Multi-Anode Photomultiplier Tube Peripheral Electron Collection
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Solution Overview
Problem
Existing photomultiplier tubes suffer from reduced effective area and sensitivity due to electrons emitted from the periphery of the photocathode failing to impinge on the dynodes, leading to non-uniform output signals and loss of image sharpness, especially at the edges during image processing.
Innovation Solution
A multi-anode type photomultiplier tube design featuring a glass faceplate, a side tube with a partitioning wall and shield electrode, and multiple electron multiplying portions and anodes, where the photocathode, partitioning wall, and shield electrode are maintained at the same potential to guide electrons effectively to the dynodes, and a flat electrode with apertures is used to adjust the electric field and reduce transit time differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional photomultiplier tube design is used with a first dynode having a cup shape, then the structure is simple, but electrons emitted from the periphery of the photocathode fail to impinge on the dynodes, reducing effective area and sensitivity
Solution Approach 1:
The first dynode is divided into multiple independent electron multiplying portions (first through fourth portions) arranged in a specific pattern. Each portion independently collects electrons from different regions of the photocathode, ensuring comprehensive coverage including peripheral areas. This segmentation allows each dynode portion to efficiently collect electrons from its designated region without interference from adjacent portions.
Solution Approach 2:
The electron multiplying portions are arranged asymmetrically relative to the center axis of the tube. Specifically, the first and second portions are positioned at different radial distances from the center axis, creating an asymmetric configuration that optimizes electron collection from peripheral photocathode regions. This asymmetric arrangement ensures that electrons from all areas of the photocathode, including edges, can reach appropriate dynode portions.
2Measurement precision
If electrons are allowed to travel freely from photocathode to dynodes, then the structure is simple, but transit time differences occur, causing non-uniform output signals and loss of image sharpness
Solution Approach 1:
Different electron multiplying portions are positioned at different distances from the photocathode surface. The first and second portions are located at different radial positions, creating varied electron path lengths. This local variation in geometry is designed to equalize transit times by compensating for differences in electron emission positions across the photocathode surface.
Solution Approach 2:
The geometric parameters of the electron multiplying portions are specifically optimized to control electron transit characteristics. By adjusting the radial positions and orientations of different dynode portions, the design achieves uniform electron transit time across the entire photocathode surface, eliminating time-dependent signal variations.
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 design ensures that electrons from the periphery of the photocathode are detected with the same sensitivity as those from the center, providing a sharp image by effectively guiding electrons to the dynodes and reducing transit time differences, resulting in uniform detection and improved image processing capabilities.
Implementation Method 1
a photocathode formed on an inner region of the one surface of the faceplate in the side tube to emit a photoelectron in response to light incident on the faceplate
Implementation Method 2
a first dynode provided in the vicinity of the side tube in the side tube for multiplying the photoelectron impinging thereon from the photocathode to emit a secondary electron
Implementation Method 3
a second dynode provided in the vicinity of the tube axis in the side tube for multiplying the secondary electrons impinging thereon from the first dynode to emit secondary electrons
Implementation Method 4
a shield electrode provided between the second dynode and the photocathode for shielding the second dynode from the photocathode; the photocathode, the partitioning wall, and the shield electrode are maintained at a same potential
Data Source
AI summary
A glass container has a faceplate, a side tube, and a bottom. A photocathode is formed on the inner side of the faceplate. The glass container includes a partitioning wall, a shield electrode, a first dynode, a second dynode, a dynode array, and an anode. The partitioning wall has a cross shape to divide an electron focusing space into four space segments. The shield electrode is provided to shield the second dynode from the photocathode. A Venetian blind type of dynodes is provided as the dynode array. The first dynode, the second dynode, the dynode array, and the anode are maintained at the potential which is higher than that of the photocathode. Electrons emitted from the photocathode in response to incident light thereon efficiently impinge on the dynodes regardless of where the electrons are emitted. The electrons are multiplied and then detected by the anode.