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Redepositing electrons on photocathode ?

  1. Sep 29, 2006 #1
    Redepositing electrons on photocathode ??

    Hello All
    I'm new to the forum and have a question i hope one of you can answer.
    I have 3 surplus image imtensifier tubes....all of which have lost there sensiitivity to one degree or another. To review; an image intensifier tube conssits of a photo cathode ( a thin layer of alkili metals deposited on a glass window) ... a micro channel plate....and a phosper screen...all located inside a vacum tube. When a photon of light hits the photocathode it knocks an electron free....the electron is then accelarted by a high voltage to the micro channel plate, where it knocks off more electrons....and then these electrons are accelerated by another high voltage and hit the phospor screen producing light. In the image tubes i have, the photo cathodes have lost sensitivity....that is they have lost some of their ability to produce a free electron when a photon of light strikes. My question is...would there be some way to resupply the alkili metals of the photo cathode with electrons....perhaps by supplying the photochode with a REVERSED high voltage..causing electrons to redeposit into the alkili metals or is that to much to hope for.
    Thanks for any help you may be able to give.
  2. jcsd
  3. Sep 29, 2006 #2


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    Er.. no. The lost in "sensitivity" is not due to a depletion of electrons in the photocathode - the photocathode is always grounded, even during operations. If not, you will have a charging effect and the photocathode will stop working efficiently after only a few seconds. So the material itself is not depleted with electrons. Thus, back bombardment will not help and in fact, may even destroy it more.

    Oxidation, surface degradation, etc.. all cause the cathode to change characteristics over time. Depending on what kind of alkali metal that was used, it may be possible to recoat the surface, but this isn't guaranteed since thin film coating depends on many things, including substrate characteristics.

    So no, back bombardment will not work.

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