Time-zero fission-fragment detector based on low-pressure multiwire proportional chambers

A time-zero fission fragment (FF) detector, based on the technique of low-p ressure multiwire proportional chambers (LPMWPC), has been designed and con structed for the heavy hypernuclear lifetime experiment (E95-002) at Thomas Jefferson National Accelerator Facility. Its characteristics and the metho d of time-zero reconstruction were investigated using fission fragments fro m a Cf-252 spontaneous fission source. The influence of the ionization ener gy loss was also studied. It is shown that Heptane, Hexane, and Isobutane g ases at a pressure of 1-2Torr are all suitable for such a FF detector. As d esired by experiment, a timing resolution of about 200 ps (FWHM) for a cham ber size of 21 x 21 cm(2) was achieved. (C) 1999 Published by Elsevier Scie nce B.V. All rights reserved.