Gamma-ray spectrometer. The sample to be measured is placed on a stand over a gamma-ray detector. The pulse-height analyzer is a device that sorts electrical impulses from the detector according to the energy of the gamma rays causing the impulses. The screen displays the gamma-ray spectrum and the electric typewriter automatically types out the data collected when the measurement is complete.
One by one the samples were placed inside a shield consisting of a big pile of lead bricks. When the heavy door was opened, the boys could see a metal can inside the shield, which housed a detector (called a lithium-drifted germanium detector) that measured the gamma rays emitted by the sample. As each sample was placed near the detector the chemist turned on a gamma-ray spectrometer to which the detector was connected.
A tiny sample of lead white is sealed in a quartz vial which is bombarded with neutrons in a reactor.
Many of the atoms become radioactive, emitting gamma rays.
The sample is placed in a gamma-ray spectrometer and the gamma rays are separated according to their energy.
- Gamma-ray spectrum
- Copper
- Zinc
- Antimony
- Lead
- Silver
- Height
- Antimony
The location (energy) of each peak indicates what is present and the height indicates how much!
A gamma-ray spectrum as it appears on the screen of a pulse-height analyzer. The gamma-ray peaks are marked with the name of the element whose radioactive isotope emits the gamma ray; two for cobalt and zinc and one for cesium.
There, on what looked like a small television screen, flashes of light appeared that gradually formed a curve with many peaks and valleys. After a few minutes the spectrometer was stopped and an electric typewriter automatically typed out rows and columns of numbers.
The chemist explained, “This curve, which you see on the screen, is a gamma-ray spectrum and tells us what elements are in the sample. The typed-out data give us an accurate measure of the shape of the curve on the screen. By measuring the gamma-rays’ energies we know what elements in the sample were made radioactive. The height of each gamma-ray peak tells us how much of that element is present in the sample.
“That gives us the information we need to calculate the concentrations of the small quantities of materials in our samples. We can do this because at the same time I irradiated a set of standards. Standards are materials that are just like the samples except that they contain known amounts of the impurities I am trying to measure.”
As the boys were leaving the laboratory, the chemist apologized for not having enough time to explain the activation analysis procedure more thoroughly, but he did give the boys a list of books to read on the subject of radioactivity and radioisotopes.[2] They thanked him for his help.
During the ride home, they discussed the paintings that were still unproven.
“It’s too bad that the method of activation analysis fingerprinting hasn’t been fully developed yet,” said Dad.
“Yes,” said Bill. “Then we could prove whether or not that last old painting was really by Aelbert Cuyp as the expert from the gallery believed. But what about those paintings that we found in the box that were not so old?”
“Well,” said Dad, “if the activation analysis method were workable, we might be able to prove if they were painted by Alfred Sisley. Meanwhile, until the method is really developed we don’t know if we can do it that way or not.”
“So what do we do now?” asked Martin.
“We’ll have to wait until scientists can thoroughly investigate this method and several others that they’re working on.”
“Other methods!” exclaimed Bill. “What other methods?”
“The Banks of the Oise”, a genuine painting by Alfred Sisley.
Other New Tools for Art Authentication
“There are several new tools that scientists are working on now,” said Dad. “These involve methods that have been developed by scientists for other purposes, but are now being explored for use in authenticating works of art.
“For example, in Los Angeles, the county museum purchased an instrument known as a Spark Source Mass Spectrometer. Like activation analysis, this instrument will also measure small traces of impurities, but they have just set that up and it will take them years to explore the use of it for the type of problem we have been discussing.
“X-ray diffraction is another method that has been around for quite awhile but hasn’t been used much for art identification until recently. With X-ray diffraction, samples of pigments can be identified by the pattern formed when X rays are bent by passing through the sample of pigment.”
“How’s that?” asked Harley.
“There are 3 or 4 different compounds with about the same chemical composition as lead white. Chemically, they are almost impossible to distinguish. But with X-ray diffraction, a chemist can easily tell them apart. The hope is that the type of lead white will indicate how it was manufactured. Until the middle of the 19th century, lead white was produced mainly by packing strips of lead in clay pots with a little vinegar in the bottom. The clay pots were stacked in a large building with layers of decaying organic matter on the floor. The building was sealed for several weeks during which time the lead corroded in the fumes and became covered with a white substance. The white substance, lead white, was scraped off, ground, and washed to make the pigment.
“But, in the 19th century, when people began to learn more about chemistry, they looked for faster ways of making lead white and some of these methods produced a lead white of somewhat different composition. By using X-ray diffraction, chemists now hope that they can tell how the lead white was manufactured. This may provide another means of dating the lead white in a painting.”
“Are there any other methods?” asked Harley.
The stack process for making lead white. Rows of clay pots containing lead and vinegar are packed to the ceiling of the building, and fermenting tanbark on the floor produces carbon dioxide and heat. The fumes of vinegar and the carbon dioxide corrode the lead in 2 to 4 months, and the corrosion is lead white.
“Yes, isotope mass spectrometry is one. All lead consists of 4 different isotopes or atoms of different weights. Three of these 4 are the end products of a radioactive decay chain. Depending upon the history of the rock formation in which the lead ore occurred, the relative amounts of the lead isotopes vary in a special way. In other words, if we know the different amounts of lead isotopes in the world’s lead ore deposits, and we have a sample of lead white from a painting, we can tell from which deposit the lead, which formed the lead white, came. If, for example, we find that the isotope pattern in a sample from a painting is the same as in lead ore from Australia, then the painting can’t be very old because lead white wasn’t produced from lead mined in Australia until about 100 years ago.”
X-ray diffraction patterns from three different lead compounds that might occur in lead white. The middle one is the ideal lead white produced for over 2000 years. While some of the bottom compound may be found mixed with it, the compound shown at the top is only a 20th-century invention.
- 4PbCO₃ · 2PB(OH)₂ · PbO
- 2PbCO₃ · PB(OH)₂
- PbCO₃
“How do you measure lead isotopes?” asked Harley.
“With an instrument called a mass spectrometer. This instrument is capable of separating the lead isotopes. First, the atoms of lead in the sample are electrically charged and ‘fired’ in a beam down the length of a tube between the poles of a strong magnet. There, the charged atoms (or ions) in the beam are deflected by different amounts according to how heavy they are. Thus the different isotopes are separated. This method is also still being studied and, although it shows great promise, it will be some time before it can solve problems of art identification. Also the study of the natural variation in isotopes of other elements, such as sulfur, is useful for identification of other pigments as well.
Diagram of a simple mass spectrometer. The ionized atoms of lead travel in a beam at the same speed. The heavier atoms bend less than the lighter ones when the beam passes the magnet. Thus two beams emerge instead of one. Actually there are four isotopes of lead so there will be four beams.
“Agostina”, a genuine painting by Jean Baptiste Camille Corot.
“Another new method that shows great promise has been developed, but this one is not applicable to the paintings that you boys found in the box.”
“Why not?” asked Bill.
“Since the Second World War, the art forgery business has been growing rapidly. For example, it has been said that of the 2000 pictures that Corot, a 19th century Frenchman, is known to have painted, more than 5000 of them are in the United States. This may be only a humorous exaggeration, but a large number of forgeries have been produced in the last several years. These are usually supposed to be paintings that are less than 100 years old. Present-day forgers like to forge paintings that aren’t very old because it’s easier to get away with. Now this new method, which will detect such recent forgeries, is based upon the presence of carbon-14, a radioactive isotope of carbon, in our atmosphere and in all things that grow on our planet.
“Ordinarily, carbon-14 is produced only by cosmic rays, and its concentrations in the atmosphere and in growing things would remain at a constant level. But since the middle of the 1950s the testing of nuclear weapons has increased the amount of radioactive carbon in our atmosphere by quite a bit. Many artist’s materials, such as linseed oil, canvas, paper, and so on, come from plants or animals, and so will contain the same concentrations of carbon-14 as the atmosphere up to the time that the plant or animal dies.
“Therefore, linseed oil (from the flax plant), for example, produced during the last few years will have a much greater concentration of carbon-14 in it than linseed oil produced more than 20 years ago. Scientists at Carnegie-Mellon University have shown that this method will work. It is only a matter of making the measurements on the small samples available from presumably valuable paintings.”
The changing concentrations of carbon-14 in our atmosphere. High levels of carbon-14 in linseed oil and other painting materials will indicate that a work of art is only a few years old.
- Carbon-14 radioactivity
- Older materials contain less as the carbon-14 decays away.
- In this period, decrease is due to the burning of large quantities of coal and oil as industry grew. This diluted the newly formed carbon-14.
- Increases due to testing of atomic weapons in the atmosphere.
- Carbon-14 produced by cosmic rays only
- Neutron → Nitrogen → Carbon-14 + proton
- Carried down by rain in carbon dioxide
“There are also a number of other methods being studied including the use of Messbauer Effect Spectroscopy to study pigments that contain iron, thermoluminescent dating of pottery and terra-cotta statuary, X-ray fluorescence analysis as a general tool, and neutron autoradiography as a means of studying the technique of artists. You can read all about them if you wish.”[3]
“It sounds like forgers are going to have a tough time in the future,” said Harley.
“That’s right. It may even turn out that producing forgeries to pass all these new tests will be so difficult and expensive that forgers will stop trying.”
One Mystery Solved
A year later an important letter arrived at the boys’ house. Dad opened it, read it quickly, and said, “Good news, boys! This letter is from the Dutch government. Remember those two paintings that we thought might have been stolen from a Dutch museum?”
“Yes,” said Bill.
“Well, it seems that after a year of studying them, the Dutch have decided that they really are the paintings that were stolen.”
“That is good news,” said Harley. “At least we know that two of the paintings we found are genuine.”
“What are they going to do with them?” asked Martin.
“Of course, they have to go back to their original owners. But this letter says that the Dutch government wants us to come to Holland as their guests as a reward for finding those paintings.”
These two paintings “The Lacemaker” and “The Smiling Girl” were thought to have been by Vermeer. A series of tests, including some of those described in this booklet, showed that the paintings are fairly old. However, some of the materials used are not typical of Vermeer, and the pictures are now thought to have been painted by a follower of the artist.
“That’s great!” said Bill. “Looks like we’re getting something out of finding that box after all.”
“Yes,” said Dad. “And don’t forget the other unidentified paintings may also be genuine. We’ve proved that one is a fake, the experts believe that three of the others are copies, and then there are the two that might be Sisleys and are only waiting for a method to prove it. And we have one more that science managed to prove was really old. I’m sure that in a few years methods will be developed to tell us exactly who painted it.
“And now let’s make arrangements for our trip to Holland.”
Reading List
About Atomic Power for People, Edward and Ruth S. Radlauer, Childrens Press, Chicago, Illinois 60607, 1960, 47 pp., $2.50. Grades 5-9.
All About the Atom, Ira M. Freeman, Random House, Inc., New York 10022, 1955, 146 pp., $2.50. Grades 4-6.
Atoms at Your Service, Henry A. Dunlap and Hans N. Tuch, Harper and Row, Publishers, New York 10016, 1957, 167 pp., $4.00. Grades 7-9.
Carbon-14 and Other Science Methods that Date the Past, Lynn and Gray Poole, McGraw-Hill Book Company, New York 10036, 1961, 160 pp., $3.95. Grades 9-12.
Experiments with Atomics (revised edition), Nelson F. Beeler and Franklyn M. Branley, Crowell Collier and Macmillan, Inc., New York 10022, 1965, 160 pp., $3.50. Grades 5-8.
The Fabulous Isotopes: What They Are and What They Do, Robin McKown, Holiday House, Inc., New York 10022, 1962, 189 pp., $4.50. Grades 7-10.
Inside the Atom (revised edition), Isaac Asimov, Abelard-Schuman, Ltd., New York 10019, 1966, 197 pp., $4.00. Grades 7-10.
Introducing the Atom, Roslyn Leeds, Harper and Row, Publishers, New York 10016, 1967, 224 pp., $3.95. Grades 7-9.
Our Friend the Atom, Heinz Haber, Golden Press, Inc., New York 10022, 1957, 165 pp., $4.95 (out of print but available through libraries); $0.35 (paperback) from Dell Publishing Company, Inc., New York 10017. Grades 7-9.
Radioisotopes, John H. Woodburn, J. B. Lippincott Company, Philadelphia, Pennsylvania 19105, 1962, 128 pp., $3.50. Grades 7-10.
The Story of Atomic Energy, Laura Fermi, Random House, Inc., New York 10022, 1961, 184 pp., $1.95. Grades 7-11.
The Useful Atom, William R. Anderson and Vernon Pizer, The World Publishing Company, New York 10022, 1966, 185 pp., $5.75. Grades 7-12.
Working with Atoms, Otto R. Frisch, Basic Books, Inc., Publishers, New York 10016, 1965, 96 pp., $3.50. Grades 9-12.
Footnotes
PHOTO CREDITS
Cover courtesy Groninger Museum voor stad en Lande
| Page | |
|---|---|
| 5 | Yale Joel, Life magazine, copyright © Time, Inc. |
| 6 | Her Majesty the Queen, copyright © reserved |
| 7 & 8 | Ullstein Bilderdienst |
| 10 | Rijksmuseum, Amsterdam |
| 23 | National Gallery of Art, Washington, D. C., Andrew Mellon Collection |
| 35 & 40 | National Gallery of Art, Washington, D. C., Chester Dale Collection |
| 43 | National Gallery of Art, Washington, D. C., Andrew Mellon Collection |
★ U.S. GOVERNMENT PRINTING OFFICE: 1974—747-556/15
The U. S. Atomic Energy Commission publishes this series of information booklets for the general public. The booklets are listed below by subject category.
If you would like to have copies of these booklets, please write to the following address for a booklet price list:
USAEC—Technical Information Center
P. O. Box 62
Oak Ridge, Tennessee 37830
School and public libraries may obtain a complete set of the booklets without charge. These requests must be made on school or library stationery.
| Chemistry | |
|---|---|
| IB-303 | The Atomic Fingerprint: Neutron Activation Analysis |
| IB-301 | The Chemistry of the Noble Gases |
| IB-302 | Cryogenics: The Uncommon Cold |
| IB-304 | Nuclear Clocks |
| IB-306 | Radioisotopes in Industry |
| IB-307 | Rare Earths: The Fraternal Fifteen |
| IB-308 | Synthetic Transuranium Elements |
| Biology | |
| IB-101 | Animals in Atomic Research |
| IB-102 | Atoms in Agriculture |
| IB-105 | The Genetic Effects of Radiation |
| IB-110 | Preserving Food with Atomic Energy |
| IB-106 | Radioisotopes and Life Processes |
| IB-107 | Radioisotopes in Medicine |
| IB-109 | Your Body and Radiation |
| The Environment | |
| IB-201 | The Atom and the Ocean |
| IB-202 | Atoms, Nature, and Man |
| IB-414 | Nature’s Invisible Rays |
| General Interest | |
| IB-009 | Atomic Energy and Your World |
| IB-010 | Atomic Pioneers—Book 1: From Ancient Greece to the 19th Century |
| IB-011 | Atomic Pioneers—Book 2: From the Mid-19th to the Early 20th Century |
| IB-012 | Atomic Pioneers—Book 3: From the Late 19th to the Mid-20th Century |
| IB-002 | A Bibliography of Basic Books on Atomic Energy |
| IB-004 | Computers |
| IB-008 | Electricity and Man |
| IB-005 | Index to AEC Information Booklets |
| IB-310 | Lost Worlds: Nuclear Science and Archeology |
| IB-309 | The Mysterious Box: Science and Art |
| IB-006 | Nuclear Terms: A Glossary |
| IB-013 | Secrets of the Past: Nuclear Energy Applications in Art and Archaeology |
| IB-017 | Teleoperators: Man’s Machine Partners |
| IB-014, 015, & 016 | Worlds Within Worlds: The Story of Nuclear Energy Volumes 1, 2, and 3 |
| Physics | |
| IB-401 | Accelerators |
| IB-402 | Atomic Particle Detection |
| IB-403 | Controlled Nuclear Fusion |
| IB-404 | Direct Conversion of Energy |
| IB-410 | The Electron |
| IB-405 | The Elusive Neutrino |
| IB-416 | Inner Space: The Structure of the Atom |
| IB-406 | Lasers |
| IB-407 | Microstructure of Matter |
| IB-415 | The Mystery of Matter |
| IB-411 | Power from Radioisotopes |
| IB-413 | Spectroscopy |
| IB-412 | Space Radiation |
| Nuclear Reactors | |
| IB-501 | Atomic Fuel |
| IB-502 | Atomic Power Safety |
| IB-513 | Breeder Reactors |
| IB-503 | The First Reactor |
| IB-505 | Nuclear Power Plants |
| IB-507 | Nuclear Reactors |
| IB-510 | Nuclear Reactors for Space Power |
| IB-508 | Radioactive Wastes |
| IB-511 | Sources of Nuclear Fuel |
| IB-512 | Thorium and the Third Fuel |
U. S. ATOMIC ENERGY COMMISSION
Office of Information Services
Transcriber’s Notes
- Silently corrected a few typos.
- Retained publication information from the printed edition: this eBook is public-domain in the country of publication.
- In the text versions only, text in italics is delimited by _underscores_.