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[Phys-L] demo apparatus radiation

I am still curious about what electricity demo apparatus is being
excited by those of you using these two devices.

Since the tesla and the induction spark coil were sold for use with
the cathode ray tubes, here is the follow up from Cliff Bettis on
safety. As you can see, I was mistaken about the tesla being safer.
But, hey, I also liked to see the bones of my toes wiggle in the
"Buster Brown Shoes" x-ray machine when I was a kid. Karl

from Cliff:
The matter of safety is complicated by two issues: one is that a
given discharge tube will behave differently depending on its use. I
think this may have to do with how much residual gas is in it and
whatever gettering action goes on in using it. You also cannot be
sure of the voltage and current supplied to the tube especially if
its to be used by someone else. The other factor is a regulatory one:
on our campus we are in violation of our safety rules if we use an
unregulated X-Ray source; these rules vary from place to place.

Tesla coils can also cause cold cathode discharge tubes to emit
X-rays. Exactly how much depends on the tube and the current and

In using these things, the individual risk for a limited use is small
(say, comparable to smoking a cigarette), but the regulatory issue is
serious. I was told by a friend in the good old days, at a well-known
University in a neighboring state, they would charge an electroscope
up in a lecture hall and cause it to discharge by turning on an X-Ray
machine across the room.

I looked around but I am afraid I wrote that several computers ago. I
do have the government's document which is about 40 pages long. I
could send you a copy, if you wish.

My recollection is that I got several R/H out of my beam tube with
the points all the way open on a spark coil. I think the hand held
tesla coil did just about as well. This was similar to the sort of
thing Properzio et al were getting (at the time, I hadn't seen their

Dr. Karl I. Trappe, outreach consultant Home (512) 264-1616
Research Scientist Associate V (retired)
Senior Lecturer in Physics (retired)
Physics Department, Mail Stop C-1600
The University of Texas at Austin
Austin, Texas 78712-1081
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