Photomultiplier Tube Dynode Segmentation for Signal Gain
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Solution Overview
Problem
Conventional photomultiplier tubes face a challenge in achieving high electron multiplying efficiency when downsized, resulting in a small signal amount due to the reduction in size of the photocathode and electron multiplying parts.
Innovation Solution
The photomultiplier tube design incorporates a housing with an insulating substrate featuring N stages of dynodes spaced along its inner surface, each with columnar parts for forming electron multiplying channels and opposing surfaces that project to enhance secondary electron emission and guide electrons efficiently between stages, improving electron multiplying efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the photomultiplier tube is downsized, then the device size is reduced, but the signal amount becomes small
Solution Approach 1:
The photocathode and electron multiplying part are segmented into multiple independent dynode stages (N stages) arranged along the inner surface. Each dynode is provided with multiple columnar parts that form separate electron multiplying channels, allowing the electron multiplication function to be distributed across multiple segments, thereby maintaining high electron multiplying efficiency even when the overall device size is reduced.
Solution Approach 2:
The dynodes are arranged in a planar configuration along the inner surface of the housing rather than in a traditional linear or spherical geometry. This two-dimensional arrangement allows for compact packaging while maintaining sufficient electron multiplication path length, effectively utilizing the surface area of the housing to achieve high gain in a small volume.
2Volume of moving object
If the photocathode and electron multiplying part are made small, then the device is downsized, but the electron multiplying efficiency decreases
Solution Approach 1:
Each dynode is provided with multiple columnar parts having specific geometric structures that optimize secondary electron emission locally. The columnar parts create focused electron multiplying channels with enhanced electric field distribution, ensuring high electron multiplying efficiency at each local stage even when the overall device dimensions are reduced.
Solution Approach 2:
The opposing surfaces of adjacent dynodes are positioned and shaped in advance to create optimized electric field configurations before electrons arrive. This preliminary structuring of the electric field ensures that electrons are efficiently accelerated and guided through the electron multiplying channels, maximizing multiplication efficiency in the compact geometry.
3Reliability
If dynodes are arranged with opposing surfaces projecting, then electron guiding efficiency is improved, but device complexity increases
Solution Approach 1:
Multiple functional features are merged into the dynode structure: the columnar parts serve both as electric field enhancement elements and as structural support, while the opposing surfaces of adjacent dynodes simultaneously provide electron guiding and define the electron multiplying channel geometry. This integration reduces the number of separate components needed.
Solution Approach 2:
The dynode structure with columnar parts and opposing surfaces serves multiple functions: it creates the electron multiplying channel, enhances secondary electron emission, guides electrons between stages, and provides structural support. This multi-functionality reduces overall device complexity by eliminating the need for separate components for each function.
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 increases the potential near secondary electron emitting surfaces, efficiently guides multiplied electrons between dynodes, and enhances electron multiplying efficiency, even when the device is downsized, while also improving withstand voltage properties and signal detection reliability.
Implementation Method 1
a photocathode which is installed on the first end side inside the housing so as to be spaced away from the electron multiplying part, converting incident light from outside to photoelectrons to emit the photoelectrons
Implementation Method 2
each of the N stages of dynodes is arranged on the inner surface and provided with a plurality of columnar parts where secondary electron emitting surfaces are formed, thereby forming electron multiplying channels having the secondary electron emitting surfaces between adjacent columnar parts
Data Source
Figure 1
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AI summary
The photomultiplier tube 1 is provided with an electron multiplying part 33 having a plurality of stages of dynodes 33a to 331 arrayed along a direction at which electrons are multiplied on an inner surface 40a of a casing 5 and a photocathode 41 and an anode part 34 installed so as to be spaced away form the electron multiplying part 33 inside the casing 5. Each of the dynode 33c to 33e is provided with a plurality of columnar parts 51c to 51e where secondary electron emitting surfaces 53c to 53e are formed, thereby forming electron multiplying channels C between adjacent columnar parts. An opposing surface 54e which opposes a columnar part 51d which is a previous stage at a columnar part 51e which is a subsequent stage is formed in such a manner that both end parts 56e, 57e in a direction along the inner surface 40a of the opposing surface 54e project to the first end side from a site 55e which opposes the end part of the second end side on the secondary electron emitting surface 53d of the columnar part 51d.