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Abstract

A hand-held radiation detector for measuring localized radiation at extremely low levels of the order of 1 CPM (counts per minute); an anode is provided in the form of a needle within a sealed chamber defined by a generally cylindrical housing having a metallized radiation window on one end; a focusing arrangement is utilized which enables efficient focusing of the electric field, such that avalanche and efficient electron multiplication occurs within the chamber responsive to the localized radiation entering the chamber, the focusing arrangement including (1) a needle point design to concentrate electric field lines on and in the immediate vicinity of the point, (2) a judiciously selected location for the needle at a sufficient distance from the radiation window such that the electric field lines emanating from the window are forced into the amplifying region (AR) of the needle, and (3) a suitably configured cathode defined by the radiation entrance window and the upper conducting tubular member of the housing, whereby the electric field lines from the conducting tubular member of the housing push the electric field lines for the edge of the window into the amplifying region of the needle point.

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First Claim