The Internal Picket Fence for BEBC

The Internal Picket Fence is a device to give a timing signal for all events occurring inside the bubble chamber. The detector has to be installed inside the vacuum region separating the chamber body and the magnet cryostat, where there is a high magnetic field of 35 kG. The device has to have high efficiency and a time resolution comparable to that of the External Muon Identifier (EMI). Two prototype pickets made out of thin proportional tubes have been working to full satisfaction for several months. The complete perimeter of BEBC will be equipped during this year. (2 refs).