An investigation into thin window photoelectronic image intensifiers
The basic requirements of an image detector are outlined and the advantages of the photoemissive cathode as a primary detector are set out. Several methods of image intensification using a photoemissive cathode as the primary detector are reviewed. In particular the advantages for use in astronomy o...
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Imperial College London
1962
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| Online Access: | https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602144 |
| Summary: | The basic requirements of an image detector are outlined and the advantages of the photoemissive cathode as a primary detector are set out. Several methods of image intensification using a photoemissive cathode as the primary detector are reviewed. In particular the advantages for use in astronomy of the thin end-window tube with a phosphor output in which the light image produced in the phosphor screen is recorded by contact-photography and the Lenard window electronographic image tube in which the electron image penetrates the end.-window to be recorded directly on an electron-sensitive emulsion are emphasized. The need to exclude caesium from the accelerating space and the advantages of an electron-optical system of uniform coaxial electric and magnetic fields are described. The theoretical performance of the thin window tube is estimated and the development of a successful design is described. Early tubes suffered from very high back-ground. A mechanism for the production of this background is postulated and a method for preventing it is proposed by using conducting annular baffles. This was found to be successful. The performance obtained agrees well with the theoretical predictions. Work was then started on a Lenard window electronographic image tube because this tube can have, in principle, a far superior performance to the conventional thin end— window tube. The theoretical performance of such a tube is estimated and its development from the thin window tube with a phosphor output is described. A special method for mounting the very thin mica window required for this tube is also described. Results obtained are found to agree reasonably well with the theoretical predictions. However the background is excessive and methods of reducing this are proposed. Finally the advantages of the above tubes in astronomy are emphasized and in particular the use of the Lenard window tube on a spectrograph. |
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