The role of the active target is to monitor the lateral stopping distributions. The active target consists of 69 plastic scintillator fibers surrounded by 8 guard-ring elements of the same material. The entire active target is a cylinder of diameter and long as shown in figure . However, each of the 69 fibers has a square cross section of and is covered with an acrylic cladding of thick for optical isolation. The fibers are then glued together with epoxy to make the active target.
Figure: The active target used during the test run of 1994 to measure the horizontal and vertical beam profiles. It contains 69 plastic scintillator fibers with 8 guard-ring elements of the same material around them. Each fiber is isolated by an acrylic cladding and they are held together with epoxy.
Each fiber is connected to a one-inch photomultiplier tube via a fiber optic light guide.
The stopping distributions are needed for an accurate Monte Carlo simulation of
the experiment and acceptance corrections for pion beta and