From: gdpusch@NO.xnet.SPAM.com (Gordon D. Pusch)
Newsgroups: sci.physics.plasma
Subject: Re: Plasma Globe effects on geiger counter ?
Organization: XNet Information Systems, Inc.
References: <bfbr6u$415l$1@saturn.cs.uml.edu>


"theother" <theother@EROLS.COM> writes:

> Why does my Geiger counter go CRAZY near my plasma globe?

Your "plasma globe" contains a small Tesla coil that produces a high-voltage
radio-frequency electrical field. This high-voltage field is sufficient to
cause electrical breakdown in low pressure gases, such as the gas that fills
your plasma sphere --- and the Geiger-Meuller tube of your geiger counter!


> I suspect it's some form of induction field or RF interference from the
> high voltage power supply acting on the G-M tube.

Good guess.


> My GC has a metal shield to cover the probe window for discrimination of
> Gamma rays from Beta and Alpha particles, using this shield brought the
> GC reading down to background levels again, but a 2" thick book over the
> probe blocked nothing. Was the metal probe shield acting as a Faraday
> cage blocking induction or RF?

Yep.

BTW, exposure to an RF field that strong is probably doing Bad Things to
your Geiger counter's sensitive circuitry...


> Interesting side note: The guy who sold me my plasma globe would place a
> loop of steel guitar string around the globe and the tip of the wire would
> emit a continuous spark up to 1/2" long to conductive materials, it would
> arc to any material that was conductive (people included).

Yet Another Example of RF Inductive Coupling.


> The manual for their globe said not to wear rings or allow metal to
> contact the globe during operation (my used globe had no manual). I must
> say my globe seems none the worse for wear after it's "abuse" and it has
> served well for 12 yrs.of albeit intermittent normal use flawlessly.

The makers are probably most concerned about deflecting potential lawsuits
from customers suffering high-voltage RF induced-current burns...


-- Gordon D. Pusch

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