Experiment 58: Alpha Particle Spark Detector

I wanted to "see" nuclear radiation, so I looked online for experiments similar to making a Geiger counter.  One of the ones I found was an alpha particle spark detector, which shows passing alpha particles as high-voltage sparks.  A wire grid hovers a few millimeters above a plate charged to a high voltage, and when an alpha particle shoots by, it ionizes the air between the grid and the plate, which allows a spark to jump across.  I enjoy this device because it helps me visualize alpha radiation emanating from a source.

I made extensive use of this tutorial, which was the only one at the time.  To generate the high voltages required for this experiment, I powered a CCFL inverter with 12V from my lab power supply.  While the inverter's 900V is high voltage, it isn't high enough for this experiment, so I fed the inverter output into a Cockcroft–Walton voltage multiplier, as per the tutorial.  I used 0.01uF ceramic capacitors and 1N4007 diodes for my multiplier, which had four stages.  When powered with my lab power supply, that increases the voltage about eight-fold, generating the approximately 10kV necessary for a successful spark detector.  I also tried to round off the solder joints to minimize sharp edges that might cause performance-harming corona discharge.

When detecting alpha radiation, it is nice to have frequent small sparks that represent individual alpha particles, rather than one large spark every now and then.  To achieve this affect, I placed a 10 mega-Ohm high voltage resistor (from Vishay) on the high voltage output of my voltage multiplier.  This makes each spark smaller, but it also enables a greater number of sparks at a time.  The resistor also limits the current--larger currents might burn out the extremely thin wire grid.  A normal-voltage resistor might possibly work, but it could fail under 10kV.

Before building the wire grid and plate assembly, I picked out a case for my project.  Previously, I had gotten a sleek enclosure from OKW Enclosures, so I decided to use it in this project.  Because the enclosure was an oval, I picked an oval-shaped piece of aluminum for my high voltage plate.  I needed a good electrical connection for the high voltage, so I tried soldering to the aluminum.  After many failed attempts, I found online instructions that suggested scratching the aluminum under a pool of molten solder.  This eventually made the solder wet the aluminum, and soldering a wire to the plate underside was simple with that done.  After sanding the top to a near-mirror finish, I used four bolts and springs to attach the plate to the enclosure top.  The wire grid sits a few millimeters above the plate, and the bolts and springs let me adjust this distance so that the spark detector does not spark while idle.  I adjust the bolts until the detector only sparks in the presence of alpha radiation.

For my wire grid, I bolted small strips of copper-clad PCB stock to the enclosure top on each side of the aluminum plate.  I used the bolts protruding through the enclosure top's underside as my feedthroughs for the ground connection.  (The wires are ground and the aluminum plate is high voltage.)  I made multiple small cuts in the PCB strips to make individual (but still connected) pads to solder my wire grid to.  I didn't cut all the way through the fiberglass, nor did I separate the pads completely.  They still have copper connecting them in the back, but they are more thermally isolated, which makes soldering easier.  After tinning each pad and using soldering flux, I soldered 10 strands of flexible copper alligator clip lead wire from one pad to its corresponding pad across the aluminum plate.  I tried to make each wire tight so that it would not sag closer to the aluminum plate and create sparks without alpha particles present.  The distance between each wire was 4mm, and the distance from the wires to the aluminum plate was 3mm.  Each wire had a diameter of 0.08mm; such a small diameter is necessary to create the concentrated electric fields which make the spark effect.

As I put everything inside the enclosure, I tried to be sure that none of the high voltage (900V or 10kV) wire were close together or overlapping.  When I finally applied power, I found out that the aluminum plate was too close to the copper pads.  I sanded the plate's sides using 80 grit sandpaper, and eventually, I stopped the continuous sparking that had been I had noticed.  Some of the wires had low spots that sparked even without alpha particles, so I gently pushed those up with a q-tip.

Eventually, I got all the bugs worked out and tested the spark detector using an Am-241 source from a smoke detector.  It worked wonderfully, making a beautiful storm of sparks and small pinging sounds.  If you open the picture on the right and look closely, you can see small sparks on the finished detector as I hold the Am-241 source above it.  Because uranium undergoes primarily alpha decay, this detector also works with uranium ore, although not quite as vigorously, since the source material is more spread out.  This project is one of my favorites because I can "see" radiation with it.  Each spark happens at the actual location of an alpha particle, thus showing me the distribution of the radioactivity, which I think is really neat.

Experiment 57: Microwave Furnace Melting Metal

A while ago, I saw a YouTube video showing someone smelting gold from ore using a common household microwave.  Intrigued, I researched microwave furnaces further.  Amazingly, the microwave found in nearly any kitchen can melt metals like gold, copper, and aluminum!  Microwave furnaces work by surrounding the crucible or the metal to be melted with something that absorbs microwaves (a susceptor) and turns them into heat.  Some common microwave susceptors are charcoal and silicon carbide, as well as water--food gets hot in a microwave because of its water content.

To make my microwave furnace, I grabbed the alumina-silica light-density firebrick that was my arc furnace body and cleaned the metal residue from its inside.  The furnace body is simply one brick with a 2" diameter hole 1.5" deep in it and another brick as the lid.  Each brick is about 4" by 4" by 2.5", so this leaves a 1" thick bottom on the furnace body.

I added a 1/8" layer of crushed lump charcoal to the bottom of the furnace's inside and put my soup can crucible on top of that.  Then, I added some aluminum TIG welding filler rod scraps and set the furnace in an experiments-only microwave.  With everything in place, I nuked my furnace for six minutes on high heat.  Amazingly, the aluminum was completely molten and glowed bright orange!  I was quite impressed, so I tried zinc in the microwave furnace.  After four minutes, it was a mere puddle.

I read on a forum somewhere that charcoal can heat things to at least 1000°C as a microwave susceptor, so I suppose I shouldn't be surprised that the furnace works so well.  With a simple soup can as its crucible, though, it has limitations.  I tried melting copper, and while the copper melted (around 20 minutes on high), it also ate through the steel and leaked out everywhere.  A graphite crucible might be a better choice.  However, I am still impressed that a common microwave can melt a metal like aluminum in less than ten minutes!

Experiment 56: Homemade Lab Centrifuge

I had an old (possibly from the 1960s) Hoover vacuum cleaner motor lying around, so I decided to turn it onto a lab centrifuge for chemistry experiments.  The motor was enormous and spun with such ferocity that I thought it would might go airborne and kill me, which scared me thoroughly.  For that reason, I used large bolts to attach it to a thick plastic/wood board, which I clamp to a table when I use the centrifuge.

The vacuum cleaner creates suction by spinning a cast aluminum turbine.  The aluminum turbine blades were relatively flat on top, so I decided to make this the centrifuge top.  I cut some plywood into a disc with a hole it in to go around the motor output shaft.  If the disc ever flew off in operation, someone could get seriously hurt, so I cut some scrap sheet steel into a large washer to go between the end nut of the motor output shaft and the plywood.  Once everything was assembled, I tightened the nut until everything was snugly in place.
Previously, I had requested and received free samples of 2mL plastic centrifuge tubes from a laboratory supply company, so I designed my tube holders around those.  I cut and drilled six wood cubes with holes sized for my centrifuge tubes and then glued these around the plywood disc.  Centrifuges can self-destruct if they are off-balance, so I carefully measured 60° increments around the circle so that the disc would be balanced.  To finish off the centrifuge, I added a cord and on/off switch salvaged from the old vacuum cleaner.

For being made from a vacuum cleaner, this centrifuge works surprisingly well.  I have successfully separated oil from mayonnaise, although mustard does not separate.  This centrifuge is extremely useful for settling precipitates out of solutions.  If I mix copper sulfate and sodium carbonate solutions, I get clear sodium sulfate in solution and blue copper carbonate precipitate.  By placing a sample of solution in the centrifuge, I can settle all the blue precipitate out and see the true color of the solution--it should be clear if I have used enough sodium carbonate.  One thing this centrifuge can't do is enrich uranium, but if that's the only complaint, I would say it works pretty well!

Experiment 55: Fresnel Lens Solar Death Ray!

A very long time ago, one of my friends introduced me to The King of Random's videos on YouTube.  I was impressed, and it wasn't long before I found his video on making a solar death ray using a Fresnel lens from a rear projection TV and some cheap wood boards.  I had to try it!

After finding a rear projection TV on craigslist for free and just barely managing to compress it into a minivan for transport, I began searching for its Fresnel lens.  The TV was absolutely enormous, and it was really heavy as well.  I eventually found out how to take off the lens and carefully set it aside so it wouldn't get scratched.  Other useful things I found in the TV were castor wheels (used in my ball mill), mirrors (CO2 laser, perhaps?), and various circuit boards and lenses that I haven't used yet.

The Fresnel lens itself is quite floppy, and it is also large and unwieldy, which isn't good.  The King of Random's video showed how to build a nice frame for the lens that held it rigidly but still allowed for easy rotation to follow the sun.  I followed his instructions closely, and the frame turned out to be inexpensive and very helpful.  I also used this Instructable to find the lens focal length so I knew where to put objects for best burning performance.  My death ray's focal length is about 35".  I put a board across the two cross-pieces on the frame so that objects can rest there at a fixed distance from the lens (instead of me holding them in midair).  Finally, I scratched each lens side with my fingernail to find out which side had grooves on it.  The grooves should face the sun for best performance.  In use, I also try to line the lens up so that it is perpendicular to the sun's rays that are hitting it.

Concentrating over a square yard of sunlight into a square inch makes a very bright spot of light, which can be problematic for unprotected eyeballs.  I bought some #10 shade cheap-o welding goggles from Harbor Freight and use them every time I play with the death ray.  It is impossible to see what is happening otherwise, although my iPad can see details inside the bright spot.

I love using my Fresnel lens.  It creates a searing-hot spot of intensely focused sunlight, capable of melting or burning many things.  Over the years, I have melted over a quarter's worth of zinc pennies using this Fresnel lens.  Yes, melting metal with sunlight!  While this lens cannot melt iron or rocks as some videos show, I have melted and compressed HDPE milk jug shreds into a usable billet by placing them in a soup can "oven" under the death ray spot.  My Fresnel lens has even burnt all the way through inch-thick wood boards!  This death ray cost less than $20 to make and uses freely available energy to do incredibly destructive things, which is exactly why I love it!

Experiment 54: Making Copper Oxide for Thermite

Next on my list of thermite reactions I want to try is copper.  For that, I will need copper (II) oxide to react with my homemade ball-milled aluminum powder.  I saw a nice video by zhmapper on YouTube about making copper (II) oxide, so I decided to try his method myself.

To start, I made concentrated solutions of copper sulfate (root killer) and sodium carbonate (washing soda).  I used about a 2:1 mass ratio of these solids and completely dissolved each.  Baking soda (sodium hydrogen carbonate) would work just as well, but the ratio might be different.  With my solutions prepared, I mixed them thoroughly together.  This made a lot of bubbles, so I had to quickly transfer my experiment to a larger container.  When the solutions mix, they make copper carbonate, which can be decomposed into copper (II) oxide.  I knew that I had added enough sodium carbonate because the blue color of the solution became clear (once the blue copper carbonate had settled out).

The byproduct of the reaction is sodium sulfate, so I filtered this off, along with the excess water, using simple coffee filters.  When the copper carbonate dried, I was left with a robin's-egg-blue powder.  To transform the copper carbonate into copper (II) oxide by releasing CO2 gas, I heated the powder in a soup can.  My hot plate wasn't hot enough, so I put the can in a bonfire for 15 minutes.  When everything had cooled, I was left with a dark black powder--the copper (II) oxide.  I also noticed some pink inside the can, so I wonder if the fire was somehow reducing some of the copper oxide back into copper metal.

Untouched, the copper oxide would probably work.  I have heard that copper thermite is very energetic, so it probably doesn't require extra fine ingredients.  However, I want the best performance from this reaction, so I milled the powder by hand using some steel ball bearings in a plastic jar.  Shaken enough, the bearings break up any clumps.  I also ran a magnet in a plastic bag over the powder to remove magnetic particles that came from the soup can.  I was left with 55 grams of fine copper (II) oxide powder for an exciting thermite reaction.