*The Victoreen comes with a mylar cap intended to screen out beta radiation.
With the cap in place, I get no readings from the coil, or either tube.*
This would definitely imply that what you ARE reading with the cap off is mostly beta (electrons) rather than x-rays.
Matt D
-----Original Message-----
From: Paul B. Thompson <mrapol@xxxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Wed, Dec 3, 2014 9:19 pm
Subject: Re: [TCML] Homemade Crookes tube does emit X-rays
*Comments interspersed . . . thanks for your reply, too.*
-----Original Message-----
From: romsigurthr@xxxxxxxxx
Sent: Wednesday, December 03, 2014 10:03 AM
To: tesla@xxxxxxxxxx
Subject: Re: [TCML] Homemade Crookes tube does emit X-rays
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.
*In this case the induction coil is solid state; it has no mechanical
interrupter. (Here's the device:
http://www.cynmar.com/ProductDetail/09528507_Electronic-Induction-Coil-For-Discharge-Tubes)*
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.
*The Victoreen 740F has a sheet metal case, which I would think would shield
the internals from most EM effects, or not?*
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.
*No, not exactly the same. I got an even "5 mR/Hr" reading from the 24 inch
fluorescent tube. My homemade cathode ray tube got varying readings: 0 at
the anode end, 20 mR/Hr in the middle of the tube, and about 5 mR/Hr at the
cathode end. I also tried the survey meter on the induction coil itself with
no bulb attached. Making a inch and a half spark between the electrodes, I
buried the needle on the X1 scale. On X10 I got a steady 50 mR/Hr reading.
When the coil is powering the Crookes tube or fluorescent, it does spark.
The readings drop with distance too.*
*The 740F is not a Geiger counter. It's an ionization chamber survey meter.
You can read a PDF of the manual here:
http://qsl.net/k/k0ff//01%20Manuals/VICTOREEN/Vic%20470F/VICTOREEN_470F.pdf.
*
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.
*The Victoreen comes with a mylar cap intended to screen out beta radiation.
With the cap in place, I get no readings from the coil, or either tube.*
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.
*I checked with the maker of the ZVS board and he does recommend 12-36
volts. My mistake. The ZVS does seem to work OK at this low level, but I
won't do it again! There's been no overheating or smoke or signs of strain,
but I won't push my luck.*
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