| CPC H01J 43/18 (2013.01) [H01J 43/10 (2013.01); H01J 43/28 (2013.01); H01J 47/002 (2013.01); H01J 47/005 (2013.01); H01J 49/025 (2013.01); H01J 49/288 (2013.01)] | 20 Claims |

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1. An apparatus comprising:
an electron multiplier comprising a series of electron emissive surfaces comprising a first electron emissive surface configured to receive a particle to be detected by the electron multiplier, and
an enclosure extending about one or more of the series of electron emissive surfaces, the enclosure having an opening,
wherein the electron multiplier has a long axis about which the series of electron emissive surfaces are disposed, and the enclosure opening is configured to allow a particle to be detected to traverse the long axis and be received by the first electron emissive surface.
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