Introduction

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Accelerator description
•
A low-energetic ion beam with charge state 1+, the
ISOLDE beam, is produced by bombarding a target
with 1 GeV protons. A vast variety of ionic species are
created, and the desired one is selected in a selection
magnet.
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The beam is injected into the REXTRAP (a Penning
Trap), where the ions are bunched into groups of ~103107 and cooled, i.e. their thermal velocity is decreased.
Every 20 ms a cooled bunch is extracted from the REXTRAP, and transferred to the Electron Beam Ion Source
(EBIS). The REXEBIS acts as a charge-breeder, and
breeds the ions to q/A1/4.
•
After extraction the desired ions are separated from
contaminating ion species originating from residual gas
in the REXEBIS in a Mass Separator.
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Thereafter the ions are accelerated in a three stage
LINAC: first in a Radio Frequency Quadrupole
(RFQ) accelerator; then in an IH-structure and finally
in three 7-gap resonators. All resonators operate at
101.28 MHz with a duty factor of 10%. When leaving
the accelerators, the beam energy is variable between 0.8
and 2.2 MeV/u.
Accelerator description
•
The accelerated ions then collide with a Secondary
target, and the ions are excited to higher energy levels.
When they later relax, they emit -rays and particles. The
former are detected in a Ge-detector array, which
almost completely surrounds the target; the latter are
detected in position sensitive silicon detectors (DSSSD).
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Typical for radioactive beams is a low production rate.
To get the ions through the complete accelerator, the
system will be optimized on a stronger beam, a so called
pilot beam. The total efficiency of the REX-ISOLDE will
be >10%.
•
The time structure of the
REX-ISOLDE beam is
shown to the right. One
day counting of a 31Na
beam on a 2 mg/cm2
Ni target results in
~90 photopeak events,
however, the detection
time is only 2 s thanks
to the bunched beam
structure.

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