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Silicon Matrix Hodoscopes Calorimeter



Hodoscope Trigger Detectors

The target section above the calorimeter has about of a nuclear interaction length of material including three 10 cm thick layers of carbon, but only a few radiation lengths, to increase the probability that the incident particle interacts while minimizing the development of the electromagnetic cascade. Further, the target section includes three plastic scintillator strip hodoscopes to provide the experiment with a fast trigger that defines the aperture, and auxiliary measurements of the in-cident particle charge and trajectory.  The three hodoscopes (S1, S2 and S3) are of similar construction and are composed of Bicron BC-408 plastic scintillator strips 2 cm wide by 1 cm thick as shown in Figure 4. To maintain a ~24 o opening angle each hodoscope has a different active area. For S1 there are 42 strips of length 88.2 cm in each layer, while 35 strips of length 74.2 cm com-prise each S2 layer and 24 strips 52.4 cm long make up S3. Each hodoscope module has two layers ori-ented by 90 o to provide a X-Y measure of the parti-cle “hit” position.


An ATIC plastic scintillator hodoscope

The strips are wrapped in alu-minized mylar and on each end is glued a UVT Lu-cite transition and a Hamamatsu R5611 PMT. The scintillator strip readout and PMT bleeder base utilizes two dynode pickoffs to cover the required dynamic range (~0.5 MeV to 800 MeV). The PMT anode is used to provide a fast “pre-trigger” signal, and a test LED is incorporated directly into the PMT base. These sig-nals are wired directly to the FEM mounted on the hodoscope honeycomb support structure as shown in Figure 4. The hodoscope FEMs are almost identical to the calorimeter FEMs and also use the ACE ASIC. Further, the ACLB and DIM boards that complete the hodoscope readout interface with the DCU are identi-cal to those used for the calorimeter and are also mounted in the electronics bays
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  Doug Granger
Doug Granger