High-resolution UV, alpha and neutron imaging with the Timepix CMOS readout

Abstract

A CMOS application-specific integrated circuit (ASIC) called the “Timepix” has been used to readout the pulsed charge signal from various microchannel plate (MCP) stacks. The Timepix 256×256 array is a newer version of the Medipix2 ASIC with added features and modes. One of these modes is the “time over threshold” (TOT) mode where the amplitude of a single charge event can be determined per pixel. With a properly sized input charge cloud from an MCP stack, the centroid of the charge cloud can be determined to sub-pixel accuracy, allowing much higher spatial resolution than the 55 μm pixel size. Using this technique, we demonstrate a spatial resolution better than 57 lp/mm for UV photons, limited by the MCP pore spacing. Also, by changing the top MCP in the stack to a neutron-sensitive MCP, we show a spatial resolution to thermal neutrons of less than 35 μm FWHM. This technique can also be applied to alpha particle imaging using silicon diode arrays bump bonded to a Timepix. Allowing the large conversion charge generated by the alpha particle to diffuse over many pixels, we can centroid 5.5 MeV alphas from 241Am to 18 μm FWHM.