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What's Cosmic Ray?
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Cosmic rays are nuclei and elementary particles always
falling very fast on the earth from the universe. Enormous
number of cosmic rays are passing through our bodies.
Galactic cosmic rays are expected to arrive at the
earth after traveling about 10 million years. They
plunge into the atmosphere and bring about nuclear reactions
with nuclei of oxygen and nitrogen in the air.
The extraterrestrial cosmic rays which come from outside
the earth are conventionally called primary
cosmic rays,
and newly produced paricles via the nuclear reactions
are called secondary cosmic rays.
What will turn out by studying cosmic rays?
Why we study cosmic rays is that a lot of information,
for instance on the origin of force working between substances
and on the structure of universe, are hidden there. The
former Minister of Education, Akito Arima, gave the following
word to the Kamioka group of this institute: "The
cosmic ray is a heavenly revelation." This
word shows the essence of the cosmic ray. The cosmic ray
is exactly a sign sent from the heaven, in which information
on a wide range of problems from the micro-world connected
with the root of substance to the macro-world of the universe
is packed.
Speaking historically, the elementary particle physics
itself was born from the observation of cosmic rays. For
quite a while after that, studies of elementary particles
have been carried out mainly using artificial accelerators,
but recently much hope is focused again on new observations
of cosmic rays using large fully high-tech detectors.
This institute, as the unique institute in the world
devoted only to the cosmic ray, keeps researches to repond
to such hope.
How to investigate cosmic rays?
There are various ways of investigating cosmic rays
depending on the object of the invesgation.
To investigate the primay cosmic rays directly,
we have to go to as high altitude as possible. We
go to high mountains, launch baloons, etc.
When an ultra-high energy primary cosmic ray enter
the atmosphere, electrons, gamma rays and muons
in the secondary particles fall on a wide area of
the surface like a shower. We call such a phenomenon
an air shower. To investigate the air shower
in a specified way, we sometimes go to a wide basin
with clean air. As it is difficult to select neutrinos
and high energy muons in the other background cosmic
rays, we go to the undergroud where the background
can not reach.
The researches in this institute cover all those
species of cosmic rays mentioned so far. |
In this institute, the gravitational wave possibly
coming from the universe is included in the research projects.
The gravitational wave is the distortion of space propagating
in the universe with the velocity of light, which is caused
when a massive object is put into motion. This is one
of the problems not verified yet among the Einstein's
predictions. To find very small distortions of space,
we maximize the detector sensitivity. Therfore the experiment
is done at a very calm place without trembles and vibrations.
By adding the study of the gravitational wave, the most
uninvestigated elementary particle, graviton, will be
lighted up, and the clarification of the mysteries of
substance and universe will be much progressed. |
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