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X-Rays in small microwave bulb?

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LAN_403

Physikfan

Mon Nov 21 2016, 11:38PM

Registered Member #60240 Joined: Mon May 16 2016, 07:01PM
Location:
Posts: 304

Hi Proud Mary

I try to give answers to your ideas.

1. You could use this apparatus to measure the strength of a magnetic field, correct
2. conversely measure a voltage, correct
3. With successive magnets you could bend the plasma flow into a helix, correct
.
4.to add a capacitor to make a resonant circuit.

In my opinion this may not work.
The velocity v of the ions is a vector.
If you change the direction of the ions by 180Â° you change also the direction of the Lorentz force also by 180Â°.

But you have also to consider what is the number of positive and vice versa the number of negative ions, ....
The electrons have higher speeds.....
You have to go deeply into physics to answer all these questions.

Regards

Physikfan

Proud Mary

Tue Nov 22 2016, 12:10AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Perhaps my idea of a plasma helix tuned circuit wouldn't work, but you have to imagine these things first to make any progresss with an investigation, as I'm sure you'll agree. :)

klugesmith

Tue Nov 22 2016, 12:41AM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Uspring wrote ...
A comprehensive table of X-Ray attenuation coefficients is here:

A barely 1mm thick aluminum sheet will e.g. reduce a 20kV flux by a factor of 2 or 5mm by a factor of 2^5 = 32.

Yes. The factor for 1mm of lead is much more than a million, for that voltage. The factor for steel is somewhere in the large interval between Al and Pb.

Uspring wrote ...
Wrt Poloniums OP, there is not much chance of X-Ray production if there is gas in the bulb, since it stops electron acceleration to high enough energies as hen918 pointed out. If there is glow only from the inner surface of the glass itself, electrons might have sufficient energy to produce X-Rays when they hit the glass.

I think the single-electrode Crookes tube depends on having some gas inside. Some of the RF current is ions which bombard the (cold) cathode and dislodge electrons. The Mean Free Path _for electrons_ is long enough for at least some to hit the envelope at full energy. The photograph here on Wikipedia

shows the path of an e-beam in a space that is slightly gassy on purpose.

Physicsfan, are you equipped to extend Po's x-ray experiment using a high-vacuum pump and pressure gauge?

Physikfan

Tue Nov 22 2016, 08:53AM

Registered Member #60240 Joined: Mon May 16 2016, 07:01PM
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Hi Proud Mary, Klugesmith

After taking a shower I believe that a part of your "idea of a plasma helix tuned circuit" could be realized.
First it should be possible to establish a stable plasma helix in a discharge sphere (as shown by Klugesmith) with a DC magnetic field and with a DC ion current.
Then one could imagine to modulate the ion current by an AC signal to measure the inductance of your plasma helix absolutely.
If this could be realized the next step should be to measure the inductance of the plasma helix as a function of the number of turns of the plasma helix.

These are my first ideas to the topic "plasma helix tuned circuit", (copyright Proud Mary).

Regards

Physikfan

Uspring

Tue Nov 22 2016, 10:15AM

Registered Member #3988 Joined: Thu Jul 07 2011, 03:25PM
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Posts: 711

klugesmith wrote:

I think the single-electrode Crookes tube depends on having some gas inside.

Makes sense. Looking at X-Ray production: Mean free path is about 0.5um at room pressure. For e.g. 5 mm, which would be about the value required for full acceleration considering the dimensions of Poloniums bulb, you'd need about 1/10000 of room pressure or 0.1hPa. Todays light bulbs contain a lot more gas than that.

Physikfan

Tue Nov 22 2016, 01:14PM

Registered Member #60240 Joined: Mon May 16 2016, 07:01PM
Location:
Posts: 304

Hi Klugesmith

"Physicsfan, are you equipped to extend Po's x-ray experiment using a high-vacuum pump and pressure gauge?"

I have in mind to do an experiment in the near future with a cold cathode discharge tube with pressure control (high-vacuum pump and pressure gauge) with different voltages (different electron energies) at low pressures.

Because of the negative current-voltage characteristic of such tubes, you can apply very high voltages to the tubes only at sufficiently low pressures.
The high voltage at the tube in my experiment shown above was only 4 kV due to the not sufficiently low pressue (really 0.03hP?) in the tube (the tube shows still one plasma ball).
Hopefully I will find a tube only with fluorescence and with no plasma ball (sufficient low pressure for higher voltages).

Bjørn

Tue Nov 22 2016, 01:48PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

There is an old post on the forum somewhere that mentions that some small lightbulbs can have quite hard vacuum in them.

Sulaiman

Tue Nov 22 2016, 03:26PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

I think that to avoid plasma the physical distance between electrodes needs to be smaller than the mean free path

e.g. 10^-3 hPa for 100mm = 0.1 Pa which is just beyond the reach of my dual stage oil sealed rotary vacuum pump.
(0.3 Pa if you believe the specifications)

vacuum lamps are still available

P.S. vacuum types are good for wien bridge oscillator amplitude control etc.
gas-filled lamps conduct heat away from the filament.

klugesmith

Tue Nov 22 2016, 10:58PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Mean free path for electrons is much greater than that for air molecules, at the same pressure.
This fellow

says his smallest DIY cold-cathode CRT could work at about 1 torr (100 Pa), and has pictures of one much bigger & better working no lower than 100 microns (10 Pa). He mentions "My reasons for building these homemade crt's should be obvious; certainly not to save money in building a TV set, but mostly because they emit a very intense fun field."

As Bjorn and Sulaiman said, it's easy to find non-gas-filled lamps today. I think C7 and C9 "Christmas lights" are in that category. Maybe also some lamps in MWO's, as demonstrated (?) in OP here. Might try breaking one under water, under a vessel to catch any gas bubble.

Here's a factoid I heard from an expert in the history of electric streetcars (trolleys). One common traction voltage was 600 volts. Cabin lighting was set up with 120 V lamps, in series-connected groups of five. Had to use special vacuum bulbs, not regular argon-filled ones. Then when the first lamp burned out, it could not carry an arc and melt the bulb or start a fire.

Sulaiman

Wed Nov 23 2016, 03:43AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

klugesmith, that is really great news for me !
I bought a dual stage rotary vacuum pump for chemistry hobby use when a single stage would have been enough,
but at the (excited) time of purchase I thought maybe I could play with vacuum tubes
(that is my excuse for the extra cost, and I am sticking to it :)
later I thought that it would not be useful for vacuum electron tubes due to the mean free path thing.
This information and the link have opened a whole new sidetrack in my hobby world.

Thanks

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