in the Antarctic.   Here experiments called AMANDA II and ICECUBE  have used hot water drills to drill deep holes into the ice.  They have sunk 677 glass optical modules arranged on 19 cables down as deep as 1,500 meters.  They form an array of detectors 500 meters high by 120 meters in diameter. 
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-  The glass modules work like light bulbs in reverse.  They detect light signals and send electric data up to computers on the surface.  The light signals come from looking down through the Earth into the Northern Hemisphere.  Only neutrinos can easily traverse through the Earth, yet some do crash in to ice atom nuclei scattering other elementary particles, called muons.
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-   These muons travel in water faster than light travels in water (ice).  (Light travels about 75% as fast in water as it does in a vacuum.)  The faster muons create a shockwave much like breaking the sound barrier, that in turn creates a blue streak of light, called Cherenkov Radiation. 
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-  It is these streaks of light that are detected.  From the array of detectors the direction and the energy levels of the neutrinos can be calculated.  Neutrinos have been detected that are 100 times more energy than we can create in our most powerful particle accelerators.
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-  ICECUBE is planning to expand the array to 4,800 optical modules covering one cubic kilometer.  This instrument will be , in effect, a neutrino telescope looking down through the Earth into the Northern Hemisphere to learn where these high energy neutrinos are coming from.
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-   By “seeing” with neutrinos it will allow us to see things we have never seen before.  We understand our Universe by seeing photons.  But, photons have disadvantages, they interact with matter, they scatter in gas and dust, they bend with gravity, they slow down in different mediums, they change wavelength with velocity.  Neutrinos can avoid some of this interference in what we see.  If we can learn to see with neutrinos we will surely discover many new things unseen before.
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-  By looking at the neutrinos emitted from the Sun we discovered only 1/3 as many as our calculations showed should be there.  The Sun burns 600,000,000 tons of hydrogen into helium every second, so we know how many neutrinos are produced.  From this study we have learned that there are really three types of neutrinos:
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-------------------            Electron neutrinos       < 2.5 eV
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-------------------            Muon neutrinos           < 170,000 eV
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-------------------            Tau neutrinos              < 18,000,000 eV
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-  We do not know the exact masses for these neutrinos but we have learned that neutrinos oscillate between the three different types.  Neutrinos leave the Sun as electron neutrinos.  In the 8 minutes, traveling at the speed of light, they arrive at Earth with 2/3rds changed into the other types and undetected.
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-  On March 30, 2006 Fermi National Labs announced the discovery of the tau neutrino.  Electron neutrinos were discovered in 1956 and muon neutrinos in 1962.  Now, all three types have been produced. 
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------------------------------      The history of neutrinos:
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1927 - The spectrum of beta decay as discovered to be continuous
1930 -  To account for energy conservation in beta decay Wolfgang Pauli  hypothesized the existence of neutrinos.
1932 - neutron is discovered
1946 - neutrino to accompany muon is proposed.
1956 - neutrinos discovered coming from nuclear reactors.
1957 - neutrinos found to be left-handed.  Neutrino oscillation proposed.
1962 - neutrinos come in 3 flavors proposed.  Muon neutrino discovered.
1965 - neutrinos discovered in natural radioactive decay in gold mine in South Africa.
1968 - solar neutrinos detected, only one third number expected.
1976 - tau lepton discovered.
1987 - neutrinos discovered from Supernova 1987a.
1989 - neutrinos determined to come in three species, electron, muon and tau.
2000 - tau particles produced in Fermilab.
2002 - neutrino oscillations between 3 species explains number of solar neutrinos detected.
2006  -  Fermi lab announced tau neutrino was discovered.
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-   Neutrinos are Fermions which are elementary particles having a spin of ½.  Spin is the angular momentum of a rotating particle.  Fermions include Leptons, quarks, and baryons.  Neutrinos are also Leptons.  Leptons do not partake in the Strong Nuclear Force interactions.  They interact only through the Weak Nuclear Force.  There are six types of Leptons:  electron,   muon,  tau,   electron neutrino,    muon neutrino,   and tau neutrino.
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-  October 18, 2018.     630.   See Review 2026 for 10 more reviews on Neutrinos
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 ---------------------   Thursday, October 18, 2018          -------------------------
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