Neutrinos: Little Neutrons. Not!

1
Neutrinos Little Neutrons. Not!
2
Discovery of Radioactivity

• In 1895 Roentgen discovered that when electrons
  accelerated by very high voltages struck hard
  surfaces, any photographic plate in the vicinity
  would get exposed and fluorescent materials in
  the region around would glow. Roentgen thus
  concluded that some radiation was being emitted
  and called it X-rays.
• Radiograph made by roentgen in 1895 of his wifes
  hand
• For this discovery, he receives the first physics
  Nobel price in 1901.
• Today, those "X rays" are well known to be a
  particular type of light, that is photons of high
  energy
• Others (Bequerel and Rutherford) discover that
  uranium emits a kind of radiation called alpha
  and beta rays.

3
Beta Decay

• In certain types of radioactive decay, an
  electron or positron is emitted. The electron
  (or positron) was referred to as a beta
  particle before people knew what it was, and this
  type of process is referred to as beta decay
• Example Copper decaying to nickel
• When this decay was first studied, it looked like
  one particle (the copper atom) decayed to just 2
  other particles the nickel and the positron.
• If this were the case, then the positron would
  have a very distinct energy. But when it is
  measured, the positron energy varies over a large
  range.
• This is not possible if energy and momentum are
  to be conserved!
• http//hyperphysics.phy-astr.gsu.edu/hbase/nuclear
  /beta.html

4
Pauli neutrino

• Wolfgang Pauli came up with a solution to save
  Conservation of Energy he proposed a completely
  new particle, which as far as he knew, didnt
  exist!
• He was so unsure of this that he didnt even name
  his own particle.
• Enrico Fermi named it the Neutrino (little
  neutral one)

Dear Radioactive Ladies and Gentlemen, .., how
because of the "wrong" statistics of the N and
Li6 nuclei and the continuous beta spectrum, I
have hit upon a desperate remedy to save the
"exchange theorem" of statistics and the law of
conservation of energy. Namely, the possibility
that there could exist in the nuclei electrically
neutral particles, that I wish to call neutrons,
.I agree that my remedy could seem incredible
because one should have seen these neutrons much
earlier if they really exist.
http//www.ethbib.ethz.ch/exhibit/pauli/neutrino_e
.html
5
How to Find Neutrinos?

• Although Paulis neutrino was a good solution, no
  one knew if it was the right solution!
• The big problem is that neutrinos are very weakly
  interacting
• A neutrino would not notice a lead barrier 50
  light-years thick!
• But physicists started incorporating the neutrino
  into their calculations
• In 1945, the first atomic bomb explodes. Despite
  of the horror it inspires, it is for the
  physicists a remarkable powerful source of
  neutrinos (assuming they exist).
• Frederick Reines, who is working at Los Alamos,
  speaks to Fermi in 1951 about his project to
  place a neutrino detector near an atomic
  explosion.

http//wwwlapp.in2p3.fr/neutrinos/anhistory.html
6
Reines Cowan

• In 1952, Reines and Clyde Cowan decide to use a
  more peaceful source of neutrinos the nuclear
  plant of Hanford, Washington.
• They use a target made of around 400 liters of a
  mixture of water and cadmium chloride.
• The anti-neutrino coming from the nuclear reactor
  interacts with a proton of the target matter,
  making a positron and a neutron.
• The positron annihilates with an electron of the
  surrounding material, giving two simultaneous
  photons
• the neutron slows down until it is eventually
  captured by a cadmium nucleus, implying the
  emission of photons some 15 microseconds after
  those of the positron annihilation.
• All those photons are detected and the 15
  microseconds identify the neutrino interaction.
• The neutrino is detected in 1956!

Reines receives Nobel prize in 1995
7
Observation of neutrinos

• http//hyperphysics.phy-astr.gsu.edu/hbase/particl
  es/cowan.html

8
What other kinds of neutrinos are there?

• It turns out that Reines and Cowan discovered the
  anti-electron-neutrino.
• The electron-neutrino is discovered in 1957 by
  Goldhaber, Grodzins and Sunyar
• Muon neutrinos are discovered in 1962 by Leon
  Lederman, Mel Schwartz, Jack Steinberger and
  colleagues at Brookhaven National Laboratories
  and it is confirmed that they are different from
  electron neutrinos
• The tau lepton is discovered by Martin Perl and
  colleagues at SLAC in Stanford, California. 
  After several years, analysis of tau decay modes
  leads to the conclusion that tau is accompanied 
  by its own tau neutrino
• As far as we know, there are only these 3
  neutrinos.

9
The mass of the neutrinos

• As each neutrino was discovered, physicists tried
  to measure their mass.
• But they only got so far as to say they are very
  very light
• In fact, the Standard Model which describes all
  of the fundamental particles has the neutrinos as
  having ZERO mass
• An important implication if neutrinos are
  massless, then they MUST travel at the speed of
  light!
• (Keep this in mind it will become important
  later!)

10
Neutrino sources

• Solar neutrinos From the process of
  thermonuclear fusion inside a star. Also
  produced copiously by supernovae. Our sun
  produces about 2x1038 per second total.
• Neutrinos from nuclear reactors and
  accelerators A standard nuclear power plant
  radiates about 5x 1020 neutrinos per second) and
  their energy is around 4 MeV.
• Neutrinos from natural radioactivity on the
  earth The power coming from this natural
  radioactivity is estimated at about 20,000 Giga
  Watts (about 20,000 nuclear plants!) and the
  neutrinos coming from this radioactivity are
  numerous about 6 millions per second and per
  cm2.
• Neutrinos from cosmic rays When a cosmic ray
  (proton coming from somewhere in space)
  penetrates the atmosphere, it interacts with an
  atomic nucleus and this generates a particles
  shower. They are called "atmospheric
  neutrinos".
• Neutrinos from the Big-Bang The "standard"
  model of the Big-Bang predicts, like for the
  photons, a cosmic background of neutrinos. There
  are about 330 neutrinos per cm3. But their energy
  is theoretically so little (about 0.0004 eV),
  that no experiment, even very huge, has been able
  to detect them.

http//wwwlapp.in2p3.fr/neutrinos/ansources.html
11
Importance of Neutrinos

• In the universe, there are
• about 1 billion photons per cubic meter
• About 100 million per cubic meter of neutrinos of
  each type (electron,muon, tau), or 300 million
  total
• About 0.5 protons per cubic meter

12
Solar Fusion

• The evidence is strong that the overall reaction
  is "burning" hydrogen to make helium
• 4H 2 e --gt 4He 2 neutrinos 6 photons
• Why do we think that this is what goes on?
• Energy output of millions of eV per reaction is
  needed if the Sun has been producing energy at
  the observed rate over billions of years.
• The reactions exist. (They have been studied in
  the laboratory.)
• There is a consistent step-by-step theory for the
  reaction.

http//ideaplace.org/Why/FusionE.html
13
Solar Neutrinos

• We know how many of these reactions happen per
  second in the Sun because we know how much energy
  each reaction releases and we know the solar
  luminosity. Thus we know how many neutrinos the
  Sun is producing per second about 2x1038
• Then we can calculate how many neutrinos are
  arriving at Earth. The answer is about 1014 per
  square meter per second - all moving away from
  the Sun at the speed of light.
• Wait one second a thousand trillion solar
  neutrinos just went through your body! Ouch!

http//zebu.uoregon.edu/soper/Sun/solarneutrinos.
html
14
Homestake Gold Mine

• Ray Davis decides to see neutrinoes from the
  sun.
• To do this he filled a huge vat with cleaning
  fluid. I am not making this up!
• The pioneering experiment in this direction was
  performed deep in the Homestake Gold Mine in
  South Dakota starting in the early 1970's. The
  experiment is deep underground to protect it from
  high energy particles from outer space called
  cosmic rays. The detection method was based on
  the reaction
• 37Cl neutrino --gt 37Ar electron.
• Chlorine, Cl has 17 protons while argon, Ar has
  18 protons. Thus one neutron got converted into a
  proton.
• After a few days, the argon decays back to
  chlorine
• 37Ar --gt 37Cl neutrino antielectron .
• Result About 1/3 of the expected number of
  reactions occurred.
• http//zebu.uoregon.edu/soper/Sun/solarneutrinos.
  html

15
Kamiokande

• Masatoshi Koshiba followed up on the measurements
  made by Ray Davis by developing a large
  water-filled detector, called Kamiokande, in a
  Japanese mine. Kamiokande was direction sensitive
  and could confirm Davis' discovery that neutrinos
  came from the sun. The Kamiokande water tank was
  lined with photomultipliers. When neutrinos enter
  the tank, they can interact with electrons. These
  produce flashes of light, which are registered by
  the photomultipliers.
• Result Neutrino reactions detected, but not as
  many as expected based on the theoretical
  calculations.
• But Kamiokande also saw something else even more
  surprising!

http//www.nobel.se/physics/laureates/2002/illpres
/kamiokande.html
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Seeing a SuperNova with Neutrinos!

• Kamiokande was operating on 23 February 1987 and
  detected 12 neutrinos emitted by supernova 1987A
  when it exploded 170,000 light years from the
  earth the first clear observation of neutrinos
  produced outside our galaxy.
• If you were in a Jupiter-type orbit a billion
  kilometers from SN1987A when it exploded and were
  protected from the other effects of the
  supernova, you would be killed by the radiation
  damage from neutrinos streaming through your body
• SN1987A probably produced 1058 neutrinos
• Based on the number and energy of the neutrinos,
  the energy released by the SN was about 1053
  ergs/sec compared to sun 1033 erg/sec
• But the neutrinos dont all arrive at the same
  time!

• Based on the direction, they came from Large
  Megellenic cloud

17
1987 all growed up!
18
Atmospheric neutrinos

• Kamiokande, and other experiments like it (like
  IMB) also looked for atmospheric neutrinos,
  which come from cosmic rays not the sun.
• All of these experiments looked for electron
  neutrinos, and muon neutrinos.
• Problem they did not see as many muon neutrinos
  as expected this is the anomaly
• When physicists have a problem like this, there
  is only one thing to do build a bigger
  experiment!
• And give it a snappy name SuperK!

19
SuperKamioka

• In 1990, in order to make more progress int hese
  fields of research, construction was started on
  the 50,000 ton water Cerenkov detector,
  Super-Kamiokande (Super-KAMIOKA Nucleon Decay
  Experiment or Neutrino Detection Experiment).
  Super-Kamiokande is bigger and has greater
  photocathode coverage than Kamiokande.
  Construction was completed in 1995 and
  observation began in April of 1996.

20
SuperK Event

• 481 MeV muon neutrino (MC) produces 394 MeV muon
  which later decays at rest into 52 MeV electron.
• Size of PMT corresponds to amount of light seen
  by the PMT. PMTs are drawn as a flat squares even
  though in reality they look more like huge
  flattened golden light bulbs.

muon
Muon neutrino
electron
http//www.ps.uci.edu/tomba/sk/tscan/pictures.htm
l
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Events point at the sun

• Super-K detects Boron-8 neutrinos when they
  scatter off of atomic electrons in the water. The
  recoil electron direction is oriented along the
  direction of neutrino travel (as in the banner at
  the top of this page). The electron makes a weak
  Cherenkov ring in the detector- only 40-50 PMT
  hits are expected for a 8 MeV electron (in a
  narrow time window, shown as bright green hits in
  this event display). At this low energy, there is
  considerable random background, mostly from radon
  gas in the water. So we count solar neutrinos by
  making an angular distribution with respect to
  the sun's known direction. This is shown if the
  figure below the sharp peak near cosine equals
  one is due to solar neutrinos. The area under the
  peak, after subtracting background, is the
  measured number of solar neutrinos.
• http//hep.bu.edu/superk/solar.html

Pointing at sun
Pointing away from sun
22
SuperKamioka

• Only(!) 500 days worth of data was needed to
  produce this "neutrino image" of the Sun, using
  Super-K to detect the neutrinos from nuclear
  fusion in the solar interior. Centered on the
  Sun's postion, the picture covers a significant
  fraction of the sky (90x90 degrees in R.A. and
  Dec.). Brighter colors represent a larger flux of
  neutrinos.
• The little blue dot is what the size of the sun
  would look like in the visible spectrum (using
  photons)
• http//antwrp.gsfc.nasa.gov/apod/ap980605.html

• Credit R. Svoboda and K. Gordan (LSU) Jun 5,
  1998

23
What else did SuperK do with Neutrinos?

• Also looked at Atmospheric Neutrinos
• Predictions exist for how many they should see
• SuperK discovered a deficit in muon neutrinos!
  They disappeared!
• And discovered that muon neutrinos which come
  upward (through the earth) are more likely to
  disappear. Hmmm
• Disappear is not quite right they oscillate
  into something else an electron neutrino!
• This can only happen if neutrinos have Mass!

24
Clinton on Neutrinos

• We must help you to ensure that America
  continues to lead the revolution in science and
  technology. Growth is a prerequisite for
  opportunity, and scientific research is a basic
  prerequisite for growth. Just yesterday in Japan,
  physicists announced a discovery that tiny
  neutrinos have mass. Now, that may not mean much
  to most Americans, but it may change our most
  fundamental theories -- from the nature of the
  smallest subatomic particles to how the universe
  itself works, and indeed how it expands.
• This discovery was made, in Japan, yes, but it
  had the support of the investment of the U.S.
  Department of Energy. This discovery calls into
  question the decision made in Washington a couple
  of years ago to disband the Super-conducting
  Supercollider, and it reaffirms the importance of
  the work now being done at the Fermi National
  Acceleration Facility in Illinois.
• The larger issue is that these kinds of findings
  have implications that are not limited to the
  laboratory. They affect the whole of society --
  not only our economy, but our very view of life,
  our understanding of our relations with others,
  and our place in time.

25
Meanwhile

• BATAVIA, IL--President Bush met with members of
  the Fermi National Accelerator Laboratory
  research team Monday to discuss a mathematical
  error he recently discovered in the famed
  laboratory's "Improved Determination Of Tau
  Lepton Paths From Inclusive Semileptonic B-Meson
  Decays" report.           "I'm somewhat out of
  my depth here," said Bush, a longtime Fermilab
  follower

• Above Bush shows Fermilab scientists where they
  went wrong in their calculations.

26
Are Neutrinos Dark Matter?

• Neutrinos dont shine. And now we know they
  have mass. And there sure are a lot of them.
  Dark Matter!?
• This mass difference, coupled with absolute
  neutrino mass measurements and the Kamiokande's
  measurements, indicates that the combined mass of
  all the neutrinos in the universe is about equal
  to the combined mass of all the visible stars.
  That means neutrinos cannot account for all the
  "dark matter" known to make up most of the mass
  of the universe.

27
Summary

• What we know
• There are 3 light neutrinos
• The sun is a copious source of neutrinos
• Supernovae produce a lot of neutrinos
• Neutrinos have mass
• What we dont know
• What are the masses of the 3 neutrinos reallY?
• How do we find out?
• Would be great if there was a way to control the
  neutrinos to study them in more detail
• But wait! There is! Fermilab can make a lot of
  neutrinos too!

28
Making a Beam of Neutrinos
120 GeV protons hit target (1020/Protons per
year!) p (pions) produced at wide range of
angles Magnetic horns to focus p p decay
to mn in long evacuated pipe Left-over
hadrons shower in hadron absorber Rock
shield ranges out m n beam travels
through earth to experiment
But the experiment is hundreds of miles
away!
29
Numi-MINOS from the Air
NUMI Neutrinos at the Main Injector MINOS Main
Injector Neutrino Oscillation Search
So the neutrinos start out at Fermilab, and are
aimed through the earth at Minnesota. Why
Minnesota?
30
MINOS Experiment
Two Detector NeutrinoOscillation
Experiment(Start 2004)
Near Detector 980 tons
Far Detector 5400 tons
31
Beam and Near Detector

• Tunneling completed
• Detector elements built
• Installation starts later this year
• First beam December 2004

Decay tunnel before installation of decay pipe
Near detector hall
32
The Far Detector
33
Minos Plans

• The basic plan of MINOS is to use the controlled
  source of neutrinos from Fermilab to really show
  that muon neutrinos can oscillate into electron
  neutrinos
• Compare interactions in the near detector with
  the far detector
• Both detectors will be able to determine the type
  of neutrinos
• Basic measurement the mass difference between
  the two neutrinos (not the actual masses)
• Will the experiment soar to great heights?
• Or will it come crashing down to earth?

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35

• Solar neutrinos are produced by the nuclear
  reactions that power the Sun. The fusion of
  proton plus proton (pp) to deuterium plus
  positron plus neutrino is responsible for 98 of
  the energy production of the sun. Therefore these
  pp-neutrinos are the most plentiful, and the most
  reliably estimated. About 60 billion pp-neutrinos
  pass through a square centimeter at the Earth
  each second. They are relatively low energy,
  however, with a continuous spectrum that ends at
  420 keV. In addition, there are several rarer
  reactions which also produce neutrinos. The
  electron capture on Beryllium-7 produces a sharp
  line of Beryllium-7 neutrinos at 861 keV. A small
  fraction of the time, Beryllium-7 captures a
  proton instead of an electron, to form Boron-8.
  The beta decay of Boron-8
• 8B -gt 8Be e nu_e
• produces a continuous spectrum of neutrino
  energies that extends to 15 MeV. Super-K is
  sensitive to these rare but high energy Boron-8
  neutrinos.        Super-K detects Boron-8
  neutrinos when they scatter off of atomic
  electrons in the water. The recoil electron
  direction is oriented along the direction of
  neutrino travel (as in the banner at the top of
  this page). The electron makes a weak Cherenkov
  ring in the detector- only 40-50 PMT hits are
  expected for a 8 MeV electron (in a narrow time
  window, shown as bright green hits in this event
  display). At this low energy, there is
  considerable random background, mostly from radon
  gas in the water. So we count solar neutrinos by
  making an angular distribution with respect to
  the sun's known direction. This is shown if the
  figure below the sharp peak near cosine equals
  one is due to solar neutrinos. The area under the
  peak, after subtracting background, is the
  measured number of solar neutrinos.
• http//hep.bu.edu/superk/solar.html

36
Did Kamioka See the Sun?
37
That bright thing in the sky!
38
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Kamioka

• Brief History
• Kamioka Underground Observatory, the predecessor
  of the present Kamioka Observatory, Institute for
  Cosmic Ray Reserch, University of Tokyo, was
  established in 1983. The original purpose of this
  observatory was to verify the Grand Unified
  Theories, one of the most impenetrable matters of
  elementary particle physics, through a Nucleon
  Decay Experiment. Thus, the water Cerenkov
  detector which was used for this experiment was
  named Kamiokande (KAMIOKA Nucleon Decay
  Experiment).
• The 4,500 ton water Cerenkov detector was placed
  at 1,000 m underground of Mozumi Mine of the
  Kamioka Mining and Smelting Co. located in
  Kamioka-cho, Gifu, Japan. The original purpose of
  Kamiokande was to investigate the stability of
  matter, one of the most fundamental questions of
  elementary particle physics. An upgrade of
  Kamiokande was started in 1985 to observe
  particles called neutrino (Solar, Atmospheric and
  other neutrinos) which come from astrophysical
  sources and cosmic ray interactions. As a result
  of this upgrade, the detector had become highly
  sensitive. In February, 1987,Kamiokande had
  succeeded in detecting neutrinos from a supernova
  explosion which occurred in the Large Magellanic
  Cloud. Solar neutrinos were detected in 1988
  adding to the advancements in neutrino astronomy
  and neutrino astrophysics.
• In 1996, Kamioka Observatory which belongs to the
  Institute for Cosmic Ray Research(ICRR),
  University of Tokyo was established. Kamiokande
  had been world famous for its achievements on the
  observation of supernova neutrinos, solar
  neutrinos and atmospheric neutrinos and also the
  study of the Grand Unified Theories of particles.
  In 1990, in order to make more progress int hese
  fields of research, construction was started on
  the 50,000 ton water Cerenkov detector,
  Super-Kamiokande (Super-KAMIOKA Nucleon Decay
  Experiment or Neutrino Detection Experiment).
  Super-Kamiokande is bigger and has greater
  photocathode coverage than Kamiokande.
  Construction was completed in 1995 and
  observation began in April of 1996.

40
Neutrino sources

• Solar neutrinos From the process of
  thermonuclear fusion inside the stars (our sun or
  any other star in the universe).
• Some other neutrinos could come from very
  cataclysmic phemomena like explosions of
  supernovae or neutron stars coalescences.
• Neutrinos from nuclear reactors and accelerators
  These are high energy neutrinos produced by the
  particles accelerators and low energy neutrinos
  coming out of nuclear reactors. The first ones,
  whose energy can reach about 100 GeV, are
  produced to study the structure of the nucleons
  (protons and neutrons composing the atomic
  nuclei) and to study the weak interaction. The
  second ones are here although we did not ask for
  them. They are an abundant product made by the
  nuclear reactions inside the reactors cores (a
  standard nuclear plant radiate about 5x 1020
  neutrinos per second) and their energy is around
  4 MeV. Neutrinos from natural radioactivity on
  the earth The power coming from this natural
  radioactivity is estimated at about 20.000 Giga
  Watts (about 20.000 nuclear plants!) and the
  neutrinos coming from this radioactivity are
  numerous about 6 millions per second and per
  cm2. But those neutrinos, despite of their
  quantity, are often locally drowned in the oceans
  of neutrinos coming from the nuclear plants.
  Neutrinos from cosmic rays When a cosmic ray
  (proton coming from somewhere in space)
  penetrates the atmosphere, it interacts with an
  atomic nucleus and this generates a particles
  shower. They are called "atmospheric
  neutrinos".
• Neutrinos from the Big-Bang The "standard"
  model of the Big-Bang predicts, like for the
  photons, a cosmic background of neutrinos. Those
  neutrinos, nobody has never seen them. They are
  yet very numerous about 330 neutrinos per cm3.
  But their energy is theoretically so little
  (about 0.0004 eV), that no experiment, even very
  huge, has been able to detect them.
  http//wwwlapp.in2p3.fr/neutrinos/ansources.html

41
Timeline

• A NEUTRINO TIMELINE
• The following is a short history of neutrinos as
  it relates to neutrino oscillation studies.
• 1920-1927 Charles Drummond Ellis (along with
  James Chadwick and colleagues) establishes
  clearly that the beta decay spectrum is really
  continuous, ending all controversies.
• 1930 Wolfgang Pauli hypothesizes the existence of
  neutrinos to account for the beta decay energy
  conservation crisis.
• 1932 James Chadwick discovers the neutron.
• 1933 Enrico Fermi writes down the correct theory
  for beta decay, incorporating the neutrino.
• 1946 Shoichi Sakata and Takesi Inoue propose the
  pi-mu scheme with a neutrino to accompany muon.
• 1956 Fred Reines and Clyde Cowan discover
  (electron anti-) neutrinos using a nuclear
  reactor.
• 1957 Neutrinos found to be left handed by
  Goldhaber, Grodzins and Sunyar.
• 1957 Bruno Pontecorvo proposes neutrino-antineutri
  no oscillations analogously to K0-K0bar, this is
  the first time neutrino oscillations (of some
  sort) are hypothesized.
• 1962 Ziro Maki, Masami Nakagawa and Sakata
  introduce neutrino flavor mixing and flavor
  oscillations.
• 1962 Muon neutrinos are discovered by Leon
  Lederman, Mel Schwartz, Jack Steinberger and
  colleagues at Brookhaven National Laboratories
  and it is confirmed that they are different from
  electron neutrinos.
• 1964 John Bahcall and Ray Davis discuss the
  feasibility of measuring neutrinos from the sun.
• 1965 The first natural neutrinos are observed by
  Reines and colleagues in a gold mine in South
  Africa, and by Goku Menon and colleagues in Kolar
  gold fields in India, setting first astrophysical
  limits.
• 1968 Ray Davis and colleagues get first
  radiochemical solar neutrino results using
  cleaning fluid in the Homestake Mine in North
  Dakota, leading to the observed deficit now known
  as the "solar neutrino problem".
• 1976 The tau lepton is discovered by Martin Perl
  and colleagues at SLAC in Stanford, California. 
  After several years, analysis of tau decay modes
  leads to the conclusion that tau is accompanied 
  by its own neutrino, nutau, which is neither nue
  nor numu.
• 1980s The IMB, the first massive underground
  nucleon decay search instrument and neutrino
  detector is built in a 2000' deep Morton Salt
  mine near Cleveland, Ohio. The Kamioka experiment
  is built in a zinc mine in Japan.
• 1985 The "atmospheric neutrino anomaly" is
  observed by IMB and Kamiokande.
• 1986 Kamiokande group makes first directional
  counting observation solar of solar neutrinos and
  confirms deficit.

42

• It appears established beyond reasonable doubt,
  through the success of the standard solar model,
  that the sun shines from nuclear fusion in its
  core. A fusion reaction involves the merging of
  two atomic nuclei into one. In the sun, a chain
  of several different fusion reactions along any
  of about four different pathways, leads from four
  hydrogen nuclei (single protons) to one helium
  nucleus (two protons and two neutrons). In this
  process, two protons have to be converted into
  neutrons through beta decays. In each beta decay,
  a neutrino is emitted (an electron-flavored
  neutrino, that is). So it is straightforward to
  calculate that, if the sun shines through
  hydrogen fusion, it ought to emit two neutrinos
  per fusion chain. And in our standard theory of
  particle physics, the neutrinos will zip straight
  out from the sun, without interacting with the
  intervening material. The total flux of neutrinos
  from the sun ought to be some 200 000 000 000 000
  000 000 000 000 000 000 000 000 per second,
  corresponding to a flux of about 6.5 1010
  neutrinos per square centimeter per second
  hitting the earth.
• Most of those neutrinos come from the main
  energy-producing reaction chain in the sun
  proton-proton fusion. Unfortunately, the
  neutrinos from proton-proton (pp) fusion have a
  very low energy. Energy in this context in
  measured in electron-volts (1 eV 1.6 10-19
  Joule), or millions of electron-volts (MeV), and
  the energy of the pp neutrinos is less than 0.42
  MeV, making them difficult to detect.
• Smaller (but still enormous) numbers of
  higher-energy neutrinos are expected from various
  side reactions, notably boron and beryllium
  decays. There is also an alternative
  energy-producing chain, CNO-fusion, where the
  fusion of hydrogen to helium is catalyzed by
  carbon. This CNO-chain is expected to be the main
  energy source in larger, hotter stars, but it
  should only give a modest contribution in the
  sun. The CNO neutrinos are otherwise easier to
  detect than pp-neutrinos, having three to four
  times more energy each.
• Number of interactions/person/lifetime from solar
  neutrinos 1.
• http//www.talkorigins.org/faqs/faq-solar.html

43

• Most physicists and astronomers believe that the
  sun's heat is produced by thermonuclear reactions
  that fuse light elements into heavier ones,
  thereby converting mass into energy. To
  demonstrate the truth of this hypothesis,
  however, is still not easy, nearly 50 years after
  it was suggested by Sir Arthur Eddington. The
  difficulty is that the sun's thermonuclear
  furnace is deep in the interior, where it is
  hidden by an enormous mass of cooler material.
  Hence conventional astronomical instruments, even
  when placed in orbit above the earth, can do no
  more than record the particles, chiefly photons,
  emitted by the outermost layers of the sun.
• Of the particles released by the hypothetical
  thermonuclear reactions in the solar interior,
  only one species has the ability to penetrate
  from the center of the sun to the surface (a
  distance of some 400,000 miles) and escape into
  space the neutrino. This massless particle,
  which travels with the speed of light, is so
  unreactive that only one in every 100 billion
  created in the solar furnace is stopped or
  deflected on its flight to the sun's surface.
  Thus neutrinos offer us the possibility of
  seeing'' into the solar interior because they
  alone escape directly into space. About 3 percent
  of the total energy radiated by the sun is in the
  form of neutrinos. The flux of solar neutrinos at
  the earth's surface is on the order of 1011 per
  square centimeter per second. Unfortunately the
  fact that neutrinos escape so easily from the sun
  implies that they are difficult to capture.

44

• Neutrinos were first suggested as hypothetical
  entities in 1931 after it was noted that small
  amounts of mass seemingly vanish in the
  radioactive decay of certain nuclei. Wolfgang
  Pauli suggested that the mass was spirited away
  in the form of energy by massless particles, for
  which Enrico Fermi proposed the name neutrino
  (little neutral one''). Fermi also provided a
  quantitative theory of processes involving
  neutrinos. In 1956 Frederick Reines and Clyde L.
  Cowan, Jr., succeeded in detecting neutrinos by
  installing an elaborate apparatus near a large
  nuclear reactor. Such a reactor emits a
  prodigious flux of antineutrinos produced by the
  radioactive decay of fission products. For
  purposes of demonstrating a particle's existence,
  of course, an antiparticle is as good as a
  particle.
• In the late 1930's Hans A. Bethe of Cornell
  University followed up Eddington's 1920
  suggestion of the nuclear origin of the sun's
  energy and outlined how the fusion of atomic
  nuclei might enable the sun and other stars to
  shine for the billions of years required by the
  age of meteorites and terrestrial rocks. Since
  the 1930's the birth, evolution and death of
  stars have been widely studied. It is generally
  assumed that the original main constituent of the
  universe was hydrogen. Under certain conditions
  hydrogen atoms presumably assemble into clouds,
  or protostars, dense enough to contract by their
  own gravitational force. The contraction
  continues until the pressure and temperature at
  the center of the protostar ignite thermonuclear
  reactions in which hydrogen nuclei combine to
  form helium nuclei. After most of the hydrogen
  has been consumed, the star contracts again
  gravitationally until its center becomes hot
  enough to fuse helium nuclei into still heavier
  elements. The process of fuel exhaustion and
  contraction continues through a number of cycles.
  
• The sun is thought to be in the first stage of
  nuclear burning. In this stage four hydrogen
  nuclei (protons) are fused to create a helium
  nucleus, consisting of two protons and two
  neutrons. In the process two positive charges
  (originally carried by two of the four protons)
  emerge as two positive electrons (antiparticles
  of the familiar electron). The fusion also
  releases two neutrinos and some excess energy,
  about 25 million electron volts (MeV). This
  energy corresponds to the amount of mass lost in
  the overall reaction, which is to say that a
  helium nucleus and two electrons weigh slightly
  less than four protons. The 25 MeV of energy so
  released appears as energy of motion in the gas
  of the solar furnace and as photons (particles of
  radiant energy). This energy ultimately diffuses
  to the surface of the sun and escapes in the form
  of sunlight and other radiation.