Negative muons reveal the economic chaos of Rome’s AD 68/9 Civil Wars

Abstract

During the AD 68/9 Civil Wars, Galba, Otho, Vitellius and then Vespasian fought for — and gained — control of the Roman Empire. Our textual sources suggest that this was a period of serious and sustained disruption. However, existing analyses of gold coinages produced in AD 68/9 show only a minor reduction in the purity of the gold coinage. Using X-ray fluorescence, we identify a number of heavily debased gold coins issued during the AD 68/9 Civil Wars, and many slightly debased coins issued in their immediate aftermath. We then confirm the interior composition of these coins totally non-destructively using muonic X-ray emission spectroscopy, thus eliminating hypothetical problems of ‘surface enrichment’ or compositional differences between ‘surface’ and ‘core’. Here we show that heavily debased Civil War gold coinages were indeed produced; that copper was used to debase Roman gold coins during this time, c. 185 years earlier than first shown; and that slightly debased gold coins were regularly issued in the years immediately after the Civil Wars. The metallurgical evidence from the gold coinage now allows us to show that the AD 68/9 Civil Wars caused significant and sustained disruption to the Roman economic system. More broadly, we have shown that muonic X-ray emission spectroscopy is a powerful tool for generating important archaeological conclusions from high-value cultural heritage objects that simply cannot be destructively analysed, but need to have their interior compositions sampled.

The non-destructive investigation of a late antique knob bow fibula (Bügelknopffibel) from Kaiseraugst/CH using Muon Induced X-ray Emission (MIXE)

“…In addition, extensive simulation of the complicated geometry of archaeological objects is necessary in order to determine the attenuation of the muonic X-rays inside the archaeological material of interest (not as high as electronic X-rays, but certainly not completely negligible) for the proper determination of the elemental composition. Nevertheless, we along with the other published works so far [4,[6][7][8][9][11][12][13] have demonstrated that MIXE is a very promising new method for completely non-destructive quantitative elemental analysis of valuable objects such as archaeological cultural artefacts. An immense advantage is that, due to the high-energy muonic X-rays, the analysis technique allows measurements up to several centimetres deep-depending on the density of the sample-and thus, if necessary, measurements can be made below the corrosion layer, coatings or surface enrichments.…”

“…Actually, in contrast to electron-induced X-ray analysis techniques, the MIXE technique can provide results below the usually distorted surface of archaeological metal objects. Examples of applications of this analysis technique to archaeological metal objects are already available [4,[6][7][8][9][11][12][13], all of which were performed at pulsed muon beam facilities. It was also shown recently [1,2] that the unique experimental setup at the Paul Scherrer Institute (PSI), which utilizes continuous muon beams, enables one to achieve high statistics measurements in short measurement periods.…”

“…Fig 7. Calibration curve for the brass and bronze CRMs: a Method 1: plot of intensity of the µ -X rays of the different elements (Cu, Zn, Sn, and Pb), normalized with the number of muons vs. the at% of the elements; b Method 2: plot of the ratio of intensity of the µ -X rays of the different elements (Zn, Sn, and Pb) and that of of Cu vs. the ratio of the at% of the elements with respect to Cu.…”

“…This technique is not uniformly named in the literature. In addition to the acronym MIXE[1][2][3][4], other acronyms like MXA (Muonic X-ray Analysis)[5], MAXRS (Muonic Atom X-ray Spectroscopy)[6] and µXES (Muonic X-ray Emission Spectroscopy)[7][8][9] have been used so far.…”

Investigation of the muonic atoms distribution in materials through muonic x-rays momentum simulation using Geant4

“…Based on these characteristics, the Paul Scherrer Institute (PSI) of Switzerland, Tri-University Meson Facility (TRIUMF) of Canada, and Los Alamos Meson Physics Facility (LAMPF) of the United States were the first to conduct μ-X ray elemental analysis experiments on biological materials [3][4][5][6]. The technology has since been employed in archaeology [7,8], the detection of extraterrestrial materials [9], lithium batteries [10], and other applications [2,[11][12][13]. Recently, the potential application of μ-X rays to the imaging of small objects was discovered.…”