| Electronics > Projects, Designs, and Technical Stuff |
| CRT Mass Spectrograph - wait don't leave! |
| << < (3/4) > >> |
| LaserSteve:
Omegatrons morphed into something simple looking with six big mesh grids with alternating DC bias and applied Rf that worked even better. Then the Quadrapole , Hexapole, Octopole, happened. That and better magnetics for generating high voltage swept RF made the Quad the beast of choice. Omegatrons became popular until Phillips / Sylvania / Leybold / NASA decided that making Omegatrons in a standard octal vacuum tube envelope were no longer needed. They actually were in production for a long time. This design has always appealed to me: http://lampes-et-tubes.info/sp/sp103.php?l=e By home made tube standards it is simple and can be brazed instead of spot welded. This is one case where the details in the RGA patents are better then the ones in scientific publications, and the USPTO server is your friend. Just looked at some historical texts. J.J. Thompson built one of the first MS widgets , with a phosphor detector! Something called a "Parabola Spectrograph" That doesn't look too bad to build, just interpreting the results will probably drive you crazy due to the display format. Steve |
| LaserSteve:
Usually the tube walls are so thin and the COE 88 LEAD or Soft glass so fragile that we use the standard glassblowing technique of melting a spot and blowing a bubble, then knocking off the bubble and fusing on new glass. Its possible to make a filter to trap the moisture out of your breath. Steve |
| ChristofferB:
--- Quote from: Kleinstein on February 24, 2020, 06:37:02 pm ---The Omega-tron seems to need a sizable magnetic field. This can interfere with other parts of the system and not so easy to just mount to an existing system. The quadrupole mass spec seem to be easier and lower weight but still good enough for residual gas analysis. There is a limited use of slightly better resolution than keeping integer atomic numbers apart. So to really get to the range where one can distinguish different molecules of same integer part (e.g. N and CH2) it may be quite hard. So it would take a really good one to get extra information. --- End quote --- That is where ionization techniques come into play. I can't imagine seeing the same ionization form generating both something like N*- (I have a hard time believing that is ever seen) as well as CH2, which is a molecular fragment. Either way, if I ever commit to building an MS, I will absolutely couple my sample in through some sort of chromatography. Maybe just a room temp. GC, similar to the one I've built previously. I'll have to keep my eyes open for an omegatron tube, though I imagine they'd be quite the collectible. If one built one themselves, mounted on a metal tube socket in a standard KF40 vacuum flange I guess it could be possible to build the tube fro scratch. The real tube looks to have elements of gold plated foil, likely nickel or something similar. If I can live with seeing copper everywhere I guess copper foil could be used, too. |
| LaserSteve:
This just got interesting: See if you can find a copy of: "Development of Mass Spectrometers from Thompson and Aston to Present" By Munzenberg... Then look at this: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97331999000300002 The above URL is: Brazilian Journal of Physics Print version ISSN 0103-9733On-line version ISSN 1678-4448 Braz. J. Phys. vol.29 n.3 São Paulo Sept. 1999 https://doi.org/10.1590/S0103-97331999000300002 100 years of ion beams: Willy Wien's canal rays Turns out the WIEN filter rods DO NOT have to be in the vacuum... May result in "Fuzzyness" but they do NOT have to be in the vacuum. Steve |
| ChristofferB:
Thanks! I'll check it out! Atmospheric pressure quadrupole is an interesting concept! but I mean, it's not uncommon for the ions to be generated at atmospheric pressure and then sucked through a pinhole into the high vacuum region, so it makes conceptual sense. Have I missed some theory, or isn't the "omegatron" just a tiny cyclotron? In that case they are still used! Ion Cyclotron Resonance - MS is totally a thing! I wonder if one could make a pocket sized conventional Dee-type cyclotron as a mass analyzer. --Chris |
| Navigation |
| Message Index |
| Next page |
| Previous page |