A major challenge facing experiments with rare-isotope beams concerns the need to detect and quantify reaction and decay products using only limited numbers of ions. The use of a gas volume that acts as both a sensitive detector and as the target itself (an “active target”) thus offers significant advantages over traditional experiments. With an intrinsic high detection efficiency, excellent angular and position resolution, and the ability to reconstruct the kinematics of every event in 3 dimensions, ACTAR TPC will play a vital role in future studies of the most exotic nuclei. Funded by the European Research Council (ERC) in 2014, ACTAR TPC is an ambitious project responsible for the development of a novel and versatile detector system for rare-isotope beam experiments at GANIL (France) and CERN-ISOLDE (Switzerland) and other facilities worldwide. The ACTAR TPC collaboration is composed of researchers and engineers from GANIL, CENBG, IPN Orsay in France, the K.U. Leuven in Belgium, and the Universidade de Santiago de Compostela in Spain.

Artistic view of ACTAR TPC with some ancillary detectors.


Our knowledge about the nuclei at the centre of atoms was based for a long time on the information collected on the few stable nuclei existing in nature. In recent years, however, nuclei far from stability (with an excess of protons or neutrons) have become accessible at large accelerator facilities. Their study has revealed truly exotic properties (unexpected shapes, new decay modes, and others) that challenge our understanding of their structure and dynamics. SpecMAT aims at providing crucial experimental information to answer key questions about the properties of the nuclei: What are the forces driving the shell structure in nuclei and how do they change in systems far from stability? What remains ofthe Z=28 and N=50 magic numbers (corresponding to well-bound configurations) in the very exotic 78Ni nucleus? Do we understand shape coexistence in nuclei, and what are the mechanisms controlling its appearance?Nucleon-transfer reactions are a reliable probe to collect information on nuclear structure. We will employ them to study two regions, the neutron-rich nuclei around nickel (Z=28) and, for the first time, the neutron-deficient nuclei around lead (Z=82). In SpecMAT a novel instrument will overcome the present challenges in performing such measurements with very weak beams of unstable nuclei. It combines high luminosity, high efficiency and a very large dynamic range and allows detection of both charged-particle and gamma-ray radiation. The instrument ownsits remarkable performances to a number of advanced technologies concerning the use of electronics, gaseous detectors and gamma-ray detectors in a magnetic field.The SpecMAT detector will be coupled to the HIE-ISOLDE facility for the production and post-acceleration of radioactive ion beams in construction at CERN in Geneva. HIE-ISOLDE will provide world-unique beams thanks to the use of the proton injector of the CERN complex.If successful, SpecMAT at HIE-ISOLDE will produce specific results in nuclear structure which cannot be reached by other programmes elsewhere. Such results will have a significant impact on the present theories and models of the atomic nucleus.

Artistic view of SPEC MAT.