|Accelerator & Separator (Vassilissa and Shels)|
by- 10 October 2008
GABRIELA Detection system
After passing through the recoil separator VASSILISSA, the heavy ions are deflected by a 37 degre 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 (shown in red in the drawing below and visible in the corresponding photography). The position sensitive detector was replaced in 2009 by a Double Sided Strip Detector with 48 front and back strips. In 2011, a larger, more pixelated DSSD was purchased from MICRON.
At the focal plane, the evaporation residues are identified by their characteristic decay properties (half-life, alpha particle energies,...).
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 segmented Si detectors forming a tunnel (2 of them are coloured in yellow in the drawing). These detectors are cooled by the circulation of a cryofluid inside the copper holding frame. Gamma-rays are detected by 7 Ge detectors, 6 of which form a ring around the focal plane chamber and 1 is placed behind the Si focal plane detector.
The electron detection efficiency peaks at 17% for electron energies of 100-300 keV. The gamma-ray detection efficiency has been improved and now reaches 16% at 120 keV.
For more information on GABRIELA, see the article published in Nucl. Instr. Meth. A (2006): GABRIELA: A New detector array for gamma-ray and conversion electron spectroscopy of transfermium elements
In 2012, an ANR grant was obtained to upgrade the gamma-detection part of GABRIELA. The envisaged array will be composed of 4 coaxial detectors in a cross around the implantation detector and a large clover detector placed right behind the implantation detector. This new geometry will increase the efficiency and granularity of the array. Furthermore, new BGO shields will be designed in order to increase the compactness of the Ge array, and therefore the overall efficiency.