How do Dynodes multiply electrons?
A dynode is an electrode in a vacuum tube that serves as an electron multiplier through secondary emission. Secondary emission occurs at the surface of each dynode. Such an arrangement is able to amplify the tiny current emitted by the photocathode, typically by a factor of one million.
How does a discrete dynode electron multiplier work?
Discrete dynode The dynodes are set up so that each time an electron hits the next one it will have an increase of about 100 electron Volts greater than the last dynode. Some advantages of using this include a response time in the picoseconds, a high sensitivity, and an electron gain of about 108 electrons.
How does a Channeltron work?
Instead of a series of discrete plates, a Channeltron electron multiplier uses a high resistance semiconductor material that also has high secondary electron emissivity. Gains of a Channeltron are typically 2 X 10E7 to 2 X 10E8. Channel plate electron multipliers are commonly used on X-ray Photo electron spectrometers.
What does a PMT do?
A photomultiplier tube, useful for light detection of very weak signals, is a photoemissive device in which the absorption of a photon results in the emission of an electron. These detectors work by amplifying the electrons generated by a photocathode exposed to a photon flux.
Is dynode a cathode or anode?
…a series of electrodes (dynodes), and an anode sealed within a common evacuated envelope. Appropriate voltages applied to the cathode, dynodes, and anode cause electrons ejected from the cathode to collide with the dynodes in succession.
What is the function of dynodes in a photomultiplier tube?
The anode of a photomultiplier tube is an electrode that collects secondary electrons multiplied in the cascade process through multi-stage dynodes and outputs the electron current to an external circuit.
How does a Faraday cup work?
The Faraday cup utilizes a physical principle according to which the electrical charges delivered to the inner surface of a hollow conductor are redistributed around its outer surface due to mutual self-repelling of charges of the same sign – a phenomenon discovered by Faraday.
How does a microchannel plate work?
The microchannel plate functions as a particle amplifier, turning a single impinging particle into a cloud of electrons. By applying a strong electric field across the MCP, each individual microchannel becomes a continuous-dynode electron multiplier.
How does a CEM detector work?
Channel electron multipliers (CEMs) are detectors, which respond to charged particles, hard and soft X-rays, and ultraviolet radiation. A CEM has a high surface resistance. When a potential is applied between the input and output end of the CEM, the resistive surface forms a continuous dynode.
What is photocathode made of?
Photocathodes are typically made of alkali-metal films such as potassium bromide (KBr), cesium telluride (CsTe), cesium iodide (CsI), or rubidium telluride (RbTe).
How is a conversion dynode used in the electron multiplier?
A conversion dynode is sometimes put in front of the electron multiplier. This dynode, on which a high voltage of 5 to 20 kV with reverse polarity to the ion is applied, makes it possible to detect negative ions and increase the signal intensity of ions, particularly in the high mass region.
How is a conversion dynode used in a detector?
Conversion Dynode A conversion dynode is sometimes put in front of the electron multiplier. This dynode, on which a high voltage of 5 to 20 kV with reverse polarity to the ion is applied, makes it possible to detect negative ions and increase the signal intensity of ions, particularly in the high mass region. Top << Hardware: Detector
How are negative ions accelerated into the conversion dynode?
In order to detect negative ions, the conversion dynode is held at a high positive voltage (15-25kV): Negative ions are accelerated into the conversion dynode because of its high positive voltage. Upon striking the conversion dynode, positive ions are emitted as secondary particles.
How are conversion dynodes used in Mass Spec Pro?
In addition to improving the high mass response of the detector, conversion dynodes also provide a means for detecting negative ions, which would be otherwise impossible with a multiplier alone. In order to detect negative ions, the conversion dynode is held at a high positive voltage (15-25kV):