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Re: [TCML] X-rays
Jim Mora wrote:
Hello List,
Since the subject has come up, I realize the x-rays generally are largely
formed in a vacuum; but, what about say a 150KV flaming Jacob's ladder (ac).
Controlled x-rays are generally are DC driven as well but that is for a
controlled anode/cathode. Are there other less obvious sources of X-rays
from some of our higher voltage/energy experiments? High Potential
Ionization is the issue yes? What about outside a vacuum?
HV+vacuum = Xrays
HV + no vacuum = no Xrays...
The Xrays come from accelerating a particle to a high speed and then
having it hit something and stop: bremsstrahlung (braking radiation..
braking as in like the brakes on your car)
If the HV is in air, an ionized particle runs into other gas molecules
so it can't get moving fast enough.
Yes, one can make Xrays in air in some cases:
1) Get a discharge under high enough pressure and hot enough so that the
it's emitting X-rays as black body radiation. Typical free burning
arcs are in the 5000-7000K range, and their black body radiation is, as
we've all observed, peaked in the visible, towards the blue end. In
free burning air arcs, the air and arc expands to limit the temperature.
Since radiation cooling goes as T^4, making it twice as hot takes 16
times the dissipated energy. And you need a lot more than twice as hot
to get Xrays
2) With a discharge that has very, very high di/dt (rate of change of
current), you can get xrays. Essentially what's going on is that the
air heats fast enough that it can't expand, nor does it lose energy by
radiation quickly enough. I can't recall the critical di/dt, but it's
pretty high (10 to the multiple digits)
So, practically speaking, your ionizing radiation hazard from HV in air
is ultra violet radiation.
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