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[Phys-L] Re: electricity demo apparatus and radiation


Back in the fifties, I made a radio graph using a spark coil similar to
the Ford model A/T type, but much bigger. I still have the negative of
a mechanical pencil. The X-ray tube was a three element (electrode)
cold cathode demo. one still found in teaching store rooms (HS and
college). My memory is a bit dim, but I'm certain the exposure was
certainly less than a few mins. Therefore, I 'd say there was a
dangerous amount of scattered radiation. My friend at North HS has such
a tube and he uses a Tesla (hand held self contained) to demo. it, I
think. I'll check w/ him.

Is the R-meter an electrometer type?


Karl Trappe wrote:

What follows is an old discussion about the safety of Cathode Ray
Tubes when used in conjunction with the Leybold spark coil. The air
stopping, which John Denker mentioned was recognized in one of the
replies. I do not know what difference the use of the tesla may make.
Perhaps its not the high frequency due to the intermittent nature of
the device, but the far lesser current available due to the air gap.
I vaguely recall that the hand held tesla's were "safer". I may be
recalling incorrectly. Karl


If you want accurate measurements of low energy x-rays see if you can find a
Victoreen R-meter.

Also remember the issue isn't a one time use; what concerned me in my work
was that I would be setting up this equipment several times a year and the
accumulated dose. That said the risk is still not that great as risks go.
Being real close to the hottest tube I had for a minute would be like
smoking a pack of cigarettes riskwise.


----- Original Message -----
From: "Sam Sampere" <>
To: <>
Sent: Thursday, October 10, 2002 2:21 PM
Subject: Re: Cathode ray tubes for demos

I think you need to be more careful here. We all do for that matter.


we're the pros and we need to KNOW, not just think. I don't know, so I'm


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