is the mass of the neutrino?
We do not
know today if the neutrino has a non-zero mass or
not. Recent results from experiments seem to indicate
that neutrinos do have a very small but non-zero
What is the flux of
neutrinos from the sun at the earth?
billion (6x1010) per second per
cm2. Only one in 1000 billion solar
neutrinos interact during the way through the
How many kinds of neutrinos
three kinds of light neutrinos, the electron neutrino
(n), the muon neutrino
(m) and the tau neutrino
(t). For every neutrino
there is also an antineutrino.
Who proposed the neutrino
Prize 1945) proposed the existence of the
neutrino in 1930. In nuclear beta-decay when a
nucleus increases its number of protons with one and
decreases its number of neutrons with one, a
negatively charged electron is emitted. Pauli
suggested that a neutral particle, the neutrino, must
be emitted together with the electron in order to
explain that the electron energy was not the same in
Why did it take so long to
detect the neutrino?
neutrino interacts only very weakly with matter and a
very large neutrino flux is needed in order to
register a neutrino interaction in an experiment.
Nuclear reactors that became available in the '50s
produce very high fluxes of neutrinos, of the order
of 1015 per second per cm2, and
in 1955 the neutrino was detected in an experiment by
F. Reines (Nobel Prize 1995).
What is a neutron
Supernova explosion can result in either a neutron
star or a black hole. A neutron star is 1000 billion
times more dense than a normal star and consists of
closely packed neutrons. The neutron star has a
diameter of 10 - 15 km and a mass of several solar
normal light X-rays are electromagnetic waves but
with much shorter wavelength, in the range 0.01 - 1
nm (visible light typically 500 nm).
Why are X-rays called X-rays?
discovered, X-rays were very mysterious - one did not
know what they were. Therefore the name
How are X-rays
charged particles meet strong electromagnetic fields
X-ray photons can be emitted. Such fields exist close
to the atomic nuclei, and most X-ray sources are made
from electrons hitting a piece of metal. Magnets can
also have strong fields and charged particles passing
through a magnetic field can produce X-ray