[AMPS] Xray levels

[George T. Daughters]

On 5 Mar 01, at 11:08, Bob & Linda McGraw K4TAX wrote:

> 
> Here's a fellow that has his act together.  Great writing.  Thanks for
> sharing it with us.
> 
> 73
> Bob K4TAX
> 
> John T M Lyles wrote:
> > 
> > We see Xrays emitted from tetrodes such as the 4CW250,000B at 28
> > kVDC. They are very low energy and can be stopped by an aluminum
> > chassis. But they are a problem for an open screened system, where
> > people can stand there and watch the tube. 

< snip, snip >

> > When we have high potted tubes such as the 4CW250,000B, they usually
> > produce stronger Xrays at about 50 kV and above. Older tubes
> > sometimes seem worse. We can tell that they are emitting by watching
> > the current on the power supply, which begins to indicate current
> > from the field emission (electrons) inside the vacuum tube, even
> > when cold. When we get a few mA or so at 55 kV, the power in the
> > Xrays is quite dangerous. Our tester is now lead shielded for this.
> > We have a written proceedure when high potting, which addresses this
> > and other hazards such as high voltage.
> > 
> > With planar triodes such as the CPI-Eimac Y820, we see a few mRem of
> > Xray dose at 3 feet away, when holding off about 15 kV. This
> > surprised me at first, when I was snooping around with a survey
> > meter.
> > 
> > So be aware, that Xrays can and will be produced by vacuum tubes,
> > even when cold, if high voltages of over 10 - 15  kV are used. 

< more snipping >

> > It is good that most amateur and broadcast radio amplifiers are not
> > running at such high voltages. Technicians using klystrons and IOTs
> > at higher voltages, as well as users of superpower tubes for radar
> > or scientific applications are almost guaranteed to be getting
> > exposed if they don't take precautions. A measurement of the
> > radiological hazard is highly advisable in those applications with a
> > calibrated Xray/gamma meter.
> > 
> > John
> > K5PRO

All very good advice; but I'd like to add that the main thing to be 
aware of is the ENERGY of the x-rays... and that's quite simply a 
function of the accelerating potential... i.e. the anode voltage.  At 
normal ham voltages, there's little to fear.  At 15 kV, the x-rays 
aren't very "penetrating"... your color TV and computer screen are 
around this level. We call them "soft" x-rays.  But 55kV and 60kV are 
the levels where our diagnostic x-ray systems typically run!  The x-
rays penetrate soft tissue and give us great pictures of bones!

73, K6GT
  
George T. Daughters, K6GT

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