Non-radioactive Electron Source for Analytic Spectrometers
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Solution Overview
Problem
Ion mobility spectrometers using radioactive electron sources pose environmental and health hazards, and non-radioactive alternatives like photo-emitters or corona discharges result in reduced ionization efficiency and shorter operational lifetimes due to high vacuum requirements and electron permeability issues.
Innovation Solution
A non-radioactive electron source utilizing a gas discharge with a partition wall that allows electron permeability but maintains a gas-tight separation, enabling efficient ionization in a wide range of pressures and extending operational lifetimes by using windows with reduced leak rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a non-radioactive electron source (photo-emitter or corona discharge) is used, then environmental and health hazards are eliminated, but ionization efficiency is reduced and operational lifetime is shortened
Solution Approach 1:
The device is divided into two separate chambers: a source chamber containing the non-radioactive electron source and a reaction chamber where ionization occurs. These chambers are separated by a window that is impermeable to gas but permeable to electrons, allowing the electron source to operate in vacuum while delivering electrons to the reaction chamber at atmospheric pressure. This segmentation resolves the contradiction by isolating the electron source from the reaction environment.
Solution Approach 2:
The electron-permeable window acts as an intermediary between the source chamber and reaction chamber. It selectively transmits electrons while blocking gas molecules, enabling the non-radioactive electron source to function effectively without requiring the entire system to be in vacuum. This intermediary component allows the system to maintain both safety (non-radioactive source) and performance (adequate ionization efficiency).
2Object-affected harmful factors
If a non-radioactive electron source operating in vacuum is used, then radioactive hazards are eliminated, but a high vacuum system is required which increases device complexity
Solution Approach 1:
The device separates the vacuum environment (source chamber) from the atmospheric pressure environment (reaction chamber) using an electron-permeable window. This segmentation allows the electron source to operate in vacuum without requiring the entire spectrometer to be vacuum-sealed, thereby reducing device complexity while maintaining the safety benefits of non-radioactive sources.
Solution Approach 2:
The electron-permeable window is a thin film structure that is impermeable to gas but permeable to electrons. This thin film allows vacuum conditions to be maintained only in the source chamber rather than the entire device, significantly reducing the complexity of vacuum system requirements while still enabling non-radioactive electron sources to function.
3Reliability
If a thick window is used to reduce gas permeability, then the leak rate is sufficiently low, but electron permeability is reduced which decreases ion currents
Solution Approach 1:
The patent optimizes the window thickness to a specific range (30-300 nanometers) that balances two opposing requirements: thin enough to allow adequate electron transmission for sufficient ion current, but thick enough to maintain low gas permeability for acceptable operational lifetime. This parameter optimization resolves the contradiction between electron permeability and gas tightness.
Solution Approach 2:
The window is made from specific materials (such as silicon nitride or other electron-permeable materials) that have unique properties allowing simultaneous electron transmission and gas impermeability. These composite or specialized materials enable the window to satisfy both requirements: sufficient electron permeability for ion current and sufficient gas impermeability for operational lifetime.
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 solution significantly increases the electron current in the reaction chamber, improving signal-to-noise ratio and lowering detection limits, while allowing for commercially viable operational periods without the need for high vacuum systems.
Implementation Method 1
A non-radioactive electron source which operates with a gas discharge is used
Implementation Method 2
electrons are produced in a source chamber and are accelerated in an electric acceleration region
Implementation Method 3
partition wall which allows electron permeability but maintains a gas-tight separation
Implementation Method 4
enabling efficient ionization in a wide range of pressures
Implementation Method 5
electrons ionize the gas in the reaction chamber, as happens in the case of a radioactive electron source
Data Source
AI summary
In an analytical spectrometer in which accelerated electrons are used to ionize analytes, a non-radioactive electron source uses a gas discharge to generate the electrons. The gas discharge is located in a substantially hermetic source chamber and the free electrons in the plasma of the gas discharge are accelerated in an electric acceleration region towards a partition wall which separates the source chamber from a reaction chamber. The partition wall is permeable to the accelerated electrons but impermeable to gas in the source chamber so that the electrons penetrate the partition wall into the reaction chamber and generate primary ions that chemically ionize the analytes.