Focal Plane Detector

Focal Plane Detector
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 36 cm x 7.5 cm. In the PSAC there are five wire planes which are made with 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 focal plane 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.

Energy Detector

A 360x75x1 mm3 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. The PMTs are standard 63.5 mm diameter high-gain, low dark-current tubes (9813B) form Thorn EMI Electron Tubes.

Particle Identification

The detector has been used in experiments to measure evaporation residue cross sections. Evaporation residues, shown in the red-gated region, can be identified in 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.


J.F. Liang, D. Shapira, J.R. Beene, J.D. Bierman, A. Galindo-Uribarri, J. Gomez del Campo, C.J. Gross, M.L. Halbert, A.I.D. Macnab, S.P. Macneal, R.L. Varner, K. Zhao
Nucl. Instrum. Methods A435, 393 (1999).

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