CsI Phosphor Columnar Crystal Orientation for X-ray Image Sharpness
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Solution Overview
Problem
Current digital radiographic image detection systems, such as computed radiography and X-ray flat panel detectors, suffer from insufficient image sharpness and spatial resolution compared to conventional screen/film systems, primarily due to scattering of emitted light within the phosphor layer, which affects the structure and efficiency of the phosphor crystal.
Innovation Solution
A radiation image conversion panel is developed with a phosphor layer composed of cesium iodide (CsI) columnar crystals formed through gas phase deposition, where the orientation degree of the phosphor crystals is maintained between 80% to 100% to minimize light scattering, using thallium as an activator to enhance luminescence efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the phosphor layer thickness is increased to improve emission efficiency, then the conversion rate of X-rays to visible light increases, but light scattering within the phosphor layer increases leading to deteriorated sharpness
Solution Approach 1:
The phosphor layer is segmented into columnar crystal structures that are vertically oriented. This segmentation allows light to travel through defined channels (columns) rather than scattering randomly through a continuous mass, thereby maintaining sharpness while enabling greater thickness for improved emission efficiency.
Solution Approach 2:
The phosphor layer exhibits local quality variations through its columnar structure, where each column acts as a light guide with specific optical properties. This local structuring allows different regions (columns) to guide light efficiently while maintaining overall high emission efficiency through increased total thickness.
2Use of energy by moving object
If an activator is added to enhance luminescence efficiency, then the visible conversion efficiency improves, but the columnar crystal structure becomes disordered leading to deteriorated sharpness
Solution Approach 1:
The activator is incorporated locally within the columnar crystal structure rather than uniformly distributed. This allows the activator to enhance luminescence at specific sites while the overall columnar structure maintains its order and light-guiding properties.
Solution Approach 2:
The phosphor layer is formed as a composite material combining the phosphor matrix compound with the activator. This composite structure allows the activator to enhance luminescence efficiency while the matrix compound maintains the columnar crystal structure necessary for sharpness.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly enhances the luminance of the radiation image conversion panel by preventing disorder in the phosphor crystal structure, thereby reducing light scattering and improving image sharpness and resolution, leading to improved image quality in digital radiographic applications.
Implementation Method 1
cesium iodide (CsI) exhibits a relatively high conversion rate of X-rays to visible light
Implementation Method 2
its light guide effect inhibits scattering of emitted light within the crystal
Implementation Method 3
a phosphor layer which is composed of a phosphor columnar crystal formed from a phosphor matrix compound and an activator with a gas phase deposition process
Data Source
AI summary
Disclosed is a radiation image conversion panel wherein luminance is improved by preventing the disorder of the structure of phosphor columnar crystals, thereby eliminating the scattering and refraction of optical elements which is emitted by an X-ray-irradiated phosphor and propagated in the direction of a photoelectric conversion element. Moreover disclosed is a radiation image detector using the same. The radiation image conversion panel is characterized in that the radiation image conversion panel comprises a phosphor layer on the substrate, that the phosphor layer is configured of the phosphor columnar crystals formed from a phosphor matrix compound and an activator by vapor deposition, and that the degree of the orientation of the surface of the phosphor columnar crystals, the degree of the orientation being based on X-ray diffraction spectrum and the surface having a fixed mirror index, is in the range of 80 to 100% without regard to the position in the direction of the thickness of the layer from the root near the substrate to the tip of the phosphor columnar crystals of the phosphor layer.