Versatile camera for imaging and particle tracking using secondary electrons and pixel detector Timepix

AbstraktAbstract

The camera uses excellent properties of particle counting pixel detectors of Timepix type. It consists of small vacuum system with exchangeable electrode (photocathode, thin metallic foil, neutron converter) and Timepix detector with optimized thin silicon sensor. The sensitive medium is the electrode emitting secondary electrons after interaction with primary radiation. The secondary electron is accelerated by electric field between electrode and detector receiving kinetic energy of 15-25 keV. The simple electron optics placed between electrode and detector assures proper imaging and enables image scaling (zoom). Additional electromagnetic focusing can be added externally. Since the sensitive material is metallic foil, its radiation hardness is very high. The camera works till the electrode is mechanically damaged. When such extensive radiation damage occurs the foil can be easily replaced. The major advantage of the camera is significant reduction of dark current due to electron thermo-emission known in other imaging systems based on similar technique (e.g. light intensifiers). The principle uses coincidence technique since it is highly improbable that single detector pixel would be hit by two thermo electrons simultaneously, but it is highly probable that there are two or more secondary electrons released by single primary particle. By setting detection threshold in Timepix detector over the known acceleration energy (e.g. 15 keV) we can easily implement intrinsic coincidence logic fully canceling influence of thermo emission.

The camera uses excellent properties of particle counting pixel detectors of Timepix type. It consists of small vacuum system with exchangeable electrode (photocathode, thin metallic foil, neutron converter) and Timepix detector with optimized thin silicon sensor. The sensitive medium is the electrode emitting secondary electrons after interaction with primary radiation. The secondary electron is accelerated by electric field between electrode and detector receiving kinetic energy of 15-25 keV. The simple electron optics placed between electrode and detector assures proper imaging and enables image scaling (zoom). Additional electromagnetic focusing can be added externally. Since the sensitive material is metallic foil, its radiation hardness is very high. The camera works till the electrode is mechanically damaged. When such extensive radiation damage occurs the foil can be easily replaced. The major advantage of the camera is significant reduction of dark current due to electron thermo-emission known in other imaging systems based on similar technique (e.g. light intensifiers). The principle uses coincidence technique since it is highly improbable that single detector pixel would be hit by two thermo electrons simultaneously, but it is highly probable that there are two or more secondary electrons released by single primary particle. By setting detection threshold in Timepix detector over the known acceleration energy (e.g. 15 keV) we can easily implement intrinsic coincidence logic fully canceling influence of thermo emission.