Date: Mon, 14 Oct 2002 13:07:26 -0500

Author: "Cliff Bettis"

Subject: Re: Cathode ray tubes for demos

Post:

Machele,

If you read from about page 36 -38 you will have the author's conclusions
about the various tubes. He also wrote about actual x-ray tubes.

Again, I don't want to get people overly excited about this, just to take
appropriate care. I am told that years ago at Iowa State University on of
the professors liked to do the following demonstration. Set up a charged
electroscope on one side of the lecture hall and discharge it with an x-ray
tube powered up at the other side of the hall.

Cliff

----- Original Message -----
From: "Machele Cable"
To:
Sent: Monday, October 14, 2002 12:33 PM
Subject: Re: Cathode ray tubes for demos


> Uhg...anyone got a 1 maybe 2 page SUMMARY of that report? Just the
> facts, Sir.
>
> Chele
>
> Jim Krider wrote:
>
> > Cliff,
> >
> > You sent me a 47 page fax in 1999 which I think is this AEC report.
> > Open this web page:
> > http://pirt.asu.edu/detail_5.asp?ID=1293&offset=248 and click on the
> > link: xray_hazard.pdf. It is 3.77 mb file.
> >
> > Jim Krider Laboratory Coordinator Senior
> >
> > PIRT - Physics & Astronomy Instructional Resource Team
> >
> > Arizona State University
> >
> > P.O. Box 8751504 Tempe, AZ 85287-1504
> >
> > 480-965-8086 FAX 480-965-7954 james.krider@asu.edu
> >
> > -----Original Message-----
> > From: Cliff Bettis [mailto:cbettis@unlserve.unl.edu]
> > Sent: Monday, October 14, 2002 7:09 AM
> > To: tap-l@listproc.appstate.edu
> > Subject: Re: Cathode ray tubes for demos
> >
> > Ed,
> > I am going to see if I can scan the AEC report and make it more easily
> > available for everyone. I had to point out to our chem folk here that
> > even an innocuous looking hand-held leak tester Tesla coil could
> > generate x-rays when used with these tubes.
> > Cliff
> >
> > ----- Original Message -----
> > From: Edward Sabol
> > To: tap-l
> > Sent: Friday, October 11, 2002 8:11 AM
> > Subject: Re: Cathode ray tubes for demos
> > That would be great since my chem folks also use the
> > equipment
> >
> > ----- Original Message -----
> > From: Cliff Bettis
> > Sent: Thursday, October 10, 2002 3:20 PM
> > To: tap-l@listproc.appstate.edu
> > Subject: Re: Cathode ray tubes for demos
> > Yeah Ed,
> > The older one is one of the tubes that could emit
> > x-rays. There is a lot of variability from tube to
> > tube depending on the hardness of the vacuum and
> > the "target".
> > I think at the Rochester meeting I had some copies
> > of an old AEC report on these tubes. I could
> > probably find it if your interested.
> > Cliff
> >
> > ----- Original Message -----
> > From: Edward Sabol
> > To: tap-l
> > Sent: Thursday, October 10, 2002 1:49 PM
> > Subject: Re: Cathode ray tubes for demos
> > Would that include the old demo at this
> > website?
> >
http://www.physics.brown.edu/Studies/Demo/modern/demo/7b3510.htm
> >
> > ----- Original Message -----
> > From: Cliff Bettis
> > Sent: Thursday, October 10,
> > 2002 1:42 PM
> > To:
> > tap-l@listproc.appstate.edu
> > Subject: Re: Cathode ray tubes
> > for demos
> > The voltage you apply
> > determines the energy, the
> > current determines the
> >
> > intensity. You can limit the
> > emission by keeping the
> > voltage and current as
> > low as possible. The problem
> > is that, traditionally, these
> > tubes were run
> > off of induction coils and the
> > only regulation was a spark
> > gap in parallel
> > with the circuit.
> >
> > As far as detecting the
> > radiation, a Geiger counter or
> > film badge will do. A
> > friend of mine turned this
> > issue into a class project
> > using the tube to make
> > some x-ray photographs!
> >
> > Usually the audience is far
> > enough away from the device
> > that there is not
> > much risk for them, however,
> > the lecturer or set-up person
> > has to be up
> > close. There is also the
> > matter of the law and in our
> > state we would violate
> > the law if we operated an
> > unlicensed x-ray source. So we
> > generally use
> > cathode ray tubes designed to
> > run at low voltages (a few kV)
> > with heated
> > cathodes.
> >
> > I don't mean to alarm anyone,
> > just to point out something
> > you should be
> > aware of if you operate these
> > tubes. I, personally, wear a
> > film badge if I
> > set up one.
> >
> > Incidentally, gas filled tubes
> > (plasma globes and the like)
> > don't emit
> > x-rays because the electrons
> > in them never get going fast
> > enough before they
> > collide with a gas atom and
> > have to start accelerating
> > over again.
> >
> > Cliff
> >
> > ----- Original Message -----
> > From: "Jim Kernohan"
> >
> > To:
> >
> > Sent: Thursday, October 10,
> > 2002 11:24 AM
> > Subject: Re: Cathode ray tubes
> > for demos
> >
> >
> > > tap-l@listproc.appstate.edu
> > writes:
> > > >
> > > >Be careful when you use
> > these old tubes as they can
> > emit x-rays.
> > >
> > >
> > >
> > > UNder waht conditions will
> > they emit x-rays? Should I
> > shorten the length
> > > of time? lessen the voltage?
> >
> > >
> > > How do I easily detect if
> > I'm emiting x-rays?
> > >
> > > thanks!
> > >
> > > Jim
> >
> >
> > -----------------------------------------
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> >
> >
> > -------------------------------------------------------------
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> >
> --
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