Detectors for High Energy and Nuclear Physics Experiments

Interpolating Cathode Pad Chamber for High Particle Multiplicity Environment

Two types of position sensitive detector using interpolating cathode pads have been studied at BNL in the late 1980s. These detectors have been used in the heavy ion experiment E814 at the AGS.

The "Pad Chamber" is a detector with a cathode plane divided into a large number of rectangular pads (see photo to right). Anode wires are placed above the pads, and field wires with ground potential are placed between anode wires. All pads beneath one anode wire are interconnected by a resistive strip. Approximately every tenth pad is read out by a charge sensitive preamplifier. An avalanche created by a charged particle traversing the detector induces localized charge on several pads. The position of the avalanche can then be found by calculating the centroid of the charge collected from these pads. Unambiguous pattern recognition is achieved because of this two dimensional segmented cathode layout. With a typical readout spacing about 1cm, position resolution of better than 100µm can be achieved.

The photo to the right shows the pad chamber with the wireframe removed. The chamber has slightly over 1000 readout nodes. The charge signal from these nodes are processed on the detector by two banks of charge sensitive triple preamplifiers. The preamp outputs are then fed to 200ns shaping amplifiers and then digitized by ADCs.

"Chevron Pad Detector," in which the rectangular pads and the resistive layers are replaced by rows of chevron shaped pads as the cathode, has also been studied. Each pad is read out by a charge sensitive preamplifier. In this scheme, position sensing is achieved by geometrical charge division.

Two large MWPCs with chevron pads planes were constructed and used in the E814 experiment.

References:

R. Debbe, J. Fischer, D. Lissauer, T. Ludlam, D. Makowiecki, V. Radeka, S. Rescia, G. Smith, D. Stephani, and B. Yu, "A MWPC with Highly Segmented Cathode Pad Readout," Nucl. Instrum. & Meth. A283, 772-777 (1989).

R. Debbe, J. Fischer, D. Lissauer, T. Ludlam, D. Makowiecki, E. O'Brien, V. Radeka, S. Rescia, L. Rogers, G. C. Smith, D. Stephani, B. Yu, S. V. Greene, T. K. Hemmick, J. T. Mitchell, and B. Shivakumar, " A Study of Wire Chambers with Highly Segmented Cathode Pad Readout for High Multiplicity, Charged Particle Detection," IEEE Trans. Nuc. Sci. NS-37 (1990) 88-94.

B. Yu, G. C. Smith, V. Radeka, and E. Mathieson, "Investigation of Chevron Pads for Position Encoding in Very High Rate, Gas Proportional Chambers," IEEE Trans. Nucl. Sci. NS-38 (2) 454-460 (1991).

B. Yu, V. Radeka, G. C. Smith, and E. O'Brien, " Interpolating Cathode Pad Readout In Gas Proportional Detectors For High Multiplicity Particle Tracks," Nucl. Instrum. & Meth. A-323 (1992) 413-418.