Curved First-Stage Dynode for Photomultiplier Tubes
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Solution Overview
Problem
Existing first-stage dynodes in photomultiplier tubes face challenges in suppressing cathode transit time difference and transit time spread due to variations in secondary electron transit times, particularly because of teacup-shaped and funnel-shaped designs that lead to inconsistent electron emission surfaces.
Innovation Solution
A first-stage dynode with a curved bottom surface and side surfaces that are concave in cross-section, where the side surfaces become closer to an electron passage opening as they move away from the center, reducing the transit distance of photoelectrons and secondary electrons, and ensuring a radius of curvature greater than 2 mm and width ratio of 0.1L, thereby minimizing transit time differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a teacup-shaped first-stage dynode with a flat bottom surface is used, then the collection efficiency of photoelectrons is improved, but the transit time of secondary electrons from the first-stage dynode to the second-stage dynode cannot be adjusted, resulting in cathode transit time difference and transit time spread
Solution Approach 1:
The patent applies curvature to the side surfaces of the first-stage dynode, forming them as curved surfaces that are concave in cross-section parallel to the predetermined direction. This curvature design allows secondary electrons emitted from different regions of the electron emission surface to have more uniform transit paths and times to the second-stage dynode, thereby reducing transit time spread while maintaining the teacup shape's photoelectron collection efficiency
Solution Approach 2:
The patent implements different surface geometries in different regions of the first-stage dynode: the bottom surface maintains a flat or slightly curved configuration for optimal photoelectron collection, while the side surfaces are designed with specific concave curvature to control secondary electron transit. This local differentiation of surface properties allows simultaneous optimization of both photoelectron collection efficiency and secondary electron transit time uniformity
2Measurement precision
If a funnel-shaped receiving port with perpendicular side surfaces is provided, then a signal current independent of photocathode incidence position is achieved, but secondary electrons from the central region travel linearly while those from regions near the side surface repel the side surface, resulting in transit time difference
Solution Approach 1:
The patent replaces the perpendicular flat side surfaces of the funnel shape with curved surfaces that are concave in cross-section. This curvature modification creates more uniform electric field distribution and smoother electron trajectories for secondary electrons emitted from all regions of the electron emission surface, eliminating the repulsion effect from sharp edges and reducing transit time differences while preserving the position-independent signal current characteristic
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
This configuration effectively reduces cathode transit time difference and transit time spread in photomultiplier tubes by ensuring consistent electron transit paths and reducing dependence on incidence position, enhancing the overall performance of the photomultiplier tube.
Implementation Method 1
a first-stage dynode to be used in a photomultiplier tube... photoelectrons... secondary electrons
Implementation Method 2
electron emission surface is formed by a bottom surface of the bottom wall portion and a pair of side surfaces of the pair of side wall portions
Data Source
AI summary
A first-stage dynode is a first-stage dynode to be used in a photomultiplier tube, and includes a bottom wall portion and a pair of side wall portions extending from both end portions of the bottom wall portion in a predetermined direction to one side. An electron emission surface is formed by a bottom surface of the bottom wall portion on the one side and a pair of side surfaces of the pair of side wall portions on the one side, and each of the pair of side surfaces is a curved surface that is curved in a concave shape in a cross section parallel to the predetermined direction.