Graphite Backscattered Electron Shield for X-ray Tube Stability
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Solution Overview
Problem
In X-ray tubes, up to 50% of incident electrons are backscattered, leading to electrical charge deposition and potential high voltage instability and tube failure, necessitating a solution to prevent backscattered electrons from entering the vacuum while allowing incident electrons to reach the anode without impacting X-ray flux.
Innovation Solution
A graphite shield with apertures is attached to the anode, creating a gap that absorbs backscattered electrons while allowing X-ray photons to pass through, ensuring free access of incident electrons and minimizing X-ray generation within the shield.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a shield is placed around the anode to block backscattered electrons, then backscattered electron reduction is improved, but X-ray flux transmission deteriorates
Solution Approach 1:
The shield is designed with an array of apertures (porous structure) that allows X-ray photons to pass through while blocking backscattered electrons. The apertures have dimensions that are large enough to transmit X-rays efficiently but small enough to stop electron trajectories, resolving the contradiction between electron blocking and X-ray transmission
Solution Approach 2:
The shield uses graphite as the material, which combines properties of being refractory (withstanding operational temperatures), conductive (handling electrical charge), and having appropriate density to block electrons while being transparent enough to X-rays when structured with apertures
2Object-affected harmful factors
If a shield material with high electron blocking capability is used, then backscattered electron reduction is improved, but X-ray photon transmission deteriorates
Solution Approach 1:
By creating a porous/apertured structure in the shield, the patent enables differential transmission: electrons are blocked by the shield walls while X-ray photons pass through the apertures with minimal attenuation, resolving the material property contradiction
Solution Approach 2:
The shield structure provides different properties in different regions: the shield walls provide electron blocking while the aperture regions provide X-ray transmission pathways, allowing each part to optimize its local function
3Object-affected harmful factors
If the shield is placed close to the anode surface, then backscattered electron absorption is improved, but incident electron access deteriorates
Solution Approach 1:
The apertured structure allows incident electrons to pass through the shield to reach the anode while positioned close enough to the anode surface to effectively intercept and block backscattered electrons before they re-enter the vacuum
4Object-affected harmful factors
If a dense shield material is used to block electrons, then backscattered electron reduction is improved, but X-ray generation within the shield increases
Solution Approach 1:
The apertured structure minimizes the volume of shield material that incident electrons must traverse, reducing the probability of X-ray generation within the shield itself while maintaining effective electron blocking at the anode interface
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 graphite shield effectively reduces backscattered electrons, preventing vacuum instability and maintaining X-ray flux integrity by blocking backscattered electrons while being conductive and refractory to handle operational temperatures.
Implementation Method 1
said shield comprises a material that blocks and absorbs backscattered electrons
Implementation Method 2
said shield comprises a material that has at least 95% transmission for X-ray photons
Data Source
AI summary
The present invention is a shielded anode having an anode with a surface facing an electron beam and a shield configured to encompass the anode surface. The shield has at least one aperture and an internal surface facing the anode surface. The shield internal surface and anode surface are separated by a gap in the range of 1 mm to 10 mm. The shield of the present invention is fabricated from a material, such as graphite, that is substantially transmissive to X-ray photons.