The focal plane detector consists of a large area Position Sensitive Avalanche
Counter (PSAC) and a plastic scintillator.
Position Sensitive Avalanche Counter
The active area of the avalanche counter is 36x7.5 cm^2.
In the PSAC there are five wire planes which are made with PC boards and 20
micron gold plated tungsten wires. The anode plane provides timing signals and
the x- and y-position sensing planes provide position signals.
The energy information is obtained by the plastic scintillator using
photomultiplier tubes as readout devices.
Photograph of the camera box of the spectrograph.
The PSAC is filled with isobutane gas at 3.5 Torr. The gas is continuously
flowing through the counter and regulated by a gas handling system.
The anode and cathode are biased at +420 V and -200 V, respectively,
for heavy ion measurements. The PSAC can be operated at a maximum counting
rate of 10,000 particles per second.
A 360x75x1 mm^3 BC400 plastic scintillator (Bicron
Corporation) is used to measure the energy of particles. The scintillator
is glued on to an acrylic light guide, BC800 (Bicron Corporation), which
also provides a vacuum seal to the back end of the PSAC. The scintillation
light is collected by two photo multiplier tubes (PMTs) on
the sides because the space behind the focal plane is
limited. The PMTs are standard 63.5 mm diameter high gain low, dark current
tubes (9813B) form Throne EMI Electron Tubes.
The detedtor has been used in experiments to measure evaporation residue
cross sections. Evaporation residues, shown in the red-gated region, can be
identified by a histogram of energy vs. time-of-flight.
A very clean residue spectrum in a time-of-flight vs. position histogram can
be obtained by requiring a gate on the energy axis in the region of interests.
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