THE SOURCES OF NEUTRINOS
(five sources and three rivers)
The neutrinos in the universe come from weak interactions
(like beta decays in atomic nuclei). Three rivers can be distinguished:
the neutrinos from space, the neutrinos from the earth, the neutrinos
from mankind activity.
But there are many types of neutrinos origins, which can be quite
arbitrarily classified in five sources:
They come along with the process of thermonuclear fusion inside the stars
(our sun or any other star in the universe).
Their energy is quite weak
(some MeV) and they can travel in a long and quite way.
They come from different nuclear reactions
whose main reaction (85% of the solar neutrinos come from it) is:
p is a proton, H is a deuterium nucleus, e is an anti-electron and the last one
is a neutrino.
Depending on the
nuclear reaction concerned, the neutrino has not the same energy.
Neutrinos from mankind activity
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
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 5 1020 neutrinos per second) and their energy
is around 4 MeV. They have been the first to be detected and the first to be used to put
some limits on the neutrino oscillation.
Neutrinos from the earth
Our great old planet has kept since its birth many radioactive atomic nuclei.
This is what we call "natural radioactivity". This radioactivity is quite important,
badly known and its main contribution could be to keep in fusion the
matter under the crust of 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. Under the same
principle which guides the neutrinos production at CERN, some neutrinos are created:
they are called "atmospheric neutrinos". Some experiments like Kamiokande and Super-Kamiomande
in Japan have tried to see the oscillations of the neutrinos inside those particle showers.
The results in 1998 seem positive.
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
that no experiment, even very huge, has been able to detect them.
Some other neutrinos could come from very cataclysmic phemomena like
explosions of supernovae or neutron stars coalescences.
They are not only pure theoretical speculations since
in 1987 a supernovae
exploded in the Magellan clouds,
150.000 light-years from our earth and... its neutrinos were detected!!
shows the rest of the star which exploded in 1987.
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Last update: 26/06/1999 : http://wwwlapp.in2p3.fr/neutrinos/ansources.html