Re: X-Rays in small microwave bulb?
woodchuck, Fri Nov 11 2016, 07:44PM

Kaye, in his book "X-Rays" describes an apple-green glow on the walls of soda-lime glass. Your pic seems to fit the description. The report of your Ludlum meter seems to buttress such a hypothesis. I'd say, yes!

Re: X-Rays in small microwave bulb?
johnf, Fri Nov 11 2016, 08:12PM

No it will not be producing x-rays.
The glow is ionised argon gas in the bulb lighting up the glass.
Glass stops x-rays up to 20keV.
Your survey meter is better at picking up electrical noise than it is capable of responding to gamma /x-ray. remember its threshold is 35millivolt so any disturbance over this will be a count.

Re: X-Rays in small microwave bulb?
Physikfan, Fri Nov 11 2016, 08:13PM

Polonium210

You can check the existence of x-rays:

the simplest way is to put a lead or iron brick or at least a sheet of lead
between your bulb and the detection device.

Please do not change the distance between your source and the detector.

If you see a significant change of your "gamma" intensity, then you have really x-rays.
If there is no change your detector may probably receive the "electric noise" from
your pulsed high voltage source.

You should measure the voltage of your source, at least the maximum of the spark length
to calculate the possible energy of your x-rays.

Re: X-Rays in small microwave bulb?
hen918, Fri Nov 11 2016, 08:31PM

I doubt there are x-rays; the gas in the tube will be preventing high enough acceleration of the electrons.

Re: X-Rays in small microwave bulb?
Polonium210, Sat Nov 12 2016, 01:13AM

I did another test with the Ludlum meter still sitting ~10ft behind me.

Test 1 - No bulb in place to see if it is the electrical noise is the issue. The meter reads nothing but background levels.

Test 2 - Bulb in place and meter screams off the x1 scale.

With test 1 only the bulb was removed and nothing else.
I'm still not sure electrical noise is triggering the geiger counter...

Re: X-Rays in small microwave bulb?
Sulaiman, Sat Nov 12 2016, 09:29AM

I agree that your detector could be picking up electrical noise
but I suspect x-rays,
ignition coils are rated for 25 - 35 kV and can produce more
crt tv tubes have had barium- or lead-loaded glass fronts since 10 kV b/w days because of x-ray hazards.

Maybe a digital camera with black tape or paper over the lens will show the x-rays, to settle the question ?

Re: X-Rays in small microwave bulb?
klugesmith, Sat Nov 12 2016, 03:10PM

Yay for the scientific method. That last experiment was a good one. Another would be to run the whole apparatus inside a metal enclosure (garbage can?) as an RFI shield. See what the rad meter says. With an opening in the purported shield, do you get behavior consistent with streaming x-rays (scattered by air)?

Your pictures are reminiscent of a classic Amateur Scientist column in Scientific American, I think the July 1956 issue, "An Inexpensive x-ray machine".

found here:

That tube, or your bulb, could not be an argon-filled type. It would have to be evacuated but not very well evacuated.

You might be irradiating yourself.

Re: X-Rays in small microwave bulb?
Physikfan, Sat Nov 12 2016, 05:16PM

Switch on your ignition coil with the bulb,
switch on your gamma detector, distance between them about 50 cm.
And then put a metal box or at least an aluminium sheet
between bulb and detector and watch the display of your detector.

Is there a significant change of the counts/second or not?

Re: X-Rays in small microwave bulb?
Polonium210, Sun Nov 13 2016, 03:28AM

Klugesmith, Thank you for the link it was a good read.

I'm looking at getting some lead sheet before I continue...

Re: X-Rays in small microwave bulb?
woodchuck, Mon Nov 14 2016, 12:12AM


The fluorescence that Kaye reports is described as occurring at the inside surface of the glass envelope, not throughout the thickness of the glass. No penetration of the glass is necessary.

Also, my first radiographs were produced via an Accel Supercoil connected to a dental tube - no multiplier or dual coils were required. I should post one or two of them here. Their quality was fairly good.

Finally, I would proffer one way to test the argon vs x-ray hypotheses: Provide what is called an 'alternate' gap. It would function as a crude voltmeter. If the alternate gap arcs only when the electrodes are close to each other, it's probably ionized argon glowing in the tube. If the electrodes can be moved apart by more than a cm w/o stopping all sparking, it's probably x-rays causing the fluorescence.

Re: X-Rays in small microwave bulb?
Polonium210, Mon Nov 14 2016, 02:46AM

My assumption was that argon would fluoresce blue.

It is hard to tell from the pic I posted but the green is projected onto the inside of the glass in a pattern.
It looks to be streams of electrons coming from the sharp filament holder wires to the glass in a spot type pattern like an electron gun?

My HV source is as Woodchuck mentioned, an Accel Supercoil powered from 120v mains through a lighting dimmer and 1uf cap.

Re: X-Rays in small microwave bulb?
Physikfan, Mon Nov 14 2016, 10:46PM

The color and the spectrum of an argon discharge tube are here:


thanks to physics stack exchange

http://physics.stackexchange.com/questions/79212/which-green-spectral-lines-are-emitted-in-a-thomson-tube

There are two possibilities:

Are the colors in your argon filled microwave bulb due to

a) a fluorescence of the glass hitted by electrons or
b) you can find some of the argon lines, shown above,
it may probably really only an argon discharge.

You can check it with a simple spectroscope.

If you can see a broad green band in the spectrum which may caused by fluorescence from the glass hitted by electrons it is a)

If you can find some of the argon lines, it may probably really only an argon discharge, it is b)

Re: X-Rays in small microwave bulb?
Mads Barnkob, Tue Nov 15 2016, 08:25AM

It is a very bright green/yellowish compared to the argon glow I have gotten in light bulbs before.

Here is my example of green colours from HV AC discharges in a light bulb:

Re: X-Rays in small microwave bulb?
Ash Small, Tue Nov 15 2016, 11:53PM

Soft xrays can be produced under 5kv.they are considered soft until around 20kv.I believe the maximum permitted voltage for a CRT TV was 36kv.

Industrial and medical xrays generally start around 50-60kv, but are usually 110-120kv, as far as I'm aware.

Soft xrays are still dangerous, not a lot of penetration, but still cause skin cancer, etc.

Re: X-Rays in small microwave bulb?
hen918, Wed Nov 16 2016, 01:43PM


Soft x-rays should be the most dangerous if there is nothing to stop them, as all of their energy is absorbed into the body. Hard x-rays pass straight through, and cause little damage. I suppose x-rays between the two are the most dangerous, as they would penetrate deeply and still expend all of their energy on living tissue.

Re: X-Rays in small microwave bulb?
Physikfan, Thu Nov 17 2016, 04:52PM

Hi all

This picture shows the luminescence of minerals in a Geißler tube caused by cathode rays, high voltage source is an induction coil.



The yellow-green fluorescence of the glass gives an indication of the existence of low-energy x-rays,
very similar color compared to the microwave bulb under discussion.

Re: X-Rays in small microwave bulb?
Ash Small, Fri Nov 18 2016, 01:11AM

You should be using lead shielding and not directly exposing yourself, your neighbours, and their cat to radiation.

Re: X-Rays in small microwave bulb?
Sulaiman, Fri Nov 18 2016, 11:01AM

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

Re: X-Rays in small microwave bulb?
johnf, Fri Nov 18 2016, 06:42PM

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??

Re: X-Rays in small microwave bulb?
Proud Mary, Fri Nov 18 2016, 09:25PM

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!

Re: X-Rays in small microwave bulb?
Polonium210, Sat Nov 19 2016, 04:02PM


My Ludlum meter has a pancake probe.


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

Re: X-Rays in small microwave bulb?
Proud Mary, Sat Nov 19 2016, 07:31PM


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.

Re: X-Rays in small microwave bulb?
Physikfan, Sun Nov 20 2016, 02:28PM

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


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


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.

Re: X-Rays in small microwave bulb?
Proud Mary, Sun Nov 20 2016, 03:31PM


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?

Re: X-Rays in small microwave bulb?
Physikfan, Sun Nov 20 2016, 04:38PM

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?

Re: X-Rays in small microwave bulb?
Physikfan, Sun Nov 20 2016, 09:44PM

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

F = q (v × 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.

Re: X-Rays in small microwave bulb?
Ash Small, Mon Nov 21 2016, 09:27AM



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

Re: X-Rays in small microwave bulb?
Uspring, Mon Nov 21 2016, 02:52PM

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.

Re: X-Rays in small microwave bulb?
Proud Mary, Mon Nov 21 2016, 09:03PM



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.

Re: X-Rays in small microwave bulb?
Physikfan, Mon Nov 21 2016, 11:38PM

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 180° you change also the direction of the Lorentz force also by 180°.

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

Re: X-Rays in small microwave bulb?
Proud Mary, Tue Nov 22 2016, 12:10AM

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. :)

Re: X-Rays in small microwave bulb?
klugesmith, Tue Nov 22 2016, 12:41AM

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.

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?

Re: X-Rays in small microwave bulb?
Physikfan, Tue Nov 22 2016, 08:53AM

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

Re: X-Rays in small microwave bulb?
Uspring, Tue Nov 22 2016, 10:15AM

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.

Re: X-Rays in small microwave bulb?
Physikfan, Tue Nov 22 2016, 01:14PM

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).

Re: X-Rays in small microwave bulb?
Bjørn, Tue Nov 22 2016, 01:48PM

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

Re: X-Rays in small microwave bulb?
Sulaiman, Tue Nov 22 2016, 03:26PM

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.

Re: X-Rays in small microwave bulb?
klugesmith, Tue Nov 22 2016, 10:58PM

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.

Re: X-Rays in small microwave bulb?
Sulaiman, Wed Nov 23 2016, 03:43AM

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

Re: X-Rays in small microwave bulb?
Uspring, Wed Nov 23 2016, 11:16AM

klugesmith wrote:

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

Yep, about a factor of 5 for 100eV electrons. Got this from the "internet" and not from my own education as well as the statement, that todays light bulbs are gas filled

Re: X-Rays in small microwave bulb?
Physikfan, Wed Nov 23 2016, 12:49PM

I found an interesting paper on gas discharge in the internet:

https://mysite.du.edu/~jcalvert/phys/dischg.htm
http://www.physics.csbsju.edu/370/jcalvert/dischg.htm.html

The mean free path of electrons in a gas is also discussed as well as
1. voltage-current characteristics
2. sparks
3. glow discharges
4. arcs

Also:

http://www3.nd.edu/~sst/teaching/AME60637/notes/Go_ions_v4_031912.pdf

Re: X-Rays in small microwave bulb?
Physikfan, Sat Apr 08 2017, 05:09PM

Hi Klugesmith

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

Now I got a vacuum pump and a pressure gauge to do an experiment with a very old selfmade cold cathode discharge tube at different low pressures and at different voltages (different electron energies).

But still I have a problem.
Last time many years ago when I did this experiment the high voltage at the discharge tube destroyed my low pressure sensor.

I could switch on the pump and also the pressure gauge to get a certain pressure inside the discharge tube.
But before switching on the high voltage I should remove the pressure sensor from the equipment to be able to use this device a second time.
Or anybody has some hints for me to keep the pressure sensor alive when connected to the discharge tube?

Re: X-Rays in small microwave bulb?
Proud Mary, Mon Apr 10 2017, 11:58AM

I'd like to point out that the radiographs mentioned above that I've made using very soft rays have been of subjects like flies' wings and microscopic plant sections.

Also: remember that the energy-response curve of uncompensated GM tubes is wildly distorted in the way of massive non-linear overcounting below about 75 keV. It wouldn't be unusual for a GM tube to over-count by a factor of twenty times and more when exposed to X-rays of 25 keV or so. This is because the counting efficiency increases in a non-linear way as more of the low energy photons are stopped in the counting gas.