Thanks for the input. I don't think there's any argon in the tube; I asked
the sign maker to make a vacuum tube and he assured me that's what he made.
All he used on this one of mine are simple electrodes. The resemble a shiny,
rounded cup with what looks like a ceramic insert (check out
http://neonopensign.net/how-neon-signs-are-made about halfway down for an
image of the electrode). A simple loop of wire is soldered to the closed end
of the electrode. This protrudes from the pinched end of the glass tubing.
The tubing appears not to be coated with anything. I requested clear glass.
-----Original Message-----
From: Co60bishop via Tesla
Sent: Friday, September 19, 2014 12:35 AM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Homemade Crookes Tube?
Paul, David is absolutely correct. I test semiconductors for radiation
hardness using x-rays and the tube you had made sounds like it has low
pressure argon gas and there is also a small amount of mercury on one of the
electrodes when a " neon" tube is made. I say neon but tube color depends on
which gas is in the tube and the phosphorous coating inside of the tube. I
can assume your tube is plain glass with no coating. I had one of every
color made years ago by our local neon sign company and I hold one end in my
bare hand and arc to my tesla coils at the other end. You need to wrap each
end with aluminum foil to spread the power out when holding it. Dangerous
x-rays require a minimum voltage of 30 kV with some tubes operating with as
much as 200 kV. Tungsten is the typical target and a very hot high current
filament is necessary to produce powerful 10 keV and higher x-rays. The
super hot filament is required to emit enough electrons to generate the
x-rays. What you have is
not much different than using a fluorescent lamp to arc to the secondary
output.
A Bishop
Principal Device Physics Tech
Sent from my iPad
On Sep 18, 2014, at 7:05 PM, David Rieben <drieben@xxxxxxx> wrote:
Paul,
I am certainly no authority on this matter but from what I have gleaned,
you are not going to produce "hard" x-rays in this manner. Besides the
hard vacuum, this would also require a white-hot filament (for an electron
source) for the cathode, a heavy metal target (usually tungsten) for the
anode, and well over ~50 kVDC potential between the said cathode and
anode to really produce the ionizing, body penetrating hard x-rays (even
dental x-ray tubes typically run about 70 kV(DC)). That being said, if you
are powering your tube with say 10 to 20 kVDC, you may produce some low
energy "soft" x-rays, but I don't think it's going to be a significantly
ionizing radiation source. I'm not even sure if you can produce any kind
of x-rays at all with AC? That's just "my" 2 cents. ;^)
David
On Thursday, September 18, 2014 6:01 PM, Paul B. Thompson
<mrapol@xxxxxxxxxxxx> wrote:
I just recently found a local neon sign maker and asked him to make me a
simple vacuum tube, which he did, gratis (!). It's 18 inches long, clear
glass tubing about 3/4 inch in diameter, with electrodes at opposite ends.
I
don't know how hard a vacuum he pulled on this, but very quick tests show
a
pale blue glow from end to end. A strong magnet placed next to the tube
pinches the beam, intensifying it at the spot.
I've not run this for more than a few seconds. I am concerned about
x-rays.