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.

• The beam is injected into the

REXTRAP

(a Penning Trap), where the ions are bunched into groups of ~10 3 10 7 and cooled, i.e. their thermal velocity is decreased. Every 20 ms a cooled bunch is extracted from the

REX TRAP

, 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

. • 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)

.

• 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 31 Na beam on a 2 mg/cm 2 Ni target results in ~90 photopeak events, however, the detection time is only 2 s thanks to the bunched beam structure.