From the Mössbauer Spectroscopy Newsletter
|Friedrich and Ursula Wagner -
A Couple of Mössbauer
Fritz Wagner was born in 1937 and studied physics at the Technical University of Munich. In 1960 he was looking for a subject for his diploma thesis. Professor Maier-Leibnitz suggested the subject of resonant absorption of gamma rays that was to be supervised by his assistent, R. L. Mössbauer. Mössbauer was content to hear that his potential new student had a car and thus could drive to Garching, then a desolate place outside the reach of public transportation. Within hours, Fritz Wagner was involved in his first Mössbauer measurements - a tedious matter at the time, but this was to become better with the advent of multichannel analyzers and electromechanichal velocity drives.
Fritz Wagner's diploma thesis was on 170Yb and he used the then rather new Munich Research Reactor to make the 170Tm sources. His first major achievment in science was to arrange a major radioactivity spill, but he was forgiven and was allowed to continue his thesis work. During this time he saw precious little of Rudolf Mössbauer, who soon left for Pasadena, though presumably not because of his student. But Mössbauer spectroscopy never let go of Fritz Wagner in the decades to come. He finished his Ph.D. thesis on the total reflection of the 169Tm gamma radiation with Maier-Leibnitz and Paul Kienle in 1965.
Ursula Wagner is a chemist who did her Diploma and Ph.D. theses at the Technical University of Munich in metal organic chemistry with E. O. Fischer, who won the Nobel Prize for his work in 1973. Her Ph.D. thesis was on hot atom chemistry with metal organic compounds, and she made use of the then new Munich Research Reactor in this work. After getting her Ph.D., she went to Brookhaven to continue this line of research with Garman Harbottle.
Ursula had her first encounter with Mössbauer Spectroscopy as early as 1962 when, because of her education in metal organic chemistry,she became enganged in Mössbauer experiments on ferrocene and iron carbonyls together with Paul Kienle, Mike Kalvius and Dr. Eicher.
She was back in Munich when Rudolf Mössbauer returned from CalTech and began to build up his group at the Technical University of Munich. Ursula became the person who ran the radiochemistry laboratory that was needed mainly to make sources for a variety of Mössbauer isotopes and materials to be studied by the Mössbauer method. With the reactor on the site the Munich group indeed excelled for years to come in work with many of the less common Mössbauer isotopes.
Among them were 139La, 141Pr, several isotopes of Er and Yb, and all those many Mössbauer isotopes of osmium, iridium, and platinum. A major effort was devoted to 99Ru and even 101Ru. A major, long time effort was on the use of 193Ir and 197Au. For these, with their short-lived source isotopes that had to be made at least one a week, the Munich Research Reactor next door turned out to be a real Godsend.
In 1971, Rudolf Mössbauer left Munich to become the director of the research reactor facility at Grenoble (ILL) and G. M. Kalvius came to Munich to replace him. When Fritz Wagner came back from a stay at Argonne National Laboratory, he joined Mike Kalvius's group.
Ursula and Fritz were married in 1973, Fritz obtained his Habilitation in 1974 and soon afterwards became a Professor of Physics at the Physics Department of the Technical University of Munich. Towards the end of the 1970s, studies of metal hydrogen systems became a major field of research in Fritz's group. Then, in 1979, a devastating fire nearly wiped out all of the Mössbauer equipment of the group. Luckily the remaining equipment was patched together within days and measurements were resumed. Ursula continued her hot atom chemistry work, now also using Mössbauer spectroscopy.
In 1977 a turning point came in Ursula's scientific career, when Josef Riederer, now director of the Rathgen Research Laboratory of the Archaeological Museum in Berlin, suggested that they use the Mössbauer capabilities available at the Physics Department to study some ancient Egyptian ceramics he was interested in. Ursula was fascinated by the idea and soon some promising results had been obtained. The subject developed into Ursula's main field of research. The studies eventually turned away from Egyptian ceramics, when she began to work on Pre-Columbian Latin American pottery together with Izumi Shimada, the director of the Projecto Arqueológico de Sicán. A young archaeologist, Rupert Gebhard, now a curator at the Archaeological State Collection in Munich, aroused her interest in Celtic ceramics from Central Europe and in particular from the oppidum of Manching in Bavaria. This was to become the second large field of ceramics research. Ursula combined Mössbauer spectroscopy with other techniques, foremost with neutron activation analysis for provenance studies of the ceramics. For this, the neighborhood of the Munich Research Reactor was once again of paramount importance.
The good times lasted until the summer of 2000, when the reactor was closed down because a new reactor had been built next to it and was supposed to become operational within no more than half a year. It became, in fact, critical for the first time in March of 2004, after a delay of about three years which was largely caused by political squabble. Ursula's archaeology project suffered somewhat from this, but Mössbauer spectroscopy, combined with X-ray diffraction and thin section analysis, the archaeometry is still going strong. Just recently Ursula edited two special volumens of Hyperfine Interactions on Mössbauer spectroscopy in archaeology. This was a formidable task that kept both the Wagners busy for the past several years. This work is now finished, but there are already new plans for new projects and major publications of the many as-yet unpublished data.
Fritz's research was also hard hit by the closing down of the reactor. In the 1990s it had largely turned to work with short-lived sources made at the Munich reactor. Gold played a major role in this, for instance with studies of gold ores containing only very small amounts of gold in chemically bound form, which had been of major interest in gold production and mineralogy. He and his group also studied gold in gold ruby glass and a number of catalysts. Catalysts quite generally became one of the other subjects that took Fritz's fancy in the 1980s and ever since, with 99Ru, 193Ir and 197Au as the mainstays and the more commonplace Mössbauer isotopes as mere additions.
Since the demise of the Munich Research Reactor, the catalysts and mineralogy research is confined to work with commercial sources, mainly 57Fe and 119Sn and 121Sb. This is a step backwards, since the Munich Mössbauer group was always proud of having the facilities and the know-how to do less common Mössbauer isotopes. But Mössbauer work is still going on in Munich, even though the number of workers has dwindled after the retirement of Mike Kalvius. The Wagners, however, still see the Mössbauer spectroscopy as a fascinating method that gives beautiful results. They hang on and hope to do so for some time to come, perhaps even making use of the neutrons of the new FRM-II reactor, when this becomes possible.
From the Mössbauer Spectroscopy Newsletter
|What Mössbauer Spectroscopy Can Tell Us About Ancient Technologies
In 1991, a 12-meter-deep shaft-tomb containing an impressive array and quantity of luxury goods was excavated at the base of Huaca Loro, a monumental mound in the Poma Achaeological Reserve on the Northern coast of Peru. The tomb belonged to a nobleman of the so far little-known Sicán civilization that flourished ca. A.D.900-1100. The news of this discovery was widely reported by the media and the objects exhibited around the world, exciting the masses. The lord of the tomb was not only buried in golden ceremonial attire that included a large mask and three sets of ear ornaments, but was also accompanied by a gilt litter and other items that attest to his elite status.
What Mössbauer spectroscopy can reveal about ancient civilizations is much less spectacular, but equally important in understanding the development and organization of societies like the Sicán culture. Since 1983, Mössbauer spectroscopy, together with a number of other methods, has been applied by the Munich group to investigate ceramic finds in an interdisciplinary approach, bringing together a large number of researchers to solve questions regarding ancient technologies, materials, and human skills.
Besides several smaller studies, two large projects have been pursued. One of them deals with the ceramics found in Celtic sites in what is now Central Europe. The second study deals with the finds made in and around the Poma Archaeological Reserve on the north coast of Peru, the focus of this article. Well-preserved ancient kilns from the Formative period (about 1000-800 B.C.) were found at the bottom of an abandoned, modern irrigation canal in the Reserve; one of them could even be fired once again in a field experiment in 1998. The project continued with the study of ceramics from the 1000-year-old elite shaft-tombs of Huaca Loro and is currently dealing with the materials in a workshop from the Middle Sicán period excavated at Huaca Sialupe west of the Reserve in 1999.
The methods we use to supplement the results from Mössbauer spectroscopy are neutron activation analysis to determine the element composition of the ceramics, and X-ray diffraction to obtain information on the mineral content without the limitation to iron-bearing compounds. Several other methods, like optical microscopy of thin sections, scanning electron microscopy, and X-ray radiography, are also applied. Using statistical analysis of the element concentrations determined by neutron activation analysis, ceramics can be sorted into groups according to the raw materials used in their production. Thus the provenance of ceramics can be established. X-ray diffraction gives information on the mineral content in the pottery and supplements the information gained from Mössbauer spectroscopy. Mössbauer spectroscopy is, however, superior in the determination of iron oxide phases, which play an important role in the impure clays normally used for pottery-making in early ceramic materials. Oxides often escape detection by X-ray diffraction due to their low concentrations and poor degree of crystallinity. Additional information on magnetic properties of the materials can be gained from measurements at liquid helium temperature.
In the course of the Sicán study, we performed a number of field experiments, taking advantage of the expert advice of a local potter who is familiar with the ethnic tradition and interested in ancient techniques. Replica kilns as well as original kilns were fired using locally available fuels, like branches of hardwood trees and llama dung. Oxidizing, reducing and mixed firing cycles were carefully monitored with thermocouples. The tips of these thermocouples were shielded with clay balls to ensure that average temperatures were recorded. These balls later served as test samples in laboratory studies. Moreover, beautiful replica vessels were made for exhibition and sale at the new Sicán Museum, which has opened in 2001 in Ferreñafe near the town of Chiclayo.
The remains of different types of pottery kilns and a great number of ceramic moulds for making small but finely decorated vessels were excavated at the
1000-year-old Middle Sicán pottery workshop of Huaca Sialupe. Mössbauer spectra of differently coloured layers of the lining of one of these kilns are shown in the cover picture. The kiln linings reached temperatures as high as 700 to 800°C. Urns about 50 cm high and 40 cm in diameter were found upside down in the ground with the top cut off and a circular hole oriented in the direction of the strong wind blowing from the sea in the afternoon. Their purpose was not immediately clear. Our recent field experiments revealed, however, that when fired with charcoal, these urns could reach temperatures as high as 1200°C as soon as the wind started to provide the necessary draft. Such temperatures are high enough for metal working. The temperature atop the chimney of the urn went up to 800°C, and would have been sufficient to anneal the copper and gold alloy sheets that were the mainstay of the Sicán metal working tradition. Though only a few finished metal objects were found in the course of the excavation, there were ingots, moulds, crucible fragments, and chisels for cutting sheet metal. Traces of gold, 10 to 100 times above the natural level of 1 to 3 ppb, were found in some of the excavated sherds and in ancient charcoal ash. It thus became apparent that the workshop of Huaca Sialupe was not only involved in the production of elite and ceremonial ceramics, but also in copper and gold alloy working.
Numerous shreds of high-quality black ware were excavated at the Huaca Sialupe workshop, probably stemming from objects broken during firing. The intriguing black sheen observed in this Middle Sicán pottery was successfully reproduced in our field firing experiments during the reducing phase of the firing. Hexagonal graphite plates were observed in the scanning electron microscope. The iron in these sherds is almost totally reduced to Fe(II). In our experiments, dried cow and llama dung proved best as reducing agents. Research at the production center, though highly informative, does not tell a complete story. About 1/3 of the sherds from the huge, 15-meter-deep, elite shaft-tomb of Huaca Loro exhibit Mössbauer patterns of well-dried but hardly-fired clay. The gray colour of these vessels is not due to reduction, but to surface deposition of soot. One can assume that these vessels were made in haste.
Using archaeological and modern materials research techniques and a teamwork approach, slowly but steadily a holistic picture of the organization of the Middle Sicán culture emerges by looking not only at the spectacular remains of the rich and the powerful, but also at the activity of artisans and commoners. The ruling elite employed and supported expert craftsmen who produced luxury and ceremonial objects as well as goods for daily utilitarian use. Sicán artisans were in control of kiln temperatures by deliberately using charcoal and controlling draft. Their technical abilities were highly developed and left a legacy that lasted to the time of the Spanish conquest of Peru in the 16th century.
Physik Department E15, Technische Universität München, 85747 Garching, Germany.
Department of Anthropology, Southern Illinois University, Carbondale, Illinois 62901, USA.
Last update: 19.07.2005