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On September 23, 2001, in Caen, France, the "Grand Accélérateur
National d'Ions Lourds" (heavy ion accelerator) delivered its first
beam of exotic ions when Spiral*, the new system of production
and acceleration, was put into operation. These particle beams will allow
scientists to understand the laws governing the structure and behavior
of matter at the level of the nucleus of the atom. GANIL, a laboratory
managed jointly by the CEA (French Atomic Energy Commission) and the CNRS,
can now offer the international community an exceptional resource to explore
fields of investigation of nuclear matter previously inaccessible.
The atomic nuclei found on
Earth represent only a small percentage of those to be found in the Cosmos.
The lifetimes of some of them, known as exotic nuclei, are so brief that
they cannot be found on Earth. However, using accelerators, they can be
produced artificially.
The study of exotic nuclei is essential in many fields of nuclear physics,
as well as in astrophysics, where they are used to model stars, supernova,
X-flares and all the cosmic cauldrons where the elements were created.
Exotic nuclei today constitute a vast terra incognita, and research on
them will certainly allow scientists to discover new nuclear phenomena.
The project for a new machine, Spiral, was launched in 1993 to further
study of exotic nuclei. On September 23, 2001, Spiral produced its first
beam of exotic nuclei. It was composed of Neon 18 ions, which do not exist
on Earth and which have a lifetime of 1.5 seconds. They were produced
by bombarding a carbon target with a beam of Neon 20 stable ions accelerated
to 1.9 billion electron-volts. In this first attempt, a beam of 100,000
ions per second was accelerated, and this figure should be multiplied
by ten in the days to come. The first experiment will take place today.
It will establish the spectroscopy of Sodium 19, a nucleus that is unknown
on Earth. Twelve laboratories — five European, one American and six
French — will be collaborating on the experiment.
In comparison to the work already undertaken by the Nuclear Physics Laboratory
of the University of Louvain-la-Neuve (Belgium), the Spiral facility considerably
extends both the range of exotic elements produced and the domain of accessible
energy.
The new beams produced by Spiral, together with equipment that is already
in place or under construction, make it a unique resource in Europe. The
Spiral project was funded with a total investment of FRF 120 million.
This sum was contributed in equal amounts by the CEA, the CNRS and the
administration of the Basse Normandie region.
* Spiral:
Radioactive ion beam facility at GANIL (Système de Production
d'Ions Radioactifs Accélérés en Ligne).
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How
is a beam of Neon 18 exotic nuclei produced?
When a carbon target is bombarded with a beam of Neon 20 ions,
a beam of stable ions accelerated to 1.9 billion electron-volts,
a small proportion of the nuclei breaks on the carbon nuclei. Among
the resulting fragments, an even smaller proportion is comprised
of Neon 18. These "exotic" nuclei, trapped in the form
of neutral atoms within the target, are extracted by heating, then
ionized in an ion source. Finally, the Neon 18 nuclei are injected
and accelerated in a new cyclotron, Cime, to the selected energy
of 126 million electron-volts. The Spiral facility is made up of
all the equipment mentioned here.
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IN2P3 contact:
Geneviève Edelheit
Tel: +33 1 44 96 47 60
e-mail: edelheit@admin.in2p3.fr
CNRS press
contact:
Martine Hasler
Tel : +33 1 44 96 46 35
e-mail : martine.hasler@cnrs-dir.fr
CEA press contact:
Corinne Borel
Tel: +33 1 40 56 18 35
e-mail: corinne.borel@cea.fr
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