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HOW DOES THE SUN SHINE?
NUCLEAR FUSION !
At 15 million degrees Celsius in the center of the star, fusion ignites !
4 (1H) --> 4He + 2 e+ + 2 neutrinos + energy
Where does the energy come from ? Mass of four 1H > Mass of one 4He
E = mc2
HOW MUCH ENERGY
4 (1H) --> 4He + 2 e+ + 2 neutrinos + energy
Energy released = 25 MeV = 4 x 10 -12 Joules = 1 x 10 -15 Calories
But the sun does this 1038 times a second ! Sun has 1056 H atoms to burn !
DO WE HAVE TO WORRY?
Sun has 1056 H atoms / 4 x 1038 times a second =
2.5 x 1017 second / 3 x 107 sec /year =
1010 years = 10 billion years
10 – 4.5 = 5.5 billion years left
NEUTRINOS FROM THE SUN ()
1017 photons/cm2/sec
Based on solar models, John Bahcall predicted that our Sun
puts out 1011 /cm2/sec
SOLAR FUSION: STEPS 1-3
SOLAR FUSION: STEPS 4-7
SOLAR FUSION: STEPS 8-11
RAY DAVIS HAD A PLAN…
to measure the neutrinos coming to Earth from the Sun and prove John Bahcall’s prediction
But how to detect such an elusive particle?
Go very deep and very large!
COSMIC RAYS ARE THE MAIN BACKGROUNDHigh energy protons and other particles from the Sun and from outside the solar system are constantly bombarding the top of the atmosphere , making cascades of muons, electrons, neutrinos and other particles.
SO RAY DAVIS WENT DEEP:to Homestake Mine
Ray Davis and John Bahcall at 4850’And he went large:
110,000 gallons of dry cleaning fluid
T
HOW HE DETECTED NEUTRINOS
Ray Davis was a chemist so he looked to nuclear chemistry for the answers:
-decay: 37Ar 37Cl + - + e
Davis looked for the inverse reaction:37Cl + e 37Ar (t1/2=35 d) + -
Davis ran He gas through the tank to purge out any gases and collected Ar in a charcoal filter. Then he looked for
THE INVESTIGATION After years of collecting
data, he found conclusively that the number of neutrinos was 1/3 that expected
No one believed him! Scientists everywhere thought they understood how the Sun worked and so the experiment had to be wrong
Davis stood by his data!
BUT WAS HE WRONG?Did scientists really understand
neutrinos? They assumed that the neutrinos from the Sun weren’t
changed by the journey The family of leptons is part of the Standard Model of
particle physics, and that model predicted neutrinos had zero mass
In the 1980s, Bruno Pontocorvo and others suggested that if neutrinos did have mass, they could ‘oscillate’ from one flavor to another. This might explain Davis’ results because his experiment was only sensitive to electron neutrinos.
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A SECOND GENERATION OF NEUTRINO EXPERIMENTS TOOK PLACE
In CanadaSNO
In JapansuperKamiokand
a50,000 tons H20
RAY DAVIS WAS PROVEN RIGHT
Neutrinos really do oscillate from one flavor to another John Bahcall was right in how the Sun works but 2/3 of the
electron neutrinos made in the Sun have changed flavor by time they get to Earth
Neutrinos do have mass and the Standard Model is wrong!
The Nobel Prize in Physics 2002"for pioneering contributions to astrophysics, in particular for the detection of cosmic neutrinos"
And Homestake Mine had its first scientific gold!
‘FIXING’ THE STANDARD MODEL
In order to refine the standard model, scientists need to understand more about neutrinos1. What is the mass ‘hierarchy’ of neutrinos, that
is which is the heaviest and which the lightest (actually measuring their absolute mass is probably impossible)
2. Are neutrinos their own antiparticles?3. What process leads to the mass of neutrinos?
Experiments are planned for the DUSEL Laboratory at Homestake to answer both
questions
MAJORANA: SEARCHING FOR 02 DECAY
