The FENICE detector at ADONE

A detector to measure the neutron e.m. form factors in the time-like region, through the e/sup +/e/sup -/ to nn reaction, is described. The FENICE experiment, at the Frascati e/sup +/e/sup -/ storage ring ADONE, has been conceived in such a way as to maximize the detection efficiency for this measurement in the c.m. energy interval from the threshold up to the J/ Psi . The apparatus is a complex array of scintillators, limited streamer tubes, and iron convertors. To reduce the cosmic-ray background a concrete shield has been built around the detector and the shield is covered by an active veto system. Antineutrons are detected by means of the charged prongs produced in annihilation events, and their energy is measured by a time-of-flight technique. Neutrons are detected by means of plastic scintillators. There are basically two types of trigger: n trigger and charged trigger. An associative memory helps to recognize the charged tracks coming from the interaction zone. The data acquisition system relies on a mu VAX 3200. A transputer module takes care of data readout and formatting. The online software is based on the Fermilab VAXONLINE system.<>