Archive for the ‘Radioactive Collectibles’ Category

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Gamma Analysis of Chagan “Atomsite”

August 19, 2012

Lake Chagan (“Atomic Lake”) was formed in 1965 following a thermonuclear cratering explosion on the Semipalatinsk Test Site in Kazakhstan.  More photos from my recent trip to the site are here.  Merely visiting the site does not answer some of the most interesting questions about its current state, such as the isotopic origin of the significant (1-2 mR/hr) gamma radiation.

I decided to take a more scientific look at the gamma rays emitted from Chagan’s fused rock—the glassy, vesiculated slag (“atomsite” or “kharitonchiki”) that covers the ground near the shore of the lake.  A grab sample was acquired, and transported home by means other than my own return flight from Almaty (this airport’s departure lounge is guarded by a notoriously-sensitive portal scintillator made by Aspect).  I filled a 3-ounce plastic jar with the material for counting.

My method of analyzing this unique “soil sample” is HPGe gamma-ray spectrometry.  I followed the same approach discussed in my earlier analysis of Japanese soils, involving comparison of the test specimen with an identically-shaped Cs-137 sand standard.  My germanium detector is operated via a homebrew LabVIEW program built around Mark Rivers’ EPICS interface for the Canberra 556 AIM MCA and Carsten Winkler’s CA Lab; I subsequently analyze the spectra (peak fitting, background subtraction, energy calibration) with FitzPeaks.  In this experiment I collected an 8000-second count of the slag sample and a 2000-second count of the Cs-137 sand standard.  An appropriate long-duration background was subtracted from each.  The quantitative calculation of activities relies on a single major line from each nuclide, chosen (to the extent possible) to be close to 662 keV.  Corrections for detector energy response were made by calibrating the energy-dependent photopeak efficiency in FitzPeaks to a point Ra-226 source, covering the range of roughly 200-1600 keV with a power-law model.  Corrections for material attenuation, including density variations from the standard, are NOT made from a calibration but are calculated based on an exponential attenuation model that assumes the sample has the elemental composition of concrete.  It’s probably not a bad comparison, and typically results in a correction of under 20%.  However, I expect better accuracy in the quantitative analysis for peaks that are closer to 662 keV.  Finally, no corrections are made for count losses to coincidence summing.  An Excel spreadsheet of this data and analysis may be downloaded here.

Referring to the 0-1600 keV gamma spectrum below, the first major observation is that most of the lines belong to europium isotopes, Eu-154 and Eu-152.  These isotopes were produced when neutrons from the “device” were captured by the ~1ppm naturally-abundant Eu-153 and Eu-151, respectively, which have remarkably high capture cross-sections.  These activation products are also long-lived enough to persist in significant quantity to the present day.  The other major long-lived gamma-emitting activation nuclide is Co-60.  Some of this cobalt could be from metal in the bomb’s well casing, but it could also be from activation of crustal mineralization.  The remaining major activity, Cs-137, is a product of fission in the bomb’s fissionable components.

Gamma spectrum of Lake Chagan atomsite

If we examine the smaller peaks in detail (click on below thumbnails), long-lived isotopes of holmium (Ho-166m), silver (Ag-108m), and barium (Ba-133) are in evidence.  Am-241 is present at a low concentration; on the basis of its 59-keV gamma line I cannot confidently estimate its concentration using the Cs-137 reference source technique.  Am-241 is the daughter of Pu-241 produced by neutron capture on plutonium in the bomb, and thus is a reliable proxy for the presence of plutonium in the sample.  The gamma radiations from plutonium itself are too weak and swamped by the spectrum’s low-energy continuum to be observed.

The chart below presents the results of the quantitative analysis.  Gamma-emitting radionuclide activity in “Chaganite” exceeds 375 Bq / g, with Eu-152 being the most concentrated.

Nuclide concentrations, July 30 2012

Chaganite versus Trinitite: when the activities are normalized to their initial values at the time of the respective explosions (1965 and 1945), a direct comparison can be made that illustrates just how much more radioactive the Chagan slag is (see beow).  The data for Trinitite is taken from Pittauerova, Kolb, et al., “Radioactivity in Trinitite: a review and new measurements,” Proc. 3rd Eur. IRPA Conference, Helsinki, 14-16 June 2010.

Comparison of “Chaganite” with Trinitite

The Chagan slag contained almost an order of magnitude more Cs-137 at the time of formation, but it is the rather staggering ratios of the activation nuclides that surprises me the most: 400 times as much Eu-154 in Chaganite versus Trinitite.  70 times as much Eu-152.  And 370 times as much Co-60.  Why?  One fairly obvious explanation is found in the facts that Chagan was a more powerful bomb, detonated in closer proximity to the crustal rock that its neutrons activated since it was underground.  Some further considerations may also be relevant.  According to Carey Sublette’s Nuclear Weapons Archive, Chagan “was reported to be a low-fission design, which had a pure thermonuclear secondary driven by a fission primary with a yield of about 5-7 kt.”  In contrast, the Trinity bomb was a pure fission core surrounded by a uranium tamper.  Thus, escaping neutrons with a hard DT fusion spectrum probably carried a significantly higher fraction of Chagan’s energy yield relative to Trinity’s.

There is not a statistically-different concentration of Ba-133 between the two slags.  I think most of Trinity’s Ba-133 came from the bomb’s explosives, while Chagan’s probably came from crustal concentrations of barium.

Finally, if the Trinity bomb had a fission yield more than three times larger than Chagan, why is the latter’s concentration of Cs-137 higher?  The best reason I can suggest is Chagan’s better underground containment of volatile fission products.  In a surface explosion, volatile Cs and its beta-decaying precursors exist as gases for a long time, enabling atmospheric dispersal.  In an underground explosion, volatiles are condensed rapidly near where they were formed.

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U.S. Radium, Then and Now

May 14, 2012

Many people know the tragic story of the “radium girls,” the luminous-dial painters of the flapper era who tipped their paintbrushes in their mouths, became sickened from internal radiation exposure, and had to fight for workers’ compensation as they died.  Although a large number of radium paint factories existed, one in particular is identified with this infamous episode: the United States Radium Corporation, sited on two acres at the southwest corner of High and Alden Streets in Orange, New Jersey.  This factory was built in 1917 for the combined purposes of radium extraction, purification, and paint application.  Two original buildings—including the paint application building—remained standing until the US EPA had them torn down as part of a Superfund remediation project in 1998.  Today, the site is a barren, fenced-in, field with no hint of radioactivity betraying its former capacity.  In this post I’ll share a few photos from my trip this month, from the Library of Congress’s archive of the recent past, and even one from the plant’s heyday.  I’ll share some quotes about the technical operation of this facility, and a pic of my samples of its product, Undark.

The former U.S. Radium site viewed from the southeast corner in 2012. A railroad track once paralleling the confined Wigwam Brook brought 100-lb sacks of carnotite from Paradox Valley, CO, as well as soda ash, to a siding here. Radium was extracted in a long-since-demolished building at this corner of the property before going to the crystallization lab and ultimately the paint shop on site.  Hydrochloric acid, the main extractive lixiviant, was stored in a tank on the opposite side of the property.

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Paint Application Building, exterior: About 300 dial painters, virtually all of them young women, came to work here between the years of 1917 and 1926.

South-easterly view of U.S. Radium’s paint application building from Alden Street, mid-1990s (public-domain photo from the Library of Congress). Grace Fryer and her dial-painting cohort probably ingested their fatal doses of radium on the second floor of this building.

A similar view today (2012): all that’s here now is an empty field behind a fence. A scintillation counter measures nothing above background levels of gamma radiation.

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Paint Application Building, interior: “Dial painting areas had four parallel rows of work benches, aligned with the building’s longer axis.  Both floors included large wooden, double-hung, triple windows, and at least one section of the upper floor appears to have skylights.”

Second floor of the Paint Application Building, interior view to the southeast in this 1922 photo belonging to Argonne National Laboratory. Note the open skylights.

The same room, late 1990s, Library of Congress photo. The skylights have been filled in, but their recesses and original plumbing are still visible.  The floor has been replaced.

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Crystallization Laboratory: From the element’s discovery well into the 1950s, the only practical chemical technique for separating radium from barium was arduous multi-stage fractional crystallization.  U.S. Radium used a chloride and bromide system, as described by Florence Wall, plant chemist: “…in the crystallization laboratory, large quantities of radium chloride solution from the plant progressed in stages from silica tubs, three feet in diameter and about a foot deep, into smaller evaporating dishes until, after conversion, the product appeared as a few crystals of radium bromide in a tiny dish, 1/2 inch in diameter.” 

The one-story crystallization lab as it looked from the northwest, in this mid-1990s Library of Congress photo. Behind it is the Paint Application Building.

In 2012, the grass covers all. (The same house can be seen in the background in both images.)

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The Product: U.S. Radium named its radioluminous paint Undark.  An article that was painted with this product was said to be “Undarked.” The formula of Undark varied with application and was a trade secret.  At the time of the “Radium Girls” poisoning, a single employee named Isabel manufactured a zinc sulfide base activated with trace quantities of cadmium, copper, and manganese.  Another employee, originally company founder S. A. von Sochocky, added a measured amount of radium to the base and fixed it in its insoluble sulfate form: “[D]epending upon the type of work the material is to be used for the element of radium varied from one part of radium element to 140,000 parts of the base—zinc sulphide, to one part of radium element to 53,000 parts of the base [about 20 microcuries per gram].  The radium element when added to the zinc sulphide [...] is in an aqua solution.  When that is added to the zinc sulfide which is in the form of a dry powder, it becomes like a paste.  The radium element when mixed with the sulphide powder is soluble.  In order to make certain that it will become insoluble and also that it will be equally distributed in the paste and also to prevent the radium element from being dissolved later when water is applied to it, I converted the radium into radium sulphate which is insoluble by adding amount of ammonium sulphate also in an aqua solution.” 

Undark, dated 1940, made to Army Specification 3-99D, packaged in 1g vials. Each produces a gamma exposure rate of about 40 mR / hour on contact, broadly consistent with about 20 microcuries of Ra-226 activity per gram.

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The Waste: Anything that was not radium—i.e. the vast majority of the ore that entered the plant—was waste and had to find a new home!  This included the uranium content of the ore; preceding the discovery of fission, uranium was effectively worthless.  One common application for U.S. Radium tailings was infill for construction projects in nearby Glen Ridge, Montclair, and Orange.  Contaminated fill was identified, dug up, and replaced throughout the 1990s.

Carteret Park (e.g. Barrows Field), located in Glen Ridge, was originally filled with waste tailings from U.S. Radium. Third base was rumored to be particularly “hot.” The entire ballfield was dug up, trucked away in drums, and restored with clean fill in 1998.

The hottest spots at Barrows Field today are along the concrete fence wall. Whether the minor detected radioactivity is owing to natural occurrence in the concrete materials, or un-remediated residues from U.S. Radium, is impossible to say.

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References:

Historic American Engineering Record HAER NJ-121, National Park Service (1996)  (All quotations in italics above are from this source.)

Photographs from above record by Thomas R. Flagg, Gerald Weinstein, 1995-1996, at the U.S. Library of Congress

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Nuclear Collection (Part VI)

March 13, 2011

Click any thumbnail image to view in full size. And, as always, if you have something radioactive and in need of a good home, contact me: I buy and trade all the time. Enjoy!

Lithograph by Leo Vartanian commemorating the CP-1 nuclear reactor.  In what has to be the winningest art idea ever,  moderator graphite from the historic reactor was actually ground up to make the ink in which the portraits of physicists Leo Szilard, Arthur Compton, Enrico Fermi, and Eugene Wigner were rendered.  Prints were distributed by Argonne National Laboratory to honor long and illustrious careers.  The ink is not detectably radioactive.  See my other mementos of CP-1 here. Size is 17″ by 22″(framed).

Though it is in many ways a modern and progressive nation, Japan steadfastly clings to certain curious anachronisms.  From the land of whaling and sailor-suit school uniforms come these examples of radioactive “quack cures”, modern instances of a fad phenomenon that, half a century ago, had largely been driven into extinction in the US and Europe.  Both items pictured—the Wellrich Co. Ltd. “Health Card” (top) and the “Mainasu ION” plaque (bottom)—contain natural thorium as verified by gamma spectrometry.    The “Health Card” claims to offer benefits that include denaturing nicotine in cigarettes.  The health benefits of the negative ion disk aren’t mentioned on it, but surely have no basis in sound science.  It is equipped with an adhesive surface on the back for mounting.  Dozens of varieties of negative ion quack products are peddled by Asian eBay sellers, and I have no idea how many of these items might be radioactive.  The Wellrich card and the ion disk measure 1400 CPM and 550 CPM respectively on a Ludlum 44-9 pancake Geiger tube.  (Donated to my collection by Bill Kolb.)

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More radioactive vacuum tubes. All the specimens in this batch were kindly donated anonymously, and all are receiver protection tubes for military radar sets.  In this application, gas breakdown, aided by deliberately-included radioactivity, dissipates any high-power RF energy that finds its way into the receiver waveguide.  From left to right in the top photo: Varian MA37002X with Co-60 (originally “0.7 microcuries max.”), date code 1995; Omni-Wave MPT-24 with (originally) 25.0 microcuries of Kr-85, date code 1984; Omni-Wave MPT-47-B with (originally) 25.0 microcuries Kr-85, date code 1976.  The gamma spectra of the two Kr-85 tubes clearly shows the residual 514-keV gamma activity of the 10.8-year fission product and even permits a coarse estimate of the quantity remaining (about 3 microcuries in the MPT-24, 0.2 microcuries in the MPT-47-B).  More radioactive tubes are described here and here.

Large receiver protection tube with tritium. The application is the same as the tubes mentioned above, but this one is a monster, measuring almost 16 inches in length.  The part number is MA3948L-12, the manufacturer is Varian, and the contents are mostly argon and a small amount of radioactive tritium (H-3), 10 mCi.  The second photo shows an electrodeless RF discharge established in the tube.
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Contaminated Geiger counter strap from Chernobyl trip. Last summer’s trip to Pripyat resulted in detectable radioactive contamination of my shoes (see description) as well as this shoulder strap.  Gamma spectrometry easily identifies Cs-137, one of the handful of long-lived fission products, in a hot spot on the strap.  The activity in the spot is small, only about one nanocurie (~35 Bq).  Some possible contribution from the synthetic transuranic americium-241 is also noted.

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More radioactive goodies from Bayo Canyon

March 2, 2011

I’ve written about this place twice before, and a bumper crop of radioactive souvenirs from a February visit compels my new assessment that Bayo Canyon, New Mexico is simply unmissable for any hardcore nuclear tourist.  Of course, there’s the historical dimension:  the radiolanthanum experiments that commenced here in 1944 provided crucial insight into the implosion weapon design validated in 1945 by the Trinity test (and embodied later by “Fat Man” and virtually all successive bombs).  But what makes Bayo so special is that the history here is tangible, collectable, and detectable provided you come with a Geiger counter.

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The next four photos at left show pieces of blast debris that were scattered across the surface near the escarpment under Point Weather (where I am standing, 2nd photo above), along with readings in counts per minute on a Ludlum 44-9 pancake GM tube.  While the great majority of findings are not detectably hot, there is so much debris available that the prospects for major finds here are good.  This is my second piece of radioactive cable, and the other two pieces appear to be aluminum metal.  For comparison, local background is about 60 CPM.

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There is sufficient gamma radiation to identify uranium in one of these samples by scintillation spectrometry and to estimate its present activity.  The piece of cable was my choice for this test, owing to easy source-detector geometry and negligible self-absorption.  The last image is the 2000-second NaI:Tl gamma energy spectrum.  The peaks are consistent with the prominent decay radiation of U-235 at 185.72 keV (emitted in 57.2% of decays).  Assuming a geometric efficiency of ~50% and an intrinsic photopeak efficiency of ~75%, the piece of cable contains about 8 mg of uranium if the uranium has its natural isotopic ratio, or about 20 mg if it is depleted. (Both DU and natural U were used in the Bayo experiments.)

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Radioactive Treasure in Bayo Canyon

November 11, 2010

Bayo Canyon, near Los Alamos, NM, was a testing ground for radioactive explosives during and after the Manhattan Project. Unfortunately, though it is public land now, it isn’t the most accessible place.  This photo depicts the canyon from its western rim last fall when I tried to get in with a friend.  The deep snow was a show-stopper on the trail leading down from the town on that day.  There is an access road that enters the canyon and provides for an easy walk to the blast sites, but it is gated, and unauthorized vehicles lured in by an open gate may find it locked when attempting to exit.  In spite of the hassle, however, I can now attest that Bayo Canyon is a bona fide destination for radioactive collectibles.

I returned to Bayo Canyon in the company of Taylor Wilson on October 16, and discovered my first radioactive token from this locality—a short piece of shielded two-conductor cable that reads about 600 CPM on a 2″ pancake Geiger tube.  It’s not screaming hot, but it means there’s more here.  (Photo credit: Tom Clynes; used with permission).

Los Alamos’ TA-10 facility in Bayo Canyon entered its decommissioning phase in 1960, and since then the canyon floor has been subject to sustained scrutiny from cleanup crews.  However, it’s obviously true that a persistent and focused hobbyist with good radiation detection equipment can beat a veritable army of government nine-to-fivers when it comes to truffling out the good stuff.  The DOE’s Radiological Survey of the Bayo Canyon, Los Alamos Final Report (1979) explains the nature of the residual contamination:

Because of the wide dispersal of debris by the tests and continuing natural erosion processes, it was recognized at the time of decommissioning that there was a reasonable probability that some high-explosive and some potentially radioactive materials remained in the canyon.  Thus, periodic surface surveys and searches were conducted in 1966, ’67, ’69, ’71, ’73, ’75, and ’76.  During such surveys a number of additional pieces of debris were located, with only a few of them being contaminated with “°Sr or including normal or depleted uranium.

Indeed there are many remaining pieces of debris, often entertaining in their own right if not detectably radioactive.  The pieces of metal in this last photo are representative; both exhibit extreme distortion from the force of whatever blast hurled them through the woods sixty years ago.

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