Radiation detector with an ionizable gas atop an integrated circuit

• US 4,804,847 A
• Filed: 01/27/1987
• Issued: 02/14/1989
• Est. Priority Date: 01/27/1987
• Status: Expired due to Term

• Current Assignee: Ongard Systems, Inc.
• Original Assignee: Medrad Incorporated (Bayer AG)
• Inventors: Uber, Arthur E. III
• Primary Examiner(s): Wan, Gene
• Application Number:
  US07/007,195
• Time in Patent Office: 749 Days
• Field of Search: 250/370 F, 250/374, 250/385, 250/388, 250/389
• US Class Current: 250/389
• CPC Class Codes: G01T 1/185 with ionisation chamber arrangements
• CPC Class Codes: G01T 7/125 Alarm- or controlling circuits using ionisation chambers, proportional counters or Geiger-Mueller tubes, also functioning as UV detectors measuring radiation intensity with counting tubes G01T1/18; measuring radiation intensity with ionisation chambers G01T1/185; flame monitoring in combustion devices F23Q7/00, F23N; fire alarms actuated by presence of radiation of particles, e.g. of infrared radiation, of ions G08B17/11; discharge tubes per se H01J47/00
• CPC Class Codes: H01J 47/02 Ionisation chambers

Abstract

The radiation detector includes tissue equivalent bubbles of plastic defining volumes of gas to be ionized by radiation. One or more integrated circuits (ICs) are disposed below the volumes of gas and a collecting electrode on the IC is in direct contact with the gas. Circuitry for generating an electric field within the volume of gas moves the ions therein to the collecting electrode. The collecting electrode is part of an amplifying circuit disposed within the IC. The output from the amplifier is representative of the collected ions and therefore representative of the radiation. The signal from the amplifier is send to an interface which conditions, buffers and stores the signal. The radiation dose and dose rate are computed in the interface. A communications section transfers that data from the radiation detector. A separate calibration and display unit calibrates the interface by controlling The conditioning of the signal. An area monitor and air monitor are further enhancements of the radiation detector.

Claims

1. A radiation detector for measuring radiation including:

means for enclosing a volume of gas from which ion leakage is minimized, said gas adapted to be ionized by said radiation;

proportional counters which use multiplication within the gas. a supporting surface in direct contact with said gas and limiting said volume thereof;

means for generating an electric field within said volume of the gas and for collecting ions produced by ionization of the gas therein;

at least one collecting electrode on said surface on which said collected ions are deposited by the electric field;

amplifying means operatively connected to the collecting electrode for generating a signal representative of the collected ions deposited thereon;

interface means responsive to said signal from said amplifying means for varying signal bias on the collecting electrode and, means supplying power to at least said amplifying means and to said interface means for establishing said signal bias on the collecting electrode;

said interface means including detector control means for minimizing data error in the signal from the amplifying means caused by the ion leakage from the supporting surface and means for registering the signal processed by the detector control means.

2. A radiation detector as claimed in claim 1 wherein said amplifying means includes a transistor having a control gate to which the collecting electrode is connected

3. A radiation detector as claimed in claim 2 wherein said means for restoring includes a transistor, switch interposed between said control gate and said power supplying means said detector control means generating a clearing control signal that controls said transistor switch and the application of said predetermined bias.

4. A radiation detector as claimed in claim 1 wherein said interface means includes a radiation dose monitor means for receiving said signal and for monitoring the radiation on the radiation detector and a human interface coupled thereto.

5. A radiation detector as claimed in claim 1 wherein said means for enclosing said volume of gas is made of a tissue equivalent material.

6. The radiation detector as defined in claim 1 wherein said supporting surface is formed by a plurality of conductive but electrically isolated surface segments in direct contact with said gas one of which is said collecting electrode

7. A radiation detector as claimed in claim 6 wherein said interface means further includes means for selecting said collecting electrode from said plurality of conductive surface segments dependent upon said respective signals.

8. A radiation detector as claimed in claim 7 wherein the remaining plurality of conductive surface segments are biasing segments connected to said means for generating said electric field.

9. A radiation detector as claimed in claim 8 wherein said means for generating said electric field electrically biases said biasing segments to discrete predetermined levels.

10. The radiation detector as defined in claim 1 wherein said detector control means includes means for sensing excessive accumulation of charge on the collecting electrode and electrode discharge means connected to the power supplying means for reversing the bias applied to the collecting electrode in polarity to discharge said accumulated charge thereon.

11. The radiation detector as defined in claim 1 wherein said detector control means includes leakage sensing means connected to the collecting electrode for detecting leakage current pulses exceeding a predetermined pulse rate and means for preventing said registration of the detected leakage current pulses in the processed signal.

12. The radiation detector as defined in claim 1 wherein the detector control means includes a compensating controller connected to the amplifying means and charge removal means operatively connecting the controller to the field generating means and the collecting electrode for discharge thereof.

13. A radiation detector for measuring radiation comprising:

at least one radiation detection subassembly including;

means for defining a volume of gas, said gas adapted to be ionized by said radiation; and

integrated circuit element having a surface segment in direct contact with said gas, said surface segment being part of said means for defining said volume of gas;

means for generating an electric field within said volume of gas and for collecting ions present therein that includes at least one collecting electrode on said surface segment collecting said ions thereon;

amplifying means incorporating said collecting electrode and disposed within said integrated circuit element for generating a signal representative of the collected ions;

interface means for buffering said signal from said amplifying means;

means for supplying power to at least said amplifying means and to said interface means;

said collecting electrode being electrically biased by said electric field and said collected ions;

a clearing voltage supply establishing said bias;

detector control means that is part of said interface means for controlling said bias of the collecting electrode dependent upon said signal from the amplifying means;

said collecting electrode being a sense electrode exposed to said volume of gas;

said amplifying means including a transistor having a control gate connected to the sense electrode;

said detector control means including a transistor switch interposed between said control gate and said clearing voltage supply and means for generating a clearing control signal that controls said transistor switch and application f said bias; and

means for compensating for leakage current from said transistor switch to said control gate.

14. The combination with a radiation detector including a gas confining chamber having an electrode therein exposed to radiation ionized gas, means generating an electric field within the chamber for collecting ions of said gas on the electrode, amplifying means connected to the electrode for producing an output in response to accumulated charges produced by said collection of ions thereon, means connected to the amplifying means for registration of the output, power supply means connected to the field generating means for applying a predetermined bias voltage to the electrode while producing said output and voltage control means connected to the power supply means for polarity reversal of said bias voltage to discharge the electrode.

15. The combination of claim 14 including means for detecting leakage current from the electrode and leakage compensating means operatively connecting the amplifying means to the voltage control means for removal of error in the registered output resulting from said current leakage

16. In combination with a radiation detector having a gas confining chamber, an electrode exposed to radiation ionized gas within the chamber, means generating and electric field within the chamber for collecting ions of said gas on the electrode, amplifying means connected to the electrode for producing an output in response to charges accumulated by said collection of ions, means for registration of the output, means for detecting leakage current for the electrode and leakage compensating means operatively connecting the amplifying means to the registration means for removal of error in the registered output resulting from said current leakage.