Accelerator description

1. 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 ~103-107 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.

2. 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-ISOLDEwill be >10%. • The time structure of theREX-ISOLDEbeam is shown to the right. One day counting of a 31Na beam on a 2 mg/cm2Ni target results in ~90 photopeak events, however, the detection time is only 2 s thanks to the bunched beam structure.