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neptunium
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i know a glass blower who is currently building a mass spectrometer for me. i had various vacuum glass tubes with electrodes built from him before and i had a lot of fun with it. my ex roomates girlfriend thought it was appropriate to throw my stuff at him while in a rage so i lost the last one .

However, i am wondering about the detection system and after some research on how to detect heavy ion i am at an impass..
scintillators must be very thin and degrade rapidly, single farady cups requires scanning and arrays are impossible to find (cheap enough) same with microchannel detector...
I will be posting pictures of the thing when it is done (maybe early January)
there is an positive ion repulsor, an ion gun, a beam focusor and negative pole have 2 vacuum pumps with gauge that measures vacuum from atm to about 1 torr and from 10-1 to 10-10 torr. i am still looking for a turbo pump.
the mass spectrometer is about 3 feet in lenght so 10-4 Torr for a mean free path of about 1 meter is required wich my pumps cannot reach.

anyways, i am looking for a way to detect, qualify and quantify the ion hitting the back of the tube. Software instead of the oscilloscope would be the best!

any ideas?

diddi
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sounds like a great project. you are lucky to have access to that kind of technical expertise.
neptunium
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thanks , its not much but time and a few bucks.... anybody with enough dedication should be able to do what i do ...
also i try those alpha spectrometer. . . most of them have NO detector (on ebay) those that do are way too expansive and i talk to the tech support guy at ortec who said they ar light sensitive and cost from 700 to 4000 dollars (US)...
so ... next!

phlogiston
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Very cool. I have been hoping someone would try building a masspec of some kind someday (lacking time and equipment to do so myself), looking forward to your progress.
Incidentally, Ben Krasnov also mentioned in one of his recentish videos he was going to work on one.

Regarding detector suggestions, a non-electronic, simple (but inconvenient) method is to use photographic paper.

How would a CCD behave in this environment? As I am sure you are well aware, charged particles of sufficient energy show up on CCD cameras. Linear CCD chips can be harvested from discarded scanners, and they are often relatively easy to interface with.

Using the search term "ionccd" you can find papers describing a modified CCD where the photosensitive array has been replaced with an array of capacitors which is even commercially used but it is probably pretty costly if at all available in single chips.

What energy do your ions have when they reach the detector?
Also, how are you deflecting them, is scanning an option you have permanently dismissed?

edit: I removed a non-electonic detector suggestion involving a dark basement, your ex-roommates girlfriend and atropine but on second thought perhaps it is a poor joke. I can hardly imagine how angry you must have been though.

[Edited on 29-12-2014 by phlogiston]

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neptunium
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a CCD seems like a great idea! ... no i did not fully rejected the scanning method yet.
the design will be such that several method of detection could be used thanks to interchangeable glass element.
i plan to use it with voltage from 1000 to 40Kv . but probably closer to 10Kv and play arround to see what is the best voltage.
the deflection will be either a permanent magnet (N55) or a strong ectro magnet on a variac.
I want to start with LiI because Iodine and Lithium are far appart in mass with 2 important natural isotopes. (3 actually but Li6 less than 8%.)
so if i put a CCD camera i should be able to see the impact of each group of ion ... im going to work on this idea... seems brilliant thanks Phlogiston!

phlogiston
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Interesting, that brings up another thing I was wandering about.
I was assuming you would initially try to resolve isotopes of residual gas in the tube, but detecting isotopes of LiL requires that you ionize the sample...

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neptunium
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yes i have a modest ion gun (homemade) i still need to work out the tray where the sample sits

diddi
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any update on this project? I am waiting for you to make me one as well
neptunium
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i just received a turbomolecular vacuum pump and i am suppose to meet with the glass blower this weekend! (if not too much snow) i also need a few more clamp and connectors .... money is always an issue as always for us home scientist! so stay tuned ill have pictures soon!

[Edited on 13-2-2015 by neptunium]

diddi
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mass spec is performed under complete vacuum? that must be a fancy pump...
neptunium
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the mean free path is really what you are looking at 10E-4 torr to 10E-5 torr gives a MFP of about 1 meter that is plenty for the size of the tube . but to deeper the better! this pump is therotically capable of getting down to 10E-9 torr ! fancy indeed! but i had a good price for it !

WeaponsRx
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Can you perform mass spec yet?!
Fulmen
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Neptunium: Sir, you are my kind of crazy.
neptunium
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 Quote: Originally posted by WeaponsRx Can you perform mass spec yet?!

no not yet i will post pictures and i have to tweek with it see what i can get....i mam not even pretanding it will work but the fun is in the journey right?

neptunium
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 Quote: Originally posted by Fulmen Neptunium: Sir, you are my kind of crazy.

i am suprised nobody here tried it before actually

morganbw
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Quote: Originally posted by neptunium
 Quote: Originally posted by WeaponsRx Can you perform mass spec yet?!

no not yet i will post pictures and i have to tweek with it see what i can get....i mam not even pretanding it will work but the fun is in the journey right?

The journey is all we have
smaerd
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Now this is an exciting thread. I'd love to see some pictures and stuff if you'd be willing to share.

neptunium
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here is my friend making a bromine ampoule for my periodic table ... he is the same one working on the mass spectrometer as i am writting these lines... you guys should see his UNBELIEVABLE shop! lab glassware everywhere ! and he can make you anything outta glass !

i will post more picture when he is done with it! i cant wait !
also my turbo vacuum pump has arrived and its a deep vacuum blast!!!

i dont know if the picture is clear enough but the vacuum gauge reads 2.2E-7 Torr !!!! after about 20 minutes!

[Edited on 25-2-2015 by neptunium]

diddi
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great to see some news about this project. that is a really good vacuum result. have you trialled your ionising mechanism at all?
neptunium
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no that will be the suprise when its completed along with the rest of the tube..
Also the 10-7 i thought i reached was a transicent pressure and i had a short in the gauge ! !
now i am confident i reached 2.0x10-5 Torr which gives a mean free path somewhere arround 10 meters !
that is way overkill for a tube only about 1 meter long! those ion should be flying !!

mayko
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This looks great!

One of my too-mad-to-work schemes has been to convert a CRT television into a mass spectrometer. I don't know if it's designed to withstand the vacuum involved, or if it could withstand being retrofitted (no matter how gently I depressurize, the phosphor screen seems to take damage.) But perhaps the electromagnets which direct the electron gun could be repurposed for a tunable deflector, and some sort of phosphor used as an inexpensive detector?

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diddi
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interesting ideas mayko. I don't know enough, but I do know that the deflectors are tunable. I cant see how you can mod the gun without causing irreparable damage to the crt?

id like to see a 10m long mass spec. ultra hi res!
neptunium
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the cathode ray tubes are(were) built to accelerate electron not heavy ion so not only you`d have to find a way to introduce them in there but also reverse the accelerating voltage to negative.

a 10 meter long spectrometer huh? i guess if you were stuck with the same magnet it would get better resolution... but why make it longer if you could increase the seperating field ?
I am working on an idea that i need to test for the detector its very simple and may not require a magnetic field , the resolution might suffer a bit or it may not work at all but hey thats why we call it research right?

IrC
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Method and apparatus for increasing the ionization of impurity ions in a mass spectrometer

A patent from 1966 but I wonder if it has useful information to apply to this project.

http://www.freepatentsonline.com/3254209.html

Attachment: US3254209A.pdf (444kB)

Analysis by imparting unequal energies to ions

Attachment: US2764691A.pdf (308kB)

Attachment: US2587555A.pdf (333kB)

Attachment: US2642535A.pdf (578kB)

One could redesign the older tube circuitry with modern semiconductors.

"Science is the belief in the ignorance of the experts" Richard Feynman
neptunium
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interesting how they are using a photomultiplier for detector , i thought about it but much of a PMT has to be removed and the glass tube may not weld on my type of glass (glue would compromise the high vacuum )
but it definitely deserve some investigating further ... thanks IrC you always dig up suprising finds!

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 Sciencemadness Discussion Board » Special topics » Technochemistry » homemade mass spectrometer Select A Forum Fundamentals   » Chemistry in General   » Organic Chemistry   » Reagents and Apparatus Acquisition   » Beginnings   » Responsible Practices   » Miscellaneous   » The Wiki Special topics   » Technochemistry   » Energetic Materials   » Biochemistry   » Radiochemistry   » Computational Models and Techniques   » Prepublication Non-chemistry   » Forum Matters   » Legal and Societal Issues