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An Optical Fiber-Based Gamma Thermometer with Simple Design and Potential for Adjustable Axial Segmentation

College of Engineering (COE)
Blue, Thomas E.
Birri, Anthony "Tony"
Licensing Manager
Hong, Dongsung

T2020-325 This invention proposes that an Optical Fiber-Based Gamma-Ray Calorimeter (OFBGC) sensor array can be designed, which does not require the metallic masses that are a part of the Optical Fiber-Based Gamma Thermometer (OFBGT).

The Need

As the world continues to grow and industrialize, the need for safe and efficient power is paramount. Currently, in nuclear fission reactors, there are Local Power Range Monitors (LPRM) which measure electric current between their anode and cathode, which is then monitored to determine the power distribution of the reactor. These LPRMs need to be inserted for each calibration, which exposes the external environment to dangerous radioactive particles.

The Technology

Researchers at The Ohio State University have created a state-of-the-art gamma thermometer in order to provide accurate power distribution measurements without the associated radioactivity risks. This invention proposes that an Optical Fiber-Based Gamma-Ray Calorimeter (OFBGC) sensor array can be designed, which does not require the metallic masses found in other such devices. an optical fiber is used to measure the temperature of an annular cylindrical thermal mass with a low thermal conductivity, such as silica glass. The thermal mass has the geometrical form of a small diameter circular cylindrical tube, that extends the total axial length of the OFBGC sensor array. For the OFBGC, the hole within the tube has a diameter that is slightly larger than the diameter of an optical fiber. An optical fiber runs the length of the tube and is used to measure the temperature of the thermal mass. The thermal mass is centered within a thin-walled metallic outer sheath. A gas gap fills the volume, between the thermal mass and outer sheath. The temperature of the outer sheath is measured with an optical fiber based temperature sensor that is attached to the outer surface of the sheath. The response of the OFBGC is the temperature difference, which is measured between the two optical fiber based temperature sensors (the one that is within the thermal mass and the one that is attached to the outside of the outer sheath). This response can be measured for any axial position within the OFBGC array; i.e. at any axial height. This design is superior to current state of the art because 1) the number of sensors in the OFBGC sensor array is adjustable and limited only by the spatial resolution of the OFBGC sensors, within the OFBGC sensor array, and 2) the OFBGC sensor design is simpler to build than the other sensor arrays available and 3) it is a permanent installation in nuclear reactors which mitigates the risk of exposure to radioactive particles.

Commercial Applications

  • Nuclear Power Plants
  • Manufacturing
  • Control Engineering


  • Efficiency
  • Safety
  • Simplicity

Research Interests

Thomas Blue is currently a Faculty Emeritus, Mechanical & Aerospace Engr. at Ohio State. His research interests include:

  • Space nuclear systems
  • Health physics/Radiation protection
  • Advanced nuclear reactor instrumentation
  • Semiconductor sensors
  • Static and dynamic characterization of radiation-induced degradation of semiconductor power devices and optical fibers
  • Radiation hardness testing