Archimedes Brought to Light
Just over 100 years ago in the summer of 1906, a Danish scholar called Johan Ludvig Heiberg travelled to the famous Metochion library of the Church of the Holy Sepulcher in Constantinople. He had got wind of an intriguing medieval prayer book that had recently been found at the library, and which contained a series of Christian prayers written on parchment recycled from older books. But underneath the scrawlings of a 13th-century medieval monk, the battered manuscript also appeared to contain some strange Greek writing as well as mysterious drawings and mathematical symbols. When Heiberg saw the book, he soon realized that the hidden material in fact contained the thoughts of Archimedes of Syracuse (287-212 BC) - one of the greatest thinkers of the ancient world. It was in November 2003, while on my way to a conference in Germany, that I first realized that the technique might help to uncover the hidden writings in the Archimedes Palimpsest. I had been reading an article in the German magazine GEO about the manuscript and, having previously used X-rays to detect metals in biological systems, realized that XRF could help to detect iron and other common elements in the ink. I immediately e-mailed Abigail Quandt, a conservator at the Walters Art Museum, who was part of a team that had been put in charge of the Archimedes manuscript. I was delighted to find that the team, led by her colleague William Noel, was looking for new ways to study this ancient book. Indeed, it turned out that two other researchers - Gene Hall from Rutgers University and Bob Morton from the oil firm ConocoPhillips - had also suggested using XRF imaging. Another team member - Johns Hopkins University physicist Bill Christens-Barry - had already been thinking of using X-rays too. In March 2004 Hall and the team carried out the first tests on the Palimpsest using X-rays from a commercial generator. Although these tests were promising, the results confirmed my belief that synchrotron radiation could be much better because it would allow the book to be scanned much faster and with higher resolution. Indeed, I had already begun collaborating with my SLAC colleague Martin George, who helped to develop an XRF system that could image and scan the Palimpsest at high speed. It consisted of a computer-controlled stage that could hold a single leaf from the book and be moved from side to side so that the X-ray beam from SLAC's powerful SPEAR3 accelerator could be scanned across the sample. A 2D image of the page could then be built up by plotting the intensity of the fluorescent X-rays at a particular energy. The problem with imaging a delicate object like the Palimpsest using intense beams of X-rays is that it can be damaged if exposed for too long. Working with Gregory Young from the Conservation Institute in Ottawa, Canada, we carried out tests on a piece of parchment from a will written in 1870 that had been given to us by Quandt at the Walters Art Museum from her private collection. We found that if the parchment is moved sufficiently quickly so that the beam dwells for no longer than 0.1 s on every area through which it is passing, then no measurable damage occurs to the document's fibers. The only snag was that when the beam reached the edges of a particular line of the document, the stage holding the individual pages had to stop briefly and step down to the next line - a process that could take as long as 1 s. To avoid overexposure during these stops, we added a fast pneumatic beam shutter to the computerized scanning system, which remained open only when the parchment was moving. Our tests at SLAC proved so successful that we were able to persuade the Archimedes team to let us use our equipment on the real Palimpsest. The team arrived in May 2005 with 3 test pages and we were soon able to image half of one page at a resolution of 250 dots per centimeter in just 30 hours (Nature 435 257). We then used algorithms developed by Keith Knox, a physicist from Boeing, to convert the raw data into 2D images. In all of our measurements we were most interested in the fluorescence from iron, which is the most common element in the ink. But by placing suitable electronic 'windows' on the detector, we were able to simultaneously also record the signal from other elements, including calcium, zinc, barium and copper. The iron XRF image clearly revealed Archimedes writing under one of the forged paintings that had been added in the 20th century and - in the next two runs during March and August last year - we were able to scan various texts that could not be revealed with other techniques as well as some writings that do not appear anywhere else. By installing better detectors and by including a new readout system that had been developed by our colleague Alex Garachtchenko, we can now scan a whole page in just 12 hours with the X-ray beam sweeping over each 40 {micro}m2 area of the sample in just 3 ms.
- Research Organization:
- SLAC National Accelerator Lab., Menlo Park, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC02-76SF00515
- OSTI ID:
- 958661
- Report Number(s):
- SLAC-REPRINT-2009-013; PHWOEW; TRN: US1000301
- Journal Information:
- Phys.World 20:39,2007, Vol. 20; ISSN 0953-8585
- Country of Publication:
- United States
- Language:
- English
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