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STOP PRESS  This is my old site last updated June 2005.  Enjoy the pics here but it is best to shift direct to the new site. Looks the same but lots more stuff and regularly updated.  The full size pictures  are only available there.

CLICK HERE to go to tesladownunder.com index page


Topics regarding nuclear physics, X-rays, electron beams and fluorescence on this page include:

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X-ray tube

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Electron beam in free air

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Spinthariscope

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Phosphorescence

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Infrared

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Measuring 0.001 grams

X-ray tube  

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This is the internals of a Siemens 120kV x-ray tube head which includes the transformer (not rectified) and a rotating anode under oil sealed and lead shielded. The glass has been removed with the outline shown in yellow.  The electron beam is shown in red and the x-rays in purple. The induction motor is outside the glass and works well on 250V with a phase delay with a 1 uF capacitor on the additional windings.  The right picture is the filament on the cathode electron gun which I have joined to some glass feed through wire from a neon tube.

I have a 100kv DC supply from a mobile x-ray unit.  I also have access to a custom neon place that can make a 2 foot evacuated tube with a filament and a tungsten target at the other.  They can evacuate to 10e-6mm which sounds very low for a diffusion pump but certainly in a good range for a beam.  100 keV electrons will produce x-rays (via bremsstrahlung radiation) and will need appropriate shielding.

I will keep it simple and not have an x-ray window.  I hope to show up the x-rays or use a phosphor screen using activated Zinc Sulphide. Alternatively I could use a geiger detector that will register down to 7 keV x-rays.  I also have an old quartz fiber dosimeter that reads up to 300 centigrays.

This is a tube with a filament in one end and a beveled tungsten cathode at the other.  As the filament was so frail, it was not able to be bombarded adequately and the pressure was nowhere near low enough to give a sufficient electron acceleration to give x-rays.

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Initially when this tube was fired, it was completely striated every 1/2 inch or so and looked very dramatic.  It fired at 2 kV.  After a day or so sufficient outgassing had occurred to blur the striations although the Cookes space near the cathode still remains in the left photo above.  The tungsten electrode is visible in the right photo with segment of yellow soda glass rather than the clear lead glass.

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Note the deviated DC beam in a magnetic field.

Electron beam in free air  If I can successfully construct a simple x-ray tube then I will proceed on to this more ambitious project. Simply put, an electron beam if energetic enough can pass through a thin titanium foil membrane from the vacuum into the air. 

A simple plan of this is shown below.

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I have the 0.001 inch thick Titanium foil below.  Strong stuff but fortunately can be cut with scissors.

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In air an  e-beam (=Beta radiation) travels about 1.2 ft in air at 100 KeV. C-14 beta radiation at 150 keV travels about 10 inches mean (mean distribution is around 1/3 of peak for Beta radiation).
Similarly C14 beta will be blocked by .003 inches of lead.  I am hopeful that .001 inches of Titanium which has Atomic No 22 (vs Lead of 82) will not be too great a barrier.  Even if I lost half the beam I could get perhaps 6 inches of external e-beam along with a fairly small dose of bremsstrahlung x-rays. Not an e-sabre, rather an e-breadknife.  Penetration into plastic is about .02 inches.

My basis for hoping that this will work is Bert Hickmans description of the LINAC used to make the spectacular Lichtenberg figures which operates at a huge 5 MeV at 30 mA.  He describes a blue glow in operation.  The .0023 inch Titanium foil port is 3 x 48 inches ( 144 in2- this sounds huge).

Mine will be using 1/50th the voltage (and hence 1/2500th the power of each electron) and a port of less than 0.25 in2. The foil is only 40% as thick. The current will only be a 100th at less than 1 mA (I haven't measured my supply performance at 100 kV).

Multiply all these factors and you arrive at one 1/40,000 the power density up to the foil. The foil may improve this ratio a bit but its absorption may still completely overwhelm 100 KeV electrons.

So, beam weapon it aint. Hopefully with a more intense focus in my favour I can get something.

After discussions it seems that the best way to get good bombarding to red heat is to use a separate cold cathode near the Ti foil target, but a bit separated so it takes the full heat rather then the Ti foil.

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This is a plan of the arrangement with a filament (from an old TV tube) plus the two cold cathodes.

So far so good.  A problem now is the glass to metal seal for the Ti foil or the metal block the Ti foil is mounted on.  Solvent free epoxy can be used in a hard vacuum.  Glass to metal seals use Dumet wire is used for soft glass and tungsten for borosilicate glass.
Another problem may be matching the impedance of tube to supply. If it draws more than 1mA then the 100kv will drop unless I pulse it with a triggered spark gap.  If I use a Marx generator  to boost the input to 200 kV DC then this is not a problem as it is a pulse generator anyway.
Dissipating the power at the Ti foil which will have air convection on one side only and will be fragile.  I am surprised that the LINAC manages with this but the beam area is huge.  I may need forced air cooling.
I also wonder about uneven charge effects along the length of the tube. At 200kv these might be significant and might need equalizing rings.
 
Photo below is a close up of a cold cathode on my argon tube at a low pressure, not a hard vacuum, running on DC perhaps 200uA, hence the striations. The cold cathode unit is glass joined (the bulge) to the phosphor tube which gives the desired colour - cold colours like blue are argon and warm colours like red are neon. Mercury is added to increase the UV excitation of the phosphor.

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A brief mention of Lenard and Coolidges historical electron beams:

For discussion of this topic on the 4HV forum click here.

These guys have a nice beam in a handheld unit.

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Spinthariscope  For a quickie weekend project I made a spinthariscope.  These date from the 1920's and are simply a phosphor screen, a radioactive source and a lens.  What you see is very faint scintillations due to individual alpha particles striking the phosphor and giving a brief flash.  In days gone by radium was used for the radioactive source.


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I made mine from items laying around the house.  The radioactive source is Americium 241 (1 micro Curie) from a smoke detector which is a small disc hot glued to a plastic rod.  The phosphor is scraped from the inside of a colour TV screen delicately smashed to get good access and with a towel over it to prevent implosion and glass fragments.  It was dusted over 5 minute epoxy to fix it and it fluoresces white under a UV light (see the nitrogen laser page).  Heavy bolts are needed to keep those Alpha particles in!

I added a small 10 X magnifying lens so it fixed the focus at a good magnification.
Your eyes need to dark adapt for 5 or preferably 15 minutes in virtually complete darkness before using this but it works with little flashes particularly closest to the Americium source.  Here is the Science.com site giving historical details and video representation of what you see.

I am awaiting some activated Zinc sulphide and some Europium oxide to do further experiments with phosphors.  I also have some processed uranium ore (yellow cake) to try that has been sitting around in the corner glowing for many years.

For discussion of this topic on the 4HV forum click here.

Phosphorescence  using Strontium Aluminate:Europium 2%.  Sr Al2O3 : Eu

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This shows the red phosphorescence after shining a green laser on the bottle. This fades over seconds with a faint glow being present after minutes.

Infrared

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These photos were taken with a video camera without and with an infrared filter, seconds apart. Note the change in shirt colour. The filter coating achieves 90% reflection of the visible, with the remaining energy attenuated by absorption, to a level of OD 5+ attenuation of the visible, while transmitting in excess of 85% of the Infra Red. Cut on wavelength; 810nm +-5nm.  Looking through the filter at a normal 150W incandescent globe shows only a faint outline of the the filament, but digital cameras light response often extends into the infrared.  One digital video camera got a reputation for being able to "see through" some visibly opaque but infrared transparent clothing in this way.


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Here a 150 W globe is shown in visible light and infrared.  The LED indicator lights and the reflected fluorescent lighting don't emit infrared . The filter is shown with its gold reflective coating.

Measuring 0.001 grams
I  was looking for a way to measure milligram (0.001g) weights using a cheap digital scale with 0.01g resolution and have set up a lever with 10:1 ratio on it with one end as the fulcrum, scales near fulcrum and weighing point at the other.  The auto zero (tare) will compensate for the lever weight and if the dimensions are right the scale should be accurate without calibration required.
 


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Picture shows wire weighing 1.01 g on balance reading 11.08 g (which divided by 10 gives 1.108 g).  Only 10% error and reads to 0.001 g.  The drop of water from a 29 G needle weighs 5 mg +/-1 mg on these scales.  The drop size average dimension is 2.04 mm = 1.02 mm radius.  Using the formula 4/3 pi r^3 for volume  of a sphere gives  4.4 mm^3 = 4.4 mg which is close enough to the measured 5mg.

If you look closely beneath the hanging drop you can see the streak from the drop where it fell during the shot.  The streak goes towards the axis of the needle as the drop slides off the bevel but remains in contact with the tip.  Hence this shows a full size drop, not a partly filled one which is why this picture was chosen to do measurements on.

For discussion of this topic on the 4HV forum click here.
 

This page was last updated August 28, 2005