Large-area fast-timing detectors developed for the TOFI spectrometer

Abstract

Large-area fast-timing detectors have been developed for use in the TOFI spectrometer. A gridless detector was constructed in which secondary electrons emitted from a thin ( ∼ 80 μg/cm 2 ) target foil were transported isochronously to microchannel plate electron multipliers by crossed electric and magnetic fields. A novel convex anode was designed to reduce the time dispersion caused by the position at which the secondary electrons were collected. Timing performance for aluminium oxide target foils was found to be superiors to that of carbon foils. Intrinsic timing resolutions of 68 and 109 ps fwhm have been measured for 5.4 MeV alpha particles from a thin 241Am source for two different detectors with active areas of 270 and 1000 mm 2, respectively. Detection efficiencies in excess of 75% for alpha particles were measured.