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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
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.
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. 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.
I have the 0.001 inch thick Titanium foil below. Strong stuff but fortunately can be cut with scissors.
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).
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). 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.
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.
A brief mention of Lenard and Coolidges historical electron beams:
For discussion of this topic on the 4HV forum click
here.
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.
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 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. Phosphorescence using Strontium Aluminate:Europium 2%. Sr Al2O3 : Eu
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.
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.
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
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. |
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This page was last updated August 28, 2005