Annular Ionisation Chamber Structure for Low-Noise Gas Detection
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Solution Overview
Problem
Ionisation chambers face challenges in accurately detecting low levels of radioactive gas in air due to issues with noise interference, leakage currents, and mechanical resonance, which affect the accuracy and stability of the measurements.
Innovation Solution
The design incorporates an annular collection electrode and an annular polarising electrode, each supported by concentric rings with hollow spokes, which increase leakage resistance and reduce microphony, while a conductive disc and earthed sleeve further minimize noise and capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If the central collection electrode is truncated to reduce chamber capacitance, then capacitance is reduced by ≈20%, but the electrode becomes a beam supported at one end which resonates mechanically and acts as a microphone
Solution Approach 1:
The electrode support structure is segmented into multiple discrete insulating supports distributed along the electrode length, rather than a single continuous support. This segmentation provides mechanical stability at multiple points while maintaining electrical isolation, preventing the electrode from acting as a microphone while preserving the truncated length for low capacitance.
Solution Approach 2:
The support structure uses composite construction combining insulating materials (to provide electrical isolation) with mechanically rigid components (to prevent resonance). This composite approach allows the electrode to be both electrically isolated and mechanically stable, resolving the contradiction between capacitance reduction and measurement accuracy.
2Device complexity
If a substantial insulating disc is used to support the polarising electrode, then the structure is simple and stable, but the large cross-sectional area and short length minimise resistance and increase leakage currents
Solution Approach 1:
The support structure transitions from a two-dimensional disc geometry to a three-dimensional configuration with multiple insulating supports extending vertically. This dimensional change increases the effective insulation path length without significantly increasing the horizontal cross-sectional area, thereby improving leakage resistance while maintaining structural simplicity.
Solution Approach 2:
The single disc insulator is segmented into multiple discrete insulating supports distributed around the chamber. This segmentation increases the total insulation path length and distributes the electrical stress, improving overall leakage resistance while maintaining ease of construction.
3Weight of moving object
If the central electrode is made from metal such as tubular aluminium or brass to minimise mass and maximise rigidity, then mass is reduced and rigidity is maximised, but the design remains susceptible to microphony
Solution Approach 1:
Multiple insulating supports are strategically positioned to provide counterbalancing mechanical support at different points along the electrode. This distributed support system counteracts the effects of electrode mass and rigidity that would otherwise lead to microphony, allowing the use of lightweight metal electrodes without susceptibility to vibration-induced noise.
4Adaptability or versatility
If the polarising electrode is made porous (rolled perforated sheet) to allow gas permeability, then gas flow is enabled for air monitoring, but the structure becomes more complex and leakage paths increase
Solution Approach 1:
The polarising electrode is constructed from porous or perforated material that allows gas to pass through while maintaining the electrode's electrical function. This porous structure enables the chamber to monitor gases in air environments while the electrode maintains its electrical properties for detection.
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 significantly enhances the leakage resistance and reduces noise interference, leading to more accurate and stable detection of low-level radioactive gas, with a notable reduction in settling time from 15 minutes to 10 seconds.
Implementation Method 1
a gas between them provides the means of creating electron-ion pairs when ionising radiation interacts with it
Implementation Method 2
each electrode is supported by an insulator... significantly enhances the leakage resistance
Implementation Method 3
each electrode is supported by an insulator... reduces microphony
Implementation Method 4
a conductive disc and earthed sleeve further minimize noise and capacitance
Data Source
AI summary
The invention provides for an ionisation chamber suitable for the detection of radioactive gas in air. The chamber has an annular collection electrode and an annular polarising electrode, each electrode having a diameter, a proximate end and a distal end, the proximate ends of both electrodes being fixed at a base plate, wherein each electrode is supported by an insulator, wherein the insulator supporting polarising electrode comprises an outer ring and an inner ring, the outer ring having a diameter corresponding that of the polarising electrode.