Pioneer actinide chemist Larned Asprey dies

Larned "Larry" B. Asprey, one of the giants of actinide and fluorine chemistry, died March 6, 2005, in Mesilla Park, N.M. He would have been 86 on March 19. He retired from Los Alamos National Laboratory in 1986 after conducting more than thirty-five years of fundamental and applied research, which was critical to the present-day understanding of the chemistry of actinides and lanthanides, as well as aspects of main-group elements.

Asprey published approximately 150 key peer-reviewed papers and held eight patents, in addition to issuing countless technical reports. His formal recognitions include the Glenn T. Seaborg Actinide Separations Award, New Mexico Chemist of the Year, Los Alamos Distinguished Service Award, and an invited one-year appointment at the Karlsruhe Nuclear Research Center in Germany. He was active in the Inorganic Division of the American Chemical Society, serving as secretary-treasurer, councilor, member of the Executive Committee, and organizer of technical sessions.

A paper co-authored by Bob Penneman on transuranic chemistry was selected for the groundbreaking first Atoms for Peace conference in Geneva in 1954, where actinide chemistry was discussed for the first time at an open international setting. That meeting marked the first interactions with Soviet scientists working in the actinide area.

Larry Asprey was both a co-worker and friend. He had a clear and focused view of his path and pursued it relentlessly, hurdling obstacles that would deter many. Early on, he stated that he wanted to spend his time in the lab and to be shielded from administrative work. As his section and later group leader, my role was his "supervisor/helper" for thirty-five years. To get the best from Larry I had only to make a suggestion, which he would immediately attack and substitute with a better one.

Larry flourished in the laboratory, using a variety of exotic and hazardous materials. They spanned the radioactive actinide elements from protactinium through californium and the potent oxidizers, chlorine trifluoride (ClF3, dioxygen difluoride (O2F2), and fluorine.

His work with such materials often led to adventures like the time a group of researchers wanted to measure the velocity of sound in chlorine trifluoride. Larry cautioned them that the cell they needed to provide had to be scrupulously clean. The cell was filled at DP Site and placed in a temperature-controlled silicone oil bath. We were in an adjacent room when we heard a low rumbling that became increasingly louder. It turns out that a tapped screw hole in the cell had not been entirely cleaned of machine oil. The chlorine trifluoride reacted with the oil, ate through the cell, and began reacting violently with the silicone oil bath. When the fume hood quit dancing, the reaction stopped, and our wide-eyed visitors rethought their participation.

-Bob Penneman, retired

In addition to his prolific and influential publication record, Asprey had a profoundly positive influence on his peers as well as younger practitioners of actinide and fluorine chemistry. He was always there to serve as professional mentor, personal friend, confidant, and fellow adventurer in the outdoors he loved. His legacy of impeccable scientific integrity, zest for hard work and play, humanity, and sense of fair play has been continued by numerous former students and collaborators now working at Los Alamos, in academia, and elsewhere. Many young staff and students were made to feel part of the wonderful Asprey family, which included his wife of more than 60 years, Margaret "Marge" Asprey, and seven children.

Asprey's legendary skills as a preparative chemist made him highly sought after as a co-investigator. His unique ability to carry out difficult syntheses was often used by other scientists to make critical contributions to broad areas of inorganic chemistry. This body of work ranged from fundamental studies of interest to the academic community to applied programs involving international security issues of the highest magnitude.

As a new summer student in June 1950, I was assigned to Bob Penneman's CMR-4 Group. Larry Asprey and Bob were the principal researchers into the then barely known intricacies of actinide chemistry. It was a wonderful experience for a young graduate student. While I'd had a course in radiochemistry, I had only dealt with small tracer amounts of activity, and that summer we were dealing with multi-milligram quantities of pure americium-241.

Back then, the word "mentor" wasn't in such common use as it is today, but Larry was a wonderful mentor. He was always willing to take the time to describe details of experiment planning and obvious precautions to take. Larry's experience with americium while working at Berkeley was a great asset at Los Alamos. He seemed to have a clairvoyant insight into basic plutonium, americium, and curium chemistry so that his shrewd guesses usually turned into scientific fact. I'm so very proud to have known him all the years since my first months at Los Alamos, and I'm even more proud that several of my publications list Asprey and Keenan as co-authors. His effervescent enthusiasm for actinide research was matched only by his love of the outdoors. Weekend fishing, hunting, or backpacking trips were exhilarating breaks from the laboratory.

—Tom Keenan, retired

Asprey was a brilliant, inspiring, and daring experimental chemist who obtained his B.S. at Iowa State University in 1940. His work in actinide chemistry began in early 1944 during his Army enlistment. He was assigned to the Manhattan Project's effort to separate and purify plutonium under Glenn T. Seaborg at the University of Chicago's Metallurgical Laboratory and quickly became an important member of the Plutonium Recovery Section. From this work, a patent application involving tributylphosphate was filed on May 8, 1947, with H.H. Anderson as lead author and Asprey as second author. This work formed the basis of the PUREX (plutonium uranium extraction) process, still used worldwide to recover plutonium. Asprey's Manhattan Project work signaled a highly auspicious beginning to a career-long involvement with the lanthanide and actinide elements.

After World War II, Asprey obtained his Ph.D. in 1949 from the University of California–Berkeley under the tutelage of the noted experimentalist B.B. Cunningham, who had isolated the first americium compounds. Asprey's thesis, "Equilibria in the Oxide Systems of Praseodymium and Americium," explored the extremely complex nature of actinide and lanthanide oxides, an area of actinide research still of interest as highlighted in recent issues of Actinide Research Quarterly.

I worked with Larry for many years, and he was a great collaborator. We used infrared spectroscopy (IR) to study molecules isolated in low-temperature matrices of solid argon. Together we studied the spectra and determined force constants for many interesting molecules, including nitrosyl fluoride and chloride (ONF and ONCl) with isotopic mixtures of oxygen(16+18) and nitrogen(14+15) and chlorine(35+37). Later we made detailed studies of uranium hexafluoride (UF6) and uranium pentafluoride (UF5) isolated in solid argon. We also studied IR spectra of pure uranium hexafluoride in the gas and solid phase at very low temperatures. References to our collaborative efforts can be found in the book Inorganic Vibrational Spectroscopy by L.H. Jones, 1971, Marcel Dekker Inc., New York.

—Lew Jones, Laboratory Fellow, retired

Asprey joined Los Alamos Scientific Laboratory in 1949 and continued to develop the fundamental and applied chemistry of the actinides. He participated in the first sub-gram and gram-scale isolation of americium and the elucidation of its chemistry, then largely unexplored. Small amounts of plutonium-241, which decays to americium-241, are formed together with plutonium-239 in neutron-irradiated uranium. Plutonium metal scrap from machining slugs for Los Alamos' Clementine reactor contained about 50 parts per million americium-241 available for americium recovery. Concentrated salt wastes with a 300:1 ratio of lanthanide to americium, but very dilute in americium, also were available from purification of Hanford plutonium nitrate. Separations processes were successfully developed and americium was isolated on the gram scale for the first time from these very lean sources.

Asprey's important early Los Alamos contributions to elucidating the basic chemistry of americium are documented in benchmark publications with his co-workers. This body of work includes discussions of the disproportionation of americium(V), the direct oxidation of americium(III) to (VI), the measurement of the americium(V)/(VI) oxidation potential, the demonstration that the linear uranyl structure is maintained in americium(VI), the demonstration of the elusive divalent state in the di-iodide, the discovery of the tetravalent state in fluoride salts, and the first absorption spectrum of a soluble and relatively stable americium(IV) species in concentrated "aqueous" fluoride solution. 

Preparative chemistry is the foundation of most chemical research and in this arena Larry was universally recognized as a master. His ability to carry out difficult reduction syntheses using esoteric techniques designed for handling dangerously unstable, toxic, or highly radioactive materials was legendary. It was these skills that made him the "go-to guy" for many talented co-investigators who were interested in doing physical studies including spectroscopic or structural investigations. In a real sense he enabled a large body of work outside his core research efforts.

In the late 1960s when I joined the group that eventually became INC-4, Larry was the kernel of a small but highly productive collection of synthetic chemists. Over the span of the next nearly three decades the synthesis effort in that group became increasingly important and, as the group expanded, formed the basis for a dazzling proliferation of programs, a list of which would span most of the interests of modern chemistry. These programs were a strong drawing card that attracted some of the country's very best young chemists to Los Alamos and, indeed, many of them now lead key efforts or hold key management positions in chemical programs throughout the Laboratory.

Over the years many of the younger staff members had direct interactions with Larry and found his dedication and enthusiasm for chemistry to be contagious and inspirational. He was extremely generous with his time and talents inside and outside the Laboratory and had the habit of inviting us all to join him in many outdoor adventures in Northern New Mexico. Indeed, he made us feel that we were honorary members of his wonderful family. Those of us who spent all or part of our careers serving a Laboratory whose success we felt was critical to the national welfare will remember Larry with a deep sense of gratitude.

—Bob Ryan, retired

In subsequent work, Asprey and co-workers demonstrated that curium, at the center of the 5f series, could be oxidized to curium(IV). His prolific investigations of unusual oxidation states of americium and curium were extended to berkelium, californium, and lanthanide elements. Observation of the fluoride solubility of americium(IV) allowed berkelium fluoride to be readily separated from its americium bombardment target, and was critical to the first observation of this new element by Ghiorso and co-workers. This portion of Asprey’s research also includes the first demonstration of the tetravalency of berkelium and californium, the preparation of the first divalent thulium compounds and two new tetravalent lanthanides: neodymium and dysprosium.

Asprey's work on protactinium, americium, berkelium, and californium metal preparation was also highly influential. Actinide metals prepared by him were indispensable for structural, magnetic, and superconductivity studies of these metals. This work also included the first distillation of americium—a matter of significant practical and fundamental importance.

Collaboration between Asprey and the great crystallographer William H. Zachariasen began in 1954 and continued for some twenty years. (Zachariasen's work is highlighted in ARQ 2nd quarter, 2004.) As an interesting example of this collaboration, Zachariasen recognized the x-ray pattern of the pentavalent americium compound, KAmO2CO3, prepared by Asprey and co-workers, as being essentially identical to that of a putative hexavalent plutonium compound of the 1940s, that "the chemist" claimed was KPuO2(OH)3. Based on the correct formula, Zachariasen deduced immediately that the original plutonium compound really was KPuO2CO3 with pentavalent plutonium, both formulas having the required five oxygens, but with carbonate instead of the proposed three hydroxyls.

Asprey became a noted fluorine chemistry authority through his work on high-oxidation-state chemistry of the actinides and lanthanides. He discovered and patented the process still used to prepare extremely pure elemental fluorine. His fluorine expertise was used to prepare many volatile transition metal, main group, and actinide fluorides for important collaborations in vibrational spectroscopic studies in gas and low-temperature matrix isolation phases. This influential body of work is among the most heavily cited of Asprey's publications and contributed significantly to the major national effort on laser-based isotope separation methods. Related frequently cited work includes publications defining fundamental structure and bonding properties of simple molecular fluorides in solution, gas, and solid phases.

In the previous tributes, it is abundantly clear that Larry Asprey was an eminent actinide chemist. However, it would be incomplete to stop there. In a broader picture, it can be more completely stated that Larry Asprey was an outstanding inorganic synthetic chemist who made creative advances not only in the chemistry of the actinide elements, but also in the synthesis of new main-group element species as well as transition metal compounds. Most notably, he was an internationally recognized fluorine chemist. The fields of actinide and fluorine chemistry regularly intermingled in Larry's hands, but he also made numerous contributions in the larger context of the fundamental reactivity of fluorine and fluorine compounds important to Los Alamos technical objectives and to fundamental inorganic chemistry.

As a postdoctoral student who studied with Larry in the early 1970s, I would also like to say that it would be even more incomplete to just pay tribute to Larry Asprey's technical accomplishments. Larry was much more than a fine chemist. He was an outstanding teacher, mentor, friend, and confidant. Although it is a clich, it is accurate to say that Larry gave the shirt off his back to those who studied with him. We spent many hours together in the laboratory and we shared a good deal of time on activities outside the formal laboratory setting.

My wife and I truly were made to feel part of the Asprey family and heaven knows Marge and Larry did not need more kids to look after! We did a lot of nice chemistry together but my most-treasured memories of Larry Asprey will be of the person. The impacts that he had in shaping my own subsequent professional and personal life are large and are highly valued by me. I am sure that all of the young chemists who worked with Larry would share this same sentiment. He will be missed but certainly remembered by all of us as we do our own mentoring of the next generation.

Bob Paine, University of New Mexico

In the last years of his career, Asprey became heavily involved with Los Alamos research on the superoxidizers dioxygen difluoride (O2F2) and krypton difluoride (KrF2), which can convert plutonium substrates to volatile plutonium hexafluoride (PuF6) at room temperature. Because of the practical implications of this observation, preparatory methods were needed for unprecedented quantities of these difficult reagents. Asprey was key to success in this superoxidizer work, as illustrated by his co-authorship of a burst of publications on the preparation and application of these remarkable compounds.

Ever the scientist, Asprey bequeathed his body to the University of New Mexico Medical School. A scholarship fund has been set up in his name at New Mexico State University. Donations made out to "NMSU Foundation" may be sent to: The NMSU Foundation, in memory of Larry Asprey, P.O. Box 3590, Las Cruces, NM 88003.

Larry Asprey strongly touched all those who were fortunate enough to work and play with him. Those who knew this remarkable man will remember his remarkable life fondly. A quote by Emile Zola-"I am here to live out loud!"-may be an appropriate description of the life and contributions of Larry Asprey, both as a scientist and as an individual.

P. Gary Eller, Bob Penneman, and Bob Ryan

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