Three terminal ion chambers
AssigneeVarian Associates, Inc.
InventorsDerek J. Day, Rolf Stahelin, Salvatore Provenzale, Heinrich Riem, Willi Fencl
Life of this patent
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Abstract
A three terminal ionization chamber includes a first electrode coupled to a bias voltage source spaced apart from a second electrode coupled to ground. A third terminal is provided which is positioned between the first and second electrodes. Measurement circuitry may be coupled to the third terminal to measure charge indicative of the amount of radiation incident to the chamber.
Claims15
A three terminal ionization chamber, comprising:
- a first electrode coupled to a bias voltage source;
- a second electrode, spaced a distance apart from said first electrode, coupled to ground;
- a third electrode, positioned between said first and second electrodes;
- a dielectric sheet positioned between said second and third electrodes;
- and
- measurement circuitry, coupled to said second and third electrodes for measuring radiation incident to said chamber.
A portal imaging system comprising:
- a matrix of three terminal ionization chambers, said matrix having a plurality of rows and a plurality of columns;
- a plurality of measurement circuits coupled to said plurality of columns of said matrix, said measurement circuits coupled between a first and a second terminal of said three terminal ionization chambers and generating signals indicative of the magnitude of radiation incident on each of said chambers;
- a plurality of bias voltage sources coupled to said plurality of rows of said matrix, said bias voltage sources coupled to a third terminal of said three terminal ionization chambers;
- and
- a storage device coupled to said plurality of measurement circuits for storing said signal produced by said measurement circuits.
A method for measuring ionization current in a liquid filled ionization chamber, the method comprising the steps of:
- placing a first electrode at ground potential;
- biasing a second electrode, spaced a distance apart from said first electrode, at a bias voltage;
- positioning a third electrode apart from said first and second electrodes;
- positioning a first dielectric sheet between said first and third electrodes;
- measuring a second voltage at said third electrode;
- and
- calculating an ionization current based upon said measured second voltage.
Dependencies are inferred from the claim text.