Portable XRF detector window repair

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steve_rb
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Portable XRF detector window repair

Post by steve_rb » Wed Oct 21, 2020 9:44 am

After droping Be window of our portable XRF detector is ruptured. Detector is very expensive and I am trying to fix the window. Be window thickness is about 13 micron (wow too thin). Thin papers are about 100 micron in comparision. I can purchase 13 micron custom ordered Be windows and do soldering after heating and removing the reminder of the ruptured Be window inside a vacuum chamber but I am thinking about using Hysol resin instead of soldering. Also I am thinking about using 50-100 micron Kapton window instead of Be window and use hysol resin to stick Kapton window in place. Any suggestion, recommendation or advice in this regard?
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Dennis P Brown
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Re: Portable XRF detector window repair

Post by Dennis P Brown » Wed Oct 21, 2020 10:15 am

Don't know your application but if kapton can be used instead that would be a safer method. Kapton is very strong and depending on whether that is a pressure window or vacuum, the film could be thinner which might be useful. Or maybe not - again, depends on its application and enviroment. Beryllium is toxic and when it breaks it creates dust particles, too. Never vacuum up the particles except with a HEPA filtered vacuum. Disposal is, of course, an issue since it is a hazardous waste and must be carefully packed, labled and disposed of properly. That is why we gave up on Beryllium (its very brittle nature tends to enhance breakage.)

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Maciek Szymanski
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Re: Portable XRF detector window repair

Post by Maciek Szymanski » Wed Oct 21, 2020 11:17 am

Standard practice at my laboratory for mounting thin foils (down to 1.8μ) is to use either minute amount of epoxy or shellac diluted in alcohol. We use a standard epoxy (even not a low vapor pressure one), sometimes the conducting one. A very thin layer of glue is usually applied with a whisker tool under a dissecting microscope. No problems with vacuum compatibility.
“Begin at the beginning," the King said, very gravely, "and go on till you come to the end: then stop.” ― Lewis Carroll, Alice in Wonderland

steve_rb
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Re: Portable XRF detector window repair

Post by steve_rb » Wed Oct 21, 2020 1:50 pm

Application is detecting low energy X-rays. I found two roll of Mylar films (12.5 and 25 micron thick) inside my old stuff which seems are made just for low energy x-ray transmission applications. I think I can use 12.5 micron one which looks the best for my case. The only think left is whether or not I need to remove the left Be ring (see above photo) around the detector opening. It shouldn't be hard. Just by heating probably up to 200 DegC solder will liquidized and Be will come off (I think of course, never done this before). If I remove Be epoxy will sit on the solder but if I don't remove left Be epoxy will sit on the Be. Which one will is better and will cause Mylar film to stick to it strongly I don't know. Any other advice?

Another problem is visible light which will go into the detector which should be prevented. Be obstruct the visible light but Mylar film will not. I think I should get Mylar film to be Al coated a few angstrom or I have to black paint it in top side with a black ink or something like that. Any advice in this?

Also there is another problem. After applying resin and starting evacuation at the end when vacuum reached 10^-6 tor I will push the film towards detector and hold it there (using a spring behind the film frame for about 48 hours for the epoxy to be cured). From this point all out gassing will be trapped inside the detector and will increase pressure inside the detector and can affect detector performance. So I need a zero out gassing epoxy. Any suggestion which epoxy has zero outgassing for this purpose?

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Dennis P Brown
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Re: Portable XRF detector window repair

Post by Dennis P Brown » Wed Oct 21, 2020 5:50 pm

The x-rays if very soft might have issues with 12 micron thick plastic. Beryllium is safe to handle if no dust is created so that might still be your best bet. Broken Be is a hazard and needs to be addressed as such. It can't be thrown into normal trash.

Very small amounts of epoxy aren't a big issue with 10^-6 torr (through not below) but I'd use proper vacuum grade if available. Certainly use as little as possible. A Beryllium surface should be fine for epoxy. Paint could cause issues with x-rays so maybe not a good idea (the Ti and other elements can absorb.) The Al coating would likely need to be over 600 A to stop most (not all) light. Again, that might be an issue for soft x-rays - depends on what you are trying to measure.

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Re: Portable XRF detector window repair

Post by John Futter » Wed Oct 21, 2020 6:02 pm

use new Be foil
http://www.goodfellow.com/catalogue/GFC ... V2hvddblfZ
BE000210 looks right.
Be careful it is not good for you
you need the Be foil to keep it light tight and to remove the low energy spectrum (noise)

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Re: Portable XRF detector window repair

Post by steve_rb » Thu Oct 22, 2020 7:23 am

John Futter wrote:
Wed Oct 21, 2020 6:02 pm
use new Be foil
http://www.goodfellow.com/catalogue/GFC ... V2hvddblfZ
BE000210 looks right.
Be careful it is not good for you
you need the Be foil to keep it light tight and to remove the low energy spectrum (noise)
BE000210 diameter is 100 mm. I need 120 mm.

I have a great idea would like to share and have comments. I was worried about brazing Be or gluing Mylar inside the vacuum chamber but I though I can do this outside. I mean drill a 1 mm hole at the side of the detector first and then do Be brazing or Mylar gluing and curing. Now put the window fixed detector inside the vacuum chamber and start evacuation until pressure go down to 10^-6 and then solder block that 1 mm hole at the side of the detector I made before inside the vacuum. Solder blocking this 1 mm hole inside the vacuum is lot easier that soldering Be window or gluing and curing Mylar inside the vacuum. Beside if there is any degassing during Mylar curing will go out during evacuation.

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Re: Portable XRF detector window repair

Post by John Futter » Thu Oct 22, 2020 9:35 am

I do not understand
I put up 15micron thickness solution over your 13 micron measurement
and you need 120mm when you said originally 13 microns

or is the detector nearly 5 inches in diameter --i doubt\\

please clarify!!!!

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Dennis P Brown
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Re: Portable XRF detector window repair

Post by Dennis P Brown » Thu Oct 22, 2020 12:09 pm

I too am a bit confused; why braze the Be window when it could be epoxied just as well.

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Re: Portable XRF detector window repair

Post by Andrew Seltzman » Fri Oct 23, 2020 11:59 pm

I can confirm that hysol-1C epoxied Be windows will work down below 1e-6 torr. I was using an in-house build windows on my PhD research, they worked quite well.
The window on the the detector prevents condensation wince the detector is TEC cooled, it may need to be evacuated, though it could work at atmospheric pressure with dry air potentially with greater heat load on the cooler for the detector.
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