Fiber optic ionizing radiation detector

• US 5,323,011 A
• Filed: 08/16/1993
• Issued: 06/21/1994
• Est. Priority Date: 11/04/1991
• Status: Expired due to Term

• Current Assignee: Johns Hopkins University
• Original Assignee: Johns Hopkins University
• Inventors: Poret, Jay C., Suter, Joseph J.
• Primary Examiner(s): Hannaher, Constantine
• Assistant Examiner(s): Glick, Edward J.
• Application Number:
  US08/106,669
• Time in Patent Office: 309 Days
• Field of Search: 250/472.1, 250/473.1, 250/474.1, 250/368
• US Class Current: 250/474.1
• CPC Class Codes: G01T 1/06 Glass dosimeters using colour change; including plastic dosimeters

Abstract

An ionizing radiation detector employs optical fibers as the medium for sensing ionizing radiation emitted by a radioactive source. Light in the infrared region is pumped continuously through an optical fiber located in an area or region where the unintentional discharge of ionizing radiation may be expected, so that such emission is detected the moment it occurs. The source of optical light emits a constant output within a specific wavelength band which changes only when irradiation of the fibers by ionizing radiation causes their internal color centers to change. The output of the fibers is optically coupled to a photomultiplier via a light pipe. A single light source, detector, and associated electronics complete the system. A hand-held unit unique for remote sensing may house these components. Due to safety conditions, these components are located at a point remote from the position liable to become under the influence of the radiation exposure field. Annealing of that portion of the optical fiber influenced by irradiation field restores the exposed portion of the optical fiber to substantially its previous level of sensitivity thereby reversibly establishing the fiber optic for any subsequent exposure. In response to particle bombardment from a cobalt-60 source, the detector reacts to the energy remaining after passage of the beam through a shielding enclosure, thereby giving a reliable indication of the shielding effectiveness of the enclosure.

Claims

1. An ionization radiation detector comprising:

a radiation sensitive optical fiber coiled around a rod;

said optical fiber having input and output ends;

a source of light;

means for passing light from said source into the input end through said optical fiber;

a source of ionizing radiation for irradiating said optical fiber;

means for shielding said optical fiber from said ionizing radiation;

and means for measuring the mass attenuation coefficient of said shielding means as a function of the intensity of the light arriving at the output end of said optical fiber in response to said irradiation.

2. A detector as set forth in claim 1, wherein the wavelength of said light is 840 nm.

3. A detector as set forth in claim 1, wherein said light passes through said optical fiber to said measuring means substantially unattenuated in the absence of irradiation from said source of ionizing radiation.

4. A detector as set forth in claim 1, wherein said optical fiber has a graded index profile with a diameter of 50 μ

m, a cladding diameter of 125 μ

m, polymer jacket diameter of 250 μ

m, and a numerical aperture of 0.20.

5. A detector as set forth in claim 1, wherein the diameter of said rod is 0.706 cm.

6. An ionization radiation detector comprising:

a radiation sensitive optical fiber coiled around a rod;

said optical fiber having input and output ends;

a source of light;

means for passing light from said source to the input end of said optical fiber thereby providing a first signal at the output end of said optical fiber;

first photodetector means responsive to said first signal;

a source of ionizing radiation for irradiating said optical fiber;

a reference path simultaneously receiving light from said source;

second photodetector means in said reference path for producing a second signal indicative of the intensity of light in said reference path;

central processing unit means for comparing the output of said first photodetector means and said second signal;

and means controlled by said central processing unit means for annealing said optical fiber after irradiation thereby making it reusable.

7. A detector as set forth in claim 6, wherein the wavelength of said light is 840 nm.

8. A detector as set forth in claim 6, wherein said light passes through said optical fiber to said first photodetector means substantially unattenuated in the absence of irradiation from said source of ionizing radiation.

9. A detector as set forth in claim 6, wherein said optical fiber has a graded index profile with a diameter of 50 μ

m, a cladding diameter of 125 μ

m, polymer jacket diameter of 250 μ

m, and a numerical aperture of 0.20.

10. A detector as set forth in claim 6, wherein the diameter of said rod is 0.706 cm.

11. A method for measuring the mass attenuation coefficient of various materials comprising the steps of:

passing light into a radiation sensitive optical fiber coiled around a rod;

exposing said optical filter to a source of ionizing radiation;

placing said optical fiber into a metallic shield whose mass attenuation coefficient is being measured;

again exposing said optical filter to said source of ionizing radiation through the wall of said shield; and

calculating the mass attenuation coefficient of said shield by plotting the percent of optical transmission of said optical fiber when unshielded to the percent of optical transmission of said optical fiber when shielded.

12. The method according to claim 11, wherein said shield is in the form of a cylinder.

13. The method as recited in claim 11, wherein the wavelength of said light is 840 nm.

14. The method as recited in claim 11, wherein said optical fiber has a graded index profile with a diameter of 50 μ

m, a cladding diameter of 125 μ

m, polymer jacket diameter of 250 μ

m, and a numerical aperture of 0.20.

15. The method as recited in claim 11, wherein the diameter of said rod is 0.706 cm.