Date: Thu, 10 Oct 2002 14:18:59 -0500

Author: "Cliff Bettis"

Subject: Re: Cathode ray tubes for demos

Post:

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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 -----=20
From: Edward Sabol=20
To: tap-l=20
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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charset=3Diso-8859-1">



style=3D"BORDER-RIGHT: medium none; BORDER-TOP: medium none; FONT: 10pt =
verdana; BORDER-LEFT: medium none; BORDER-BOTTOM: medium none"=20
bgColor=3D#ffffff>

Yeah Ed,

 

The older one is one of the tubes that could =
emit x-rays.=20
There is a lot of variability from tube to tube depending on the =
hardness of the=20
vacuum and the "target".

 

I think at the Rochester meeting I had some =
copies of an=20
old AEC report on these tubes. I could probably find it if your=20
interested.

 

Cliff

style=3D"PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; =
BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
----- Original Message -----

style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black">From:=20
href=3D"mailto:edwardsabol@hotmail.com">Edward=20
Sabol

To: title=3Dtap-l@listproc.appstate.edu=20
href=3D"mailto:tap-l@listproc.appstate.edu">tap-l

Sent: Thursday, October 10, =
2002 1:49=20
PM

Subject: Re: Cathode ray tubes =
for=20
demos



Would that include the old demo at this website?

 

=
href=3D"http://www.physics.brown.edu/Studies/Demo/modern/demo/7b3510.htm"=
>http://www.physics.brown.edu/Studies/Demo/modern/demo/7b3510.htm V>
 

 

style=3D"PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; =
BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
----- Original Message -----

style=3D"BACKGROUND: #e4e4e4; FONT: 10pt Arial; COLOR: =
black">From:=20
Cliff Bettis

Sent: Thursday, October 10, =
2002 1:42=20
PM

To: =
href=3D"mailto:tap-l@listproc.appstate.edu">tap-l@listproc.appstate.edu A>

Subject: Re: Cathode ray =
tubes for=20
demos

 
The voltage you apply determines the energy, the =
current=20
determines the
intensity. You can limit the emission by keeping =
the=20
voltage and current as
low as possible. The problem is that,=20
traditionally, these tubes were run
off of induction coils and =
the only=20
regulation was a spark gap in parallel
with the =
circuit.

As far as=20
detecting the radiation, a Geiger counter or film badge will do. =
A
friend=20
of mine turned this issue into a class project using the tube to=20
make
some x-ray photographs!

Usually the audience is far =
enough=20
away from the device that there is not
much risk for them, =
however, the=20
lecturer or set-up person has to be up
close. There is also the =
matter of=20
the law and in our state we would violate
the law if we operated =
an=20
unlicensed x-ray source. So we generally use
cathode ray tubes =
designed=20
to run at low voltages (a few kV) with heated
cathodes.

I =
don't=20
mean to alarm anyone, just to point out something you should =
be
aware of=20
if you operate these tubes. I, personally, wear a film badge if =
I
set up=20
one.

Incidentally, gas filled tubes (plasma globes and the =
like)=20
don't emit
x-rays because the electrons in them never get going =
fast=20
enough before they
collide with a gas atom and have to start =
accelerating=20
over again.

Cliff

----- Original Message =
-----
From: "Jim=20
Kernohan" <Jim_Kernohan@Milton.Edu>
To:=20
<tap-l@listproc.appstate.edu>
Sent: Thursday, October 10, =
2002=20
11:24 AM
Subject: Re: Cathode ray tubes for demos


> =

tap-l@listproc.appstate.edu writes:
> >
> >Be =
careful when=20
you use these old tubes as they can emit=20
x-rays.
>
>
>
> UNder waht conditions will =
they emit=20
x-rays? Should I shorten the length
> of time? lessen the=20
voltage?
>
> How do I easily detect if I'm emiting=20
x-rays?
>
> thanks!
>
> =
Jim
clear=3Dall>


Get more from the Web. FREE MSN Explorer download : href=3D"http://explorer.msn.com">http://explorer.msn.com



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