On Saturday, September 20, 2014 3:46 PM, David Rieben <drieben@xxxxxxx> wrote:
Stefan, Dave(s),
Repeating my previous "disclaimer" - I am no authority on this subject matter BUT ;^)
I really don't think that just a few thousand volts applied to a hard vacuum is going to
pose a significant ionizing radiation hazard. Remember the old CRT computer monitors
or better yet, the 25" or 27" CRT-type color TVs? Those "big screened" colored TV
picture tubes required 25 to 30 kV to operate properly and I do seem to recall as a
teenager (1970s) the concern for "some" x-ray exposure if one stood with their face
pressed against the TV screen "for hours" while it was on ;^) Of course, thanks to the
inverse-squared law, they were considered completely safe if viewed from a "proper
distance". ;^)
BTW, Cobalt 60 DOES appear to be somewhat of pro in this matter and he also seems
to agree with me that such relatively low voltages are NOT going to produce significant
radiation hazards with hard vacuums.
Yet another David (Rieben)
On Saturday, September 20, 2014 8:35 AM, Dave Halliday <dh@xxxxxxxxxxxxxx> wrote:
Hi Stefan
Blue glow is perfectly normal:
http://www.thetubestore.com/Resources/Matching-and-other-tube-info/Blue-Glow
Dave
Subject: Re: [TCML] Homemade Crookes Tube?
>
> 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
>
>
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
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