Building an electron multiplier tube

In summary, the conversation discusses the use of a photomultiplier tube in a DIY mass spectrometer project and the materials that can be used as dynodes in the tube. However, the process of making and measuring the secondary emissivity of these materials is not recommended for amateurs and specialized equipment may be needed. It is suggested to contact a company like Hammamatsu for assistance in obtaining a suitable photomultiplier tube.
  • #1
tyrant91101
13
0
This is for a mass spectrometer project so the photomultiplier tube will be hit by charged proteins or other macromolecules. This project is mostly DIY so I'm trying to avoid buying any expensive parts.

Anyway, from what I understand, electron multipliers work by releasing secondary emission electrons when hit by the ion and the tube is either curved or straight and it has a bunch of lined up dynodes which create an electron cascade which then leads to an anode.

However, how would I go about making one? Wikipedia lists the following materials as usable as the dynode:
  • alkali antimonide
  • beryllium oxide (BeO)
  • magnesium oxide (MgO)
  • gallium phosphide (GaP)
  • gallium arsenide phosphide (GaAsP)
  • lead oxide (PbO)

However, how do I go about making and measuring the secondary emissivity of these materials and then making a tube out of them? (Or any other material with high secondary emissivity)
 
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  • #2
First, macromolecules will stick to and poison any photomultiplier (PMT) cathode. PMTs are usually designed for measuring photons or electrons. Maybe some are good for ions.

Second, designing any PMT, and getting the electric field profiles correct, is not for amateurs.

Third, I believe (moist?) air will poison a dynode coating. You will need to coat it under vacuum.

Fourth, you will need a front surface, solid cathode. It is possible you could take a window cathode off an end-window PMT and use the first dynode for the cathode. Or you could use a side-window tube like a 1P21 and take the glass off.

Fifth (best), contact Hammamatsu.

http://jp.hamamatsu.com/en/product_info/index.html

Click on "photosensitive electron tubes".

Bob S
 

1. How does an electron multiplier tube work?

An electron multiplier tube works by using a series of dynodes, which are metal electrodes with high voltage applied to them. When an electron enters the tube, it is accelerated towards the first dynode and causes multiple secondary electrons to be emitted. These electrons are then accelerated towards the next dynode, causing even more electrons to be emitted. This process continues until the electrons reach the last dynode, resulting in a significantly amplified electron signal.

2. What are the main components of an electron multiplier tube?

The main components of an electron multiplier tube include the input electrode, a series of dynodes, and the output electrode. The input electrode is where the initial electrons enter the tube, while the dynodes are responsible for amplifying the electron signal. The output electrode collects the amplified electrons and sends them to the next stage of the circuit.

3. How is the gain of an electron multiplier tube calculated?

The gain of an electron multiplier tube is calculated by dividing the number of output electrons by the number of input electrons. This gain can vary depending on the number of dynodes and their geometry, as well as the voltage applied to each dynode. Typically, an electron multiplier tube can have a gain of several thousand to millions.

4. What are the applications of electron multiplier tubes?

Electron multiplier tubes are commonly used in scientific instruments such as mass spectrometers, particle detectors, and photomultiplier tubes. They are also used in night vision devices and photomultiplier tubes in cameras, as well as in medical imaging equipment such as X-ray detectors and scintillation counters.

5. How can I maintain and troubleshoot an electron multiplier tube?

To maintain an electron multiplier tube, it is important to keep it clean and free from any physical damage. It is also crucial to use appropriate voltage levels to prevent damage to the dynodes. If troubleshooting is needed, it is recommended to check the voltage levels, connections, and any possible sources of interference. If necessary, the tube may need to be replaced if it is damaged beyond repair.

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