-
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.
-
-
-
-
---------------------------------- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
------------------------
There are 18,750,000,000,000,000 eV in
an uncontrollable sneeze.
-
------------------------
A
Sneeze = 3*10^-3 joules / 1.6*10^-19 joules/eV = 1.875 * 10^16 eV
-
- 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.
-
- 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.
-
- Hopefully, these numbers give you some flavor
of energy in electron volts. Now we will
use this measure to describe the sources of neutrinos:
-
- (1) Neutrinos from stars, and from our Sun:
-
--------------------------------------
.000006 neutrinos / cm^3 at 20,000,000 eV
-
- 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.
-
- (2)
Neutrinos from high energy particle accelerators and from nuclear
reactors, or from nuclear bombs:
-
----------------------------------------
5*10^20 neutrons per second at
4,000,000 eV
-
- 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.
-
- (3)
Neutrinos from natural radioactivity in Earth’s crust:
-
----------------------------------------
6,000,000 neutrino / second /
centimeter^2
-
Natural
radioactivity occurs from beta decay of Uranium, Thorium, and Potassium
40. It is equivalent to about 20,000
nuclear plants.
-
- (4)
Neutrinos from the Big Bang:
-
------------------------
330 neutrinos /cm^3 over the whole
Universe at .0004 eV
-
- 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).
-
- 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.
-
- 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
-
- (5)
Neutrinos from Supernova explosions:
-
---------------------------------------------
0.0002 neutrino / cm^3
-
- These were first detected in the Supernova
1987a in the Magellan Cloud exploding 150,000 lightyears from Earth.
-
- (6)
Neutrinos from Cosmic Rays:
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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.
-
- 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:
-
------------------- Electron neutrinos <
2.5 eV
-
------------------- Muon neutrinos < 170,000 eV
-
-------------------
Tau neutrinos < 18,000,000 eV
-
- 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.
-
- 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.
-
------------------------------
The
history of neutrinos:
-
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.
-
- 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.
-
-------------------------------------------------------------
- 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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