X-ray shielding and the argument for ZnSe viewports

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Andrew Seltzman
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X-ray shielding and the argument for ZnSe viewports

Post by Andrew Seltzman »

TLDR: ZnSe is a better x-ray shield then stainless steel, and much better then pyrex. Consider using ZnSe viewports.

Lately when running my fusor I have noticed an interesting effect concerning x-ray detection. I have both 1/4" thick pyrex (SiO2) and 3/8" thick zinc selenide(ZnSe) viewports on my fusor(for IR transmission). There is detectable x-rays at the pyrex viewports, requiring a lead glass shield over the port, there is no detectable x-rays at the ZnSe viewport.

The x-ray transmission coefficients for a 1/8" thick viewport at 30keV are:
Fe: 4e-9
ZnSe: 1e-14
SiO2: 0.6

At 30keV energies the ZnSe port is 5 orders of magnitude better at x-ray shielding then the stainless steel shell and the pyrex is 60% transmissive, in addition round lead glass plates are more difficult to find then ZnSe, thick are mass produced as lenses for CO2 lasers. They can also be placed over a pyrex viewport as a shield i not used as the vacuum seal itself.

The cheapest lead glass round shield for a 2.75CF port is about $70, I have ordered one for comparison.
http://www.lesker.com/newweb/flanges/vi ... cfm?pgid=0

x-ray transmission plots can be calculated here, note that photon energy is entered in eV and thickness in microns (for reference 0.125"=3175microns):
http://henke.lbl.gov/optical_constants/filter2.html

Here are x-ray transmission plots for the 3 materials:
Fe:
xray3175Fe.gif
ZnSe:
xray3175ZnSe.gif
SiO2:
xray3175SiO2.gif
Andrew Seltzman
www.rtftechnologies.org
JohnCuthbert
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Re: X-ray shielding and the argument for ZnSe viewports

Post by JohnCuthbert »

According to this
http://www.edmundoptics.co.uk/optics/wi ... dows/2721/
the list price for a 40mm dia 4mm thick ZnSe window is £359.20
I can buy a lot of lead glass for that (or, being a chemistry nerd I can use a clear plastic cell culture bottle filled with lead acetate solution)
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