A single x-ray photon interacting in a channel of the MCP produces a charge pulse of about 1000 electrons that emerge from the rear of the plate. Since the individual tubes confine the pulse, the spatial pattern of electron pulses at the rear of the plate preserve the pattern (image) of x-rays incident on the front surface. When coupled to an additional MCP and an electronic readout and display the MCP becomes an x-ray image intensifier. The same microchannel plate technology is used to make visible light image intensifiers for night vision goggles and binoculars.
An incident x-ray photon enters a channel and frees (via "photoelectric emission") an electron from the channel wall. An electron accelerating potential difference (approx. -1500 Volts) is applied across the length of the channel. The initial electron strikes the adjacent wall, freeing several electrons (via "secodary emission"). These electrons will be accelerated along the channnel until they in turn strike the channel surface, giving rise to more electrons. Eventually this cascade process yields a cloud of several thousand electrons which emerge from the rear of the plate.
A hollow billet of lead oxide cladding glass is mechanically supported by the insertion of a rod of etchable core glass and then pulled through a vertical oven, producing a "first draw" fiber of approx. 1 mm diameter. Lengths of first draw fiber are then stacked (usually by hand) in a hexagonal array which is itself drawn to produce a hexagonal "multifiber". Lengths of multifiber are stacked in a boule and fused under vacuum. The boule is sliced and polished to the required thickness and shape. The solid core is then etched away, leaving the channel array to be fired in a hydrogen oven to produce a semiconducting surface layer with the desired resistance and secondary electron yield. (Source: Philips Photonics)
Uniformity of size and spacing of the channels of an MCP is critical to the detection and intensification of high quality x-ray images. Details as finer than 25 microns (0.025 mm) are faithfully reproduced. The photomicrograph above was taken in our laboratory of a sample MCP manufactured by Philips Photonics, the supplier of the MCPs for HRC-S. The channels are 12.5 microns in diameter and spaced 15 microns apart. For comparison a human hair is 60 - 80 microns in diameter.
