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History
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The Institute for Cosmic Ray Research (ICRR), University
of Tokyo, conducts observations and studies of cosmic rays
in various aspects.
 
The forerunner was the Asahi hut on Mt.Norikura built in 1650
with the Asahi (newspaper) Bounty for Science. This hut developed
into the Cosmic Ray Observatory of University of Tokyo in 1953.
This observatory was the first institution for the whole Japan
collaboration.
As early as 1956,
the Cosmic Ray Observatory participated in IGY (International
Geophysical Year), and set about international activities. In
the same year, it started observation of air showers, and in
1958 it also started detailed observation of cosmic rays using
emulsion chambers. For a quite while after that, steady observations
using these detectors continued.
In 1972,
the construction of MUTRON (electromagnet spectrometer) began,
and general experimental equipments and facilities were getting
prepared. In 1973, two international research projects, which
had belonged to the Japan Society for the Promotion of Science,
were absorbed into the work of the Observatory. One of the two
was the deep underground experiment at the Kolar Gold Mine in
India, and the other is the high mountain experiment at Mt.Chacaltaya
in Bolivia. In 1975, MUTRON was completed, and then the construction
of the Akeno Observatory was started.
In 1976,
Cosmic Ray Observatory was renamed to Institute for Cosmic Ray
Research, University of Tokyo. At the same time, three cosmic
ray divisions in Institute for Nuclear Study, University of
Tokyo, which had engaged in similar researches as those in ICRR
were transferred to ICRR. In total, the new ICRR had six divisions
plus one attached institution. In 1977, the Akeno Observatory
became the second attached institution officially, and in 1979
the 1 square km air shower detector at Akeno and the emulsion
chamber at Mt.Fuji were ready. In 1981 the Japan-China collaboration
on experiments using emulsion chambers came into existence.
In 1983, the experiment of proton decay search started at Kamioka
as a collaboration with other universities, and also the facilities
for the study of primary cosmic rays were prepared.
In the latter
half of 1980s' and the succeeding years, big
experimental results became yielded, and further expansion and
improvement of the experimental facilities came to be made.
In 1987, the neutrinos from a supernova were detected at Kamioka
for the first time in the world. In the same year, the construction
of the 100 square km wide area air shower detector was started.
In 1988, the deficit of the solar neutrinos was observed at
Kamioka, and in 1989 the very large increase of solar neutrons
accompanied with a solar flare was observed at Norikura. In
1900, the the wide area air shower detector was accomplished.
In 1901, the construction of Super-Kamiokande was commenced.
In 1902, as a product of the collaboration in Australia, very
high energy gamma rays from an astronomical source were observed
for the first time in the southern hemisphere, and the observation
group of gravitational wave was newly added to ICRR. In 1993,
the construction of detector for air shower gamma rays was started
in Tibet. In 1994, a most energetic air shower, which was not
considered to exist theoretically, was observed at Akeno. At
Kamioka, an anormalous flux of the atmospheric neutrinos was
measured. In 1995, the Kamioka Observatory restarted as the
third attached institution. In 1996, the Super-Kamiokande was
completed and the full operation began. Then as a result of
two-year observation, the discovery that neutrinoes have masses
was announced in 1998.
From 1999,
to investigate more details of neutrino masses, the long base
line neutrino experiment started, in which artificial neutrinos
ejected from KEK (High Energy Accelerator Research Organization)
down to Super-Kamiokande were examined. Moreover, to merge a
variety of the observational information and explore a new way
of the neutrino study, Research Center for Cosmic Neutrinos
was established. Also substantial fund from the Japan Grant-in-aid
for Scientific Research was approved to realize a major improvement
of the very high energy gamma ray observation in Australia.
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