The beam line has at least two timing detectors in the path of the beam.
The timing detectors use only a thin foil in the path of the beam and
are capable of timing resolution of about 150 ps. Some of these timing
detectors are also position sensitive. The principle of operation of
this detector is described in Ref. 1. The actual detector used in this
beam line is described in Ref.2.
Fig. 1 - (a) Schematic of the experimental set-up. (b) Partial electronic circuit illustrating the timing discrimination between beam-beam and beam-residue coincidences. (c) Photograph of the target, CD-detector, MCP, and window of the ion chamber housed in an 8-inch ID large-flange cross. Beam direction is indicated by the red arrow.
A compact end station of this beam line was instrumented to study fusion reaction with radioactive ion beams at energies below the Coulomb barrier - where cross sections are as low as 1 mb. Fig.1 shows this end station and a full description is provided in Ref. 2. A position-sensitive timing detector monitors beam position and selects reaction products to be processed. An ionization chamber provides particle ID allowing the separation of evaporation residues. The station is most suitable for measuring evaporation residues in inverse kinematic reactions with neutron-rich radioactive ion beams. It can run at beam intensities up to ~60,000 ions/s (limited by pileup in the ionization chamber). A double-sided CD-shaped silicon strip detector is used to detect two-body fragmentations in coincidence. The distance of this detector from the target can be adjusted to avoid elastic coincidences and detect about 5% of the fusion-fission products.
Fig. 2 - The energy-loss (vertical axis - y) vs. total energy spectrum (horizontal axis - x) gated by time. The evaporation residues are grouped about (x,y) = (160,210).
Figure 2 shows a two-dimensional energy-loss vs.energy spectum from the collision of 132Sn with 64Ni at 530 MeV bombarding energy - it shows that the evaporation residues are well separated from the beam. Figure 3 shows the granularity of the CD-shaped DSSSD. The 16 wedges are in the back (n-type electrodes - good for energy readout) and the 48 rings are p-type and in the front.
Samples of data taken with this detector system have appeared in a several publications listed in Ref. 3 and preprints from recent conference procedings listed in Ref. 4-7.
Fig. 3 - Hit pattern of events on the CD-detector. One of the 16 wedges and a few of the circular strips are dead.
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This file last modified Monday January 08, 2007