PUREX is the major chemical technique for recovering uranium from spent nuclear fuel. Based on the highly-selective extraction of uranyl nitrate from aqueous solution by tributyl phosphate  (TBP) in a nonpolar organic solvent, the technique is straightforward for home chemists to exploit in order to refine their personal uranium stockpiles.  The photo illustrates the supplies used in the following procedure: nitric acid, tri-n-butyl phosphate (from QualityBiological.com), Kleen-Strip 1-K kerosene (Home Depot), and 4.8 g of homemade uranyl oxide.

Caution: the PUREX procedure involves intimately contacting nitric acid with highly-flammable organic material!  Work with small quantities.  Concentrated acid will form explosive oils, so always dilute it to 6M or less.  This discussion presupposes essential safety understanding of the chemicals and techniques involved.

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Part I: Planning a Successful Extraction Scheme

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Feedstock for the PUREX process is impure uranium dissolved in aqueous nitric acid.  One question concerns the optimum acidity for the process, i.e., what quantity of acid results in the highest ratio of uranium concentration in the organic phase to that in the aqueous phase.  This ratio [U]_org/[U]_aq = K_d is called the distribution coefficient.  K_d is not constant, but depends on the concentrations of various dissolved species, on the temperature, and on other factors.  At left is a plot taken from Marcus Y. (1961), relating log(K_d) to various acid concentrations in the aqueous phase, for some very low concentrations of uranium.  The different curves represent different TBP concentrations in the organic phase.

The question about nitric acid concentration is answered conclusively here; the curves all peak between 5-6M.  Higher acid concentrations are associated with a slow roll-off in K_d, while at lower concentrations it rapidly plunges even to the point that high aqueous concentrations of uranium are favored.  Thus we should prepare an initial aqueous phase with 5-6M acid.  The data also suggests that ~20-25 w/o TBP in kerosene are good values for the organic solution.  I will plan a procedure around uranium oxide dissolved in excess 6M HNO₃, and 20 w/o (0.66M) TBP / kerosene.

Actual values for K_d from Marcus’s plot are themselves not useful to us, because they relate to “tracer quantities” of uranium and we are interested in production quantities (more accurately, higher concentrations).  To find quantitatively applicable data, we must look elsewhere.

At left is a McCabe-Thiele diagram relating [U]_org in a TBP / kerosene phase to the equilibrium concentration [U]_aq in an aqueous phase, for concentrations of uranium useful in production.  In this particular data, from Stas J., Dahdouh A., et al. (2005), the concentrations were measured at room temperature, [HNO₃]aq = 5.75M, and two different TBP solutions were used (0.726M, filled squares; 0.363M, circles).  The 0.726M data is very applicable to our 6M HNO₃ / 0.66M TBP preferences from above; as a tool for predicting extraction yields it should be accurate to within 10%.

We begin an extraction with a quantity of uranium dissolved in nitric acid, and a barren solution of TBP.  During an extraction, the uranium concentration in the aqueous phase decreases by an amount Δ[U]_aq.  Simultaneously the uranium concentration in the organic phase rises by an amount Δ[U]_org.  Uranium is conserved (the amount lost from the aqueous phase must equal the amount gained in the organic), so V_aq×Δ[U]_aq = V_org×Δ[U]_org.  A line of slope Δ[U]_org/Δ[U]_aq = V_aq/V_org = 1/Φ connects the initial state with the final equilibrium state on the black curve.  Shown in red is the line for Φ = 1, [U]_{aq_1} = 0.34M.  [U]_{org_1} is about 0.23M, meaning that on this first contact we can expect that about 68% of the uranium will have been extracted.  If we save the aqueous layer and contact it again later (with bare organic), the blue line shows that we will have complexed essentially all the initially-present uranium with TBP.  No more than two contacts will be needed to effectively process all the uranium.

The remaining component of PUREX is stripping pregnant organic phase with a barren aqueous phase in order to recover the uranium as purified uranyl nitrate.  It’s evident that equilibrium favors uranium in the TBP at low concentrations (just look at the steep slope on the McCabe-Thiele diagram), so what can be done to move K_d in the direction of more aqueous uranium?  Two easy things, evidently: raise the temperature, and reduce the nitric acid concentration.  Data showing these effects is in the cited papers (and for nitric acid, the first figure above); unfortunately, these particular data are not quantitatively applicable to the present problem.  I will use distilled water near the boiling point as the strippant, in as many contacts as are necessary to get the bright-yellow uranyl color out of the organic phase.

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Part II: Doing The Experiment

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The reactants. 69.5 g TBP was diluted to 400 ml with kerosene; 50 ml of the resulting solution was set aside for use in this extraction.  4.8 g of homemade UO₃ were dissolved in 50 ml of 6M HNO₃ to give a characteristic yellow solution that is approximately 0.34M in uranium and 5.4M in HNO₃.

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Both phases are placed in a separatory funnel and vigorously shaken together for about a minute.  At left is before shaking, at right is after.   The organic phase begins water-white and picks up a uranium-yellow coloration.

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The aqueous (bottom) layer is now drained. While it still retains some coloration, it is not nearly as yellow as it was initially.  The TBP / kerosene layer carries much of the uranium.

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50 ml of hot distilled water is contacted with the uranium-loaded TBP / kerosene by shaking for about a minute, taking care to properly vent the kerosene vapors.  The photo at left shows the colors before shaking; at right, after shaking and settling.  Uranium is moving into the water.

The aqueous layer is drained and kept; the organic layer is washed again with a second 50-ml portion of water, which is also drained and added in with the first.  I now repeat the entire procedure again on the original nitric acid solution—i.e. it has two contacts with the organic layer, and two more 50-ml portions of hot water strippant are collected.

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The last water aliquot being collected, leaving behind a barren and nearly white organic layer.

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The final state of the three solutions. The  nitric acid solution containing impure uranium began bright yellow; now (diluted to 200 ml for a fair comparison) it is almost white.  The four strippant aliquots combined are a nice yellow color.   The organic solution is white.  The original uranium has been transferred almost in its entirety to the strippant.

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Pure uranyl nitrate, UO₂(NO₃)₂·6H₂O,  is recovered from the aqueous solution by evaporation of excess liquid in a microwave oven.  This should be done outdoors (nitric acid vapors are evolved) with constant supervision; the melting point of uranyl nitrate is only 60°C and it is important to stop heating when excess water is gone and one begins decomposing the salt.   The clue that this is happening is when little specks of orange uranyl oxide begin precipitating.  Immediately remove the container from the oven and  vigorously stir the molten salt with a stirring rod to prevent it from freezing into an intractable mass.  A powder will result.

My yield was 7.0 g, about 83% of the original uranium.  Most of the losses can probably be chalked up to incomplete recovery of the nitrate after solidifying.  Again, you must stir the living bejesus out of the salt as it freezes or it will stick on your glass like epoxy.

Posted in Projects ]]> http://carlwillis.wordpress.com/2009/09/18/refining-uranium-by-the-purex-process/feed/ 1 carlwillis PUREX_0 Markus STAS_DAHDOUH_3a PUREX_1 PUREX_3 PUREX_4 PUREX_5 PUREX_6 PUREX_7 PUREX_9 PUREX_10 PUREX_11 http://carlwillis.wordpress.com/2009/09/11/new-crusher-for-uranium-processing/ http://carlwillis.wordpress.com/2009/09/11/new-crusher-for-uranium-processing/#comments Sat, 12 Sep 2009 06:23:42 +0000 carlwillis http://carlwillis.wordpress.com/?p=352 ]]>

Time to kick it up a notch in the uranium kitchen, since I got tired of crushing ore solely by hand with a hammer.  The new equipment to turn big rocks into very small rocks consists of a three-inch jaw crusher made by Al Yates, coupled to a 3.75-horsepower Briggs & Stratton Model #094202 gas engine.  To match the engine’s 3600 RPM at full throttle down to a safe speed at the crusher cam (and store some rotational energy for particularly resistant rocks), a 1.75″ pulley is used on the engine shaft and a heavy 11.75″ cast-iron pulley on the crusher shaft (both from McMaster-Carr).  The belt is a standard A50 size.  The whole deal is mounted on a wooden base.

This crusher can produce about 15 kg (a two-gallon pail) per hour of fine rock flour from 1-3″ Utah uranium ore.  It would take many tedious days to accomplish this with a hammer, seives, and a ball mill.  Now the slow step in my artisanal mining and processing scheme is acid leaching, and the attendant gravity filtration of sediment in the leachate.

Coming up soon…a look at the PUREX process—solvent extraction of uranyl nitrate into an organic phase.

A hand-cranked Wimshurst static generator, coupled with a modern-production “magnetic effect” Crookes tube, can produce just enough x-rays to make useful digital radiographs and excite Geiger counters.  The Wimshurst machine and the discharge tube can be readily obtained from online retailers in educational science apparatus for as little as $120.  To make radiographs, I employed a 6-inch fluoroscopy image intensifier tube with a custom mount for my Canon S3 IS digital camera.  All photos in the following gallery were 15-second exposures with moderate hand cranking.

Magnetic-effect tubes contain a slotted cathode that allows a beam of electrons, formed in a high-vacuum glow discharge, to impinge upon a phosphor screen at near-anode potential.  In the classic usage, the experimenter observes deflection of the electron beam when a magnet is brought near the tube.  The only contemporary American manufacturer of a magnetic-effect demo tube, Electro-Technic Products Inc., was enjoined from offering the product on the domestic market precisely because of x-rays.  So tubes of this type available in the US are invariably of Chinese or Indian manufacture—all the better because they’re cheap.  I bought mine from www.sci-supply.com for $79.95.

So what’s the possible utility of this?  Radiography in third-world outposts with no electrical supply?  Hardly…the image quality is too poor, 15 seconds too long for practical exposures, and ever since the vacuum tube went the way of the dinosaur it’s been easy to get enough power from batteries to energize small, intense, pulsed cold-cathode x-ray machines.  But the novelty factor is nice, and in museums or other didactic settings, the literal hands-on nature of this x-ray apparatus should be appealing.

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Fingers of a 28-year-old male hominid.  This hominid’s other hand was busy cranking the Wimshurst to power the tube for the exposure.  Field uniformity is poor, and the source-to-detector distance is a mere six inches–but contrast is OK and this is a perfectly serviceable human radiograph.  Exposure was approximately 100 μR.

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PVC and polyethylene hoses of the same size (left and right, respectively), vividly illustrating the x-ray attenuating power of the chlorine in PVC.

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Electronic stopwatch. Decent detail, including individual wires, can be discerned.  Remember, the x-ray source is a Crookes tube, not a modern line-focus x-ray tube!

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Iodine tincture (a few percent iodine in alcohol) from the drugstore is black to x-rays.

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Geiger tube from a CDV-700 civil-defense Geiger counter.  Prominent features visible by x-ray include the thin beta window in the middle of the tube’s active region, and the thin anode wire running down its axis.

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A hand tap set contained in a plastic box. No big surprises, but the taps are slightly magnetized and some resulting warpage of the image-intensifier output can be seen.

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The handle of a cheap steak knife, showing how the blade is anchored into the plastic.

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Package of “AA” lithium batteries.

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.

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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…

Where to buy:

• www.sci-supply.com is where I bought mine; has new lowest price 4/2/09
• www.unitednuclear.com
• www.enasco.com

The electrical circuit is illustrated above in a scan from the manual.  None of the components are exotic or expensive.  The IC is a regular 555 timer, which when triggered by 60-Hz line-voltage ripple delivers a ~5 ms pulse to the gate of a BT151 SCR.  The SCR dumps a capacitance (chosen from one of six panel-switch-selectable values, 2.2 μF through 13.2 μF) through the primary of the coil.  The manual’s diagram neglects the polarity switch that swaps the direction of current flow through the primary.  The primary capacitors are charged right off the bridge-rectified 120-VAC power line through a beefy current-limiting resistance.  The coil itself is comprised of a 720-μH primary and a two-bobbin, 105-H secondary magnetically coupled on an open ferromagnetic core and packaged in a cylindrical plastic tank (see x-ray above).  The coupling constant is ~0.95.  From radiographs it is evident that the coil is insulated / cooled by a liquid–and that the manufacturer even took care to leave a small compliance bubble of air so the tank doesn’t burst when the coil warms up!  Electrical wiring is surprisingly well-done; the rotary switches are of decent quality, most resistors are 2%, the capacitors are high-Q, 400-V film caps.  All diodes are 1N4007s.

Performance is reliable, with noisy sparks exceeding 4″ and no mechanical interrupter to fiddle with.  I should note that in consideration of the secondary design, in which the inside leads of the bobbins are in close proximity to the core and primary and the output voltage is balanced with respect to these components, one should not attempt to ground either end of the secondary.  This is asking for breakdown that will likely destroy the primary semiconductors and possibly damage the secondary coils.  All loads must be isolated.  This is not a suitable supply for Farnsworth fusors for this reason.  On the other hand, this induction coil is perfect for operating Crookes, Geissler, or x-ray tubes.  The top-right photo above shows a cathode ray tube operating and generating low levels of x-radiation (150 mR / hr. on the ion chamber, easily stopped by a 1/8″ lead sheet).  The lower-left photo shows excitation of a canal-ray (ion) tube belonging to Explora.

Documentation supplied with the coil is useless.  In fact, the English is so poor it’s almost endearing.  Some examples:

• We use them do experiments,such as the performance of electric-flash,,electric-bomber  between liquid solid medium,O 3-produce in laboratory.
• Adhisement: There’s a pair of electric-delive-needle in the package
• Intervolmeter   of Electric-Delive::50mm~60mm(More than two chips of electric-flashes)
  
• Surely put your hands away from the electric-delive-pole.

Safety should be a minor issue with these coils.  While the discharge feels mildly unpleasant and would likely elicit tears and screams from children, this is not Abu Ghraib material.  A more serious potential issue is the power cord; it is possible to yank it out of the chassis due to inadequate strain-relief.  I made a knot in the cord on the inside of the chassis to prevent this occurence.  Would make a great gift for kids of any age who have a budding interest in electromagnetism or x-radiation.

Aesthetics are pretty sorry.  The galvanized sheet-steel chassis has an uneven paint job and an ill-fitting lid on the bottom that fastens in with four sheet metal screws.  If you want a beautiful induction coil, break open your piggy-bank and visit the artisans at PV Scientific Instruments.

Some Induction Coil Links:

• A 1900-vintage text on induction coil construction and repair
• Kurt Schraner’s site, featuring his large homebrew induction coil, experiments, and theory

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.

Posted in Radioactive Collectibles ]]> http://carlwillis.wordpress.com/2009/03/01/nuclear-collection-part-ii/feed/ 0 carlwillis radcollection_tubes radcollection_lenses radcollection_radium radcollection_resistors http://carlwillis.wordpress.com/2009/02/08/rf-ion-source/ http://carlwillis.wordpress.com/2009/02/08/rf-ion-source/#comments Mon, 09 Feb 2009 05:45:01 +0000 carlwillis http://carlwillis.wordpress.com/?p=160 ]]>

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

Posted in Projects ]]> http://carlwillis.wordpress.com/2009/02/08/rf-ion-source/feed/ 0 carlwillis ion_source_mod ion_source_2 ion_source_3 am-6155_highpower am-6155-innards schemat_ltuner ion_trap_3 d2_is_2 10kv_t http://carlwillis.wordpress.com/2008/07/29/spring-cleaning/ http://carlwillis.wordpress.com/2008/07/29/spring-cleaning/#comments Wed, 30 Jul 2008 03:59:30 +0000 carlwillis http://carlwillis.wordpress.com/?p=137 ]]>

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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High voltage vacuum feedthroughs: The large fluted ceramic feedthrough at left is mounted in an 8″ ConFlat flange and is easily capable of 100 kV in air-insulated service. There is no lead passing down the axis of the insulator; you’d have to supply your own. The “hot” end of the insulator contains a 1 1/3″ rotatable ConFlat on a hollow tube, which as the photo shows has been bent off-axis. 8″ flange knife edge is in good condition. Exterior of fluted insulator has some gummy residues that are soluble in acetone. Suggested price: $250.

The small ceramic feedthrough at right is probably vacuum-rated, but I don’t know for sure. The fluted side would be rated in the neighborhood of 30 kV in air. A solid piece of steel threadstock passes down the axis. Flange looks to be a custom elastomer seal (of which this is the female side). Suggested price: $25

Manual high vacuum valves: At left, a KF-50 bellows-sealed stainless steel valve in good used condition. Suggested price: $75.

Middle: KF-25 bellows-sealed stainless Key valve in good used condition. Suggested price: $40

Right: a brand-new, never-used MKS bellows-sealed stainless right-angle valve with rotatable 2-3/4″ ConFlat flanges. Heck, I even have the manufacturer’s original bag that this came in, it’s that fresh! Suggested price: $150

Foreline trap from MDC. KF-25 flanges, stainless steel construction. Comes with a full charge of 13X molecular sieve from Kurt Lesker (you might want to change it though). No heater supplied. Suggested price: $40

NIM stuff: I have an Ortec Model 452 spectroscopy amplifier and an Ortec Model 929 high voltage supply. Both are working, although the 929 has no side panels and the 453 amp is missing a 4-40 screw from one of its side panels. The 452 is suitable for general-purpose linear amplification and pulse shaping for radiation measurements. The 929 HV supply is +/- 10 kV and the polarity can be internally switched. $30 each.

Brand-new Hamamatsu photomultiplier tubes! Here’s a good deal for those folks wanting to build miniature scintillation detectors. These are 10-stage / 12 pin 3/4″ (19 mm) PMTs, brand-new in the box. The tube is a #6813341. I don’t know if an alternate “R” number is associated with these or not, but they share the same pinout as the R1450 and probably behave similarly. $20 each or $70 for all four.

Scintillation detector for prospecting: This Bicron 2M1/2 NaI(Tl) unit has been a constant companion on uranium collecting trips for many years. It has taken a beating physically in the field. Therefore, I doubt it would be any good for gamma spectroscopy, but it still works fine in its intended application. This detector comes with a socket assembly, made by George Dowell (K0FF). The dynode resistors are 10M each. Connector is BNC. The detector operates from ~1 kV on a Ludlum 3 ratemeter. $50

Victoreen 592B ion chamber ratemeter: an oldie but goodie, in working order. Requires a number of 22.5-volt batteries for chamber bias (included, have charge, but not new). Physically in decent shape. Last calibrated in 1992, according to sticker on side. Converted to use 1.5-volt alkaline batteries for the meter circuit in 2002 by Richard Hull. Measures exposure from 1-1000 mR / hr in three ranges. User must keep the desiccant packs inside dry. $60

High-power semiconductors: Powerex CM400HA-34H IGBT, CM300HA-24H IGBT, ND4414180 dual-diode block, and LS4414300P diode block. These parts came from a high-power switching circuit in a monstrous Crymer HV supply. Should be attractive to folks building switch circuits entailing hundreds of amps and thousands of volts. $20 each.

High voltage filter capacitors: 0.125 μF / 27 kVDC made by Westinghouse. $25 each or $40 for both. Heavy!

High-voltage filter capacitors: 0.075 μF / 16 kVDC. Electrical check OK, physically somewhat ratty looking. May contain PCBs. $10 each, $15 the pair.

High voltage doorknob capacitors: 650 pF, 18 kVDC. 8-32 thread on each side. $1 each.

Refractory crucibles: the large unit is magnesium oxide (“magnesia”), suitable for reducing uranium tetrafluoride to uranium metal. It holds about 50 ml. New and never used. $25

The small crucible is alumina and holds about 20 ml. $10

Voltage multiplier from x-ray power supply: Each of the big caps is rated 0.035 μF at 10 kVDC. Also, there are a plethora of nice high-voltage fast rectifiers on this board. Output voltage was intended to be 80 kV, according to some script on the board. Requires high frequency, high voltage AC to operate correctly. I recall checking the unit out a few years ago and found that it was functional. However, it is designed to operate under oil at 80 kV to eliminate corona and sparking. $25

High voltage transformer: salvaged from a large Universal Voltronics supply, this transformer seems to produce about 20 kV from an input of 240 VAC. It must be operated under oil. Likely capable of at least 1 kVA. Some rust is evident on parts of the core. $30. Remember, this is heavy!

Single-stage regulator from Air Products. Has neoprene diaphragm. Inlet / outlet pressure gauges. 1/4″ NPT inlet / outlet fittings. Supply your own CGA adaptor to use with a gas cylinder. $15

High voltage power supply: Bertan Model 2854-8. For specs, refer to photo. Output is via MHV connector. $20

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…

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Results

(Click any image for a larger version.)

The gamma spectra are dominated by a 4.44 MeV gamma energy from the the neutron source itself. When the ⁹Be(α,n)¹²C reaction occurs, the carbon residue is frequently left in its first excited state at 4.44 MeV, from which it de-excites by gamma emission. The peak is broad, but the poor resolution is due to Doppler broadening rather than the detector (the ¹²C nucleus de-excites very rapidly, while still hauling ass post-conception). This radiation effectively masks any (n,g) counts at lower energies. However, the high-energy region above 5 MeV is left wide open, and expected signature radiations from neutron capture in ³⁵Cl, ⁵⁶Fe, and ⁴⁸Ti can be clearly seen in the respective experiments. In each case, I’ve marked the spectra with colored lines indicating expected radiation. Single-escape peaks are prominent at these energies, and are marked as “E1″ and color-coded according to which photopeak they are associated with.

A few concluding points:

• The AmBe source derived from smoke detectors took hours because of how weak it is. Similar results could probably be obtained in about a minute with a suitable Farnsworth Fusor. However, electronic neutron sources have the disadvantage of creating copious electrical noise that can interfere with the detector.
• Water is added to each “target” material to act as a moderator. The (n,g) reactions producing these gamma rays are more probable for slow neutrons than for the fast neutrons directly from the AmBe source.
• Other elements for which this high-energy prompt-gamma technique should be easy include Hg, Ni, Cr, and possibly N. A good data reference for prompt gamma neutron activation analysis (PGNAA) is the “Database of Prompt Gamma Rays from Slow Neutron Capture for Elemental Analysis,” an IAEA publication.

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.”

To their credit, the TA-10 crew selected a short-lived isotope to use for these tests: La-140 has a half-life of only 40 hours. Unfortunately, though, this lanthanum came in a stew of mixed fission products from the Graphite Reactor in Oak Ridge, including long-lived, bone-seeking Sr-90. A radiochemical lab situated at the east end of the Bayo site purified the La-140, dumping the fission-product waste (much of the Sr-90) into lagoons on the canyon floor. Contamination remaining today is mostly associated with this chemical lab and its lagoons. (More information available here, from the DOE’s Office of Legacy Management.)

Back in May I accompanied Taylor Wilson (who has more photos on his website) and his father on a little radioactive scavenger hunt in Bayo Canyon. Access is via the dirt road (“Pueblo Canyon Road”) leading to the Los Alamos Sewage Treatment Plant. (Caution visitors…this road is gated and may be closed. Enter at your own risk!) On this day we were armed only with scintillation detectors, unfortunately a poor choice for hunting the pure beta-emitting Sr-90 that constitutes most of the remnant contamination. The area around the former radiochemical building (TA-10-1) site is well-marked though, with a combination of chain-link fence, roped-off areas, and little markers as shown in the top photo. We did detect a few above-background areas with the scintillometers, but nothing to get too excited about. Next time, I’ll take a pancake GM detector!

Bayo Canyon is a great place for a quiet day hike and picnic near Los Alamos, with some interesting history for the nuclear tourist to boot. Where else on earth can you picnic on dirty-bombed ground?