Today, research on nuclear structure far from stability is one of the most exciting frontiers in nuclear physics since such nuclei allow to amplify and isolate particular aspects of nuclear interaction and dynamics. REX-ISOLDE accelerates radioactive ion beams and thus the full variety of beams available at ISOLDE become accessible as accelerated beams for experiments.

REX-ISOLDE uses the method of charge-state breeding to enhance the charge state of the ions before injection into a linear accelerator. The charge multiplication of the radioactive ions allows access to the heavier mass region of the nuclear chart, which cannot be reached by accelerating monocharged ions.

REX-ISOLDE makes use of the large variety of radionuclides that have been extracted from the on-line mass separator ISOLDE. The radioactive singly-charged ions from the separators are first accumulated, bunched and cooled in a Penning trap, REXTRAP. The trap stores the ions during the breeding in the subsequent charge breeder. Bunches of ions are then transferred to an electron beam ion source, REXEBIS where the ions are charge bred to a mass-to-charge ratio below 4.5. Finally, the ions are injected into a compact linear accelerator via a mass separator.

The normal conducting linear accelerator has a total length of about 11 m. It consists of a Radio Frequency Quadrupole (RFQ) accelerator which accelerates ions from 5 to 300 keV/u, a rebuncher section, an Interdigital H-type (IH) structure that boosts the energy to 1.2 MeV/u, three seven-gap spiral-resonators and a 9-gap IH resonator, which allow the variation of the final energy between 1.2 and 3 MeV/u.

A superconducting linear accelerator, which is due to start operation in 2015, is under construction downstream the normal conducting accelerator (HIE-ISOLDE project). With this new accelerator post-accelerated radioactive ion beams with up to 10 MeV/u (A/q = 4.5) will be available at ISOLDE.