“Poor [wo]man’s mass spectrometer” (Resources – 2020) [WIP]

On Nov 29th, 2019 (Applied Science) uploaded a video called DIY mass spectrometer measures potassium in dietary salt substitute^a880 where he built a mass spectrometer based on the American Association of Physics Teachers article Poor Man's Mass Spectrometer (1967)^34d2 by: John W. Dewdney.

This topic–like many of the projects on Applied Science–is something I have had in the back of my mind for a long time, and even something I had put some of my time in to researching. However I didn't get very far. So I had to get ahold of the paper and figure things out.

See: CircuitJS of original circuit (below)

The original article

Poor Man's Mass Spectrometer [LOCKED]

Original thesis


Follow up pieces

A piece in The Amateur Scientist
How to Construct a Molecular-Beam Apparatus and a Mass Spectrometer [LOCKED] (July, 1970) by: C. L. Stong^4acc

  • Here we get many hints, as well as a decade later update
    • Like LMC6001 for the amplifier!
    • Was the magnet hint here?

??Where is the paper about this thing, I think we saw stuff about the magnet there?

The instrumentation amplifier

In the second article (How to Construct a Molecular-Beam Apparatus and a Mass Spectrometer) There is mention of the LMC6001 amplifier, so lets start with that.

Potential guides

Can I get help with measuring particle charge using oscilloscope? (Physics - Stack Exchange)^6847


  • Here we see the usage of 1Mohm resistance, and a shunt capacitor of 2nF

An electronic electroscope^5e58 Pay-dirt! Pretty much a guide to building the amplifier circuit using the aforementioned LMC6001!

The magnet setup

Original (Alnico) Magnet

aluminium (Al), nickel (Ni) and cobalt (Co) - al-ni-co

In the original they are using a modified radar (Cavity Magnetron Tube) C-magnet (see below)

Like this one! (Magnet 1A14) [PDF]

More info and history on this type of magnet (Forum)

Electomagnet (based on "Undergraduate Mass Spectrometer")

[The electromagnet used in conjunction with Randall and Boot's original magnetron](https://en.wikipedia.org/wiki/Cavity_magnetron#/media/File:Manetron_Magnet.jpg)

[CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/) Elektrik Fanne

Dipole Electromagnet [PDF]

The vacuum system

I know that time and time again it is advised against, but I want to try a household service compressor as a vacuum. Possibly with modifications for cooling and lubrication. Weee!

CircuitJS of original circuit

I made it!^61a6

[^a880]: "DIY mass spectrometer measures potassium in dietary salt substitute", Applied Science, Nov 29th, 2019, https://www.youtube.com/watch?v=nIKhUizkXxA
[^34d2]: "Poor Man's Mass Spectrometer", American Journal of Physics 31, 932 (1963); https://doi.org/10.1119/1.1969211 / American Association of Physics Teachers, John W. Dewdney, 1967
[^7c93]: Dewdney, John W. "Undergraduate Mass Spectrometer." The American Journal of Physics 28.5 (1960): 452-456.
[^4acc]: "How to Construct a Molecular-Beam Apparatus and a Mass Spectrometer", The Amateur Scientist, C. L. Stong, July, 1970
[^6847]: "Can I get help with measuring particle charge using oscilloscope", Physics stackexchange (web), Anjan Tripathi, Jun 2nd, 2015, 18:40
[^6c7f]: "LOW CURRENT MEASUREMENT", Tektronix and Keithley Web Forum, vitsrt, July 19th, 2015, 11:15 am
[^61a6]: "CircuitJS of original circuit", Circuit Simulator version 2.2.12js, Jane Hacker, Feb 25th, 2020
[^5e58]: "An electronic electroscope", Article in Physics Education Volume 49, Number 1, Frank Thompson, January 2014, DOI: 10.1088/0031-9120/49/1/18

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