Hi Paul,
There is an issue with your experiment procedure here; omission of EMI/RF shielding.
Induction coils, as the term is commonly used to mean, refers to discontinuously driven resonant transformers/coupled inductors, often switched by a mechanical spark gap. The discontinuous nature alone creates a tremendous hash of high frequency harmonics which radiate, but the use of a spark gap as the switch greatly exacerbates this.
To compound the issue, nearly all produced Geiger counters and scintillation devices are not EMI shielded. Despite the fact that a very thin low density foil, such as aluminium, would not significantly shield beta, xray, or gamma emissions to which the counting/survey devices are calibrated to (there would be measureable loss of low energy sensitivity, but only specialty devices are energy compensated for accurately measuring low energy photons and betas) it is not an included feature because it is assumed that the end user would not be in an EMI noisy environment.
Additionally, as I referenced above, nearly all survey meters and counters are calibrated to the characteristic emissions of Co-60 or Cs-137, which have peak gamma emission energies at 1.17MeV/1.33MeV and 662KeV (respectively). This causes the equipment to be overly sensitive to lower energy photons and betas. The unit eV (electron volts) for a beta particle (electron) or gamma/xray (photon) is equivalent to the voltage under vacuum that must be supplied for the generation of such a particle. That is to say, the 70kVpk the output of a dental xray transformer produces xrays in a continuum of ~10KeV to 70KeV. The lowest energy photons are filtered out by the glass envelope of the xray Coolidge tube and shielding. Some dental xray units even have additional beam forming and shielding that helps to narrow the band further as low energy xrays cause more tissue damage than high energy xrays.
So, all that taken into consideration, here is what I recommend. Use the same ignition coil and Geiger counter you used before, with the same placement, power supply, arrangement, and overall geometries you used before. But this time do not use your neon sign maker’s “crookes” tube. Simply use a cheap fluorescent light bulb instead. It can be linear or CFL, it doesn’t matter. Observe your Geiger counter and see if it reacts similarly. This experiment tests whether EMI was the source of “false counts” in the Geiger circuitry. If the Geiger counter registers nothing above background (typically 10uR/hr for most areas) then it is possible your crookes tube is evacuated to a hard enough vacuum that some cathode rays are braking against the electrode, creating bremsstrahlung xrays. If the counter reacts as it did before with the crookes tube, you’ve confirmed that there are no xrays being generated. An additional test is to wrap your Geiger counter in the thinnest cheapest aluminium foil you can find, and ground that foil, then repeat the test with the crookes tube. This should provide some EMI shielding without greatly diminishing sensitivity to xrays.
Sincerely,
Matt Sig Giordano
Sigurthr Enterprises
www.SigurthrEnterprises.com
P.S. I’ve been a member of the GCE Geiger Counter Enthusiasts mailing list and family of lists for many years and we’ve seen this exact discussion come up regularly (EMI generating false counts). To my knowledge no one has yet had a confirmed case of a *luminous* (not glass fluoresced!) tube generating xray emission.
P.S.S.: NEVER run a ZVS circuit on less than 11 volts. The standard ZVS “Mazilli” driver relies on supply voltage remaining in a critical range to prevent cross conduction between the switches. I’ve seen many people get injured from exploding fets/igbts when they ran a ZVS circuit on battery or low voltage power supplies. A standard deep cycle marine battery or HAM radio 20A 13.8V supply is the accepted go-to voltage source.
Message: 17
Date: Tue, 2 Dec 2014 10:44:24 -0500
From: "Paul B. Thompson" <mrapol@xxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Subject: [TCML] Homemade Crookes tube does emit X-rays
Message-ID: <D9F856A9DC744D9B960EBDD9945C98D1@Number6>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=response
A while back I mentioned a homemade Crookes tube I had a local neon sign
maker make for me. I had questions about safely using it. Did it emit
x-rays? This launched me on a long search for radiation detectors, etc.,
which has been enlightening and fun. I now own a couple of vintage
instruments for detecting radiation.
One of these is a Victoreen 740F "Cutie Pie" survey meter. This ray gun-like
device will detect x-rays if the beta shield is removed from the detector
tube. See
http://national-radiation-instrument-catalog.com/new_page_26.htm
Now, powered by a 6 volt battery, ZVS driver, and flyback, the Crookes tube
emits no detectable radiation. When I switch to 10 kv induction coil, things
changed! I got readings up to 20+ mR/h from the center of the tube, and easy
10 mR/h from the ends. Even 6 feet away I detected 5 mR/h. Needless to say,
I shut the tube off. I won't be using it with the induction coil again, I
think.
Does this all sound reasonable?
End of Tesla Digest, Vol 86, Issue 1
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