Scintillator dosimetry probe

• US 5,006,714 A
• Filed: 02/24/1989
• Issued: 04/09/1991
• Est. Priority Date: 02/24/1989
• Status: Expired due to Fees

• Current Assignee: Radiation Measurements, Inc.
• Original Assignee: Radiation Measurements, Inc.
• Inventors: Attix, Frank H.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Eisenberg, Jacob M.
• Application Number:
  US07/315,321
• Time in Patent Office: 774 Days
• Field of Search: 250/368, 250/252.1 R, 250/336.1
• US Class Current: 250/368
• CPC Class Codes: A61N 2005/1076 using a dummy object placed in the radiation field, e.g. phantom
• CPC Class Codes: A61N 5/1048 Monitoring, verifying, controlling systems and methods
• CPC Class Codes: G01T 1/02 Dosimeters G01T1/15 takes precedence
• CPC Class Codes: G01T 1/169 Exploration, location of contaminated surface areas

Abstract

A probe (10) employs a scintillator (18) as a detector for high-energy beam dosimetry. The scintillator (18) is positioned in an ionizing radiation beam (52) which creates a light output that is proportional to the radiation dose-rate incident upon the scintillator (18). The light is conducted from the scintillator (18) through a light pipe (16) to a photomultiplier tube (28), which converts the light to an electric current. The scintillator (18), the light pipe (16), the photomultiplier (28), and associated optical connections have opaque coverings or sheaths to prevent extraneous light from being introduced into the probe (10). The electric current produced by the photomultiplier tube (28) is proportional to the radiation dose-rate incident upon the scintillator (18). The radiation dose-rate may then be displayed or recorded by a measurement of the electric current. The light pipe (16) is flexible so that the scintillator (18) may be repositioned in a number of locations in the radiation beam (52) to map the radiation field. The scintillator (18) is made of a material that approximates water or muscle tissue in atomic number and electron density to minimize perturbations in a phantom water tank (50). A compensating light pipe 60, paralleling the first, and connected to a second photomultiplier tube, generates a current that, when subtracted from the first photomultiplier tube current, corrects for radiation interactions in the light pipe and photomultiplier tube.

Claims

1. Apparatus for characterizing a radiation field by measuring the dose-rate at a plurality of points in the radiation field, the apparatus comprising:

a phantom filled with water in the radiation field;

a scintillator positioned in the phantom, the scintillator producing a light output proportional to the dose-rate of radiation that impinges upon the scintillator;

a light pipe having a first end and a second end, the first end being optically connected to the scintillator so that the light pipe conveys the light output from the scintillator;

means connected to the second end of the light pipe and located outside of the phantom for converting light to an output signal proportional to the dose-rate of radiation that impinges upon the scintillator; and

mechanical scanning means for moving the scintillator with the end of the light pipe attached through the interior of the phantom to map the radiation field within the phantom.

2. An apparatus as claimed in claim 1 further comprising a waterproof scintillator enclosure that envelopes the scintillator and optically connects it to the light pipe.

3. An apparatus as claimed in claim 1 wherein the material of the scintillator is selected to have an electron density within about 1% of the electron density of water, 3.34×

10²³ electrons per gram.

4. An apparatus as claimed in claim 3 wherein the material of the scintillator is polyvinyltoluene.

5. Apparatus for characterizing a radiation field by measuring the dose-rate at a plurality of points in the radiation field, the apparatus comprising:

a phantom filled with water in the radiation field;

a scintillator positioned in the phantom, the scintillator producing a light output proportional to the dose-rate of radiation that impinges upon the scintillator;

a first light pipe having a first end and a second end, the first end being optically connected to the scintillator so that the first light pipe conveys the light output from the scintillator;

a second light pipe having a first end and a second end, the first end being positioned adjacent the first end of the first light pipe to convey stray light in the phantom through the second light pipe;

separate means connected to the second end of each of the first and second light pipes and located outside of the phantom for converting light to an output signal proportional to the dose-rate of radiation that impinges upon the scintillator and the first end of the second light pipe respectively;

means for subtracting the output signal representing the stray light from the output signal representing the dose-rate of radiation that impinges upon the scintillator; and

mechanical scanning means for moving the scintillator with the end of the light pipe attached through the interior of the phantom to map the radiation field within the phantom.

6. An apparatus as claimed in claim 5 further comprising a waterproof scintillator enclosure that envelopes the scintillator and optically connects it to the light pipe.

7. An apparatus as claimed in claim 6 wherein the material of the scintillator is selected to have an electron density within about 1% of the electron density of water, 3.34×

10²³ electrons per gram.

8. An apparatus as claimed in claim 7 wherein the material of the scintillator is polyvinyltoluene.