Direct reading dosimeter

• US 4,484,076 A
• Filed: 11/13/1981
• Issued: 11/20/1984
• Est. Priority Date: 10/02/1981
• Status: Expired due to Fees

• Current Assignee: CAL Corp (Honeywell International Inc.)
• Original Assignee: Canadian Astronautics Limited
• Inventors: Thomson, Ian
• Primary Examiner(s): Smith, Alfred E.
• Assistant Examiner(s): FIELDS, CAROLYN
• Application Number:
  US06/321,081
• Time in Patent Office: 1,103 Days
• Field of Search: 357/29, 250/370, 250/371, 250/388
• US Class Current: 250/370.07
• CPC Class Codes: G01T 1/026 Semiconductor dose-rate meters

Abstract

A direct reading dosimeter having a range such that it can be used by personnel workers in the medical, nuclear and industrial fields, and provides and indication of dose rate as well as total received dosage. The dosimeter uses a semiconductor sensor of MOS or bipolar transistor or MOS capacitor form which traps positive charge under the influence of ionizing radiation. A current is applied to the sensor substrate, the voltage across a portion of the substrate is sensed, differentiated and displayed. The dosimeter circuit can be integrated and packaged in a wrist watchcase, in a probe, or other convenient form.

Claims

1. A direct reading dosimeter comprising:

(a) a semiconductor sensor including a semiconductor substrate, an insulating layer defined a predetermined area disposed over the substrate for trapping positive charge under the influence of ionizing radiation,

(b) means for applying a current to the substrate,

(c) means for sensing the voltage across the portion of the substrate underlying the insulating layer,

(d) means for differentiating the sensed voltage, and

(e) means for displaying the differentiated voltage as a dose rate.

2. A direct reading dosimeter comprising:

(a) an MOS device, including a source, drain and gate, the gate being insulated by an insulating layer of a kind which traps positive charge under the influence of ionizing radiation,

(b) means for applying a constant current through the source-drain circuit of the transistor,

(c) means for switching the gate between a source of positive and negative bias sufficient to turn the source-drain circuit off and on,

(d) means for detecting a voltage across the source and drain, and

(e) means for indicating the detected voltage.

3. A dosimeter as defined in claim 2, in which the means for detecting includes means for differentiating the voltage across the source and drain, and for presenting the differentiated voltage to the indicating means.

4. A dosimeter as defined in claim 2, including means for switching the detected voltage directly or through a differentiating circuit to the indicating means, whereby the indicating means is caused to correspondingly display total dose or dose rate of said radiation.

5. A dosimeter as defined in claim 2, 3 or 4 in which the indicating means is comprised of a digital display calibrated in radiation units.

6. A dosimeter as defined in claim 2, 3 or 4 in which the indicating means is comprised of an alarm having a predetermined voltage threshold of operation.

7. A dosimeter as defined in claim 2, 3 or 4 in which the MOS device is a P channel type field effect transistor.

8. A dosimeter as defined in claim 2, 3 or 4 in which the MOS device is a P channel type field effect transistor, including means for applying the constant current to the source, the gate switching means being comprised of means for switching the gate between said source of positive bias and the drain at predetermined sampling intervals, said indicating means being comprised of a digital display calibrated in radiation units.

9. A dosimeter as defined in claim 2, 3 or 4 in which the MOS device is a P channel field effect transistor, further including means for applying a constant current of about 10 microamperes to the source, the gate switching means being comprised of means for switching the gate between said source of positive bias and the drain at predetermined sampling intervals, said indicating means being comprised of a digital display calibrated in radiation units.

10. A direct reading dosimeter comprising:

(a) a bipolar transistor having a collector, emitter and base,

(b) means for applying a constant current to the base,

(c) a load connected in an emitter-collector circuit of the transistor,

(d) means for applying a current through said emitter-collector circuit,

(e) means for detecting either the current through the emitter-collector circuit or the voltage across the load to provide an output signal, and

(f) means for indicating the output signal.

13. A dosimeter as defined in claim 10, 11 or 12 in which the transistor has a large emitter periphery to base area ratio.

14. A dosimeter as defined in claim 10, 11 or 12 further including means for differentiating the output signal prior to indication thereof.

15. A dosimeter as defined in claim 10, 11 or 12 including means for switching the output signal directly or through a differentiating circuit to the indicating means, whereby the indicating means is caused to correspondingly display total dose or dose rate of said radiation.

11. A direct reading dosimeter comprising:

(a) a bipolar transistor having a collector, emitter and base,

(b) means for applying a constant current to the base,

(c) a load connected in an emitter-collector circuit of the transistor,

(d) means for applying a current through said emitter collector circuit,

(e) means for detecting the voltage across the load to provide an output signal, and

(f) means for indicating the output signal.

12. A direct reading dosimeter comprising:

(a) a bipolar transistor having a collector, emitter and base,

(b) a load connected to the emitter, to form a collector-emitter circuit,

(c) means for applying a constant current to the collector-emitter circuit,

(d) means connected in a base-emitter circuit for applying a base direct current to the transistor,

(e) means for detecting one of the base current, load current or load voltage to provide an output signal, and

(f) means for indicating the output signal.

16. A direct reading dosimeter comprising:

(a) an MOS capacitor including a substrate, an insulating layer disposed over the substrate, and a conductive layer disposed over the insulating layer,

(b) means for applying a bias voltage across the capacitor,

(c) means for applying a high frequency signal through a load across the capacitor,

(d) means for detecting the voltage across the capacitor during or following irradiation of the capacitor by ionizing radiation,

(e) means for differentiating the detected voltage prior to indication thereof, and

(f) means for indicating said detected voltage.

17. A direct reading dosimeter comprising:

(a) an MOS capacitor including a substrate, an insulating layer disposed over the substrate, and a conductive layer disposed over the insulating layer,

(b) means for applying a bias voltage across the capacitor,

(c) means for applying a high frequency signal through a load across the capacitor,

(d) means for detecting the voltage across the capacitor during or following irradiation of the capacitor by ionizing radiation,

(e) means for differentiating the detected voltage prior to indication thereof,

(f) means for indicating said detected voltage, and

(g) means for switching the detected voltage directly or through a differentiating circuit to the indicating means, whereby the indicating means is caused to correspondingly display total dose or dose rate of said radiation.

18. A direct reading dosimeter comprising:

(a) an MOS capacitor for exposure to ionizing radiation,

(b) means for applying a bias voltage across the capacitor,

(c) a first oscillator connected to the capacitor whereby the frequency of the oscillator is determined by the capacitance of the capacitor,

(d) means for detecting the frequency of the oscillator, and

(e) means for displaying the detected frequency of the oscillator as an ionizing radiation dosage indication.

19. A dosimeter as defined in claim 18, including means for converting the frequency of the oscillator into an analog signal having a voltage which varies with said frequency, means for differentiating said analog signal, and for applying said differentiated signal to the displaying means.

20. A direct reading dosimeter as defined in claim 18, including a second oscillator, a trimmer capacitor connected to the second oscillator for varying the frequency of the second oscillator, the detecting means including mixer means for receiving output signals of the first and second oscillators and a counter connected to the output of the mixer, the displaying means being connected to the output of the counter, and further including means for adjusting said bias voltage.

21. A direct reading dosimeter comprising:

(a) a semiconductor device including an insulating layer for trapping positive charges upon said device being irradiated by ionizing radiation, and having at least one electrical parameter varying as a result of said trapped charge,

(b) means for applying a signal to said device whereby said signal is varied as a result of the variation of said parameter,

(c) means for detecting said varied signal, and

(d) means for displaying said detected varied signal.

22. A dosimeter as defined in claim 21, further including means for differentiating said varied signal prior to display.

23. A dosimeter as defined in claim 21 or 22 in which the applied signal is a constant current.

24. A direct reading dosimeter comprising:

(a) a watchcase,

(b) a digital display on the front face of the watchcase,

(c) an audio alarm triggered by a signal having amplitude greater than a predetermined threshold contained within the watchcase,

(d) a first and second manually operated switches fixed within the watchcase for external control,

(e) a semiconductor sensor substantially exposed to ambient ionizing radiation and disposed adjacent the front face of the watchcase, including a semiconductor substrate, an insulating layer disposed over the substrate, and a conductive layer disposed over the insulating layer, said insulating layer being of a type which traps positive charge under the influence of ionizing radiation,

(f) means within the watchcase for applying a bias current to the semiconductor sensor sufficient to offset at least part of any buildup of said positive charge,

(g) means within the watchcase for detecting change in a conductive parameter of said sensor with buildup of said positive charge under the influence of said radiation, and for generating an output signal dependent thereon,

(h) a differentiating circuit within the watchcase,

(i) said output signal being applied via one pair of contacts of one of said switches to the digital display, and via a second pair of contacts of said one of said switches through the differentiating circuit to the digital display,

(j) said output signal also being applied via a pair of contacts of the other of said switches to the audio alarm.