The separator

    The heavy nuclei of interest are produced in fusion-evaporation reactions in which the dominating process is fission. The evaporation residues are cinematically and electrically selected from the beam particles and the overwhelming background of fission products by a recoil separator called VASSILISSA.

The detection system

    After passing through VASSILISSA, the heavy ions are deflected by a 37° bending magnet, pass through a time-of-flight detector and a degrader foil and are then implanted into a 16-strip position sensitive Si detector at the focal plane of the separator.

    At the focal plane, the evaporation residues are identified by their characteristic decay properties (half-life, alpha particle energies, etc).

    Gamma ray and internal-conversion-electron spectroscopy of the evaporation residues or their decay products can be performed at the focal plane by tagging on the signal (recoil and/or alpha) detected at the focal plane.

   Conversion electrons are detected at backward angles with respect to the Si focal plane detector in four 4-fold-segmented Si detectors forming a tunnel (two of them are coloured in yellow in the drawing). The circulation of a cryo-fluid inside the copper holding frame cools these detectors and their corresponding preamplifiers. Seven Ge detectors, six of which form a ring around the focal plane chamber, detect gamma rays and one is placed behind the Si focal plane detector.

    The gamma-ray detection efficiency reaches ~9% at 120 keV. The electron detection efficiency peaks at ~17% for electron energies of 100-300 keV.

    For more information on GABRIELA, see K. Hauschild et al., Nucl. Instr. Meth. A 560(2006)388