Nuclear Collection (Part III)

Radioactive chemical reagents (and a bit of non-radioactive fake yellowcake) constitute this instalment of my Nuclear Collection feature.

Depleted uranium metal from United Nuclear. These two rough-hewn triangular slabs weigh in at about 13 g apiece.  No idea what Bob Lazar cut up to put these on the market, but they’re not a bad deal while they last. They sport very rough, sharp edges and have to be stored under oil because of the risk of pyrophoric ignition.  Uranium fires are a bummer, especially when they occur in your living room.

Fake yellowcake memento from the Conquista Project.  About 20 cm³ of a canary-yellow, non-radioactive powder that resembles a diuranate salt is contained in a small vial embedded in this commemorative plastic paperweight.  The Conoco-Pioneer strip mining and milling operations in Karnes County, Texas commenced in 1971, for a time producing most of that state’s uranium.

Real yellowcake, or actually a chemically-pure grade of depleted U₃O₈ in a 1-lb reagent bottle from Research Organic /Inorganic Chemical Corp.  After calcining, this is indeed what most modern “yellowcakes” resemble both in chemistry and appearance.  This bottle is a gift from Tim Koeth, builder and operator of the beautiful 12″ cyclotron at Rutgers University.

Uranyl acetate reagent bottles, also from Tim Koeth.  Uranyl acetate is still widely available as an electron-microscopy stain.  It’s a beautiful color, and like most uranyl salts, exhibits striking UV fluorescence.  The yellow crystals have a faint odor of vinegar.  Likely they taste accordingly (although taking uranium internally is generally frowned upon).

Vial of urea labeled with 50 microcuries of carbon-14.  C-14 is a weak beta emitter that is best known for its role in carbon dating.  Because of the importance of carbon in biological processes (durrrh!), C-14 is also useful as a tracer in research, which is the suspected purpose of this product from New England Nuclear.  The label says “Use only as authorized by Atomic Energy Commission,” effectively dating this carbon to 1974 or earlier.  Activity is only detectable by removing the lid and holding a Geiger tube over the opening.  A gift from Tim Koeth.

Calibrated bismuth-210 beta sources. Bi-210, or archaically “radium E”, appears in the uranium decay series.  The sources actually contain lead-210 (radium D) with a half-life of 22 years in secular equilibrium with the 5-day Bi-210 daughter.  The weak betas from Pb-210 are absorbed in the source, while the 1.2-MeV betas from Bi-210 are free to escape.  The set is incomplete; present are four sources ranging in activity from 7.73 nCi to 0.364 μCi (measured in 1962).  A gift from Tim Koeth.

Quarter pound of thorium nitrate. This bottle of Baker ACS-grade reagent is still sealed, preventing radon from escaping and allowing the delicious thorium decay chain to build up.  The penultimate thorium decay product, thallium-208, is responsible for one of the most energetic gamma rays found in nature: 2.62 MeV.  I use this bottle as a source of 2.62-MeV gamma radiation to calibrate the high end of the energy scale in scintillation spectrometry.

Cheap Chinese Induction Coils

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The induction coil, once an essential tool of modern physics that lay behind the discovery of the electron, x-rays and radio, has been relegated to the toybin.  Most of the modern ones are made in China like the rest of our toys.  While the coils of yore were mahogany-cased artisanal masterpieces destined for the most prestigious laboratories, today’s product is pitched at the Wal-Mart Shopper: sloppy mass production and everyday low prices.  I recently bought one such coil for use in an outreach program at Albuquerque’s Explora museum.  Billed as a 60-kV Ruhmkorff coil, the same product seems to have several outlets in the US.  This is a quick review.  Click below for more…

Nuclear Collection (Part II)

Here are some more photos of my radioactive material collection. Featured today are radioactive vacuum tubes, radioactive optics, radioluminous items containing radium, and some recently-acquired resistors containing uranium.  I collect and buy radioactive material (duh!).  If you have some, and it’s in need of a good home, let me know!

Many types of electronic tubes contain radioactive material. Click on the thumbnail for a larger, numbered image. The purpose of adding a radioisotope to a vacuum tube is usually to ionize residual gas in gas-filled types, improving the timing characteristics or helping to “strike” a discharge.  Uranium glass saw much use in the metal-to-glass seals for tubes of all kinds.  Its coefficient of expansion more closely matches the metal than the regular soda glass of the package, and the slight radioactivity is merely incidental.  Various isotopes are found in tubes: these can include artificial H-3, Ni-63, Kr-85, Co-60, and Cs-137; and natural Ra-226 and Th-232.  The activity is usually internal to the tube, but some of the examples shown here feature external radium sources.

Some lenses contain thoria (ThO₂) to improve the refractive index while keeping dispersion low.  The thorium content can range from barely-detectable to major constituent of the glass.  Along the back row, left to right:

• Unknown first-generation image-intensifier tube from a military night-vision system.  The output optic on this tube is, as far as optics go, the most radioactive thing I have encountered–it reads 50 kcpm on a pancake GM tube, and about 1.5 mR / hr on an ion chamber.
• Kodak Pony 135 Model C camera (mid-1950s), with thoriated Anaston lens.  Not all Ponies have radioactive lenses.  Reads 4500 cpm on a pancake GM tube.
• Angenieux zoom lens for television or film, Type 10 x 15 B.  Reads 350 cpm on a pancake GM tube (the radioactive lens itself is buried deep within the assembly).
• In front are some small lenses salvaged from a variety of ’50s-’60s-vintage still and movie cameras.  Hottest among these is a Kodak 3″ f/2.8 Ektar lens, reading 10 kcpm on a pancake GM tube.

Radium paint was used for glow-in-the-dark applications from the 1910s through the ’60s.  Many people know of the tragedies suffered by early watch dial painters due to ingestion of radium.  The articles in my collection were probably all machine-painted, however.  The glow from these devices is feeble today, the result of radiation “burnout” of the zinc sulfide phosphor and NOT because the radium has decayed.  It remains virtually as radioactive as it ever was.

• In the back are WW-II / Korean War vintage military aircraft instruments: gyrocompasses, a radio compass, fuel gauges, an “oxygen flow indicator” and a small pressure gauge.  The latter item was sold in large quantities in 2002-2003 by various surplus dealers.   The larger dials probably contain a few microcuries of Ra-226.
• Lower left: radium-tipped toggle switches.  Radium content is probably a few tenths of a microcurie.
• Right: some consumer timepieces with radium–Westclox “Pocket Ben” watch and a Phinney-Walker travel alarm clock.  The older Westclox “Big Ben” clocks are also reliably radioactive and still inexpensive and commonplace collectibles.
• Center: two instrument knobs with external radium paint: “Pull out before preset tuning” and an illuminated on/off knob
• Center right: 10 ampere circuit breaker with radium strip that is visible when breaker is open
• Center foreground: two radium drawer pulls (or glowing eyes for a radioactive teddy-bear?)

Radioactive power resistors obtained at “The Black Hole” in Los Alamos.  The activity appears to be due to uranium and its daughters as determined by gamma spectroscopy.  At first I thought the uranium was in the black vitreous glaze, but it actually appears to be distributed throughout the volume of the resistor material (also black in color).  The activity is relatively mild–only about 300 CPM above background on a pancake GM detector.

RF Ion Source

I have been working on an ion source to support my next fusor and other small accelerator projects.  Criteria for this source were that it had to be easy and inexpensive to fabricate myself with common components from reliable sources.  My goals were to obtain high beam current and long service lifetime.  I settled on an RF ion source  concept with specific influences from Kiss and Koltay (1977).  Tests of the prototype indicate stable sub-milliampere currents of deuterium ions over hours of operation.  Cost (excluding RF and vacuum equipment): about $250.

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RF ion sources function by extracting ions from radiofrequency electrodeless discharges.  These sources can deliver high-purity beams of atomic H+ ions.  The vessel supporting such a discharge can be as simple as a glass test tube surrounded by an inductive coupling to the RF supply, as my design at left illustrates.  The discharge is “enhanced” with the field from a strong magnet.  Some builders attempt to exploit specific enhancement effects, e.g. electron cyclotron resonance or helicon phenomena.  My goal with the magnet is just to promote generic electron trapping / heating, possibly by the above-mentioned modes if conditions are appropriate.  Components, with suppliers’ names and stock numbers, are provided in the drawing.

Construction techniques involve drilling, lathe turning, silver brazing, and soft silver soldering.  Photos at left show components of the source  (most prominent are the extraction electrodes) during assembly on a ConFlat cube for testing.

Extraction of ions is accomplished by a strong DC electric field imposed between the negatively-biased “nozzle” on the 5/16″ tube and the grounded septum on the 1/2″ tube.   I use up to -5 kV for extraction of ions.  The extraction nozzle also throttles neutral gas flow from the discharge region into the vacuum chamber.

RF power is supplied by an FAA-surplus AM-6155 power amplifier operating at 200 MHz.  These amplifiers are a common hamfest bargain.  Circuit details and modifications for the amateur radio hobby are easy to find online.  To date I have not produced more than ~60W with this amplifier, driving it with signals below 1W.  Beam current depends very strongly on RF power, and I plan to upgrade the driver for the AM-6155 to produce more.  The top photo shows this amplifier producing power (lighting a mercury-vapor discharge), and the bottom photo shows the tube compartment of the amplifier modified for shunt feed of plate current.

Inductive coupling of the 200-MHz power to the discharge plasma is effected with a single loop of heavy conductor that forms part of a resonant “L-match” circuit, providing an easy interface to 50-Ω cable.  This is illustrated schematically at left.  The right photo shows the ion source ready for testing, with the RF coupling loop visible along with other components including gas for the discharge (deuterium lecture bottle).

Photos from operation.  The top photo shows the RF deuterium discharge in a standard 19-mm (3/4″) Pyrex test tube, and below it a beam of extracted ions impinging on a graphite Faraday cup target.  RF power is about 50W, extraction voltage -3 kV, and target at -10 kV.  Background pressure has been raised into the millitorr range to enhance beam visibility.  Extracted current is 0.25 milliampere.  Bottom photo shows the exit aperture clearly, with deuteron beam passing through a ring electrode at -10 kV.  Here the extraction voltage was -5 kV.  It is not possible to accurately measure the beam current in this arrangement, but it is probably on the order of 0.5 mA.  Not surprisingly, a few neutrons from ²H(d,n) fusion reactions can be detected with higher potentials on the ring cathode.

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More information about this ion source

• Original description
• Discussion of AM-6155 RF supply
• A bit of operational data
• More recent modifications
• Improvement to the discharge bottle involving a little glassblowing

Spring Cleaning

Yes, it’s mid-summer now, but “spring cleaning” is better done late than never! With work gearing up on the Carl’s Sr. fusor project and the requisite demands on my space and funds, I’m parting with some loot that will probably be more useful to someone else. Call 505-412-3277 or email willis.219@osu.edu with questions or counter-offers. I accept PayPal at my email address.

• High voltage vacuum feedthroughs
• Vacuum valves
• Foreline trap
• NIM modules
• Radiation detectors
• High-power semiconductors
• High voltage capacitors
• Crucibles
• Other stuff

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