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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Experiments with a Tiny Radioisotope Neutron Source

By placing beryllium in intimate contact with an alpha-emitting radioisotope, neutrons are produced. At home, one can approach this well-known reaction by lining up the sealed americium sources from a quantity of old-fashioned ionization smoke detectors on a sheet of beryllium metal. The neutron yield is easily detected; see this link for more information. My own toy AmBe neutron source currently produces an estimated 1000 neutrons per second. That makes it more than three orders of magnitude weaker than my Farnsworth Fusor. But are there enough neutrons to perform some detectable nuclear reactions? As it turns out…yes.

Neutrons give rise to prompt gamma rays when they are captured by many nuclei. The following experiments involve the detection of high-energy (> 4.4 MeV) gamma signatures from neutron capture in chlorine, iron, and titanium, in the form of inexpensive and readily-available compounds mixed with water and placed near the 1000 n / s AmBe source. A gamma ray spectrum is collected with a very efficient scintillation detector (2×2″ BGO) over a period of hours.

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Setup

For the chlorine experiment, a 40 lb. bag of rock salt was purchased at Lowe’s for about $4. A two-gallon pail was filled to the brim with salt, followed by successive additions of water and more salt to obtain the highest chlorine density possible. A piece of PVC pipe, capped on the bottom, enters the salt pail from the top. The neutron source fits down in this pipe so that it is nearly surrounded on all sides by salt. The lead-shielded BGO scintillator views the side of the pail at the level of the source.

The iron experiment is similar, except the medium in use is 10 lb. of ferrous oxide (FeO) purchased at New Mexico Clay here in Albuquerque. The oxide is divided among two PETE jars and water is added to wet the oxide, drive out air, and fill the jars. The neutron source is taped behind one of the jars and the assemblage is surrounded by UHMW-PE bricks to act as a neutron moderator / reflector.

Titanium was obtained in the form of titanium dioxide powder from New Mexico Clay. Enough dioxide (~8 lb) was loaded into a large cylindrical Rubbermaid food-storage container to fill the sonofabitch. Water was added to displace air and top off, and as before, PE bricks were arranged around the outside. In this instance the neutron source sits in an acrylic tube penetrating the TiO₂ from the top.

Results follow below…

2142 AD

2142 AD is the year in which Bayo Canyon, New Mexico will be safe for unrestricted use. But today, it has a radioactive contamination problem on account of the TA-10 complex, Los Alamos National Laboratory, that occupied the wooded canyon until cleanup 45 years ago. What was done here was rather interesting:

The Los Alamos National Laboratory [...] conducted 254 radioactive lanthanum implosion experiments from September 1944 through March 1962. The purpose of these experiments was to test implosion designs for nuclear weapons. Conventional high explosives surrounding common metals (used as surrogates for plutonium) and a radioactive source, as small as one-eighth inch in diameter and containing up to several thousand curies of radioactive lanthanum, were involved in each experiment detonated. (Dummer, Tascher, Courtright 1996)

In other words, they built and detonated huge, open-air “dirty bombs.”