A time-zero detector utilizing isochronous transport of secondary electrons

Abstract

A time-zero detector has been developed for use in reaction product mass identification which has as its novel feature a 180° isochronous transport of secondary electrons in a magnetic field. The secondary electrons produced when particles pass through a thin carbon foil are accelerated to approximately 2 keV by a parallel-wire harp of 99% transmission. The accelerated electrons are then transported 180° in a uniform magnetic field of 80 G containing a collimator placed at the 90° position. A background suppression grid is placed just in front of the electron detector which is comprised of two microchannel plates in series acting as an electron multiplier. The device allows placement of the thin foil perpendicular to the fragment flight path and permits shielding of the electron detector from the beam and reaction products while using only modest accelerating voltages. The time-of-flight resolutions measured between this timing detector and a 120 μm silicon detector when using 104 MeV 16O ions and 8.78 MeV alpha particles were 90 and 150 ps, respectively (full widths at half maxima).