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SOLAR NEUTRINOS
CAN ONLY BE SEEN
WITH A VERY LARGE
DETECTOR
THE HOMESTAKE EXPERIMENT
IN CONTEXT
KEY ASTRONOMER
Ray Davis (1914 –2006)BEFORE
1930 Austrian physicist
Wolfgang Pauli proposes
the existence of neutrinos.1939 Hans Bethe outlines
two main processes by which
stars obtain their energy.1956 American physicists
Clyde Cowan and Frederick
Reines confirm the existence
of the antineutrino, the
antiparticle of the neutrino.AFTER
1989 The Kamiokande II
experiment in Japan,
organized by Masatoshi
Koshiba, demonstrates
conclusively that the sun
is a source of neutrinos and
confirms Davis’s abnormally
low detection rate.D
uring the first half of the
20th century, scientists
figured out a process by
which the sun produces energy
by fusing hydrogen into helium.
In the sun’s core, four hydrogen
nuclei, which are single protons,
are changed into a helium nucleus,
two positrons (also called anti-
electrons), and two tiny ghostlike
particles called neutrinos, with
the release of energy. The neutrinos
produced were envisaged to escape
easily from the sun.Although this theory was accepted
by the 1950s, it was not proven. In
1955, an American chemist named
Ray Davis set out to show that the
sun produces energetic neutrinos
by detecting just a few of them. He
faced a huge problem in achieving
this goal, however. Apart from
the fact that their existence was
uncertain, scientists thought that
neutrinos had zero electric charge
and a tiny mass (if any at all), and
very rarely interacted with other
particles. If the sun fuses hydrogen,Neutrinos barely
interact with other
particles, but they may
interact in a form of
radioactive decay.The detection rate in
the interaction is likely
to be very low.If the sun obtains energy from nuclear fusion, fast-moving
low-mass particles called neutrinos should be produced.A very large detector is required.