A XRay Help -- Xrays are generated "accidentally" in a HV machine

[CEDEng]

TL;DR Summary

Finding Xray Energy

First post here, thanks in advance...

It may seem like xrays aren't something to play around with at home - but that's not my intent! I just need to get some paperwork done (no, it's not homework...). Does anyone have any insight into this question - or know of an expert source I could contact?

In some high voltage applications, xrays are generated "accidentally." I.e., xray generation is not the main function of the machine, but they happen, nevertheless. How can I calculate the energy (in whatever unit you prefer) of such an xray?

Example: I have a (hypothetical) 100kV DC source. I apply that across some slightly separated elements in a vacuum. The purpose is to measure the withstand (voltage) abilities of the gap, the materials, or the vacuum. BUT - xrays happen. Can't be helped.

So - is the keV of the xray "not higher" than my applied DC voltage? Or - could it be higher, and must be calculated in some way?

A slightly more detailed question - these "accidental" xrays aren't continuous...I have no way to know if it's 1 per moment or 1 million per moment - or how that plays into the potential hazard to bystanders - which makes me think my fundamental and basic understanding of xrays is deeply flawed! Nevertheless, some elementary guidance would be appreciated. Thanks, all, I really enjoy the knowledge here.

 

[Vanadium 50]

Here's the bad news.

Yes, you can produce accidental x-rays.
Yes, their energies can exceed the applied voltage, but this is rare and most x-rays will not.
No, one needs to know the system in extreme detail to predict the x-rays and in most cases measurements will be more accurate than calculation.

 

[CEDEng]

Thanks, Van - excellent info, I'm surprised it's so hard to find.

The 2nd half of my question was related to annual dosage - and I got the (perhaps wrong) feeling that these "accidental" xrays are not a steady stream (as they might be with a medical device) but instead, unpredictable and random. With that in mind, most "online" dosage calculators simply use keV and distance, and if duty cycle is considered at all, it's only very broad, e.g., "50%." While I think the "duty cycle" in this case is probably something very low, even if the supply is on continuously, it's still probably best to guess a high duty cycle.

This would give an exaggerated view of any potential dosage, but the error would be on the "safe" side.

Does that make any sense at all?

 

[Vanadium 50]

You are probably getting x-rays from the highest voltage part of your apparatus. Do you know where it is? It's probably some metal whisker somewhere. Again, do you know where that is? And when it burns off where the next one is? This is just one example.

The problem isn't that the underlying physics is not understood. It's that any real apparatus is too complex to describe well enough to get an accurate answer.

 

[CEDEng]

Thanks again - we know exactly where they're coming from - but it's unavoidable. The point is to apply a high potential in a vacuum between two slightly separated materials, mainly copper.

BUT - your description of a "whisker" is not far off - it's more like a dot, a bubble, some imperfection somewhere...but even if the material were flawless, I don't think I could rule out the xrays.

Best advice from many folks, obviously, is to just use a Geiger counter and see what's what. And that will definitely happen.

 

[Vanadium 50]

You probably want something called an "X-ray survey meter".