Novel Radiation Detector Based on Ionic Junctions

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Schematic illustrations of the ionic junction and radiation detector
Professor Harry Tuller
Department of Materials Science and Engineering, MIT
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Sean Bishop
Department of Materials Science and Engineering, MIT
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Jim Freedman
MIT Technology Licensing Officer - Chemicals, Instruments, Consumer Products
Patent Protection

Ionic junction for radiation detectors

US Patent 8,723,186


Radiation detectors based on Thallium Halides have been found to provide very promising performance — having features such as high stopping power (ability to detect many kinds of radiation) and good resolution (ability to distinguish between types of radiation). However, they suffer from long-term degradation. The current technology describes an alternative design to reduce this issue.

Problem Addressed

The major drawback of Thallium Halide-based detectors is that the Thallium ions tend to migrate over time, causing electrochemical decomposition of the material. As a result, the radiation detection becomes less effective over time. Even if supplementary materials (such as dopants) were to be used to increase the resistance of the material and thus reduce the migration of the Thallium ions, the degradation would still be significant.


This technology describes a transformative design to significantly increase the Thallium Halide-based radiation detector's lifespan. As opposed to one continuous medium of Thallium Halide, the technology proposes separating it into two regions, thereby developing an ionic junction similar to the "p-n" junction in semiconductors. Using the example of the Thallium Halide TlBr: one region would be dominated by Br vacancies and thus be positively charged, while the other region would be dominated by Tl vacancies and thus be negatively charged. The resulting electric field (used to detect radiation) has properties which can be controlled using dopants or by changing the electric potential applied across the regions. 

Such a design allows for the amount of degradation to be significantly reduced, extending the lifetime of the device by orders of magnitude. Furthermore, properties of the electrical field can be systematically designed to fit different detection needs. This technology also describes various methods of fabricating such a design.


  • Increases the lifetime of Thallium Halide-based radiation detectors by orders of magnitude
  • Allows the systematic design of their properties