Part 5: The discovery of cesium 137: The untold story

Part 5: The discovery of cesium 137: The untold story

A Selected History of Radiology Apropos of the Radiologic Centennial Part 5: The Discovery of Cesium 137: The Untold Story Dennis D. Patton, MD arli...

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A Selected History of Radiology Apropos of the Radiologic Centennial

Part 5: The Discovery of Cesium 137: The Untold Story Dennis D. Patton, MD

arlier in this series, we saw the key role the element barium played as the fluorescent substance barium platinocyanide in the discovery of X-rays by Roentgen and as insoluble nontoxic barium sulfate in the development of gastrointestinal radiology. Barium has been important in many advances that have paved the way to modern radiology, including the discovery of X-rays, radium, nuclear transmutation, and nuclear fission and the development of gastrointestinal radiology, ultrasound, photography, teletherapy, radiation dosimetry, calibration, and positron emission tomography. Remarkably, not only has barium figured in many ways in the development of modern radiology but also, in each one, the critical property of barium or its compounds that influenced the new development is different and unique. The subsequent parts of this series will explore the development of these facets of modern radiology and show h o w the element barium played an influential role in each one. Practitioners of radiation oncology or nuclear medicine are familiar with cesium 137, one of the most widely used radioactive isotopes today. Cesium 137 is in worldwide use as a teletherapy 1 source in radiation oncology and as a standardization source in nuclear medicine. It has a wide application in industry as well (e.g., industrial radiography, equipment sterilization, food irradiation). This is the story of the discovery of cesium 137. The story is remarkable in that cesium 137 was discovered by an undergraduate chemistry student.

E

1Teletherapy (tele = distant): radiation therapy with a distant (50-100 cm) source, such as X-rays, cobalt 60, or cesium 137. Brachytherapy (brachy = close): therapy with the sealed source at or inside the body (radium, radon, iridium 192, cesium 137, and others).

EARLY RADIOTHERAPY

One of the earliest medical applications of X-rays was in the treatment of cancer. Within a few weeks after the discovery of X-rays, it was found that the tissue damage caused by X-rays was usually greater in malignant than in normal tissue. Thus radiation therapy, or radiotherapy, had its beginnings early in 1896. Shortly after the discovery of radium, it was established that the gamma rays from radium were similar to X-rays and brought about similar effects in tissue. In the early days of radium, physicians thought of it as a portable, continuous source of X-rays for radiation therapy. Radium 226 has a long half-life of 1600 years, so for practical purposes the activity of a radium source is constant. Radium 226 gives off penetrating gamma rays with a number of different energies. Most of them originate from numerous decay products. The unit of radium activity is the curie, 2 defined as the activity of I g of elemental radium 226 in equilibrium with its decay products. Radium salts have a lower specific activity, less than 1 Ci/g. Radiation therapy with the use of a chemical was a radical departure from the technology involved in X-ray therapy. The source of the radiation was a small sample of a radium salt encased in a metal jacket to stop the particulate radiation and the very low-energy gamma rays. Radium gives off a little over 8 R - hr -1 9 mCi -1 at a distance of 1 cm. Sources were not strong enough to deliver a tumoricidal dose from outside the body, so the source had to be implanted temporarily in or near 2It is not clear whether the curie was named after Marie or Pierre. It was named in 1910, after one of them but not both. The naming of the curie will be discussed in an upcoming article in this series on the discovery of radium.

From the Department of Radiology, Division of Nuclear Medicine, University Medical Center, Tucson, AZ. Address reprint requests to Dennis D. Patton, MD, Department of Radiology, Division of Nuclear Medicine, University Medical Center, Tucson, AZ 85724. Received April 12, 1994, and accepted for publication without revision April 12, 1994. Editor's note: The first four articles on the history of radiology were published in Investigative Radiology in the section "Insights on the Radiological Centennial: A Historical Perspective."

Acad Radio11994 ;1:51-58 9 1994, Association of University Radiologists

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the tumor (brachytherapy). To deliver the required dose of several thousand rads over a few days, several hundred milligrams were needed. The scarce, element was expensive: a 1941 price quotation 3 was $27.50 per milligram (per millicurie) [1]. Furthermore, the 1941 German occupation of Belgium closed off the normal supply from the Belgian Congo, and the outbreak of war in Europe and Asia completely suspended radium supplies from overseas. Finally, the military had a great demand for radium to make luminous military instrument dials and watches. The war made it impossible to buy radium, causing a severe hindrance to the rapidly developing field of radiation therapy. For all its benefits, radium did have significant limitations: 1) it was expensive; 2) it had a maximum specific activity of 1 Ci/g, which ruled it out as a teletherapy source (a gram costing $27,500 could deliver only 3 rads/hr at a treatment distance of 50 cm); 3) as a brachytherapy source it sometimes overtreated local tissue because of the greater local absorption of the lowenergy gamma rays and the inverse square law; and 4) radium spontaneously decayed to a gaseous radioactive product, radon, with the constant danger of pressure buildup and leakage. Although X-rays and radium had value in the treatment of superficial or accessible tumors, teletherapy of deep tumors required more penetrating radiation than either could deliver. The demand for radium by doctors and hospitals would have far exceeded the available supply. As other naturally occurring radioactive isotopes were discovered, it was hoped that one of them might be the sought-for substitute for radium that would provide the high-energy gamma rays needed to penetrate deeply into the body, but none was found.

Vol. 1, No. 1, September 1994 ARTIFICIAL

RADIUM

The first practical artificial radium was cobalt 60, which could be made cheaply by irradiating ordinary cobalt 59 (100% natural abundance) with neutrons in a nuclear reactor. However, it needs frequent recalibration and replacement every few years because of its 5year half-life, and its high-energy gamma rays (1.1-1.2 MeV) require heavy shielding. Still, it has become the most widely used radioisotopic teletherapy source in the United States. In many other countries, for practical reasons, another radioisotope, cesium 137, is far more commonly used for this purpose. SEABORG

PREDICTS

RADIOCESIUM

Radiocesium was predicted before it was actually found. Glenn T. Seaborg (Fig. 1), a young member of the chemistry faculty at the University of California at Berkeley, noticed that, in the products of the fission of uranium, no long-lived group I radioisotopes occurred

THE IDEAL SOURCE

An ideal radioisotope as a radiation therapy source would have a long half-life, making frequent replacements and recalibrations unnecessary. !t would have a penetrating monoenergetic gamma ray with energy of at least 0.6 MeV to penetrate to deep tissue while sparing the skin but not much higher than 1 MeV to keep shielding requirements modest. It would have a specific gravity (activity per gram) much higher than that of radium (1 Ci/g). Unlike radium it would have no gaseous products, simplifying containment, and it would be inexpensive and readily available. When it became clear that nuclear fission could provide an undreamed of assortment of artificial radioisotopes, the search began for an ideal source of gamma rays for radiation therapy. 3A1941 quotation is used because that is the year in which cesium 137 was discovered.

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FIGURE 1. Glenn T. Seaborg in 1941, the year cesium 137 was discovered (courtesy of Dr. Seaborg).

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(sodium, potassium, rubidium, cesium, unknown element 87), although one would expect to find them in fission products and elements of other groups. Why should fission produce no group I elements? With a curiosity that characterized his subsequent career, Seaborg set out to find them, enlisting the aid of an undergraduate chemistry student named Margaet Melhase (Fig. 2). Glenn Seaborg's story is one of talent, determination, and success. Seaborg was born at the right time to enter the atomic age, but he did not merely enter it--he organized it and left an indelible imprint on it. Born to an immigrant Swedish family in Ishpeming, Michigan, in 1912, he developed a strong interest in physics and chemistry in high school. Seaborg did graduate work in chemistry at the University of California at Berkeley and served as a research assistant under the renowned chemist Gilbert N. Lewis, earning his PhD in 1937. (His thesis was on the inelastic scattering of fast neutrons. The neutron had been discovered only 5 years earlier.) In the heady atmosphere of Berkeley during the early days of the cyclotron of Ernest Orlando Lawrence, Seaborg worked on the radiochemical separation and identification of radioactive isotopes produced by bombardment of various elements and later did similar work with the products of uranium fission. In the course of his work on radioisotope identification, he was the discoverer or codiscoverer of many radioisotopes used in medicine, including iron 59, cobalt 60, iodine 131 (with Jack Livingood), and (with Emilo Segre) technetium 99m. Seaborg and his physicist coworker Edwin McMillan won the 1951 Nobel Prize in chemistry for the discovery of the transuranic elements and advances in their chemistry. Seaborg also initiated the Plutonium Project (1942), characterized most of the early transuranic elements, and established that element 89 (actinium) began a separate group in the periodic table (actinide series, elements 89-103), as did the rare earths (lanthanide series, elements 57-71). Seaborg was Chancellor of the University of California at Berkeley (1958-1961) and served an unprecedented 10-year term as chairman of the Atomic Energy Commission under Presidents Kennedy, Johnson, and Nixon. Seaborg's contributions to the field of radiochemistry can hardly be overstated. 4 This is the man who in 1940--just a year or so after the discovery of fission by Otto Hahn, Fritz Strassman, and Lise Meitner in Berlin--was wondering why no long-lived radioisotopes of the group I elements cesium and rubidium had 4perhaps the ultimate tribute to Seaborg's contributions to radiochemistry is the official naming of element 106 after him: seaborgium. Other elements (and atomic number) named after persons: samarium (62), gadolinium (64), curium

(96), einsteinium (99), fermium (100), mendelevium (101), nobelium (102), lawrencium (103), rutherfordium (104), hahnium (I05), nielsbohrium (107), and meisnerium (109).

T H E D I S C O V E R Y O F C E S I U M 137

ever been found among the fission products, though one would expect to find them. ENTER THE UNDERGRADUATE: EVENING

THE MUSICAL

While Seaborg was planning to look for group I ele-

in fission products, Margaret Melhase, an undergraduate chemistry student, was looking for a research project. Melhase, a senior honors student at Berkeley, was planning a career in chemistry and needed a challenging project to demonstrate her ability to carry out original investigation. In a recent interview with the author, Margaret Melhase (Mrs. Robert) Fuchs, at her home in Pacific Palisades, California, recalled the exciting days in Berkeley in 1941 (author's comments in brackets): 5 ments

In 1940 I was a senior honors student in the college of chemistry and president of the Student Affiliates of the American Chemical Society at the University of California at Berkeley. I was seriously considering going for a doctoral degree

FIGURE 2. Margaret Melhase in 1941, the year cesium 137 was discovered; now Mrs. Robert Fuchs (courtesy of Mrs. Fuchs).

5It is a rare privilege for a historian to be the first to interview someone who has shared in such an important discovery, all the rarer when the first interview takes place 50 years later! With all that has been published about the widely used cesium 137, the story of its discovery has not hitherto been published, although Seaborg referred to Meihase as the codiscoverer in a 1970 speech. (G. T. Seaborg, Reminiscenceson the development of some medically useful radionuclides. Address delivered at the 17th Annual Meeting of the Society of Nuclear Medicine, Washington, DC, July 10, 1970. Text of address provided by Dr. Seaborg.)

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and pursuing a career in chemistry. It was customary for honors students to undertake a research project, to learn more about research techniques and stimulate interest in original investigation. One of my d o s e friends was Gerhart Friedlander, a graduate student in chemistry Who was doing research on tellurium isotopes under Glenn Seaborg. Once I borrowed a book from Gert, and it reeked so much of gadic (an odor characteristic of tellurium) that there could be n o doubt what element he was working with! Gert Friedlander loved music, and every Friday he hosted a musical evening at his home, with his colleagues in the chemistry department. Gert had come to the United States from Germany, and his musical taste reflected his love of the German classics; those who played instruments usually wound up playing music of Bach, Handel, Telemann, and Mozart. As a close personal friend of Gert, I was also invited. At one of these evenings he suggested that I go to see Glenn Seaborg and ask him to propose a research project for me. I followed up on this suggestion and found Seaborg in his lab. Seaborg thought it over and remarked that no one had ever found any of the group I elements (rubidium, cesium) in the fission products of uranium, though on theoretical grounds one would expect to find them. Seaborg said we could work together looking for them. Seaborg arranged research space for me on the top floor of the old chemistry building on the Berkeley campus that was affectionately known as the "Rat House." My laboratory was fight above the lab spaces occupied by Willard Libby (who was to win the 1960 Nobel Prize in chemistry for radiocarbon dating), and Melvin Calvin (who was to win the same prize in 1%1 for characterizing photosynthesis). From the radiochemical standpoint, I was in very good company. I've often wondered if my radioactive wastes ever bothered them. (M. M. Fuchs, letter to Glenn Seaborg, "November 5, 1%9, courtesy of M. M. Fuchs; and M. M. Fuchs, interview with the author, November 4, 1990.)

Vol. 1, No. 1, September 1994

extraction. Most other metals were removed as insoluble sulfides or carbonates. To an acidified aliquot of the supernatant, carrier (i.e., nonradioactive) cesium nitrate was added, and the cesium was precipitated as silicotungstate. The chemical pathway had removed all metallic elements other than those in group I, and rubidium, the only other group I element likely tO be a fission product, was removed separately. The radioactivity of the purified cesium fraction was intense enough to measure with a gold-leaf electroscope. Seaborg had won his point. Over 14 weeks, the activity showed essentially no change. Melhase could conclude only that the radiocesium had a very long half-life. (The half-life is now known to be 30 years; the change in activity over 14 weeks would have been less than 1%, far too small to detect with a gold-leaf electroscope.) We can now identify this radioisotope with certainty as cesium 137. In a way, it is surprising that radiocesium had not been isolated from fission products before. The fission yield of various radioisotopes is shown in Figure 3. The

Mr

mC=

1000

NUMBER PER I 0,000 FISSIONS

100

THE MOMENT OF DISCOVERY

On March 3, 1941, Art Wahl, a graduate student working under Seaborg and the first person to extract plutonium from fission products, handed Melhase 100 g of uranyl nitrate, a uranium compound that had been irradiated with neutrons from the 60-inch Berkeley cyclotron. 6 The uranium compound was removed by ether 6Because the cyclotron can work only with charged particles, neutrons are produced by secondary reactions, e.g., deuterons on beryllium (4Be9 + ld 2 --> 5B 10 + on I). The reactor had not yet been invented.

54

I 80

= 90

I 100

I |10 lASS

I 120

l 130

I 140

| |50

I 160

NUMBER.

FIGURE 3. Fission product yield. Note that cesium 137 lies nearthe upper peak; it is a high-yield fission product (over 6%). One would expect it to have been one of the first fission products isolated. Reprinted with permission from Meredith end Massey (14).

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two peaks, each representing about a 6% yield, center about A = 95 and A = 139, the latter very close to cesium 137. (The 1938 discovery of fission by Hahn, Strassman, and Meitner was based on identification of 12.8-day barium 140.) A significant fraction of the total activity in the fission products earlier chemists had worked with must surely have been coming from cesium 137, yet it remained unexplained until the Seaborg-Melhase discovery. The significance of this discovery was not evident at the time, but it did establish Melhase as a promising young experimental radiochemist. She was in the right place at the right time to make a contribution to the scientific knowledge of fission products, because Seaborg had the knowledge of this new p h e n o m e n o n and access to fission products through the Berkeley cyclotron. Her findings validated Seaborg's conviction that fission must produce group I elements. On the other hand, because this discovery occurred in 1941, when absolute secrecy was being imposed on all aspects of nuclear research (suddenly, almost all mention of fission vanished from the physics literature), both Seaborg and Melhase were deprived of timely recognition through publication. Cesium 137 continued to be the subject of classified research at Oak Ridge and elsewhere, but none of the results was released until after the war, By then the trail of discovery was cold. THE PAUCITY OF EARLY REFERENCES

Few references exist to the early work with cesium 137. In the 1946 table of isotopes issued by the Plutonium Project and edited by Siegel [2], C. D. Coryell, and others, under cesium 137 there is a rather oblique reference: "Seaborg, G. T. and M. Melhase, private communication to C.D. Coryell (1941)," and also in CoryellSugarman [3] in 1951 on radiochemistry: "G. T. Seaborg, private communication to C. D. Coryell, May 1942; M. Melhase, Research Report, University of California, Berkeley, September 1941." In Lederer and Shirley [4], there is a similarly oblique reference under cesium 137: "M. Melhase, unpublished data (Sept. 1941)." Wartime and postwar security prevented publication in the open literature. Aside from these obscure references, there seems to be no acknowledgment of the undergraduate chemistry student who should share the credit with Seaborg for discovering this exceptionally useful radioisotope. In a 1969 letter to Melhase, Seaborg wrote: I am considering including a short description of the discovery of radioactive cesium 137 in one of my talks. I believe that the work you did with me during 1941 on the identification of this iso-

T H E D I S C O V E R Y O F C E S I U M 137

tope as a fission product of uranium constitutes the first observation of this isotope. (G. T. Seaborg, letter to Margaret Melhase Fuchs, October 25, 1969, courtesy of M. M. Fuchs.) And in a 1990 letter he concurs: "... it is appropriate to credit both G. T. Seaborg and M. Melhase for the 'birth' of cesium 137." (G. T. Seaborg, letter to the author, March 8, 1990.) Although Seaborg played a key role in the discovery of cesium 137, the actual moment of discovery belongs instead to the undergraduate chemistry student working under his direction at Berkeley in 1941. It is certainly a credit to Seaborg's character that he shares credit with his student. Seaborg tells the story in his 1970 address to the Society of Nuclear Medicine 5. My involvement with the discovery of cesium 137 presents an entirely different sto W . After the discovery of fission by Hahn and Strassman in December 1938 many radioactive fission products were characterized in laboratories all around the world, but the evidence concerning radioactive isotopes of rubidium and cesium was scanty or lacking. Therefore, in the late fall of 1940 I asked an undergraduate student, Margaret Melhase (now Mrs. Robert Fuchs), to take some uranium which had been bombarded with neutrons furnished by the 60 inch cyclotron (at Crocker Radiation Laboratory, University of California, Berkeley) and make chemical separations designed to look for hitherto u n k n o w n radioactive fission products such as cesium. She performed her chemical separations on the top floor of the old "Rat House" which even at that time was an ancient, ramshackle w o o d e n building dating from the earliest days of the Department of Chemist W at Berkeley. Her measurements of the radioactive decay and radiation absorption properties were performed through the use of a Lauritsen quartz fiber electroscope. Miss Melhase continued her work until the summer of 1941, by which time she had established the presence of a very long-lived radioactive fission product in the cesium fraction which on the basis of subsequent work we can now identify as being due to the 30-year cesium 137. This isotope has found substantial applications as a gamma ray source in medical therapy similar in its use to that of cobalt 60.7 7This is another example of how support of student research can lead to significant advances that benefit medicine.

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Vol. 1, No. 1, September 1994

THE B A R I U M C O N N E C T I O N

After the discovery of this n e w cesium radioisotope, a full understanding of its m o d e of decay was rather slow in coming. The long-lived cesium radioisotope was officially identified as cesium 137 by R. I, Hayden and L. G. Lewis in 1946 by mass spectrometry [5]. As late as 1948, it was still believed that the cesium 137 decayed b y both beta and g a m m a emissions to stable barium .137. 8 In July, 1948, Townsend et al. [6] publ)shed their data on the "beta- and gamma-spectra of Cs-137," and made the prophetic observation that the "monoenergetic nature of the gamma-ray combined with the long halflife of Cs-137, 33 years, suggests its use as a gamma-,'ay standard." Thus the 660-keV g a m m a ray was thought to come directly from the decay of cesium 137. Townsend did not leave the matter a!one, though, for only 6 w e e k s later he was able to report two additional key findings: 1) there were no beta-gamma coincidences in cesium 137 decay, which indicated that the two emissions were separated in time, and 2) the Xrays observed during cesium 137 decay were characteristic of barium and not cesium [7]. The first observation is significant in that radioisotopes that decay by both beta and g a m m a emissions usually give off both emissions in such a brief time that to our measuring instruments they appear to be simultaneous or to occur "in coincidence." Lack of beta~gamma coincidence means that there is a delay between the two; one emission occurs first, and a measurable delay occurs before the nucleus gives off the second emission. Townsend knew, then, that the decay sequence of cesium 137 must be either g a m m a - - d e l a y - - b e t a (extremely unlikely) or b e t a - - d e l a y - - g a m m a . The significance of Townsend's second observation is that if the g a m m a ray had c o m e out of a cesium nucleus and undergone internal conversion giving rise to characteristic X-rays, the X-rays would have been characteristic of cesium. But exact measurement of their energy showed they had b e e n created in a barium atom. The fact that the X-rays were characteristic of barium meant that, w h e n the g a m m a ray was emitted, the transmutation to barium had already occurred. The g a m m a rays were coming from barium, not cesium. Townsend's 1948 observations s h o w e d that 33-year cesium 137 decayed by pure beta emission to a metastable radioisotope of barium, which after some delay gave off the 660-keV g a m m a ray. Townsend estimated the half-life of the metastable barium radioisotope to be 158 + 5 sec (2.63 min; the current value is 2.55 min) [4]. 8When a cesium nucleus (55 protons) decays by beta emission it is as if a neutron had been converted to a proton and a negative electron; the latter is emitted as a beta particle, and the nucleus then has 56 protons, which makes it a barium nucleus. A nucleus undergoing ordinary (negative) beta decay is transmuted to a nucleus of the next higher element.

56

'37c (-3oy)

' • m a =x0.51 MeV

\"-22 \----I----

1,17 MeV \ | 5% ~=O.66MeV

I

1371Bo

55 56 ATOMIC NUMBER FIGURE 4. Cesium 137 decayscheme.The 660-keVgamma ray associated with cesium 137 is actually emitted from the barium 137m nucleus. Reprinted with permission from Hendee (15).

The barium radioisotope was n a m e d barium 137m (m for metastable). The existence of the metastable radioisotope also was discovered independently by Engelkemeir (8). Recognition of the sequence cesium 137--(beta)---) barium 137m--(gamma)--+ barium 137 was quick in coming. The h a n d b o o k Nuclear Data [9] diagrams the decay as we k n o w it today (Fig. 4). C E S I U M 137 IN R A D I O T H E R A P Y

It was the late nuclear pioneer Marshall Brucer (Fig. 5) w h o first suggested cesium 137 be used as a teletherapy source, pointing out some of the unusual advantages of cesium 137 in this application [10-13; Marshall Brucer, interview with the author, August 14, 1989]. Cesium 137 is a high-yield fission product, being near the second p e a k of the uranium 235 fission-product curve (Fig. 3); it is relatively inexpensive because it is made from waste products in the neutron economy. It can be prepared with a specific activity as high as 25 Ci/g, freeing us from the radium-based limitation of 1 Ci/g. The source needs to be replaced only every 30 years (compared with every 5 years or so for cobalt 60). 9 There are no gaseous products as there are with radium, and because there is no significant change in output from year to year, frequent recalibrations are not required. Some of these advantages over cobalt 60 (longer half-life, low cost) have m a d e cesium 137 especially valuable as a radiotherapy source in Third-World countries with lim9Brucer once remarked that the radiation therapy source should have a halflife comparable to that of the radiation therapy facility.

Vol. 1, No. 1, September 1994

FIGURE 5. Marshall H. Brucer (1961 photo, courtesy Mrs. Pat Brucer).

ited resources. Brucer, with his special relationship with the Atomic Energy Commission, was the champion of cesium 137 for teletherapy, as he was for so m a n y other radioisotopes in medicine. For various reasons, cobalt 60 has found more widespread application in the United States as a teletherapy source than cesium 137. Its g a m m a emissions of 1.1 and 1.3 MeV are more penetrating than those of cesium 137, and its salts are not deliquescent like those of cesium. Cobalt 60 can be prepared cheaply by the neutron irradiation of stable cobalt in a reactor. Iridium 192 is also widely used, although its short 75-day half-life limits its range of application. Cesium 137 has b e c o m e one of the most widely used radionuclides in the world. Besides its use in medicine, the radionuclide is used as a radiation source for the sterilization of disposable medical supplies. It is a standard radiation source for sterilizing foods and food products (destroying trichinella in pork and salmonella in poultry), and agricultural insect pests, the latter of special interest to Third-World countries. It is estimated that in the United States alone, production of cesium 137 for industry and medicine has t o p p e d 7 x 107 Ci (R. Chitwood, U.S. Department of Energy, Office of Isotope Production and Distribution, interview with the author, March 18, 1991; this amount of cesium 137 in metallic form would weigh nearly a ton).

THE DISCOVERY

OF CESIUM

137

Gilbert N. Lewis, the venerated head of the Department of Chemistry, refused for the time being to allow any m o r e w o m e n to enter the Berkeley graduate school in chemistry. After all, the last w o m a n he had admitted got married shortly after graduation and "wasted her entire education! 'a~ Melhase went to work in industrial chemistry and w o r k e d on the Manhattan Project for a while but, lacking an advanced degree, did not pursue a career in science. Margaret Melhase Fuchs: American housewife, mother of three, active in her church, first person to discover cesium 137. She did no further work in chemistry. 11 Who should be credited with the discovery of cesium 137? Melhase, the undergraduate student, was the one w h o actually found the treasure; but Seaborg k n e w it was there, and he supplied the map, the materials, and the means of transportation. The discovery should be credited jointly to one of the greatest chemists of our age and to a capable undergraduate chemistry student w h o was in the right place at the right time. 12 The property of barium that played a role in the development of teletherapy is the useful 660-keV g a m m a energy of barium 137m, a short-lived daughter of long-lived cesium 137. This property is independent of the other properties of barium that have led it to play a role in other discoveries and developments in radiology. The role played by barium in other developments will be explored in future parts of this series. ACKNOWLEDGMENTS

The author thanks Dr. Glenn Seaborg, Margaret Melhase Fuchs, and the late Dr. Marshall Brucer for sharing recollections of the events described in this article. REFERENCES 1. McDannald AH, ed. The Americana annual New York: Americana; 1941 ;605. 2. Siegel JM, ed. Nuclei formed in fission: decay characteristics, fission yields, chain relationships. Issued by the Plutonium Project. Rev Modern Phys 1946;18:513-544. 3. Glendenin LE, Metcalf RE Radiation characteristics of 33y Cs137. In: Coryell CD, Sugarman N, eds. Radiochemical studies: the fission products. New York: McGraw-Hill; 1951;1063-1066. 4. Lederer CM, Shirley VS, eds. Table of isotopes, 7th ed. New York: Wiley, 1978;711 and RC-5. 5. Hayden RJ, Lewis LG. Assignments of mass to fission isotopes by mass spectrograph (abstr). Phys Rev 1946;70:111. 1~

Me]hase Fuchs insists that she recalls these words clearly.

MELHASE AFTER THE DISCOVERY

11On October 25, 1969, Seaborg wrote to Melhase asking her for some details regarding her separation of cesium 137. In her reply she wrote, "My kids will never get over the thought that Glenn Seaborg had to ask anybody anything about radioisotopes--least of all their methed" (M. M. Fuchs, letter to G. Seaborg. November 5, 1969). Seaborg wrote in reply, "1 hope you have succeeded in convincing your kids that you made an important contribution to the radioisotope field (resulting in many practical applications) during those days at Berkeley" (November 8, 1969).

The plans of Margaret Melhase to continue into graduate school in chemistry were thwarted in 1941 w h e n

12Ironically, no mention is made of Margaret Melhase Fuchs in American Women of Science, despite the fact that the cesium 137 she helped to discover is used worldwide to treat carcinoma of the cervix, a common malignancy in women.

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6. Townsend J, Owen GE, Cleland M, Hughes AL. Beta- and gamma-spectra of Cs137 (abstr). Phys Rev1948;74:99. 7. Townsend J, Cleland M, Hughes AL. The disintegration of Cs137. Phys Rev 1948;74:499. 8. Engelkemeir DW.The 2.5m Ba daughter of Cs137 (thesis). ,~ECD-2125 (ANL-4139). Washington, DC: Atomic Energy Commission, April 1~), 1948;16. 9. Way K, Fano L, Scott M, Thew K. Nuclear data. Washington, DC: U.S. Government Printing Office, 1959 (National Bureau of Standards circular 499). 10. Brucer M. Special report of the medical division on teletherapy design

11. 12. 13. 14. 15.

problems: Cs137 (1st rev). TID-5086. Oak Ridge, TN: Oak Ridge Institute of Nuclear Studies, 1952. Eastwood WS. Possibilities of fission-produced cesium-137 for telecurie therapy. Nucleonics 1952;10:62. Brucer M. Teletherapy design problems. AJR 1954;62:91-98. Brucer M. Automatic controlled pattern cesium-137 teletherapy machine. AJR 1956; 75:49-55. Meredith WJ, Massey JB. Fundamental physics of radiology, 3rd ed. Chicago: Year Book, 1977;38. Hendee WR: Medical radiation physics, 2nd ed. Chicago: Year Book, 1979;17.

Announcement 9th European Congress o f Radiology--ECR '95--Vienna. New Date: March 5-10, 1995--Austria Center, Vienna. European Congress of Radiology '95 will offer a comprehensive continuing education program in diagnostic and interventional radiology (refresher courses and workshops), based on recent developments and applications in all subspecialty areas of radiology, developed in joint sponsorship with most of the European societies of radiologic subdisciplines, the European Federation of Organisations for Medical Physics (EFMP), and International Society of Radiographers and Radiological Technicians (ISRRT). Highlights will be a categorical course on musculoskeletal imaging, a specially dedicated 22.5-hour categorical course on clinical radiology, a refresher course for the general radiologist presenting a balanced overview and update of advances in the different fields of diagnostic radiology with simultaneous translation into several languages, and a specific refresher course program for physicists in medical imaging and for radiologic technicians. Accreditation for category I for the Physician's Recognition Award of the AMA will be given. The deadline for submission of scientific papers will be September 20, 1994. Contact: Administrative and Scientific Secretariat: ECR Office, Neutorgasse 9/2a, A-1010 Vienna, Austria, telephone: (+43/1) 533 40 64, facsimile: (+43/1) 533 40 649. Technical Exhibition: MAW, International Exhibitions & Advertising, Freyung 6, A-1010 Vienna, Austria, telephone: (+43/1) 533 23 20, 533 21 99, facsimile: (+43/1) 535 60 16. Travel--Accommodations--Social Programs: MONDIAL Congress, Faulmanngasse 4, A-1040 Vienna, Austria, telephone: (+43/1) 58 804-0, facsimile: (+43/1) 56 91 85.

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