S&TR March 2014

Radiochemists apply Radiochemistry nuclear test experience and unique capabilities to new national security and Renaissance scientific challenges.

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BOUT a century ago, the enduring A dream of alchemists was realized when physicist Ernest Rutherford and his collaborators demonstrated that one element can change into other elements through the process of radioactive decay. Rather than turning lead into Livermore scientists have engaged in radiochemistry, nuclear chemistry, and heavy-element research gold, Rutherford’s discovery led to the since the Laboratory’s founding in 1952. In the photo above, Wes Hayes works in hot cells on debris founding of radiochemistry—the study collected from the Hutch Event, a 1969 underground nuclear experiment that produced large quantities of radioactive isotopes—and nuclear of rare, heavy isotopes for debris analysis. At left, Roger Henderson prepares a uranium sample for chemistry, which focuses on the properties electrodeposition onto a stub for testing a resonance ionization mass spectrometry technique. of atomic nuclei and the processes involved in element transformation. Together, these fields form a pillar that Nuclear chemist Dawn Shaughnessy, research and isotope production facilities, supports Lawrence Livermore’s nuclear who leads the experimental and nuclear including the Center for Accelerator Mass security mission, a role they have held radiochemistry group in the Physical Spectrometry (CAMS) and the National since the institution was founded in 1952. and Life Sciences Directorate, notes Ignition Facility (NIF). Nuclear chemist (See S&TR, June 2002, pp. 24–30.) that many potential collaborators and Narek Gharibyan observes, “We have Radiochemists provided crucial project sponsors are surprised by the places to safely perform irradiation, contributions to the Laboratory’s nuclear breadth of radiochemistry capabilities chemical separation, and nuclear counting, weapons test program. They created tracer at the Laboratory. Says Shaughnessy, all on-site. CAMS also produces radioactive components for test devices by using “In the past, Livermore radiochemistry isotopes for a variety of chemistry actinides—radioactive elements with atomic to most people really meant nuclear test experiments. It’s unusual to have all of numbers from 89 through 103, the most analysis, although even in the heyday of these facilities in one place.” common of which is uranium. They also underground testing, that was only part Shaughnessy adds, “As radiochemists, assessed a weapon design’s performance of the endeavor.” we see NIF as a giant neutron source, one by studying the radioactive debris and Today, Lawrence Livermore offers a of the brightest in the world. For instance, gases produced in an experiment. Since the unique recipe for radiochemistry research, it can help us make samples for nuclear moratorium on underground nuclear testing combining nuclear testing expertise and forensics experiments.” But for everything began in 1992, radiochemistry research resources, such as rare radioisotopes Livermore offers, the recipe would be at Livermore has grown to encompass collected from past underground incomplete without Shaughnessy’s team of a wider range of national security and experiments, with robust materials a dozen or so innovative chemists, working scientific missions. handling capabilities and an array of in such diverse areas as fission, nuclear

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forensics, radioactive target fabrication, 10 and 15 megaelectronvolts. The foils are Gharibyan, 40 to 50 spectra are collected transactinide chemistry, and rapid thin enough for protons to pass through and analyzed for each sample. radiochemical separations. without losing much energy, yet thick The more quickly samples arrive at enough to generate an adequate number of Livermore’s nuclear counting facility, the Mapping Fission’s Outcomes fission reactions for study. Yttrium foils more radioactive products researchers are During fission, an excited nucleus splits act as a proton flux monitor, allowing the likely to detect. For many of the team’s into two (or occasionally more) lighter team to calculate the likelihood of a fission early experiments, samples received only fragments and in the process releases reaction occurring in the uranium foils. 10 minutes of proton irradiation, to limit by-products such as neutrons or photons Most fission products are unstable and radiation levels and obviate the need for a in the form of gamma rays. Although will decay by emission of a beta particle cooldown period before sample removal the results of an individual fission event and characteristic gamma rays. High-purity and analysis. The fast turnaround enabled are random, the distribution pattern for germanium radiation detectors record the researchers to detect products with half- the particles emitted for a given parent signatures of gamma rays emitted after lives as short as 5 minutes. isotope and initiating energy is statistically decay, and automated analysis software Longer-lived and lower-yield products predictable. Precisely determining these processes the data to determine the identity experience fewer decay events and patterns benefits important national and quantity of the gamma-emitting thus can be more difficult to detect. To security efforts, from nuclear forensics nuclides in the source. According to create these elusive particles in greater investigations of postexplosion debris to nuclear reactor safety. Gharibyan and his colleagues are refining techniques for measuring the products emitted during proton- and neutron-induced fission of several isotopes, including uranium-238. Researchers have extensively studied neutron-induced fission of uranium-238 because of its importance 10 to nuclear power, but the proton-induced reactions are not as well understood. To examine these events, researchers stack uranium, aluminum, and yttrium foils at the end of an accelerator chamber at CAMS and bombard the target with protons accelerated to energies between

A team of nuclear chemists at Livermore is Cross section, millibarnsCross 1 refining techniques for precisely determining the unique patterns of isobars—nuclides of different elements with the same mass number—produced by the fissioning of various parent isotopes at different energies. This graph shows the likelihood 14.5 ± 0.4 MeV 12.8 ± 0.3 MeV of various isobars being produced during fission 11.9 ± 0.4 MeV of uranium-238 when the proton inducing the 10.6 ± 0.4 MeV reaction is moving at different speeds. Colored symbols indicate proton energy measured in megaelectronvolts (MeV); 1 millibarn is equivalent to 10–27 square centimeters. 10–1 80 100 120 140 160 Mass

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numbers, the Livermore team increased Nuclear forensics readiness exercises use samples of synthetic the irradiation period to a full day Actinides and the nuclear counting period to nuclear debris to test participants’ two months. After days or weeks, the skills at isotope identification. interfering signatures produced by many The current method for preparing of the shorter-lived fission products samples is to irradiate a single Fission products are eliminated, so that longer-lived and fuel in a reactor and collect the lower-yield products are somewhat easier Matrix material fuel and its fission products. A truly to distinguish. realistic sample would include all the pieces of the puzzle—fuels Chemically isolating and removing Activation selected fission products from some products plus fission and activation products samples before nuclear counting also mixed in the right proportions helps the researchers fill in data gaps. and embedded in a matrix of dirt “Radiochemistry allows us to detect and debris. emissions produced in small quantities or those that have interferences,” says Gharibyan. In one uranium-238 experiment, the researchers demonstrated that, by chemically separating samples, are prepared at one facility, typically in 2012 and two round-robin exercises they could measure fission yields for by irradiating uranium in a reactor and with Los Alamos, Pacific Northwest, and about 50 percent more isobars—nuclides splitting it into chunks. The samples are the United Kingdom’s Atomic Weapons of different elements with the same then sent to the participating laboratories Establishment in 2013. mass number—than they could identify for analysis. Nearby facilities such as CAMS and the by nuclear detection alone. In future About three years ago, Livermore cyclotron at Davis (about 135 kilometers experiments, the team will measure nuclear chemists, led by Kevin Roberts, or 85 miles north of Livermore) are fission product distributions for other began designing more realistic debris to preferred for sample preparation because actinide isotopes. further challenge their fellow chemists many of the fission and activation and modelers. A fully realistic sample products are short-lived. Samples must Mixing a Radionuclide Cocktail would include a carefully curated selection be created and shipped promptly so that If an illicit nuclear explosive were of fuels, fission products, and activation exercise participants can measure the more detonated on U.S. soil, nuclear forensics products embedded in a matrix of dirt ephemeral products. In fact, logistics and experts would be tasked with examining and debris. Drawing on the Laboratory’s handling are no small part of the research rubble from the explosion for traces of experience in analyzing nuclear test debris project. Roberts notes that at first, his fissile material, fission products, and (see S&TR, April/May 2012, pp. 11–13) as group adopted radiochemical methods activation products—nearby debris or well as the results of Gharibyan’s fission from the underground test program structural components of the bomb made investigations and other research efforts, because those approaches were established radioactive by neutron activation. The the team is determining how best to create and effective. Now, the researchers want more information experts could glean by a “radionuclide cocktail” with ingredients to modernize the techniques so they can characterizing these materials, the better in the right amounts and proportions. prepare testing materials more efficiently able they would be to trace the weapon’s Using a mix of different fuels and and safely. “Making this kind of sample is design and origin. reaction energies will likely achieve not a trivial exercise,” says Roberts. “The To ensure readiness in the event of the most realistic results. Laboratory debris can end up being fairly radioactive, such a scenario, research teams at Los researchers have access to isotopes from and not many facilities can handle such Alamos, Pacific Northwest, and Lawrence past experiments and can generate new materials. We can, and we couple it with Livermore national laboratories have, materials using accelerators, test reactors, the weapons knowledge here.” for the past decade, engaged in isotope and other sources. In conjunction with As part of the sample preparation effort, identification exercises using simulated the Crocker Nuclear Laboratory at the Livermore researchers have partnered with debris samples. Exercises last from days University of California at Davis, the scientists at the University of Nevada at to weeks and involve both chemical Livermore team completed several practice Las Vegas (UNLV) to fabricate a potential analysis and computer modeling. Samples runs to demonstrate sample production matrix material made of equal parts

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glass and concrete dust. The substance radioactive sources and targets for in uranium and plutonium isotopes in is then combined with fuels irradiated Laboratory experiments that require experiments at the Los Alamos Neutron at a test facility at the Nevada National a broad range of isotopes. Some of Science Center. Wu’s targets are made Security Site, and the resulting samples these materials are created in facilities of freestanding foils, each only a few are characterized. The Laboratory team such as CAMS. Others are acquired by micrometers thick but up to 4 centimeters also is investigating the feasibility of using dipping into the Laboratory’s archive of in diameter—quite large for heavy-element additive manufacturing to create samples isotopes collected from various sources, experiments. In addition, the fragile foils that can be precisely reproduced, which including Oak Ridge and Savannah often require uranium or plutonium on would aid in data intercomparison. River national laboratories. The archive both sides instead of the standard one side. Kimberly Budil, who manages the is one of a kind, offering such items as To limit handling, Henderson developed Nuclear Counterterrorism Program in the world’s only supply of a metastable an apparatus that electroplates both sides Livermore’s Global Security Principal form of americium-242 and the only of the foils simultaneously. He also built Directorate, stresses the importance of separated batch of plutonium-244. Nuclear an instrument that generates a three- using realistic debris samples for the chemist Roger Henderson, who leads the dimensional map of the target surface, readiness exercises. “It’s important to fabrication efforts, says, “At Livermore, allowing researchers to characterize how challenge the participants in a way that we have access to unique, irreplaceable smoothly and evenly the radioactive mimics the response to an actual incident source materials. Part of our job is material is deposited on each surface. and at the same time to thoroughly test stewardship of these materials because no Having an in-house capability to supply their diagnostic capabilities.” one knows when they will be produced in quality-tested radioactive sources and Roberts notes that his team is 5 to experimentally usable quantities again.” targets has been a boon for Livermore 10 years from routine production of truly For one Laboratory project, Henderson researchers. In particular, the electroplating realistic samples, but those developed for created 60 monitor foils of uranium-235 technique and the surface-mapping the round-robin exercises in 2015 should enclosed in aluminum holders to calibrate tool have increased the consistency of have materials in the proper proportions. dosimeters being designed for field radiochemistry experiments. Collaborators By engaging in readiness exercises deployment following a nuclear accident. at GSI Helmholtz Centre for Heavy Ion and sample development, Livermore He also crafts targets for experiments to Research in Darmstadt, Germany, are also researchers are helping to establish a study nuclear reactions, most of which interested in using the automated mapping significant national capability and fostering are relevant to both stockpile stewardship system to characterize their targets. stronger partnerships with forensics and fundamental science research. “Target specialists at other laboratories and with making is a specialty process,” says Extracting Elemental Behavior sponsors in the Departments of Defense Henderson. “No two clients have identical Other radiochemists at Livermore are and Energy. specifications. There’s always some using Henderson’s target foils to explore difference in the substrate, size, amount of the chemical behavior and fundamental A Source for Radioactive Targets material, or other specifications.” properties of elements at the far end of the In addition to their work on nuclear Henderson often prepares targets for periodic table, which have short life spans fission and forensics, the radiochemists Livermore physicist Ching-Yen Wu, and low production yields. Examining the in Shaughnessy’s group are fabricating who studies neutron-induced reactions transactinides, elements 104 and above, is especially challenging. Their high nuclear charge causes the inner electron orbitals An automated surface mapping system developed at Livermore examines targets such as the foil on Pinhole the left and produces a three-dimensional surface map such as the one on the right. This information allows researchers to evaluate coating consistency, which could affect an experiment, and to characterize features such as the pinhole in the foil.

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to move very close to the speed of light, which can affect an element’s atomic and chemical properties. This relativistic effect may become more extreme for the heavier transactinides, making their characteristics and behavior more difficult to predict. Six of the newest and heaviest transactinide elements were discovered by Livermore researchers in collaboration with colleagues at the Flerov Laboratory of Nuclear Reactions (FLNR) in Russia. (See the box on p. 10.) While an element’s atomic number is determined by the number of protons in its nucleus, the element’s placement in the periodic table is based on the chemical properties it shares with elements nearby. The question that intrigues Lawrence scholar John Despotopulos is whether the newest elements belong where they are currently situated. “Flerovium, element 114, is just beneath lead on the periodic table, so these two elements should have similar chemical properties,” says Despotopulos. “But some An element’s position in the periodic table is based on its properties. Because the heaviest elements scientists predict that flerovium is more are short-lived and produced only in tiny quantities, scientists must extrapolate their characteristics by like mercury or an inert gas such as radon.” systematically studying related but longer-lived elements. For example, the properties of flerovium (Fl) Two gas-phase experiments of flerovium may be similar to tin (Sn) and lead (Pb) or cadmium (Cd) and mercury (Hg). produced contradictory results. Wet- chemistry experiments, which are more complicated than gas-phase studies, would isotopes are present. Carrier-free isotopes crown ethers extracted the targeted provide more insight into where the element of bismuth and lead are isolated from surrogate efficiently and precisely. fits in the periodic table. Despotopulos and samples of uranium-232, while antimony Despotopulos and his colleagues are colleagues at Livermore and UNLV are thus and tin are created at CAMS. The extending the extraction study to include devising efficient and precise wet-chemistry flerovium surrogates, lead and tin, are mercury and cadmium, which may share methods to isolate the two elements. To then mixed together, as are the element properties with flerovium. They are evaluate these methods, they are using 115 surrogates, bismuth and antimony. also synthesizing various crown ethers surrogates—lighter elements with putatively The research team then uses extraction to determine the best combination of similar properties to the transactinides and chromatography to separate the desired extractant properties for different elements. more atoms available for study. (See S&TR, isotopes. For this technique, a resin coated September 2011, pp. 4–10.) with an extractant is affixed inside a glass Chemistry at the Push of a Button A short nuclear lifetime and low column along with a small amount of the Producing enough atoms to study the production rate prevent flerovium from sample. When the column is flushed with heaviest transactinides requires weeks or reaching chemical equilibrium in its a solvent, usually hydrochloric or nitric months of accelerator beam time. Because environment. As a result, measuring the acid, the component of interest adheres to these rare, short-lived elements can form element’s chemical reactivity is difficult. the extractant. Everything else is washed at any time, scientists must constantly The Livermore and UNLV collaborators through the column. The extractants monitor the experiments. With funding are working with carrier-free isotopes to selected for the Livermore experiments from Livermore’s Laboratory Directed more accurately replicate that behavior in are crown ethers, cyclical molecules that Research and Development Program, the surrogates. In a carrier-free isotope, selectively bind with certain metals. radiochemists in Shaughnessy’s group are all the atoms of a given element consist Tests on the four surrogates in varying collaborating with researchers at UNLV of the same radioisotope; no stable concentrations of solvent showed that and Texas A&M University to design

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A Smashing Collaboration In 1989, nuclear chemists Ken Hulet from Lawrence Livermore team and Dubna city officials. The festivities began with a Laboratory- and Georgy Flerov, founder of the Flerov Laboratory of Nuclear hosted colloquium, titled “Elemental Science: Livermorium and the Reactions (FLNR) in Dubna, Russia, met at a conference and decided Periodic Table.” In one lecture, Livermore nuclear chemist Ken Moody to work together to synthesize new elements. (See S&TR, October/ discussed the history of heavy-element research and the long-standing November 2010, pp. 16–19.) Transcending international politics and collaboration between Lawrence Livermore and FLNR. “A collection intense competition within the heavy-element research community, of people with good will and shared vision can make wonderful things scientists from the two institutions have built an enduring research happen,” he observed. Following the colloquium, the city of Livermore partnership and discovered six new elements, 113 through 118. hosted a dedication ceremony at the newly renamed Livermorium The names chosen for elements 114 and 116, the two newest Plaza and unveiled a plaque dedicated to the discovery team. additions to the periodic table, pay tribute to that collaboration. All elements with more protons than uranium, element 92, are Flerovium, the name for element 114, honors Flerov and FLNR, and radioactive and were discovered in a laboratory. None of these livermorium, for element 116, recognizes Lawrence Livermore and elements has a half-life long enough to have survived since Earth’s its hometown, Livermore, California. Bill Goldstein, the Laboratory’s formation. Essentially all transuranic elements were first synthesized deputy director for Science and Technology, says, “These names at one of three facilities—FLNR, Lawrence Berkeley National honor not only the individual contributions of scientists from the Laboratory, or the GSI Helmholtz Centre for Heavy Ion Research two laboratories to the fields of nuclear science, heavy-element in Darmstadt, Germany—where inside an accelerator, a stream of research, and superheavy-element research, but also the phenomenal lighter atoms was smashed into a heavier atom for hours or days cooperation and collaboration that has occurred between scientists in until, finally, a pair combined. Synthesis experiments for many of the the two countries.” newest and heaviest elements yield only a single atom with a lifetime Element discovery is a lengthy process. Before an element can be ranging from microseconds to a few seconds, making detection and added to the periodic table and named, its existence must be detected study a challenge. Despite the difficulties, scientists persist with these independently at more than one laboratory and preferably through investigations because each addition to the periodic table expands more than one method. Elements 114 and 116 were first glimpsed their knowledge of atomic structure and behavior. by the Livermore–FLNR team in 1998 and 2001, respectively. (See S&TR, January/ February 2002, pp. 16–23.) In May 2012, A mural at Livermorium the International Union of Pure and Applied Plaza in downtown Chemistry (IUPAC) officially accepted Livermore, California, the element names. In its decision, IUPAC commemorates stated that it found the name livermorium the U.S.–Russian appropriate because of Livermore’s breadth of collaboration that led nuclear and radiochemical research. to the discovery of six On June 24, 2013, Laboratory employees heavy elements. and the city of Livermore celebrated the discovery and naming of livermorium and flerovium with a daylong celebration, attended by members of the U.S. and Russian discovery

a system that captures, prepares, and chromatography. The development team scientists working on underground measures samples with limited interaction estimates that the system will reduce the nuclear experiments,” he says. “They from researchers. time spent on chemical separation tasks by did need to capture the short-lived The system, which is being tested a factor of up to 10. fission products, but they had more at CAMS, will connect directly to the A system that automates some of time to analyze their results. We beamline where the element is produced. the repetitive and time-consuming would face a much different scenario After screening out the incomplete fission activities in chemistry has numerous in the event of a nuclear explosion. products, it will collect complete products, other applications. Roberts, for instance, We’d need results immediately.” An dissolve them in solution, and subject wants to apply the technique to expedite automated wet-chemistry system could them to automated chemical processing, nuclear forensics research. “Urgency also be used for medical imaging and including ion exchange or extraction was not always a pressing concern for treatment, astrophysical research, or even

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Livermore nuclear chemist John Despotopulos works with the Laboratory’s automated ion chromatography fraction collection system, which can chemically separate up to 12 samples simultaneously.

serve as a magnet for nuclear research. In the meantime, radiochemistry researchers are working to secure beam time on other large accelerators, such as the 88-inch cyclotron at Lawrence Berkeley National environmental remediation—for example, for new approaches to address evolving Laboratory. by accelerating the extraction of lead and threats,” says Budil. “NIF is a great Whatever the future holds, the need for mercury, two heavy-metal pollutants. (See example. It offers unique capabilities for expertise in radiochemistry and nuclear S&TR, November 1999, pp. 17–19.) exploring nuclear science and nuclear chemistry is unlikely to wane. “Issues Portability is a key design consideration chemistry at a fundamental level, but involving radioactivity will never go for the automated system because it will forensic scientists need to learn to apply away,” says Roberts. “Even if we were likely be transported to partner facilities these capabilities to our mission space. The to get rid of our weapons stockpile, we’d for element synthesis and characterization radiochemistry team is helping us define need to understand nuclear weapons and efforts. A reasonably compact system could the role for NIF experiments in current and radioactivity for nuclear waste disposal, also facilitate field deployment for nuclear future research.” for example.” As they have demonstrated forensics and environmental purposes. An effort to build a new accelerator in the posttesting era, Livermore’s In a complementary effort, the team is center at Livermore has begun to gather radiochemistry researchers are ready to evaluating a slimmed-down design for momentum. The proposed center would respond to new challenges as national an extra-sensitive germanium detector to include a medical cyclotron, a larger needs change. rapidly identify specific isotopes at remote accelerator that could be used for nuclear —Rose Hansen locations. With improved nuclear counting science and as a rare isotope source, and techniques, the detector could identify a facility with modular laboratory spaces. Key Words: actinide, activation product, certain isotopes in the presence of others, “Our current facilities for nuclear science carrier-free isotope, Center for Accelerator thus eliminating the chemical separation are not flexible enough for 21st-century Mass Spectrometry (CAMS), crown ether, step—a process Roberts compares to experiments,” says Budil. “We need to be extraction chromatography, fission yield, flerovium, Flerov Laboratory of Nuclear “finding the needle without removing able to modify work areas to accommodate Reactions (FLNR), heavy elements, high- the haystack.” new technologies as they become available. purity germanium radiation detector, isotope, We also want to design spaces that foster livermorium, National Ignition Facility (NIF), Radiant Prospects collaboration and cross-talk among nuclear chemistry, nuclear forensics, radioactive Budil adds that the expertise developed scientists—not just with our teams at decay, radiochemistry, transactinide. by Shaughnessy’s group is broadening Livermore but with the nuclear forensics the scope of nuclear forensics research at community at large.” For further information contact a national level. “In the nuclear forensics If the accelerator project reaches Dawn Shaughnessy (925) 422-9574 community, we are continually looking fruition, Lawrence Livermore will likely ([email protected]).

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