Building an electron multiplier tube

[tyrant91101]

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)

 

[Bob S]

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