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Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
Proud Mary wrote ...
Klugesmith wrote ...
By coincidence, speaking of shielding boxes, I'm about to find out if 5/8" drywall (gypsum board) can practically block x-rays at NST voltage (15 kV RMS). If so, then I'll make a box out of that, this weekend, and play at the limited voltage before getting out the lead and the oil.
That sounds exciting! I'll be interested to hear how you get on with that.
Not to steal Grenadier's thread, but here are the early results. Experiment: connect a little Coolidge tube across 15 kV NST (with momentary-contact switch). Heat filament enough for 1 mA average anode current. Aim at Geiger counter about 8 inches away, and interpose experimental materials attempting to block the x-rays. (The counter responds vigorously with half the voltage and 1 microamp of anode current).
No way in hell: 1/2 inch drywall 1 inch drywall -- this was disappointing, it ain't 1 inch of crystalline CaSO4.2H2O for sure 1/4 inch cement-based backer board 0.1 inch glass 0.063 aluminum 0.019 steel
marginal: 1/4 inch FR-4 fiberglass 0.027 steel
probably good: 0.050 steel (a sheet-metal bookend) 0.125 steel 3/4 inch thick terra-cotta quarry tile
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
No problem, I encourage thread hijacking. It leads to conversations and discoveries that might've never happened otherwise. Sorry to hear about your gypsum failure. I had a feeling that it wasn't going to stop anything. Also remember a 15kV NST has a peak voltage 21kV.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Klugesmith wrote ...
Proud Mary wrote ...
Klugesmith wrote ...
By coincidence, speaking of shielding boxes, I'm about to find out if 5/8" drywall (gypsum board) can practically block x-rays at NST voltage (15 kV RMS). If so, then I'll make a box out of that, this weekend, and play at the limited voltage before getting out the lead and the oil.
That sounds exciting! I'll be interested to hear how you get on with that.
Not to steal Grenadier's thread, but here are the early results. Experiment: connect a little Coolidge tube across 15 kV NST (with momentary-contact switch). Heat filament enough for 1 mA average anode current. Aim at Geiger counter about 8 inches away, and interpose experimental materials attempting to block the x-rays. (The counter responds vigorously with half the voltage and 1 microamp of anode current).
No way in hell: 1/2 inch drywall 1 inch drywall -- this was disappointing, it ain't 1 inch of crystalline CaSO4.2H2O for sure 1/4 inch cement-based backer board 0.1 inch glass 0.063 aluminum 0.019 steel
marginal: 1/4 inch FR-4 fiberglass 0.027 steel
probably good: 0.050 steel (a sheet-metal bookend) 0.125 steel 3/4 inch thick terra-cotta quarry tile
In the gypsum board/CaSo4 experiment, Ca characteristic rays will have been added to those photons which transit the gypsum board unmodified, so whilst there can only be a net loss, it will not have been as great as might have been expected from other material of similar density
The iron in your steel will also have emitted its characteristic rays, but what photons of its 6keV peak made it through to the other side of the steel, and through the air, will not have made it through the counting tube wall.
For the benefit of the uninitiated casual reader of this thread, I feel I should point out that even a teensy weensy little X-ray tube like the famous Svetlana BS7 with its maximum anode voltage of 15kV @ 50uA will still produce a dose rate of ~1000Sv/hr at 1 cm from the beryllium exit window - so just a few minutes of casual handling of the live tube is likely to lead to ulceration and necrosis of the skin, and other irreversible changes.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
Well soldering went off without a hitch. At first it wouldn't work with the pen torch, but it was smooth sailing once the 40 watt iron joined the party.
Overall it took me only three hours to put it together, and it was a lot easier than expected. One thing if certain: this box isn't going to come apart again in only 6 pieces. I'm a pretty good leadsmith if I do say so myself.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
Lately I've been trying to figure out how to make a 12V battery powered variable HVDC supply for this thing. I figured why bother making it modular when I can just build this aforementioned supply and use a step-down xformer to run it off the mains.
So, any ideas? Ideally it would supply 20 to 70kV, and at least 3mA.
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
I was thinking of something with an induction coil. Not only would a CW require pretty expensive capacitors, Finding a suitable AC flyback would be a job in itself.
Remember, I need to make the voltage adjustable too. I'm not too sure how to accomplish that. A tapped CW might work, but to have any real good control I'll need a whole crap load of stages, and a whole crap load of switches to control where the tap is.
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Grenadier's big thread of Röntgen related shenanigans
