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X-Rays in small microwave bulb?

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Proud Mary

Fri Nov 18 2016, 09:25PM

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

A few years ago, here on 4HV there was a wave of enthusiasm for generating x-rays from unconventional sources, mostly from TV valves (tubes) driven in cold cathode/field emission mode.

To make my measurements I used a Fluke 440RF/D Low Energy X-ray Survey Meter, which gave quite accurate dose-rates at energies down to 12.5 keV. Below this, I used mica end-window GM tubes, which could count at energies below 4keV - so long as the rays didn't have to pass through too much air - a few cms - on their way into the window!

Anyway, the lowest PD at which I could detect any X-rays at all above background, and with a long integration time, was in the range 16 - 18 kV. As folk have suggested above, for all practical purposes, no quantity of X-rays will transit the glass wall until you get to a PD of about 20 kV.

Why not get one of those strong little Nd magnets and see how that affects the glow distribution in your tube. Could be interesting!

Polonium210

Sat Nov 19 2016, 04:02PM

Registered Member #3450 Joined: Sun Nov 28 2010, 05:01AM
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Posts: 61

johnf wrote ...

And you do not need lead.
ordinary iron / stainless steel stops x-rays up to 60kV.
Which deterctor does your ludlum have you have not specified this yet??

My Ludlum meter has a pancake probe.

Proud Mary wrote ...

Why not get one of those strong little Nd magnets and see how that affects the glow distribution in your tube. Could be interesting!

So these could be cathode rays? The magnet would affect the patterns being projected on the inside of the bulb?

Proud Mary

Sat Nov 19 2016, 07:31PM

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

Polonium210 wrote ...

Proud Mary wrote ...

Why not get one of those strong little Nd magnets and see how that affects the glow distribution in your tube. Could be interesting!

So these could be cathode rays? The magnet would affect the patterns being projected on the inside of the bulb?

If you have an ionized gas in there, sure an external magnetic field will affect it in some way - but you'll have to do the experiment to find out if you can see the change with the naked eye. If you do a google search using key words 'magnetic field' and 'ionized gas' you'll find out more stuff than you could carry home in a wheelbarrow.

Physikfan

Sun Nov 20 2016, 02:28PM

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

The images show a gas discharge at about 0.03hP, voltage 4kV DC

Gas4kVohneMagnet0komma03hP

Without magnetic field, exposure time about 1s.
The yellow-green fluorescence of the glass is caused by electrons, "cathode rays".

Gas4kVmitMagnet0komma03hP

With magnetic field, the permanent magnet is a strong disc-shaped nickel iron-boron magnet, exposure time about 1s.

As Proud Mary already mentioned "If you have an ionized gas in there, sure an external magnetic field will affect it in some way, the magnetic field deflects the plasma as well as the electrons, visible through the changed fluorescence.

Proud Mary

Sun Nov 20 2016, 03:31PM

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

Physikfan wrote ...

As Proud Mary already mentioned "If you have an ionized gas in there, sure an external magnetic field will affect it in some way", the magnetic field deflects the plasma as well as the electrons, visible through the changed fluorescence.

Wow, that's a really strong effect!

I really like these kind of experiments because they take you straight back to the beginning of particle and plasma physics, where you can do the same experiments that were being done in the 1890s without having to pay a fortune for special materials and equipment.

I wonder if you arranged bar magnets coaxially in a ring around the circumference of the tube if the plasma stream might be accelerated?

Physikfan

Sun Nov 20 2016, 04:38PM

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

Hi Proud Mary

I agree with you, acceleration and deacceleration of the ions should be possible with a magnetic field with directions from any point of a circle around the glass tube towards the center of the tube according to F = q (v x B), Lorentz force, but not in the direction of the originally speed.
The force would be perpendicular to the speed of the ions, so you will have no acceleration in the direction of the originally speed
in a linear tube.
Or what kind of different magnetic fields around the tube you have in mind?

Physikfan

Sun Nov 20 2016, 09:44PM

Registered Member #60240 Joined: Mon May 16 2016, 07:01PM
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The second picture shows also the effect of the Lorentz force:

F = q (v Ã— B)

The force (F) acts perpendicular to the velocity (v) of the ions (charge q) and perpendicular to the magnetic field (B),
as seen by the distortion of the ion current.
This force therefore acts not only on current-carrying conductor loops (electric motor!), but also on plasmas.

Ash Small

Mon Nov 21 2016, 09:27AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Sulaiman wrote ...

Really !
you expect 10's kV x-rays to penetrate walls

Well, you can obtain an image from a 5kv x-ray source, PM has done it and posted the results here in the past.

I maybe wouldn't expect 20kv x-ray's to penetrate most walls, depends on the wall

Uspring

Mon Nov 21 2016, 02:52PM

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

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.

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.

Proud Mary

Mon Nov 21 2016, 09:03PM

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

Physikfan wrote ...

The second picture shows also the effect of the Lorentz force:

F = q (v Ã— B)

The force (F) acts perpendicular to the velocity (v) of the ions (charge q) and perpendicular to the magnetic field (B),
as seen by the distortion of the ion current.
This force therefore acts not only on current-carrying conductor loops (electric motor!), but also on plasmas.

I've been thinking about this all day. You could use this apparatus to measure the strength of a magnetic field, or conversely measure a voltage. With successive magnets you could bend the plasma flow into a helix, that is to say an inductance, and then pair it with a capacitor to make a resonant circuit.

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