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Neutrinos – mysterious Particles
Did you know, that the sun is blowing out huge amounts of
neutrinos permanently? On the earth, every second 100 billion
(100.000.000.000) neutrinos are passing through each area of one
square centimeter. Nuclear fusion is the energy source of the sun,
during these processes the many neutrinos are just a side-product. Most
neutrinos pass through the entire earth without any interaction, as well as they
pass unseen and unnoticed our bodies.
The gigantic neutrino observatory KAMIOKANDE in Japan managed to catch
200-500 neutrinos per year. They computed the originating direction of the
nightly detected neutrinos, which came from downwards – surprisingly, they
pointed downwards and towards the sun - they had passed the entire planet
earth!
KATRINs purpose is to measure the neutrino mass, right? I do not
understand, why we always talk about electrons!
Neutrinos are fleeting. After the tritium decay they just disappear – through any walls.
They cannot be catched or detected directly. The physicists can trap electrons much
easier than neutrinos. And they can draw conclusions from the energy of the electrons
to determine the mass of the neutrino. Thus they measure the neutrino mass indirectly by
measuring the energy of the electrons.
And how does this work?
Think of the released energy during the tritium decay as a cake. The electron and the neutrino
need to share this cake. Each particle needs a minimal amount of of energy to produce its mass.
The remaining part of the energy cake can be shared arbitrarily between both of them – this
becomes kinetic energy of the according particle. The larger the piece of cake, the faster will be
the speed of the particle after the decay.
Now imagine the electron grabs the largest possible piece of cake. This piece will always lack a
tiny piece – the energy piece, which is required to produce the mass of the neutrino.
And how do the physicists actually realize the measurement of the neutrino mass?
They measure very precisely the speed (=kinetic energy) of the electrons. It will always lack a tiny
piece of energy. This difference corresponds to the neutrino mass!
KATRIN – The Karlsruhe Tritium Neutrino Experiment
Neutrinos are the lightest known elementary particles; they are
electrical neutral and rarely interact with ordinary matter. There are
3 families/types of neutrinos. Neutrinos are produced in multiple
reactions, e.g. in nuclear fusion like inside of our sun. Scientists
tried to weigh the mass of the neutrino, however, no scale was precise enough
to date. So it is lighter than one part in a billion (10-9) the mass of a proton.
For this reason, scientists are currently building the KATRIN experiment on
the KIT site to measure the mass of the neutrino.
Our
Sun
p + p → 2H+ + e+ + νe
Thermonuclear FUSION inside the SUN
Two protons fusing together to a deuterium nucleus (by transforming a proton to a neutron while releasing a positron and a electron-neutrino).
Deuterium 2H+
Positron e+
Neutrino νe
Protons p
The sun seen in “neutrino light”
through the entire earth.
Simulation of Troels Haugboelle: Todays mass distribution of the universe;
Left: assuming neutrino mass 0;
Right: assuming neutrino mass
2.3 eV/c2;
resulting in different distributions.
During the Big Bang many neutrinos were
produced. They play a important role in the
structure development of our universe (filaments,
clusters, galxies), as they are so numerous,
although their mass is so tiny – for the past as well as for the
future.
1 square centimeter →
100.000.000.000 neutrinos per second
1 cm2
KAMIOKANDE (Japan):
Image of the sun in
“neutrino light”
Transport of the KATRIN main spectrometer vessel from Rhein harbour to the experiment hall on the KIT site
electron e-
neutrino νe
electron e-
decay
energy
Electron and neutrino share the energy,
both get kinetic energy.
Electron grabs maximum energy, all remaining energy needed for neutrino mass, no kinetic energy; electron has maximum speed.
e-
decay
energy
Neutrino mass 0 eV/c2
Neutrino mass 2.3 eV/c2
neutrino νe
Interesting facts:
The main spectrometer is the core of KATRIN; its diameter is 10 meter, its length 23 meter and its weight 200 tons.
Europe’s largest heavy-duty crane was necessary to lift it into the experiment hall.
2015 KIT Karlsruhe Institute of Technology Till.Bergmann@kit.edu, TillBergmann@web.de