-----Original Message-----
From: Tesla [mailto:tesla-bounces@xxxxxxxxxx] On Behalf Of Teslalabor
Sent: Friday, September 19, 2014 04:35
To: Co60bishop; Tesla Coil Mailing List
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
----- 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 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
>>
>>
>> On 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, clear
>> glass 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
>> a
>> pale 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
>>
>>
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