Lecture III

The start of the Super

I want to start by reiterating that I use the term A bomb for a fission bomb, one that uses the splitting of the heaviest of atoms, such as uranium and plutonium.

I use the term H bomb for the opposite effect, the joining together of fusion of hydrogen.

Enrico Fermi and Edward Teller had a casual conversation in 1942, typical of the way physicists muse out loud about possible reactions. Fermi was in charge of building the first nuclear reactor,or pile, in Chicago as a step towards creating an atomic bomb. He realised that the temperatures at the centre of such an explosion would be enormous. In fact, temperatures turn out to be of the order of a 100 Million degrees. At such temperatures, hydrogen is no longer an atom because the extreme temperature will cause the electrons to be stripped away, leaving bare protons. These protons will repel one another because they have like charges. Therefore, under normal conditions, they will never get close. But at these enormous temperatures, they are moving with incredible speeds, about 6 million km/hr, which is about 6% of the speed of light. That means they move so fast they can get quite close to one another before they are repelled by their like charges. But when protons get incredibly close, they feel a new force called the nuclear force. This is the force that holds protons together to form the Carbon atoms in us. Without this force, protons could never make nuclei and we wouldn’t exist. This nuclear force is attractive and over 100 stronger than the repulsive electrical force. Thus, after such a high speed collision, the protons will stick together. Two protons in a nucleus mean we have one Helium nucleus rather than two Hydrogen nuclei. Normal helium has two protons AND two neutrons in its nucleus. An isotope of Helium called He3 has two protons and only one neutron. The neutrons are not necessary in this fusion reaction and two protons together form the most unusual isotope He2.And, because of the energy that sticks them together, the overall mass is less than the mass of the two hydrogen nuclei separately. This “loss of mass” shows up as energy, through the E = mc2 formula. And the amount of energy is enormous. Fusion of hydrogen energy is 7 or 8 times greater than the energy released in the fissioning of uranium. This doesn’t mean, though, that a hydrogen bomb is, by definition, 7 to 8 times stronger than an atom bomb. For reasons to be discussed later, it can be hundreds or thousands of time stronger.

It is this energy which fuels the Sun and the stars. In the Sun, the enormous mass of all that gas crushes protons together, rather than making them go at the speeds we discussed earlier. The temperature of 100 million degrees at the centre of a fission bomb is greater than the approximately 30 million degrees at the centre of the Sun. And the fusion (joining nuclei) or hydrogen bomb is much more powerful than a fission (splitting nuclei) uranium or plutonium bomb.

Fermi meant this comment in an offhand way, as physicists often have such discussions of principle. But Teller took it enormously seriously and changed the history of the world in doing so. Partly out of serious interest and partly because of a wounded ego when he wasn’t appointed to head the Theory Division at Los Alamos by Oppenheimer, he refused to work on the fission bomb. His absence meant that the British were called upon to provide extra help, which came in the form of Rudolf Peierls. He brought other people with him, amongst whom were both the enormously useful Otto Frisch and the enormously useful spy Klaus Fuchs.

Edward Teller was a Hungarian refugee to the US. Along with him came a group of extraordinarily creative scientists, Leo Szilard, Eugene Wigner, John von Neumann, Theodor von Kármán, George de Hevesy, and Karl and Michael Polyani. Wigner and de Hevesy won Nobel prizes. They were a remarkable and unique group. von Neumann has been described as an alien who had landed on

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Earth and learned to imitate a human. He was a child prodigy who could divide two eight digit numbers in his head and converse in ancient Greek by the time he was Six. By 8 he was interested in history and had read all 46 Volumes of the Monograph on General History, in German. School did not begin in Hungary until he was 10, so he was tutored at home, in English, French, German, and Italian. He enrolled in a Lutheran gymnasium in Budapest at ten, a school where most of the students were Jewish. All of the great Hungarians had gone to that school. He was considered the greatest mathematician of his age and in the same line as Euler, Gauss, Poincaré and Hilbert. That is exalted company indeed, the greatest mathematicians of the past 300 years.

von Neumann worked together with another brilliant mathematician, this time a Pole named Stanislaw Ulam. Ulam was also a mathematician of the first rank and he came to Los Alamos in 1943 where he met von Neumann and Teller. Teller’s dreams of the fusion bomb were plagued by a major and serious physics problem, known as inverse Compton scattering. This occurs because there are a huge number of X-rays produced in a fission explosion. And there are also all the enormous number of electrons freed from their parent hydrogen atoms at such high temperatures. There are a huge number of collisions between the electrons and the X-rays and this causes the electrons to slow down, That means the entire system cools and cooling means that the temperature is no longer high enough to get the positive protons to overcome their electrical repulsion. Thus this process ruins the possibility of creating a fusion bomb. And it remained so for quite a number of years. This was pointed out by Hans Bethe, who did become the head of the Theory Division, giving Teller an even greater chance to dislike him.

At the end of the war, George Gamow offered Teller a position at George Washington University in Washington DC, although he went to Chicago in 1946, and Ulam had a position at the University of Southern California in Los Angeles. Both men had lost relatives in the Holocaust and both had become American citizens so there was no question of returning to Europe. In LA, Ulam was struck down by a terrifically painful brain infection. Penicillin was quite a new drug at the time and he got massive doses. But he lapsed into a coma , waking a few days later and greatly improved thanks to the antibiotic. He was hugely worried about a loss of intellect due to the brain infection. The surgeon asked him to add 13 plus 8 which embarrassed him greatly. He was also asked the square root of 20 and said about 4.4. He then said, Isn’t it? And the doctor replied I think so but I don’t really know. Made him laugh. He stayed in hospital for several weeks. Just as he was leaving Paul Erdös visited. Erdös, also Hungarian, was a wonderful mathematician who had no real home base but wandered around the world visiting people he knew, staying with them for a while, doing maths there and the moving on. When he played chess with Ulam played chess and Ulam won, he decided he was alright. I don’t know if Erdös let him win or not, but it’s possible. During his recovery at home, he played solitaire. But, as a brilliant mathematician, he realised soon that he could estimate how a game would turn out just by looking at a few trial cards. Solitaire is a branching game, where many things occur in a random way. Ulam then realised that fission is very similar, where there are many possibilities for a neutron to scatter from a nucleus, to be absorbed, to change its velocity (angle and or speed), produce a fission and thus more neutrons, etc. Following all these processes was extraordinarily difficult but Ulam quickly realised that the first few thousand trials, seeing which of the possible processes might happen as you used a random number to determine what would happen to the neutron, and take the outcomes as an approximate answer to the problem. This kind of iterative process was ideal for a computer, a device then being invented as ENIAC. This name stands for Electronic Numerical Integrator and Computer and was dedicated in February 1946, in time for calculations on the Super. It was invented in the Electrical Engineering Building at the University of Pennsylvania, where I studied physics in a building just across the street about a decade later.

Ulam was invited to a conference on the Super in April 1946 and asked to return to Los Alamos. There he discussed his new idea with von Neumann and together they worked out the complete

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mathematical procedure, which they named the Monte Carlo method, after the Monaco casino. This is extensively used in calculations today and I used it for all the work on my dissertation, without knowing who had invented it.

There were great problems with the Super from the beginning and, after the war, Los Alamos was occupied making fission bombs, its primary task. First, the fusion of two protons required an enormous temperature. It had been discovered during the war that using the isotope of hydrogen called deuterium would fuse at a considerably lower temperature. So instead of p-p they would used D-D interactions. All possible, and Teller’s Super design consisted of a pipe of deuterium with an atomic bomb screwed on one end. This had all sorts of problems, such as the inverse Compton effect discussed before but also even more trivial things. The atomic bomb was surrounded by chemical explosives and a heavy uranium tamper designed to reflect neutrons back in and cause more fissions. All of this would prevent the hot stuff from escaping into the deuterium and thus preventing fusion. In addition to that, the temperature provided by current fission bombs was not even high enough to fuse D on D. That meant that a newly discovered hydrogen isotope, Tritium, would be needed. The reaction Deuterium on Tritium will fuse at the lowest temperature. But Tritium is a hydrogen isotope with 1 proton (which makes it hydrogen) and TWO neutrons. It symbol would be 1H3 meaning atomic number (number of protons) of ONE and atomic weight (number of particle in the nucleus) THREE, one proton and two neutrons. Unlike both normal hydrogen and deuterium, tritium is a radioactive isotope, with a half life of 12.3 years. I use the symbol 1H3 and 1T3 interchangeably.

It decays via

It doesn;t occur naturally and is produced from a fairly rare isotope of Lithium Li6.

The much more common isotope of Lithium which is Li 7 can also be involved, something that was not understood in the early days. This made a huge effect eventually as we shall see.

The first reaction produces energy but the second one needs energy in the form of heat in order to work. An exploding hydrogen bomb provides lots of heat energy as again we shall see.

SLIDE 36 These reactionsBy 1947, Teller was on the faculty at the University of Chicago, working with Fermi. But he spent his summers at Los Alamos, working on fission bomb improvements but most interested in the problems of thermonuclear bombs. In 1946, he had devised a different version from the ordinary super, something he called the Alarm Clock. This was a device with alternating spherical layers of fusion materials within alternating shells of fissionable material and explosives for implosion. It was, in fact, very similar to early Soviet designs, created by Andrei Sakharov which he called the 3

Sloika or Layer Cake in Russian. This new design was also heavily criticised. Fissionable material involves nuclei of uranium or plutonium, elements with lots of protons, which means high atomic number. After all Uranium is Element 92 in the Periodic Table, meaning 92 protons and Plutonium is 94. The more protons involved, the greater the X-rays produced and therefore the greater the inverse Compton losses. It was not a happy outcome. It was pretty clear that this would work, but the question was ’how well’?Teller was most interested in using the Lithium reactions shown above. Working on a hydrogen bomb was much harder than working on the fission or atomic bomb. For the later, you needed a critical mass. To see what that meant, you could assemble small amount of uranium-235 or plutonium and see how many fissions occurred. Then you could gradually increase the amount of fissionable material until you got closer and closer to a critical mass. It was important, of course, to stop before you really got there or you and the lab would disappear. At Los Alamos during the war, this assembly was called “Tickling the Dragon’s Tail.” At least one man, Louis Slotkin, died doing this when he got too close to a critical mass and the number of neutrons striking his body gave him radiation poisoning, a particularly horrible way to die. When these experiments were done, Fermi would take his group off to clim the mountain Pecos Baldy, 3800 m high and about 100 km from Los Alamos.

But with the hydrogen bomb, you could only initiate the reaction by exploding a fission bomb first, not something you’d want to do in the lab. Calculations were needed instead and computers were not yet invented. For these problems, much of the early work on computers was done to solve such problems.

The first problem to really solve was the complete fission process. During the war the work had been done by trial and error. Also, no computers existed so calculations could not be done. After the war, and with the birth of crude computing devices, such description became both possible and necessary for improved weapons design.

While the number of available cores for bombs in 1946 was only one, by 1947, the situation was “improving.” There were 13 solid all-plutonium cores, thirty-six composite cores with both U235 and plutonium, and five levitated cores, a design not yet tested. The idea behind these was discussed yesterday. They are now the standard idea.

There were enough non-nuclear components for 104 Fat Man type bombs. By the end of 1947, the US had fifty-six weapons, each powerful enough to destroy a city. They had thirty-five B-29s available to deliver them, a frighteningly large force. And, of course, they were the only country in the world to have this capability.

The General Advisory Council for the AEC had Oppenheimer as Chairman. The AEC Commissioners had basically no experience at all in the physics and so the GAC not only answered their questions but also tried to suggest policies they should try to follow. High among the suggestions was the use of nuclear power for naval propulsion and the support of basic science. But the Commission was primarily interested in making more and more weapons.

One of the Commissioners was Lewis Strauss, who had played a role since the 30s and had been Assistant Secretary of the Navy. He was also on the Board of the Institute for Advanced Study in Princeton, where Einstein, von Neumann, and Kurt Gödel were all located. Oppenheimer was trying to teach at Cal Tech but called upon so often to be in Washington that he needed to be closer to that city. When an opening at the Institute for Director became available, Strauss nominated Oppenheimer.

The creation of the AEC meant the transfer of atomic policy from the military to civilian control. In doing so, there was a new and thorough series of investigations. Oppenheimer’s file was

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particularly thick. He had had early discussions with his friend Haakon Chevalier back in 1942, and was vaguely involved with George Eltenton, a known spy. His wife Kitty had been married to Joseph Dallet, an American Communist killed fighting in Spain in the 30s. She had numerous contacts in the Party and some of those people had met Oppenheimer through her. All of this cast suspicion on him and, moreover, he had lied about Chevalier during his first interview with Security back in 1942. This was to prove devastating later in his life. Because of this it took several months to clear Oppenheimer but by August 1947 he was given a Q-clearance, the highest level for atomic secrets.

Strauss was a difficult man, as was Oppenheimer. Strauss was self-educated, never having been to university but working since he was 16. He was a very conservative Republican, dedicated to secrecy in the area of atomic science. Oppenheimer was a rather snobby intellectual, very sarcastic, very liberal politically and dedicated to openness of atomic secrets. This was not a happy combination and Strauss, prickly and defensive, grew from a friend to a deep hatred of Oppenheimer. He would play the crucial role in destroying the physicist. One of his fellow Commissioners described Strauss “If you disagree with Lewis about anything, he assumes you’re just a fool at first. But if you go on disagreeing with him, he concludes you must be a traitor.”

SLIDE 37 These wordsThe Cold War was beginning in earnest by 1947. The Air Force’s Curtis Lemay was concerned about his troops in Germany, a nation divided into four zones at the time. A simple advance of Soviet troops could cut off his supply lines entirely. Therefore, he made secret arrangements with French and Belgium military to place stocks of material and weapons on their soil. This was illegal and done solely by secret military arrangements, without the knowledge of civilian authorities. But he did what he thought necessary and wanted to do, and the hell with laws and regulations.

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at all.

By Spring 1948, the Cold War was in full swing and any attempt at collaboration with the Soviets had ended. There was a military alliance with France and the Benelux countries, soon to turn into NATO. The Marshall Plan had created some stability in Western Europe and Soviet expansion hadbeen slowed. Still, Stalin occupied eastern Europe and this served to focus US attention. The US Congress was dominated by conservative Republicans who were not terribly inclined to support the Marshall Plan and rearmament. To get this funding, numerous American officials conspired to create a significant military scare. The occupation of Prague helped but it was not sufficient to convince the isolationist Senators, and so hints were dropped that the Soviet Army might move against Berlin. The city was deep inside the Soviet Zone but divided into four sectors just as the country was. In the negotiations that led to NATO, the British delegation had Donald Maclean as a member. Because of Maclean, on April 4, 1948, a Polish newspaper published a report of these discussions which included a proposal to rearm West Germany. It is possible that such discussions were what led the Soviets to move against Berlin, establishing the blockade that was broken only by the Berlin airlift. The US did consider the possible use of nuclear weapons to lift that blockade but, fortunately, were informed that there weren’t any available. All weapons and all personnel were involved with a test series, called Sandstone, to be held at the Pacific testing ground at the Eniwetok atoll. This was meant mostly to test the new levitated core idea, designed to improve the yield with smaller amounts of fissionable material. These cores worked and are now used throughout the US arsenal, and likely others as well. The Sandstones test series, with explosions, shots they are called as if they were dollops of whisky, were X-ray on 15 April, 1948 which yielded 37 kilotons, more yield with half the Plutonium. Remember that the Nagasaki bomb was order 20 kT. Yoke, on 1 May was 49kT, the largest yield yet from any atomic weapon. This was three and a half times the Hiroshima bomb. There was also Zebra, a levitated all uranium core, with 18 kT. A Soviet warship and submarine were in the vicinity as Beria wanted someone to see a real atomic explosion. He wanted such a person or people at the first Soviet test shot to be sure it was a real atomic explosion and no one was trying to fool him.

These levitated cores used less than half the plutonium as Fat Boy and ten times less uranium than Thin Man, which used a gun to assemble. Implosion was far more effective than the gun assembly. This test series made a radical and substantial change in the military position of the US. It represented a 63 percent increase in the number of bombs available and a 75 percent increase in their yield. It marked the change from a bomb as a complicated laboratory device which required specialists to set off, to a weapon directly ready for war.

Because all the weapons and weapon experts were off in the Pacific, there was no chance to use nuclear weapons in Berlin. This blockade was a short and “test” one lasting only a few weeks. The serious blockade would occur soon.

Meanwhile, the US was preparing terrifying war plans which envisaged dropping fifty atomic bombs (basically the entire arsenal) on twenty Soviet cities. Truman hated these proposals, which called for pre-emptive use of nuclear weapons, ignored this plan and ordered the adoption of an alternate plan.

The Western powers, US, Britain, and France, the occupiers of West German, were preparing a new German currency, the Deutsch mark. The old currency was valueless and leading to inflation such as had wrecked Germany in the 20s. The US commander in West Germany, General Lucius Clay, was concerned about what to do in Berlin and he sought a common currency with the Soviets. This was not acceptable to them so Clay introduced the new Mark to West Berlin as well. This greatly damaged the value of the Soviet Mark. The result was the serious Soviet blockade of Berlin which

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began at 6 AM on 24 June, 1948. The western sectors of Berlin had 2.5 million people who now had no supplies. A serious airlift was to be instigated.

As I mentioned yesterday, the Berlin blockade was, of course, ended peacefully, by the use of an enormous number of aircraft. But it was also the time when the possible use of nuclear weapons again arose. Truman ordered the transfer of most of the Air Force’s transport planes to West Germany, against the wishes of the military. But they sent sixty B-29s to England, announcing that they were “atomic capable” and hinted they actually carried the bombs. This was completely untrue as they were not atomic capable, nor were their crews trained to deliver such weapons. But this ploy by the Air Force led Truman to consider the entire question of authority over the bombs. Despite the fervent pleas of the military for control, Truman insisted they remain in civilian hands. He said, “I don’t want some dashing lieutenant colonel to decide when would be the proper time to drop one.” In the new calculus of the atomic age, enthusiasm for using atomic weapons varied inversely with responsibility for doing so.

SLIDE 38 These words on responsibilityTruman was unwilling to use nuclear weapons and Stalin was recorded as believing that the Americans would not use them either. It was, therefore, unlikely there would be such a horrific conflict. But Stalin, having seen the failure of the Luftwaffe to supply the German army at Stalingrad by air, thought that the Americans would fail in a similar fashion. The flying was made difficult because of the 1948, 49 winter weather but the Americans were expert at instrument flying. The blockade laster until May 12, 1949 and ended peacefully.

By 1948, the Soviets were making rapid progress in Mayak. At the end of May, the first major reactor was finished. By the end of June it had reached it’s design power of 100,000 kilowatts, which is not huge. It would produce about 100 grams of plutonium in a day. That meant 10 days for a kilogram but they would need 6.2 kg to replicate Fat Man. It would take sixty days. But they ran into an unexpected problem in going from a small test reactor to a larger production one. They were aware of Wigner’s disease and had taken that into account. They did not know that a high flux of neutrons and the fission they created would generate gases such as Argon. The gases trapped inside the uranium blocks caused them to swell, change shape and therefore get stuck inside the tubes. They couldn’t then be removed for obtaining the plutonium. This problem was regarded as sabotage by Beria and he threatened the lives of the scientists. But he couldn’t do without them so all he could do was rant. The problem was fixed and it really didn’t matter at that time because the chemical plant necessary to recover the plutonium was not yet ready.

There had been a decision, forced either directly by Beria or by the intense fear he generated, to make an identical copy of Fat Man. The scientists knew all the details, mostly from Klaus Fuchs but also from their own work, and realised they could make an improved bomb, but they did not dare. Failure was not an option if you wanted to stay alive.

The Soviets had received notes from Fuchs, who had also attended the Super Conference in 1946 that Stanislaw Ulam had attended. Sakharov was put in charge of the Super problem and was given these notes so he knew where the US stood on the prospect of a thermonuclear device. It was then that he came up with the layer cake or Sloika idea. This consisted of alternating layers of light elements, deuterium and tritium with heavy elements such a U238. A plutonium core would heat the light elements to fusion temperatures, The neutrons released here would then fission the U238

releasing more neutrons. The heavy element fission would compact the deuterium and tritium causing the fusion reaction to continue. This would work, the only question being how well would it work.

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Sakharov’s name led to amusement amongst the scientists as Sakhar means sugar in Russian. So there were lots of puns on his name.

Sakharov was working in Moscow, spending time on pure physics research and on weapons such as the Sloika. He was asked to move to Sarov and work permanently on weapons and he hesitated. A call from Beria made it clear he had no choice and so he moved.

Back in the US, the Soviet espionage during the war was becoming ever clearer. A young FBI agent, Robert Lamphere, started working on Soviet code analysis in Washington. This was very difficult but the Finns had found a partly burned codebook in 1944 and had sold it to the Americans. The Soviets had changed the system in 1945, knowing that such a book had been found, but still the Americans had a key to spying in 1944 and 1945. Max Elitcher’s name appeared, even though he never was actually a spy. But he had been contacted by Julius Rosenberg and that started the trail. He was also an even more serious contact to Morton Sobell. The first name of a woman ETHEL also appeared although, at first, there was no surname. The FBI started following Elitcher and traced him to Sobell’s house.

The Berlin airlift led the US Airforce to review many of its procedures and training. In doing so, they found that there were basically no B29s and crews capable of dropping nuclear weapons, as they were supposed to be able to do. This caused the Strategic Air Command to sack the general in charge and that’s when Curtis Lemay was appointed to the post. A very tough and angry man, he started working to make sure that nuclear weapons could be delivered with accuracy where they were intended to go.

Winston Churchill, who had an undying hatred for the Soviets, was out of power at the time but had urged a much more major confrontation. He said that, if and when the Soviets got nuclear weapons, war would become a certainty. Therefore, the US should tell the Soviets to leave East Germany entirely, withdraw to the Polish frontier, or else. Else meant atomic bombs on Russian cities. But deterrence was already, de facto, in place and only Truman viewed the use of these weapons as a horror to be avoided, if possible.

The race for weapons was heating and by the end of February 1949, the Soviets had enough plutonium for a bomb. It was moved from Mayak to Sarov for assembly. It had been rushed through so quickly that no concern for health was made. Many people were exposed to radiation and prisoners and soldiers died.

When the project leaders told Stalin in Moscow that they were ready for a test, he told them to stop and wait until they had produced enough plutonium for a second bomb. He was afraid that testing a bomb would cause the Americans to attack his country and he would not have any bomb with which to retaliate. The fact that he had no means to deliver such a weapon did not seem to matter. But a second core could be ready by August and the test was postponed.

And so, in late summer 1949, the first Soviet bomb left Sarov for Kazakhstan and an arid desert northwest of Semipalatinsk, a place I have visited. It was a precise copy of the Fat Man bomb, the only thing that Beria would allow. Beria was there along with the two men he had sent to Bikini to witness the American bombs. On August 29, the bomb was on a tower and ready. As at Trinity, there was rain and the test was postponed for an hour. But it did work and was about 20 kilotons in power, roughly the same as the Nagasaki bomb. Beria was originally overjoyed but then, suspicious as always, called his Bikini observers who were in a different location. When they corroborated the explosion was a nuclear one, he was overjoyed and called Stalin. But the dictator would allow no announcement of the test until he had more bombs in his arsenal.

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SLIDE 39The Americans had run the Sandstone series of tests in 1948. These were the Bikini tests that the Soviets had spied upon. It was during these tests that the US developed techniques to detect radiation in the atmosphere that was above normal levels, radiation which always exist. There is radioactivity around us all the time and we have evolved so as to be relatively immune to these levels. But the fallout from a bomb is very much greater. And, in September 1949, a B29 over the Pacific picked up radioactivity that was some 300 times normal. Moreover, the isotopes, when analysed, showed this was definitely the result of a fission bomb. The radioactive cloud blew east of course, as high altitude winds are almost always westerly. A week later, the British noticed high levels of radioactivity just north of Scotland and off the Norwegian coast. The cloud actually split in two and the British detected the northern half. The southern half drifted down over Washington and hung there. Rain brought the radiation to the ground. I was a child in Philadelphia at the time and therefore was also exposed to what became known as radioactive fallout. It was quickly clear that the Soviets had the bomb and it was dubbed Joe-1 after Stalin.

It took until the 23rd of September, some three weeks after the detection of the test, before the US announced publicly that the Soviets had exploded a bomb. The Americans at that time had an arsenal of about 100 such bombs but they no longer had a monopoly. The world had changed.

The US had made a huge mistake in underestimating the quality of Russian physicists. Kurchatov, Sakharov, Flerov, Zeldovich, Khariton, Tamm, and many others were absolutely first-rate talents. It is true there was significant espionage but that has been estimated to make about a six to twelve month difference. It saved some mis-steps but there was so much suspicion that such information was misleading that everything to be investigated from scratch. The Soviet bomb made the Americans certain that there had been significant espionage, and the hunt was on for the culprits. The Canadian spying of Alan Nunn May was out in the open, Elitcher had been followed, Sobell identified, the name Ethel found. The FBI agent Lamphere found a summary of a theoretical paper on gaseous diffusion which showed that there were spies in the US and not just in Canada. It became clear that the paper was written by Klaus Fuchs. They did not suspect, at first, that he was a spy but it soon became clear as they found references to his sister, and evidence from captured Gestapo documents that he had been a member of the German Communist Party. By this time, Fuchs was back in Britain working at Harwell on the British version of a bomb. It was also clear that there had been a spy in the British Embassy in Washington, which turned out to be Donald Maclean.

The problem of the bomb, the Soviet Union, espionage and the Berlin blockade were all symptoms of the increasing Cold War. Strauss on the AEC, was becoming increasingly angry with Oppenheimer, despite having nominated him for the Institute job. In the Senate, there was a Joint Committee on Atomic Energy, chaired by a very right-wing Republican with the startling name of Bourke Hickenlooper. He had an even more reactionary figure as his chief counsel, a young lawyer named William Borden. Borden had already written a book called There will Be No Time, in which he prophesied the start of World War III.

The entire emphasis now was on more bombs and the idea of a “quantum jump meaning thermonuclear weapons. The US was already planning another series of tests at Eniwetok, the Greenhouse tests. These were to be of implosion bombs with a levitated core to boost the output.

SLIDE 40 Levitated Core with booster (repeat)

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As a step toward a thermonuclear bomb, the Greenhouse tests would have a small amount of deuterium and tritium as additional boost. A serious fusion test would require large amounts of deuterium and this would have to be liquid (gas not being dense enough). Deuterium becomes liquid at about 23 Kelvins which is -250 C, not easily attainable.

Here we begin the discussion of why the hydrogen bomb can be so much greater than the 7 to 8 times energy boost per fusion. In a fission weapon, there is a limit to the size of the bomb. Fissioning stops when the bomb blows up and separates the material enough for no more fission to take place. This is of the order of a 100 kilotons or so. But a thermonuclear bomb is quite different. If you add more hydrogen (deuterium or tritium of course) you get more power. You could make a bomb the size of the Sun if you wanted. The Alarm Clock design of Teller, the only one available at the time, was enormous and could certainly never be carried by an airplane. It would have to be on a train or a boat, which, for a land-based empire like the Soviet Union, was not very attractive. Still, the Soviet bomb test gave great impetus to many American politicians to move ahead with a Super bomb.

It was not only the more conservative politicians, but also the more conservative scientists who thought the hydrogen bomb should be pushed. The foremost of these was the most politically conscious scientist, Ernest Lawrence. He had a close ally in Luis Alvarez, a remarkably bright young man who won the Nobel Prize in Physics in 1968. Along with his geologist son Walter, he was part of the discovery of the meteor impact in the Gulf of Mexico which precipitated the death of the dinosaurs.

Lawrence and Alvarez went to Los Alamos and spoke to Teller, Ulam, the Associate Director John Manley, George Gamow, and the Head of the Theoretical Division, J. Carson Mark. The problem was that the calculations to see if thermonuclear burning could be achieved, were hugely complex. Remember that you needed a fission bomb’s heat to initiate the reaction and not something you could do in the lab!

Remember also that there were no serious computers at the time, the only machine, ENIAC, was not capable enough. But von Neumann was building a machine dubbed MANIAC (for Mathematical Analyser, Numerical Integrator, And Computer) at Princeton and a copy was being made at Los Alamos. Lawrence was pushing for stopping plutonium production in the Hanford reactors and pushing for tritium production instead. You couldn’t do both at the same time. He also proposed encouraging the Canadians, who had a heavy water reactor at Chalk River, to produce tritium. They pointed out that the Soviets had Peter Kapitza, one of the world’s greatest experts on such light elements as deuterium and tritium. The presence of a small heavy water reactor in Iran was major impetus in closing the P5+1 deal with Iran, which resulted in the destruction of that reactor.

The two men went to Washington and Lawrence found little enthusiasm amongst the civilian authorities but a much warmer reception with the military. When the Joint Chiefs of Staff, the military top brass, testified before Congress, they emphasised that the new Soviet bomb meant that the US needed to push ahead with the hydrogen bomb, that defence was impossible and offence was critical. The development of nuclear weapons, including thermonuclear, meant a complete change in military thinking. Previous to nuclear weapons, if attacked, one could respond defensively, using, for example, the immense industrial strength of the US to create enough weapons to win. But an attack with nuclear weapons would destroy a country and its industrial capacity and so one needed the weapons in advance. And there was great debate about their pre-emptive use. There was great moral concern and debate on this issue. Teller, in particular, argued strongly that the Soviet development of a Super bomb before the US would make the US situation hopeless. But the US had, at that time, about 170 nuclear bombs so why they should be hopeless was very unclear.

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The rest of 1949 was filled with discussion, debate, doubts and conflict. What would it mean to fight a thermonuclear war, a war in which a city of the size of New York could be destroyed by a single bomb, with 8 or 10 million dead. Winning? There would not be a world worth having under such circumstances. Teller, Alvarez, Lawrence were pushing hard. James Conant was definitely opposed. Many physicists, Oppenheimer, Bethe, Fermi, Placzek, Weisskopf Szilard, Rabi, amongst the greatest names of 20th century science, were caught in what felt like a terrible dilemma. But the military and the Congress were strongly for what Teller still called the Super.

The General Advisory Committee of the AEC met at the end of October 1949 and went through very serious and difficult discussions. The major part of their report considered purely the technical problems and possibilities of a thermonuclear weapon. That was their responsibility. But they didn’t stop there as the moral concerns pressed heavily on them. There was a majority annex signed by most of the members including Oppenheimer, the Chairman. The annex looked at possible global effect of radioactivity and feared that this might become a genocidal weapon. They wrote that the US development would not prevent the Soviets from pursuing one. Moreover, if the Soviets should develop such a bomb, the US had a superior number of fission bombs with which to respond. They also saw a unique opportunity of providing an example of some limitations on the totality of war and thus of limiting the fear and arousing the hopes of mankind.

There was a minority report provided by Rabi and Fermi, which also opposed the development. They thought that Truman should announce the US renunciation of this weapon and invite the other nations to join in a pledge not to build such hideous weapons. If such an effort should prove impossible then the US would be justified in pursuing this new bomb. But they criticised the Super idea of Teller in very strong language. “By its very nature it cannot be confined to a military objective but becomes a weapon which in practical effect is almost one of genocide.”

“The fact that no limits exist to the destructiveness of this weapon makes its very existence and the knowledge of its construction a danger to humanity as a whole. It is necessarily an evil thing considered in any light.”

SLIDE 41 All these words by Fermi and RabiThe members of the GAC had nearly all worked for international control of atomic energy. They did not view the Soviet Union as a remorseless, obdurate enemy, bent on world domination. But their opponents, Teller, Strauss, Borden and many Senators, did indeed view the Soviets as exactly that. They were afraid of an enemy they considered ruthless, with large and powerful armies. The very fears of destruction expressed by the GAC were exactly the impetus that encouraged them to pursue this weapon. They understood the incredible power of the bomb as a potential threat and imagined the consequences if it were used on the United States. One of the most important Senators on the Joint Committee on Atomic Energy, Brien McMahon, was furious. He thought that war with the Soviet Union was inevitable and it was necessary to “blow them off the face of the Earth, quick, before they do the same to us - and we haven’t much time. He echoed the lawyer, Borden, in his book There Will Be No Time.

Teller and Alvarez blamed Oppenheimer for the report and bet that, if they did not go ahead, he would be a Soviet prisoner of war within five years. A bit dramatic that. The AEC received the report of the GAC and voted 3-2 in favour if it, preventing a crash program. Then it went to Truman, who had on his desk The Buck Stops Here. He forbade all further debate and appointed a committee of the Secretary of State Dean Acheson,the Secretary of Defence Louis Johnson who replaced James Forrestal after Forrestal committed suicide, and the Chairman of the Atomic Energy Commission David Lilienthal. The major figure was Acheson, who saw no hope in getting the 11

Soviets to agree, even on the time of day as he put it. The end of the world would be nigh if the Soviet Union beat the US to a thermonuclear bomb. But there is also the possibility that he was heavily influenced by domestic politics as he thought the Senate, a very conservative body, would make huge propaganda of a contrary decision. There would be serious Senate repercussions if there was a decision not to build the thermonuclear bomb. On January 19, the President announced to the world that he was directing the Atomic Energy Commission to continue its work on all forms of atomic weapons, including the so-called hydrogen or super-bomb. It appears, in testimony a few years later, that Truman had decided early that it was necessary to build this horrific weapon. And that he had used the lengthy and painful debates as a public-relations ploy to make it look as if he made serious considerations of opposing viewpoints. But Truman announcing that we were going to make a hydrogen bomb occurred well before any scientists knew how to do so. Teller, who advised Truman that he knew how to do this, was lying. The clock had started on a new, ultimate arms race!

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