A TIME DETECTOR DESIGN FOR MEV PARTICLES USING SECONDARY-ELECTRON EMISSION AND MICROCHANNEL PLATES

In this article we present some basic considerations in the design of a time detector for high energy (0.2-1.0 MeV) particle detection. Base d on these considerations, a novel time detector design is proposed in order to overcome some of the problems in existing designs. Improveme nt in the timing resolution (<50 ps) and efficiency (>70% for 4.0 MeV alpha particles) is expected and a compact detector structure with ult rahigh vacuum compatibility is achieved. The new design employs a nove l form of crossed electric and magnetic fields to deflect the electron s emitted from a thin foil to form a timing signal. In this design ele ctrons are transported in a grid-free region and the energetic particl e needs to pass through the grid once only. The electric field was pro duced by three metal plates forming a triangular prism. The magnetic h eld was generated by a coil pair which creates a uniform held in the e lectron transport region. Computer simulation and numerical analysis w ere performed to calculate the electric and magnetic field as well as the electron trajectory and flight time. The detector timing resolutio n is analyzed and the spread in electron initial energy contributes a significant portion. To avoid the complicated numerical details in fie ld and trajectory calculations, we use an empirical approach in this a rticle to illustrate the design principle. Some experimental results a re presented to compare with the calculations. (C) 1997 American insti tute of Physics. [S0034-6748(97)05210-6].