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Accelerators for Dating and Forensics Thomas A. Cahill

Crocker Nuclear Laboratory, University ofCalifornia, Davis

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Accelerators for Dating and Forensics Thomas A. Cahill

Crocker Nuclear Laboratory, University o/California, Davis

Accelerators have long been at the cutting edge of basic research in physics. Fermilab is a classic example of this, the traditional role of particle accelerators.

But there are also numerous applications of accelerators in applied physics, placing them at the cutting edge of a diverse range of disciplines. One such ex­ample is the use of accelerators as analytical instruments. Whole new disci­plines have been opened up through accelerator mass spectroscopy (AMS). One recent example is the Shroud of Turin controversy. Another analytical use of accelerators is proton-induced x-ray emission, which today is analyzing air pol­lution at about 70 national parks and monuments. The Crocker Nuclear Labora­tory of the University of California, Davis, has pioneered analytical applications of its cyclotron since 1970, and these form the topic of this article.

There is a lot of kinship between Fermilab and the University of California, Davis. Just 50 years ago, the Davis cyclotron was the world's largest ac­celerator, as the Fermilab Tevatron is today. Robert R. Wilson, Fermilab's founding Director, worked on the Davis accelerator when it was at Berkeley around 1940. At that time it was called the" Sixty Inch." The Atomic Energy Commission, the forerunner of the Department of Energy, who sponsor Fer­milab, was the organizatioll that upgraded the Davis accelerator to a copy of the Oak Ridge machine. At the National Science Foundation, Dick Carrigan (the father of the Dick Carrigan who coordinates the Fermilab Industrial Affiliates) was instrumental in getting some of the Davis applied-physics programs going back in the early days of the National Science Foundation "Research Applied to National Needs" in the 19705. Without that encouragement and money the Davis program wouldn't exist today.

The only cyclotron older than Davis is a museum piece. That one, the old Berkeley 21-inch machine, sits out in a parking strip at the Lawrence Hall of

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Science. Remember, the Crocker magnet was designed in 1937 not to do basic physics, like looking for Higgs bosons, but "to join the fields of the physical and biological sciences" and "to study a new way of treating the age-old scourge of mankind, cancer," with neutrons. So from the first, the Crocker Cyclotron had an interesting mission. Along the way it was used for many things, including discovering plutonium and six other elements. In 1960 it was replaced at Lawrence Berkeley Laboratory by the 88-in. cyclotron. The 60-in. was surplused, and it was grabbed by D.C.-Davis with the help of the Crocker Foundation and Ernest Lawrence. At the Davis campus, it was once more des­tined to finally "join the fields of the physical and biological sciences" and study ways to treat cancer.

Why put an accelerator at a campus like Davis, which is known for its agri­cultural products? Indeed, Davis and Fermilab are both agricultural havens. Fermilab is famous for its herd of buffalo. At Davis we have the famous Crocker pigs (Fig. 1). When they relocated the magnet, it was placed right next to the pig barns. We shared this area with them. When Bob Wilson came to Davis as a visiting professor several years ago, he pointed out that the pig pen was an excellent place for a beamline. Eventually, a high-resolution neutron line may go under the pigs. But by now, I have heard all the pig jokes in the world and devised a few new ones. Some wags have suggested we raise bacon that fries itself in the pan.

Despite the agrarian background, Davis got going in basic nuclear physics, 1965-1971. Figure 2 shows some of the equipment. Notice that the scale is dif­ferent than that of Fermilab. Although devices like drift chambers and magnets are similar, the people at Davis seem to be too large. But, while the nuclear physics program got the laboratory going, we were (it turns out) fortunate to lose all of our funding in 1971, although it did not seem fortunate at the time. The laboratory was forced to operate on a pay-as-you-go basis, or close its doors. Fortunately, the cyclotron was running well at the time, and we had al­ready begun studies of analytical uses of the cyclotron. So, what I'm going to talk about is several of the applications of the laboratory, in particular the one involving forensic analysis and historical analysis.

The laboratory is a very convenient size. It's a copy of Oak Ridge and it is large enough to be too expensive to be easily duplicated by industry. That

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Figure 1: Crocker Pigs.

rure 2: Crocker Nuclear Laboratory apparatus.

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would now cost $12- to $14-million. But it's small enough to operate on a pay­as-you-go basis doing a variety of things. Its physics program, employing polarized neutrons and polarized protons, was effective. But after 1972 we were forced to go into a mode where we looked over our shoulders to see where the money was coming from. One of the programs I won't talk about much is the medical-isotope program. It has been very successful and has raised millions of dollars over the years. However, after a few years, it got spun off as companies went into commercial production. There are two cyclotrons that happen to have exactly the same energy as Crocker Laboratory, 70-million electron volts, right here in Chicago, as well as one in Japan. These cyclotrons are paying us license fees, which is very nice. In fact, even Fermilab paid fees to Crocker Laboratory for its medical technology for a while.

The key factor that saved us was the Los Angeles smog, that brown haze you see in California. During the 1970s there was an effort to bring modem technol­ogy, including accelerators, into the fight to understand and hopefully solve some of California's air pollution problems. We felt that this was a place that we could do our job. In 1971, Project Clear Air encouraged us to use a tech­nique developed by the Swedes. They used proton beams passing through a sample to generate characteristic x-rays. This technique is called PIXE, Proton Induced X-ray Emission. PIXE was the start of a process which enabled us to look beyond the major species that were in particles in the atmosphere and com­pare it against what you'd weigh on a scale. Techniques like this require not just atomic procedures, but laser-induced and nuclear techniques like scattering reactions. That's the great advantage, we feel, of an accelerator. It opens up many options, which are limited merely by our ability to fund them or find them. Table I lists some of the advantages and disadvantages of PIXE.

By 1979 this program had gotten good ratings in California and we started to look at the national problem of visibility at national parks and monuments. Now, everything in the atmosphere that scatters light is important. At Davis we are not interested in "health," because health involves a doctor. To address those problems you must surmount the M.D. barrier. Visibility questions can be handled by physicists. It's a physical phenomena. Crocker Laboratory is look­ing at what causes summertime haze.

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ANALYSIS BY THE "NON-DESTRUCT IVE" METHOD OF THE PI XE MILL IPROBE

PartIcle Induced X-Ray EmIssIon In A,r)

ADVANTAGES:

2. QuantItatIve. r.producIbl •• and pr.CIS. to a f.w p.rc.nt

3. Analyz.s entIre sample In a b.am down to 0.1 mm dIam.t.r

4. L.s. s.nsItIv. to contaminatIon and surfac. sOIIInO than mlcro-partlcle m.thods

5. In.xp.nslv. p.r analy.,s, allowlno hundr.ds or .v.n thou.ands of analy••s per .ampl. as the compl.xlty warrant.

6. R.sults avallabl. 20 s.cond. aft.r analy.i., thus OUldlng the cholce of locatlons to b••tudi.d or allowino confirmation of un.xpect.d r ••ult •• Thl. ,. e.pecially i~ortant a. the humanlst is a participant in the analytical proc•••.

DISADVANTAGES:

I. Need. a part,cl. acc.l.rator of a f.w M.V and x-ray analy.t • • xp.ri.nc.d ln the type. of .amapl•••ncount.r.d.

2. Only .l.mental data. no ch.mlstry, .tructur., .tc.

J. Analyze. total sampl., 1 •••• to oet lnk. on. mu.t mea.ure first the parch..nt, th.n parchment-plu.-ink, and finally .ubtract. Thl. r.duc.s ••n.itivity for comp.ting ele••nts.

4. Th. minlmum ma•• d.t.ctabl. i. much more than that for mlcro-partlcl. m.thods due to the all-inclu.iv. nature of the PIXE beam

5. Due to the .hortaO. of fac,l,t, •• and fund., d.lays are often encountered ln gettlno analyses sch.duled

Table I: Advantages and Disadvantages of PIXE.

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The Davis accelerator was used to analyze the air pollution across the coun­try using a series of monitoring stations. Basically the accelerator underbid the competition and gave more information for the dollar. Air pollution studies don't sound very sexy. The facilities to collect the samples can be sturdy and cheap, because at the far end, we have an accelerator to analyze the samples they collect. Please realize that the Davis accelerator may be a big one, but there are about 100 accelerators like it around the world fully capable of doing this work. The map shows the sulfate levels in the United States for the last several years. In the eastern U.S., sulfur levels are as high as 5.2 micrograms/m3. Out in God's country, around the Grand Canyon, it's 0.95. If you wonder why the visibility is so much better at the Grand Canyon than Shenandoah National Park, here is a real clue. (Figure 3)

This type of analysis is something that's rather easily done by a cyclotron. In the last year the program has been funded at about $1.5 million a year. Further, the data are important. Last year a group presented information to Con­gress that said 60 percent of the haze of the Grand Canyon carne from organic matter from trees. We didn't think that was realistic based upon our previous work, but we hadn't looked for organic matter in the haze. Fortunately, I had been doing proton-proton scattering at 4.5 MeV on Teflon as an undergraduate­student project. We did not know how good the data were, but why throw the data away? We soon realized that our nuclear technique was measuring the hy­drogen in organic matter, and better than traditional methods. Our data showed that only about 15 percent of the haze carne from trees. Last June, the original data were retracted by a very large group of people who had been paid $11 mil­lion for the work. Proton-proton scattering at 4.5 MeV had done the job! As a result, Davis now has a five-year, sole-source program with the Environmental Protection Agency (EPA) and National Park Service for aerosol monitoring and analysis. It is our largest source of support.

That's the serious work we do. It is worth about $3.5 million a year right now, with the Park Service and EPA, the Naval Research Laboratory, and re­search hospitals providing most of the funds.

But we also have some projects simply for fun. Some time ago Gutenberg met the Davis cyclotron. In 1970, my wife, a French major, worked with Dick Schwab, a Davis historian. As long as I was doing things like proton-helium 3

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AMMONIUM SULFATE

gure 3: Sulfate levels across the U.S.

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scattering, he couldn't care less what I did. But when I started doing air pollu­tion work, we realized we had some similar problems. His problem was forgeries, ancient documents that had been pirated and copied a few years after the original document. He had difficulty detecting which ones were fake. My problem was air pollution, something I monitored using paper air filters. One night we were chowing down at a cocktail party and he was bemoaning the fact he had difficulty detecting a forged copy from the original. Naively, I asked, "Why not just analyze it? After all, your books and my air filters aren't that different. They are both made of paper and my garbage is called smog and your garbage is called ink." Schwab agreed to give it a try. The problem was that our filters were all 2-inch squares and most books are larger than that.

The technique is the following (Fig. 4). A helium-neon laser beam is used to align a beam of protons which goes through the paper and ink and gives off characteristic x-rays. By catching the beam in an electrostatic, or Faraday, cup, you know how many protons went through. With the x-rays, you can tell what elements are there and how much there is. It's quantitative and cheap.

The point is that the proton beam has about 4-million volts of energy, so it will penetrate small amounts of material very easily. When we first did this, we grabbed some items that were cheap enough so they could be cut up. The first thing we tried was a newspaper, The California Aggie. It was as uninteresting in its elemental makeup as it was editorially. The project almost died because that newspaper was just wood and carbon. Fortunately, we had a few little pieces of old paper. When we analyzed them we found out that, 10 and behold, other elements like manganese, chlorine, and sulfur jumped out all over the place. This was the key that something interesting was going on. I went to the Dean and said, "Look, we just can't keep chopping up pieces of books to put inside the cyclotron. If the mountain won't come to Muhammed, Muhammed will go to the mountain." We built a new beam-port for the accelerator beam to target books. The beam comes out through a layer of kapton, the same stuff used here at Fermilab for insulation. After passing through the kapton window, the beam travels through air and passes through the paper. One nice feature is the page can be lying out in the open and the operator can stand right next to it. The radiation levels are essentially zip as long as the operator doesn't put his

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TO CURRENT INTEGRATOR

....... PAGE

BEAM INTERCEPTOR AND MIRROR

PLASTIC COLLIMATOR

ADJUSTABLE COLLIMATOR

FARADAY CUP

MIRROR ~-----+----;He- Ne LASER

DETECTOR

TO X-RAY AMPLIFIER

'igure 4: Davis document analyzer.

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hand in the beam itself; there the level is 25 kilorad. As a result, it's possible to have the historian or the archaeologist near the sample while it's analyzed.

The system worked very nicely. We started looking at more complicated documents. Figure 5 shows a page of Diderot's Encyclopedia, Dick Schwab's major historical work area. There is also a picture of a book of hours from Italy (Fig. 6). The pages are twentieth-century fake, the cover is real. The partial fake is owned by Berkeley; no further comment is needed. Figure 7 may, or may not, be a letter drafted by Muhammed to the King of Rome.

I say "maybe" because we physici~ts are simple folk in this subject. The point is, we can analyze the material and say what's there elementally. However, until we do comparisons, we know nothing. So we had a problem. We were doing this work but we didn't know where we were going because we had a nice tool in search of a problem.

Finally the problem found us. Figure 8 shows a page of the Gutenberg Bible. One of the people we talked to pointed out that there were real mysteries about the early history of printing. One was why the Gutenberg Bible was so clear, why the ink was so sharp, after 500 years. The printing 100 years later was in much worse shape. Fortunately, we knew a piece of the Gutenberg Bible was down at the University of California, Riverside. We brought it to Davis and placed it in the proton beam. Figure 9 shows an x-ray excitation spectrum from this page. The ink looks a little bit like Los Angeles smog with all the lead. It was clear the inks were not made of carbon, as most had thought; they were made of a metallic, almost paint-like substance composed of copper and lead. Further, the copper and lead ratios told us something about how the ink was made.

Suddenly we were on to something really neat. We went ahead and analyzed a series of loose pages and found that all the Gutenbergs that were known to be authentic were grouped in the same cluster for the ~opper-lead ratio. The Gutenberg inks were very metal-rich and always had the same ratio. It's as though he had signed every page that he'd published.

Until we had come up with a non-destructive technique using an accelerator, analytical tests of these documents were impossible. They couldn't be touched. When you see a Gutenberg Bible, the paper is white. The inks are shiny black,

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Figure 5: Page from Diderot's Encyclopedia.

Figure 6: Book of hours.

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Figure 7: Possible letter from Muhammed to the King of Rome.

Figure 8: Gutenberg Bible.

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COIClll1II KG

Figure 9: X-ray excitation spectrum from Bible page.

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with blues and red. When you flip a page, there's no crackling. Remember, this is the world's first book. Those of you with simple computers should note the fact it's left and right justified. There are about 250 separate letter types; the "a" followed by an "m" and the "a" followed by "0" are quite different. It's a little strange that the first book should be so good. It's like having a 1987 Mercedes-Benz be the first car.

We also found out that Gutenberg would use the same ink batches for awhile and then go and make another batch because the price of wood in Mainz, Ger­many, was rather expensive - there was an energy crisis even then. Gutenberg went to the forest to make ink in batches. You can detect when the batches changed to within a few hours, but we needed a complete bible to test this hypothesis.

We finally found and analyzed an entire Gutenberg Bible page by page, tak­ing 41 hours with the historians hovering over our shoulders in a laboratory sur­rounded by pipes and cables. Figure 10 shows what we found. The ratio jumped around in a funny way from page 1 up to page 324. Our original hy­pothesis about the ink coming in batches looked like it was shot down. But if you look closely, you can see a pattern. We took scissors and cut the computer print-out in pieces and here's what we found. A clear pattern emerged. (See Fig. 11) Note that at one point, two new presses suddenly appear. Gutenberg had started printing and had taken out a loan. Now we even know in what year he received that loan. The figure shows that when he got the loan, he went out and bought two more presses. Now he had Press A, Press B, Press C, and Press D. These data establish within a day or so in the year 1454, when he doubled his presses.

Figure 12 indicates details of how he did the printing. It was widely thought that Gutenberg printed the same way it is done now. Nowadays you print page one and four, flip it over, print page two and three, and fold it as a book. Page one, two, three, and four in the right order. Not Gutenberg. When he started printing, Gutenberg went along page by page. The ink was in two batches. It was kept fluid by an interesting technique, too long to go into here. Since he did the ink in batches, we immediately guessed he had no master model for the book. He was actually printing a page at a time. Prior to the accelerator analy­sis this was not known. Since then Dick Schwab has gone ahead and changed

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Figure 10: Analysis of Gutenberg Bible pages.

RATIC6 Of UljPb BY PRESS

Figure 11: Pattern uncovered by analysis.

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2.0

.~ 1.5 ~

~ .a a. 1.0 ...... :> U

gathering 8gathering 6 gathering 7

52 56 60 62 66 70 72 76 Folio number

Figure 12: Gutenberg printing sequence.

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his entire research, coming up with a model for how Gutenberg printed the en­tire Bible. With the accelerator, we can actually detect a crew at work and where they fell behind for a few pages. We have such detail because of the non-destructive nature of the accelerator. The reason it's important was because Gutenberg was the Thomas Alva Edison of the fifteenth century. He was a very interesting inventor.

There are a few more examples where the accelerator analytic technique has been used. Is the Gutenberg Bible really the first book? There are several other pieces of printing floating around in the same period. One of them is called the Sibyllenbuch Fragment of 1447. To make a long story short, we were able to find one page from this document. We also had a few pages of the mysterious 36-line Bible, the world's rarest early-printed book. We analyzed them with the non-destructive accelerator technique. What we found is that all these early documents - the Sibyllenbuch Fragment, the 36-line Bible - had almost the same kind of ink. I believe the 42-line Gutenberg Bible is the world's third book. There are at least two earlier books in which Gutenberg developed his printing process. Perhaps the first part of the process he invented was the ink, not the method of printing. He probably developed the ink around the year 1445 in Strasbourg. Over a ten-year period he developed the printing press but did not change his inks.

The group that does this work at Davis is an interesting mixture of historians, medievalists, physicists, analytical chemists, and microscopists. An area like this is fraught with hazard. If one opens one's mouth the wrong way, one can get oneself in real trouble. But I am a physicist, after all, and no expert in these areas. I can say what I think, and nobody pays much attention.

Speaking of trouble, Fig. 13 shows the so-called Vinland Map at Yale Uni­ersity. This is a map that purports to show North America prior to Columbus. Now, this map was a wild find when it was discovered, but in 1974 it was shown to b~ a fake by use of microparticle techniques. However, the Smith­sonian just wouldn't buy this explanation. What the expert, a world-famous microscopist named Walter McCrone, located in Chicago, said was that the map had been drawn twice, once with a titanium-based ink to make it look brown, and then it was overdrawn again with a black ink which later flaked away. His proof was based on the high titanium level in the inks.

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Figure 13: Vinland map.

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After much discussion, the map came to Davis three years ago. We used non-destructive techniques to look at it without the necessity of pulling off small crystals. This is a non-trivial point. If a small crystal is pulled off, how can you be sure it represents the body of the map itself? You make an ex­trapolation of 100,000 to 1. An accelerator beam goes through the entire page, and has no need to make extrapolations.

Figure 14 shows an example of the two ink lines, the brown line and the black line slightly out of gauge. We used the accelerator to see what it looked like. Remember, Yale had a document that is worth either $3 million or about $25,000. When it was found to be a fake, people left the university and a major contributor stopped giving them millions of dollars. This was serious business.

We analyzed some of these lines. We also analyzed the ink and the parch­ment right next to it. In effect, we analyzed both of them together. Now, McCrone claimed that the ink was 30 percent titanium by weight. Figure 15 shows our results. These numbers are in billionths of a gram, like .3 billionths of a gram. In our results there was hardly any titanium at all. This was a real shocker. We scanned a 300-micron proton beam across a typical ink line and compared the parchment to the ink line to the parchment as an example, Figure 16. Here the focus capability of the ion beam becomes absolutely essential. There was just not enough titanium there. We believe what happened was the earlier investigators pulled a few loose crystals off the map, analyzed them, and then said, the map is made of those crystals. We know the person who did it was not an expert in historical documents, before or after the map. But she had looked at air filters. In an air filter, everything there is foreign matter. In the case of the map, that's not at all sure.

We presented our data last spring in Kalamazoo, Michigan, in a panel with Walter McCrone. The data have now been published.

We have another example of an accelerator detective story, the Dead Sea Scrolls. Figure 17 shows a fragment of the Dead Sea Scrolls. These fragments have gone to two places in the world, Paris and V.C.-Davis. The fragments are turning brown. One question is, was it the smog of Jerusalem that was making them unreadable or not? Remember, we're not experts on the Dead Sea Scrolls, but we knew about analyzing parchment. The question was whether there was anything different about the parchment. We found that it acted like any other

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Figure 14: Two lines from the Vinland map.

Titanium Levels for Part of the Vinland Map

0.3

I"'J .57

'14~@~~@~~ ~ @ 6)

.86 @ 0 0 <.3

0<.2

~ @<:, f7

~ @~<.30 ~ .85

- c: I> Ti values in ngtcm2 Q

2 D rink plus parchment »@ ..,.(DParchment

1.1 «~p

Figure 15: Titanium levels for Vinland map.

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120

100

80

I-z ::> 0

602: <l

0 .... N ::; <l 2: a: 15 0 z

10

5

o

Ti

Fe

K

S

CI

« 12.9

72 73 74 75 76 77 78

LOCATION NUMBER

Figure 16: Analysis of a line on the Vinland map.

Figure 17: Fragment from the Dead Sea Scrolls.

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parchment but it had much more bromine. The expert was very excited by the bromine. He pointed out that the people of the Dead Sea mined bromine. The sea has been there so long that the chlorine-bromine ratio is very bromine-rich. Our accelerator results suggested the parchment had actually been cured in the Dead Sea itself. We could also see a change in ratio. And that time cor­responded to a change of the rules of the Essenes community.

Most of the machines doing this type of analysis work are existing accel­erators at small universities. Figure 18 shows the famous glass pyramid under construction at the Louvre. Under that pyramid are several layers of labora­tories. The Louvre has a very impressive analytical capability. They have any­thing you can think of - scanning electron microscopes, microprobes, the whole spectrum. Recently they decided that they had to be the best in the world, and so they went ahead and built an accelerator especially for this type of analysis. Their installation is illustrated in Fig. 19. It uses a National Electrostatic Ac­celerator Tandem manufactured in Wisconsin. The accelerator sits three stories below the flowers and the marigolds of the garden next to the Louvre. It is now in use. The man in the picture is Dr. Bruce Kusko, who is there on a Fullbright Scholarship for this year to analyze paintings using a semi-microprobe analysis in air.

I hope this survey shows that accelerators have proved to be remarkably use­ful little beasties. The combination of nuclear and atomic techniques gives you options you cannot get from other approaches. The fact that you can focus a beam to a small point is very helpful. An accelerator like this is not terribly ex­pensive compared to other modem analytic instrumentation. For $500,000, you can have a pretty good little laboratory. As time goes on I believe these ac­celerators are going to have a larger role to play. More of them will be built for projects like this by the major museums and laboratories which have serious analytical problems.

For our part at Crocker Laboratory, it's fun and we enjoy doing it. We get to work with all these experts in many fields. They come out to Davis and bring their treasures, and leave bearing new insights into their problems. This type of work is only four percent of our budget, so I can't spend a whole lot of time on it. But it is yet another indication that accelerators have a bright future on the forefront of many disciplines far from nuclear and particle physics. I doubt that

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Figure 18: Louvre pyramid.

Figure 19: Louvre accelerator.

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even Ernest Lawrence, despite his fertile imagination, could have anticipated the uses to which his 60-in. cyclotron has been applied. Somehow, there is a strange symmetry in that the same device that discovered plutonium would now be delving into the Dead Sea Scrolls.

Please fell free to contact us at Davis should you become involved in some mystery in art and archaeology. Perhaps the result might be yet another Af­filiates Meeting talk a few years hence on a topic that none of us has even guessed.