Chemical & Engineering News,
July 17, 1995

Copyright © 1995 by the American Chemical Society.

Chemists Reminisce On 50th Anniversary Of The Atomic Bomb

They recall their work on the Manhattan Project, the first atomic bomb test, and the ethics of using the bomb against Japan

Stu Borman,

C&EN Washington

Fifty years ago this week - at 5:30 AM on July 16, 1945 - the first atomic bomb was exploded at the Trinity test site in Alamogordo, N.M. The successful test ushered in the nuclear age and led directly to the devastation of two Japanese cities - Hiroshima (with a uranium-based bomb) on Aug. 6, and Nagasaki (with a plutonium bomb similar to the one tested at Trinity) on Aug. 9.

The first atomic bomb was tested at the Trinity site, Alamogordo, N.M., on July 16, 1945.

The development of the atomic bomb was the culmination of the Manhattan Project, an organized effort to develop the most powerful weapons ever known for use in ending World War II. Much of the credit for the success of the Manhattan Project goes to the physicists, but chemists also played a major role.

Many chemists made crucial contributions at the Los Alamos, N.M., laboratory established to design and construct the bomb, as well as at several university labs participating in the project. Some helped set off the Trinity explosion. Others observed it. And many have strong feelings on the ethics of the atomic bomb - an issue raised very publicly recently when the Smithsonian Institution had trouble writing an acceptable script for an exhibit on the Enola Gay, the plane that dropped the atomic bomb on Hiroshima.

The type of bomb that destroyed Hiroshima was never tested beforehand."The uranium bomb was a relatively simple arrangement in which you fired one piece of metal into another," says Henry Linschitz, emeritus professor of chemistry at Brandeis University, Waltham, Mass., who directed a group at Los Alamos during the Manhattan Project. "By Aug. 6, enough work had been done on mock-ups, measurements of the multiplication time of the neutrons as a function of distance, and whatnot, so that one knew almost exactly what would happen when the bomb went off. It was not necessary to test it. And if they did test it, they would have used up all the uranium they had."

Because enriched uranium was so scarce and atomic-bomb technology so untried, a second type of bomb, based on plutonium, was also developed by the Manhattan Project. However, a plutonium bomb is inherently much more complex than a uranium bomb. In a plutonium bomb, subcritical pieces of fissionable material must be brought together much more quickly than in a uranium bomb to avoid predetonation. The simple gun design used in the uranium device wouldn't work.

So researchers working on the plutonium bomb turned instead to an implosion design. "They took a sphere that was subcritical and uniformly imploded it from all directions so that the plutonium was brought to a high enough density [to exceed] the critical mass," says chemistry professor Glenn T. Seaborg of the University of California, Berkeley. "They had to test that [bomb] first because it wasn't that straightforward that it would work, and that's why they made the test at Alamogordo."

In the Trinity test, a plutonium bomb was detonated in the top of a tower

After the explosion, Oppenheimer (left) and Groves inspected ground zero, where reinforcing rods from concrete footings were all that was left of the tower.

In the plutonium bomb, the implosion was accomplished with explosive "lenses" - devices that focus fast, highly symmetric explosive force on the subcritical mass. "The biggest uncertainty of all was how well the lenses would actually work - whether you could really get them to do the job with the given precision and with fine tolerances of millionths of seconds - and sure enough they did," says Linschitz. "The Trinity shot came pretty much within the calculated anticipated magnitude, explosive equivalentwise."

A sine qua non in the development of this weapon was the discovery of plutonium in 1941 by Seaborg, graduate student Arthur C. Wahl, and research fellow and chemistry instructor Joseph W. Kennedy. The discovery was the subject of Wahl's Ph.D. thesis - "probably one of the most significant theses in the history of the world," says Seaborg. It also was one of the findings honored by Seaborg's 1951 Nobel Prize in Chemistry.

We discovered the isotope plutonium-238 first," says Seaborg. "But we were able to show after we produced the longer lived isotope plutonium-239 that it was fissionable with slow neutrons and hence was eligible material to be the explosive material in an atomic bomb. This led to the plutonium part of the Manhattan Project." Seaborg also later developed a process for separating weapons-grade plutonium from uranium and fission products in nuclear reactors.

Linschitz joined the Manhattan Project after interrupting his graduate work in chemistry at Duke University in an effort "to get involved in the war against the Nazis and Japan," he says."Among several jobs offered at an ACS[ American Chemical Society] Clearing House, I chose what seemed to be the most directly war related, a post at the Explosives Research Laboratory, near Pittsburgh" - a government lab headed by chemistry professor George B. Kistiakowsky of Harvard University, now deceased.

Kistiakowsky and Linschitz later moved to Los Alamos, where Kistiakowsky was in charge of the explosives division and Linschitz worked on implosion problems and lens development. "I recall, on a visit to the chemistry labs, gazing awestruck at the first few milligrams of plutonium salts, which arrived at Los Alamos at a cost of roughly a billion dollars!" Linschitz says. "Since that time, the global stock of separated weapons-grade plutonium has risen to over 200 tons - giving some idea of the scale of the arms race."

Donald F. Hornig, an explosives expert who served as science adviser to President Lyndon Johnson from 1964 to 1969 and is now emeritus professor of chemistry at Harvard University, was also at Los Alamos. Hornig worked on the development of a safe and reliable firing unit to set off the implosion in the plutonium device, and he conceived a triggered spark-gap switch that was used to initiate the explosive lenses within a millionth of a second.

His wife, Lilli S. Hornig, also served on the Manhattan Project at Los Alamos, working initially on plutonium chemistry. "Then at some point they decided plutonium chemistry was too dangerous for women," says Donald Hornig, "so she went on to high-explosive lenses instead - which was a little crazy." Lilli Hornig later became a chemistry professor at Brown University and chairman of the chemistry department at Trinity College, Washington, D.C.

Another Los Alamos alumnus, William Spindel, is a physical chemist who later worked as a science policy analyst at the National Research Council."When I was an undergraduate at New York University, in the Army, I was recruited to serve on some sort of secret project called the Manhattan Project," he says. "That's all I knew - that it was a Manhattan project, and being a New Yorker that sounded wonderful."

Once he got to Los Alamos, he was filled in on the nature of the project and was given a report containing the words "plutonium" and "neptunium." "These were not elements that I had ever learned anything about in chemistry," says Spindel, "so I was convinced they were code names for something. It wasn't until a couple of weeks later that I found out that that's what we were working on." Spindel's assignment was to help develop corrosion-resistant coatings for plutonium and uranium by high-vacuum gas-phase deposition techniques.

Great efforts were made to maintain secrecy about Los Alamos activities vis-à-vis the outside world. For example, incoming and outgoing mail was screened and censored. But people on the inside "knew everything," recalls Walter Kauzmann, emeritus professor of chemistry at Princeton University, who also served on the Manhattan Project at Los Alamos. Laboratory director J. Robert Oppenheimer's policy" was that you can't design a thing like that where one group knows one thing and another group knows another. He encouraged interaction. The bomb probably wouldn't have been made if that hadn't happened."

Hornig says Oppenheimer "held staff meetings from time to time at which difficult problems were aired quite freely to get as many people thinking about them as possible. This was quite different from any other super-secret laboratory." Spindel agrees that "Los Alamos was unique in not having that much compartmentalization of information."

Linschitz says, "This was Oppie's great achievement - that he was able to maintain that kind of openness. And he sold it to Groves" - U.S. Army General Leslie R. Groves, head of the Manhattan Project. "Here you have what you might call traditional enemies - soldiers and scientists, totally different mentalities. Yet, Oppie was able to accommodate himself to Groves, and Groves was able to accommodate himself to Oppie. In a sense, they needed each other both so badly that they had to do that."

Kauzmann points out that one of his acquaintances at Los Alamos "was a guy named Klaus Fuchs, an Englishman who had not gone through the American security system. Fuchs knew everything. He had been a Communist in Germany and had fled Hitler."

Seaborg in recent photo and working in his lab in 1941, the year he and his coworkers discovered plutonium.

Kauzmann says Fuchs "was very closemouthed. He was a nice guy - very, very quiet. I'd have lunch with him. He never said very much - never any expression of political views or anything like that. But he was in a very high position, and he was feeding all his information to the Russians. The bomb that the Russians set off in August 1949 was an exact replica of the Trinity bomb."

Kauzmann adds that Fuchs "worked very hard on the bomb; he wasn't trying to scuttle it. His motivation was he wanted the Russians to have it as well. He was pro-Soviet, but he was also anti-Hitler and anti-Japan. The role of Fuchs was discovered after the war. He went back to England and was accused of spying several years after the war. He admitted it, was sent to jail, served his term, was released from jail, and went to East Germany, where he spent the rest of his life."

And Spindel knew a man named David Greenglass at Los Alamos."Greenglass was a GI who was with me in the barracks for a while," says Spindel. "Five years later this came to haunt me. He was the one who ... testified and sent his sister and brother-in-law [Ethel and Julius Rosenberg] to the electric chair. The [Federal Bureau of Investigation] came and questioned me about Greenglass around 1950."

Academic researchers also played an essential role in the Manhattan Project. For example, chemistry professor Harold C. Urey at Columbia University made significant contributions to development of the process for separating fissionable 235U from 238U.

George H. Morrison, professor of chemistry emeritus at Cornell University, worked for the project at Princeton University while in the U.S. Army. "H. S. Taylor, a physical chemist who was chairman of the department, had a group working on isotope separation, and in [chemistry professor] N. Howell Furman's group we were concerned with the analytical chemistry and chemical purification of uranium," Morrison says.

Morrison developed a method for separating trace impurities from uranyl nitrate. "If you had parts per billion even of cadmium, boron, or things like that that had high capture cross-sections for neutrons, they would stop the chain reaction," he says. "So we had to have every last bit out."

By July 1945, only three years after establishment of the Manhattan Project, both the uranium and plutonium atomic bombs were ready, but the plutonium device still had to be tested. Shortly before the test, the implosion bomb was hoisted atop a steel tower at the Trinity site. Hornig helped guard the bomb in the tower prior to detonation and also helped set off the bomb from the main control bunker.

"Early in the afternoon before the bomb went off, I climbed to the top of the tower - it was about 100 feet high - and connected up all the detonators," recalls Hornig. "In the early evening Oppenheimer got really very worried about sabotage. ... He decided that somebody ought to stay with the bomb until it got near the firing time." Hornig was selected as the baby-sitter.

"I climbed up at about 9 o'clock at night, in the darkness," he says. "It was already beginning to rain, and there was lightning all around. I was up there about three hours, and there was a fierce, fierce storm. Lightning was banging down all around."

Hornig sat in the tower under a bare lightbulb, reading a paperback book - "Desert Island Decameron" - with the atomic bomb and its several tons of high explosives nearby. If the lightning had set off the explosives, a nuclear detonation presumably would have followed. "One of the most welcome telephone calls I ever got was when the phone up there rang," Hornig says. "Kistiakowsky was at the other end and said, 'Hornig, you can come down now.' Nobody went up to replace me after that."

Kistiakowsky and a coworker "connected the bomb up to the firing lines that went back to the control center five miles away, and then locked up the box," says Hornig. "GIs then cleared away everybody from the area. The bomb was scheduled at that time to go off at 4 o'clock [in the morning]. But because of the storm everything was a mess, and it didn't look at all feasible."

In the control bunker, Hornig says he was responsible for "the one mechanical means of holding up the operation - the so-called chicken switch. If any small thing went wrong at all, my job was to open up that circuit so that the thing wouldn't go. I sat and watched my meters and red lights with a hand on that switch." But use of the chicken switch proved unnecessary.

At 5:30 AM, the bomb was set off."The lights went out, and outside through the door I could see the most brilliant light I'd ever seen on all the mountains around," says Hornig. "I dashed through the door to watch it. ... The bomb was bright and very luminous, like lots of neon signs. I remember beautiful billows of peach and green, and some rosy reds too. ... I don't think many people appreciated what an awesome spectacle it would be."

Science policy analyst Spindel now and during wartime.

Spindel also viewed the Trinity test."They formally only took group leaders and above to see the test," he says. "There was no specific reason for me to be at Alamogordo, except that the Army decided that for safety reasons they wanted to have a number of Army trucks available to evacuate ranchers ... in case there was some weather phenomenon or something that would drop fallout on them." Spindel volunteered as a driver.

During the test, he was about 15 miles from ground zero. "It was an overwhelmingly impressive event," says Spindel. "We were told to keep our eyes averted for the first tenth of a second because there would be large amounts of ultraviolet radiation and whatnot. But even with your eyes averted and your head covered, you couldn't help but see the extreme bright flash. By the time you picked up your head, the brightest of it was over. Then one watched this fireball growing and changing colors and finally moving up in this typical mushroom shape - a rising cloud, a mixture of dirt and ionizing radiation, with colors changing in the fireball."

Particularly striking, says Spindel, was the delayed shock wave. "Because of the difference between the speed of sound and the speed of light, at 15 miles it took more than a minute for the shock wave and sound to reach me. That was a very long minute."

Kauzmann was in a group that drove to Socorro, about 25 miles from Alamogordo, to observe the test. "Six of us climbed up to the top of a small mountain and spent the night," says Kauzmann. "We knew the time the bomb was supposed to go off, but we woke up and nothing happened. We decided the thing hadn't worked. So we gathered our things together. It was ... kind of dark. We started walking down the hill, very slowly. You had to look down to watch your footing. There was no path."

Suddenly, says Kauzmann, "there was a tremendous bright light. We looked up and there was this huge thing, brighter than the sun, expanding. ... For two minutes there was no sound that went with this. When the shock wave reached us, there was a tremendous crash and then several minutes of rumbling, like thunder. That crash was even more terrifying than the flash. The reverberations went on for a long, long time."

Nuclear chemist Gerhart Friedlander, now retired from Brookhaven National Laboratory, was also present. A Jewish refugee from Nazi Germany, Friedlander had been one of Seaborg's first two graduate students before joining the Manhattan Project. At Los Alamos, he was in charge of a project in which highly radioactive gamma ray sources were used to test the symmetrical nature of the implosion weapon's explosive lenses.

One of Friedlander's most memorable recollections of Trinity was an experiment he saw physicist Enrico Fermi perform. "Before the final countdown, Fermi took a piece of paper and tore it into small pieces," says Friedlander." He had calculated how long it would take for the blast wave to reach our position, which was less than a minute. At the appropriate time he dropped those pieces of paper and observed how far the blast wave pushed them. He took out his slide rule, did a quick calculation, and said, '20 kilotons.'"

Donald and Lilli Hornig served on the Manhattan Project at Los Alamos.

Fermi, says Friedlander, "had of course prepared the calculation beforehand so he could translate the displacement of the pieces of paper into the power of the bomb, but it was a pretty damned impressive demonstration. I don't remember if the number he said was exactly '20,' but it turned out to be within 20 to 30% of the result that was later verified. That was just an incredible demonstration of genius, as far as I was concerned."

Linschitz also saw the dawn of the nuclear age at Trinity. "After completing the assembly of the bomb on top of the tower - my job was to wire the firing cables to the detonators - I joined a group on a ridge overlooking the valley, about 15 miles from the bomb," says Linschitz. "It is really difficult to describe adequately the overwhelming impact of the shot. Someone later wrote that the sun rose twice that morning, but the dazzling white light all around on the desert and mountains seemed far brighter than any sun, and the ensuing blast, even at that distance, was a sustained echoing roar."

Linschitz adds, "I remember most vividly, after putting aside the dark welder's glass and watching the fireball die away, a great blue-violet glow in the sky. This was either an afterimage from my bleached-out eyes or, more probably, light from an enormous volume of nitrogen ionized by the high temperature and intense radiation of the fission products. The dawn finally rose on that unforgettable towering mushroom cloud. The steel tower, of course, had simply disappeared. At first we were jubilant - release of tension. But later that morning, driving back to Los Alamos, we were all silent."

An exhibit on the Enola Gay that recently opened at the Smithsonian Institution in Washington, D.C., has stirred up questions about the ethics of the atomic bomb and its use on two Japanese cities. But with only minor reservations, chemists who worked on the bomb have few second thoughts about the moral implications of the bomb.

"I have no regrets," says Donald Hornig. "Whatever anyone says about how the strategy might have been different, I guess our view was that the bomb probably would stop the war, and if it did it would be worth it." At Los Alamos, he says, there was relatively little discussion of the ethics of using the bomb, "although Lilli signed a petition urging that the first one be used on an unpopulated island as a demonstration."

Hornig says, "You also have to remember that the casualties from each one of the bombs [were] not particularly higher than the 1,000-plane fire raid on Tokyo, which preceded it by only a few weeks. So this was comparable to the scale of war that was going on."

Hornig concedes that the bomb "was pretty awful. But the idea was, in the end, to terminate the war and save lives, and it might be that we saved Japanese lives as well as American lives."

Some historians have suggested that the bombing of Hiroshima and Nagasaki did not really cause the end of the war because the Japanese were already prepared to surrender. But Donald Hornig and others disagree. "In fact, the bomb did have the effect of stopping the war," he recollects. "The facts are simple and quite clear. We had set an ultimatum before using it. ... They turned it down. We used one bomb, and we again asked for a surrender. ... There was a three-day interval, we did use the second one, and within 24 hours they sued for peace. I don't see how you could look at that sequence of events and say the bomb didn't have the effect of stopping the war," Hornig says.

Linschitz in 1979.

Development of the atomic bomb, says Kauzmann, "was an entirely justifiable thing to do. ... Under the circumstances I think there was absolute justification for working on this thing. I have no shame or doubts that I did the right thing."

Morrison says, "Today's generation can't appreciate what life was like during World War II. Every family was touched, everybody had some relative in the service, and people connected with the A-bomb development didn't have any guilt feelings. The point was the Japanese were going to kill us if we didn't kill them."

Linschitz says, "During World War II, bombing of cities gradually became an acceptable means of warfare, particularly following German bombings of Warsaw, Rotterdam, and finally London. The worst bombings of the war by far, in fact, were the firebomb raids in the spring of 1945 when [Air Force General Curtis] LeMay and his B-29s essentially burned down many of the major Japanese cities. And the casualties were tremendous." Linschitz believes the atomic bomb must be viewed in this context.

The late George Kistiakowsky in 1980. He was head of the explosives division at Los Alamos during the Manhattan Project.

Spindel says, "The real issue is whether civilian bombing is appropriate. It was happening. We were doing firebombing in Europe, in Dresden and so forth, we were doing firebombing in Japan. In spite of all the reconstructed history, I'm convinced that [the atomic bomb] certainly shortened the war and I believe probably saved more lives than it took.

"I know it has become fashionable to say the Japanese were ready to surrender," says Spindel. "Nevertheless, they fought bitterly at Okinawa just two months before the end of the war, and they were going on with kamikaze bombing of our fleet all this time. ... I don't think anybody in the Army at the time who was sitting in the Pacific expecting to have to invade the home islands was that convinced that the war was all over."

Friedlander worked on explosive lenses at Los Alamos.

Seaborg observes, "The Japanese, after all, started it all with Pearl Harbor. ... So you can't really regard this as the U.S. attacking Japan. The U.S was in a sense defending itself, trying to bring the war to an end as soon as possible."

Seaborg says he was a member of a committee chaired by physicist James Franck that "in June 1945 came out with a report recommending that the bomb not be used against Japan, except following a demonstration at which Japanese observers would be present, giving them the chance to surrender without use of the bomb on their homeland. That report received quite a bit of attention, but somehow the other side prevailed. I don't know the inside story on that, but President Truman decided to use the bomb."

Seaborg points out that a possible rationale for this decision was that, after Trinity, the U.S. had only enough uranium and plutonium to produce one of each type of bomb. "That's one of the reasons they didn't take our recommendation for a demonstration first," he says. "Because if that demonstration had failed, they wouldn't have had enough plutonium for another bomb for a while yet, and that could have led to a continuation of the war."

Analytical chemistry professor Morrison today and in 1943.

Seaborg was not the only one who had doubts at the time about the bombing program. "During the war, I had no compunctions about Hiroshima at all," Friedlander says. "What bothered me at the time - and I think bothered many of us - was the second bomb, the Nagasaki bomb. I could not really understand, and I still can't understand to this day, why we couldn't have waited a few extra days after the Hiroshima bomb to see what would happen. I think eventually the Japanese would have surrendered even after the one bomb, after they realized what was involved."

Spindel says, "I do think that certainly the first bomb was completely ... necessary. There's been some question of whether we needed to drop a second one three days later. On this I have no viewpoint. I'm not sure."

According to Linschitz, "The claim that the Japanese in World War II were defending their culture against American aggression is, of course, an outrageous, even grotesque, distortion of the situation. Unfortunately, this controversy has obscured some of the main related issues that now confront us at the close of the 20th century. These include particularly the dissipation of vast resources in gigantic military budgets - even after the collapse of the Soviet Union.

"In August 1945, the UN [United Nations] had just come into being, and we hoped that this demonstrated power of nuclear bombs would pose a clear, common threat, against which we could take united action," he says."The antinuclear movement, led passionately by scientists from the Manhattan Project, tried to do this, but the forces of the Cold War were too strong.

"Perhaps the balance of these weapons has actually helped to avoid large-scale war, as some claim," says Linschitz. "But surely we can find better, less dangerous, and certainly more productive means to do so in the future."

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