Other Slides
The SAMURAI time-projection chamber saw its first traces of cosmic rays this past week. The main component of the TPC cosnists of a field cage which forms the walls of the detector and provides a uniform electric field. Cosmic rays passing through the detector ionize the argon/methane gas inside. Under the influence of the electric field, the ionized electrons drift toward a set of wire planes near the top. These planes form a high-electric-field multiplication region which causes an electron avalanche, amplifying the signal on the anode wires
To identify a cosmic ray we use two plastic-scintillator paddles. When the cosmic ray passes through the TPC, we observe coincident signals on two sections of the wire plane (see figure above). The timing of the two peaks, relative to the paddles' coincidence trigger, is related to the drift time of the electrons. It gives us information about the vertical position of the particle. This is the "time-projection" information of the detector, which provides a 3D image