A Fast Parallel Encoding Scheme for the Anger Camera

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Abstract
In an Anger camera, only seven photomultipliers generally receive any significant signal from any one event; more distant tubes contribute only noise and background. The basic unit for two-dimensional position determination is thus a "receptive field" of seven photomultipliers. In the new encoding scheme, position determination is performed in two steps: first, the PM with the largest signal is identified, giving the coarse position. Then linear combinations of that signal and its six neighbors are used to interpolate within that receptive field. Since the analog sums are used only for interpolation, less precision is needed and faster electronics can be used. Speed is also increased by forming the linear combinations of all possible fields in parallel; this is done in a circuit called the "brain". Total time to digitize the position of an event is 400 ns; the precision is 1/26 of the photomultiplier spacing.

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