Hi Cobalt 60,when I was experimenting with large transmitting tubes (graphite anodes) at only arround 6kV anode voltage, there was a bright blue glowing visible arround the complete inner surface of the glas bulb. I'm sure, this "fluorescence" was generated by x-rays, hitting the glas. Although not sure, which amount of x-rays really was able to go through the glas and hitting me, this was the main reason, I immediately canceled all my further experiments with such tubes, because I was afraid of x-rays, even at such low voltages. So I think the dangerous level is far below 30kV, as you stated. I even have some QB5/1750 Tetrodes, which are only 5kV anode voltage or so, and this tubes have "Danger X-Ray radiation" warning's on it.
Regards, Stefan----- Original Message ----- From: "Co60bishop via Tesla" <tesla@xxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx> Sent: Friday, September 19, 2014 6:35 AM 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 iPadOn 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. ;^)DavidOn 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, clearglass 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 apale 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.I'd like advice about operating this tube safely. Thanks, Paul _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla _______________________________________________ Tesla mailing list Tesla@xxxxxxxxxx http://www.pupman.com/mailman/listinfo/tesla_______________________________________________ Tesla mailing list Tesla@xxxxxxxxxxhttp://www.pupman.com/mailman/listinfo/tesla
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