[ RadSafe ] X-ray Production in Power Supplies

[Richard L. Hess]

Hi, Randy,

As a resident non-health physicist, grab your salt shaker. I have played 
around with electronics for many years and have some understanding of this. 
Here is what I recall.

My basic assumption is that X-rays are produced when electrons hit 
something. That's why the X-ray tubes have a target at 45 degrees, sending 
the x-rays out where you want them, right?

If this assumption is broadly correct, then what do we have that could 
produce this?

Cathode Ray Tubes (CRTs) produce some ionizing radiation and that is why 
there is lead in them. The current emissions are extremely low. The higher 
the 2nd anode voltage, as I understand it, the more likely the device is to 
produce radiation. I must say that I've never seen an indication using a 
working (according to the check source) CDV-700 survey meter on a computer 
monitor. I don't think I ever tried my 25" TV. The larger the TV, the 
higher the required 2nd anode voltage.

In old TVs, there was a high-voltage rectifier tube and I believe that was 
also the cause of radiation emissions. It had a large gap (to avoid 
arcing), as I recall.

Other than that, I don't think there is a mechanism to produce ionizing 
radiation from contemporary solid-state power supplies.

There are other issues with contemporary solid-state power 
supplies,  however, that your questioner may be getting confused about:
  (a) they can produce electrostatic and electromagnetic fields
  (b) the high frequency (as in above audibility, but under 1MHz typically) 
switching
       regulators can produce  hash. A worst-case example of that was the 
Sylmar
       terminus of the Pacific DC Intertie where there are solid-state 
switches running
       at 60Hz. They produced enough hash (high-order harmonics) to 
interfere with nearby
      AM radio reception that the whole facility was covered by a mesh 
shield. This is
      a +/-500,000 DC link from the Columbia River to the LA basin.
  (c) Some of this hash from power supplies can be conducted back into the 
powerline
       contaminating that.
   (d) Some power supplies have a poor power factor, but that is currently 
being regulated
        in the EU and that problem will disappear.

One annoyance of magnetic fields is that over 10mG they will cause CRTs to 
"swim" 2-10mG is considered by some to be the safe threshold (fortunately 
no one is proposing an LNT theory for that, but 2mG is very low).

So there may be issues with power supplies, but without knowing the 
topology of the supply and the power levels, I can't provide a better 
answer. Have you asked the manufacturer?

Good Luck!

Cheers,

Richard


At 10:34 AM 2/22/2005, Redmond, Randy (RXQ) wrote:
>Have any of you run across any articles on, or actually measured, X-rays
>being produced by power supplies, for example, an X-ray power supply?  I have
>not been able to figure out how this could be possible, if it is possible.
>It's a long story.
>
>

Richard L. Hess                           email: richard at richardhess.com
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