  Particle beams focused to micrometer-sized spots play a crucial role in
forefront research using low-energy positrons. Their expedient and wide
application, however, requires highly-resolved, fast beam diagnostics. We have
developed two different methods to modify a commercial imaging sensor to make
it sensitive to low-energy positrons. The first method consists in removing the
micro-lens array and Bayer filter from the sensor surface and depositing a
phosphor layer in their place. This procedure results in a detector capable of
imaging positron beams with energies down to a few tens of eV, or an intensity
as low as 35 particles/s/mm2 when the beam energy exceeds 10keV. The second
approach omits the phosphor deposition; with the resulting device we succeeded
in detecting single positrons with energies upwards of 6 keV and efficiency up
to 93%. The achieved spatial resolution of 0.97 micrometers is unprecedented
for real-time positron detectors.
