Lecture IV

The Hydrogen Bomb

As the 1940s transitioned to the 1950s, the atmosphere in the United States was turning from concern to paranoia. The FBI had passed information on espionage to the British by September 1949. The British then came to the US State Department in January 1950 with the information that Klaus Fuchs had confessed to espionage on behalf of the Soviets. This had devastating effects on the Americans, especially as Fuchs had mentioned passing information to an American for transmission to the Soviet Union. This was, of course, Harry Gold but no one knew that at the time.

Even before that, Julius Rosenberg knew that Fuchs was under suspicion and he warned his brother-in-law, David Greenglass, to leave the country, to go to Paris where he would be contacted about fleeing behind the Iron Curtain. Greenglass was very loathe to go as his wife was six months pregnant and he wanted to be in America. Then a serious accident really prevented departure as his pregnant wife went too close to a gas heater, her nightgown caught fire, he put it out with his hands and she was hospitalised with second and third degree burns.

Harry Gold was completed panicked by the news of Fuchs’s arrest and he was advised also to “disappear.” But he was afraid of what the word “disappear” meant and was afraid the Soviets would kill him. Meanwhile, the FBI learned that there was another spy at Los Alamos, a lower level person than Fuchs, and someone in the Army. This, of course, was Greenglass.

After Truman’s decision to go all out on a thermonuclear weapon, Los Alamos organised a Super committee by February 1950. The idea was to make Teller the Chairman but not to let him run any organisation. He had the responsibility for the thermonuclear programme but not administrative control. Everyone knew, in the words of Emilio Segrè, that “he was dominated by irresistible passions much stronger than even his powerful rational intellect.” Other comments were “If things were going happily, he was an exciting person to have in the group. But there were just so many problems and Edward, who could throw out intriguing new ideas, was always doing so and each new one was the important one today. It was very difficult to make progress if he was deciding, with as great frequency as he did, that one should drop that and do this.” There was “a tendency to put up with Edward, but also to ignore him in the laboratory. He didn’t get along with his ideas of what the Lab should do and yet he was tolerated. I don’t believe anybody ever told him to ‘get the hell out of here’ for his views. It was a matter of trying to balance Edward.”

In February 1950, Teller published a 72 page paper in which he used the Super as the basis for a thermonuclear weapon but with the Alarm Clock as an alternative. Remember that the Soviets had the idea of the layer cake design, which was similar. They started research in March of 1950 in Sarov, when Sakharov moved there from Moscow.

There were many problems with Teller but a major one was his absolute insistence on a megaton bomb. He would consider nothing else. The problem with any of his designs for a bomb in this range was that it was big, too big to be delivered by airplane. He considered delivery by boat but the Soviet Union was primarily a land-based country and detonating such a bomb in Leningrad would have no effect on Moscow or any of the rest of that vast territory. Robert Serber recalls passing Teller’s office one day and noticing on the blackboard a list of bomb sizes and delivery methods. One such device had delivery listed as “Backyard.” It was so big that it would destroy everything on Earth so it could be put in your backyard anywhere. He listed a thousand megaton device which would destroy Leningrad. But, delivered by boat, its effect would be limited by the curvature of the Earth. Only if detonated a mile up would it reach Moscow. A thousand megatons dropped, say, on Cape Town would destroy everything east to George and north to Carnarvon. That’s quite an area to 1

be devastated. Not one living thing within that area and severe problems much farther away due to the radiation and fallout. It was turning out to be a lot easier to create a crash programme than actually to build a weapon. Moreover, the work put into this thermonuclear bomb meant that far fewer fission bombs could be made.

The political atmosphere was growing more paranoid daily. A US general name Herbert Loper put together a report in which he made the worst possible assumptions about every possible issue. He wrote that the Soviets had a massive store of fission weapons and were well ahead in creating thermonuclear ones. None of this was even close to correct but it was widely accepted in political circles.

Stanislaw Ulam was working away with slide rule and electronic calculating machines, trying to see if the Super would work, would ignite a mass of deuterium. The calculations were crude, due to the instruments available, but everything pointed to failure for the Super. Teller was angry and accused Ulam of mistakes, which infuriated the mathematician. Teller, meanwhile, was trying desperately to recruit more scientists to Los Alamos. He blamed Ulam and his calculations for discouraging possible scientists and accused him of deliberately biasing the calculations, which was madness.

In London, Fuchs was sent to prison for the maximum time, fourteen years. The penalties in the US were much more severe as we shall see. The FBI was working feverishly to find the American contacts and they interviewed Abe Brothman and Gold in particular. Then the FBI agent Robert Lamphere went to Britain with pictures of Harry Gold and others. Fuchs identified Gold from the photos, and then FBI agents in Philadelphia searched his house. They found a map of Santa Fe, which Gold had denied ever visiting. After thinking for a few minutes. Gold confessed that he was, indeed, the man whom Fuchs had contacted. He was arraigned in May of 1950.

The arrest and arraignment of Gold panicked Julius Rosenberg yet again. He went to David Greenglass and gave him a thousand dollars, telling him to take his wife and leave the country. Mexico City, then Stockholm then Prague, then the Soviet Union. Ruth Greenglass had just come home from hospital after giving birth to their daughter and they did not want to go anywhere.

The FBI were after spies and considered all sorts of people. Ulam, Peierls, Weisskopf, and Edward Teller, were all under investigation. Teller was considered especially suspicious because of his refusal to work on implosion. That decision was the reason Fuchs wound up at Los Alamos. There were lots of incriminating leads that pointed to him and the FBI followed them all. It was Gold’s confession that removed all these physicists from suspicion but Teller and his allies, such as Lewis Strauss and William Borden did not hesitate to compile such hypothetical charges against Oppenheimer just a few years later.

Gold’s confession led to Greenglass and Julius Rosenberg now gave the couple four thousand dollars, which was a very big sum in those days. Greenglass earned about $100 a week as a machinist. He went to upstate New York, thinking to take his wife and kids and disappear into the mountains somewhere. He was followed by the FBI the entire way. He was arrested in June 1950 and he said he would not cooperate at all if his wife were arrested. He threatened suicide if that were to happen. Meanwhile Julius was arrested in July and Ethel in August. Ruth Greenglass was questioned but never arrested. I’ll talk more about their fates on Saturday.

In 1949, the Chinese Communists under Mao Zedong, took control of the Chinese mainland. Stalin, somewhat reluctantly apparently, supported him but was clearly concerned about the military superiority of the US. Then Kim Il Sung, the dictator of North Korea, proposed to Stalin to “liberate” South Korea, a step of which Stalin was very wary. Mao was even more cautious than Stalin, all fearing a war with the Americans. Kim was sure the Americans would not defend South

2

Korea and Stalin was concerned that the Chinese would make a deal with the Americans. A war in Korea would keep China well within the Soviet realm. He wanted to isolate China from the West. Kim prepared through the Spring of 1950 for a war and a surprise attack which would be won in three days. This sort of optimism about the outcome of wars has been repeated many many times. The war began on 25 June, 1950, the UN authorised a military response which the Soviets did not veto, and the North Koreans pushed almost to the end of the peninsula before the Americans and other UN forces, under Douglas MacArthur, drove them back.

Curtis LeMay had built the Strategic Air Command into a formidable force by then and offered to destroy North Korean cities, an offer that was rejected because of civilian casualties. The Americans came closer to using nuclear weapons than was apparent at the time, as MacArthur thought he could destroy all routes from China and Russia into North Korea to prevent outside intervention. By 1951, the Americans were threatening to cross the border into either China or Russia and Stalin moved large amounts of bombers and submarines into the region. The US considered then using nuclear weapons. The military Joint Chiefs were arguing for nuclear weapons to be turned over to them from civilian control. Truman finally agreed to this, in exchange for sacking MacArthur whom he did not trust or like. That was accomplished and MacArthur was removed. It appears that bombs were transferred to Guam in readiness, which never, of course, were used. But the US had sharply reduced its Army forces in return for a dependence on the atomic bomb, a weapon which proved of no use whatsoever in the Korean conflict.

Shortly before the start of the war in June 1950, Ulam and his colleagues finished a set of calculations in the possibility of the Super. They were very discouraging. Then Enrico Fermi came to Los Alamos for the summer and he and Ulam considered yet another problem. If a tank of deuterium could, in fact ever be ignited by a fission bomb, would this nuclear “burning” continue throughout the entire tank. The result of this was also disastrous for Teller’s dream. But the plans for a test series at Eniwetok called Greenhouse were being planned. This would be in Spring 1951 and two devices involving thermonuclear reactions would be explored. The first test, called Item, was a fission bomb with a small amount of D-T gas at the centre to boost the yield. It was clear that this would work, the only question being how well. The second test, called George was more ambitious. The idea here was to put the D-T mixture farther way, with the radiation from the fission bomb coming down a pipe to the gas so that one could see the results of the burning. It was thought this was bound to succeed, the analogy being to use a blast furnace to light a match. In a bomb, nearly all of the energy released is in the form of electromagnetic radiation. These are largely X-rays

SLIDE 1 Graph of radiation producedwhich travel at the speed of light. This speed is one metre every three nanoseconds, where a nanosecond is a billionth of a second. Nothing travels faster than that. The Big Bang that started our universe also generated a curve not unlike this but has cooled over the 13.7 billion years to an average temperature of only 2.7 K, or -270.5 C. You can see that radiation on your TV set when there is no signal and you just get “noise” on the screen. That noise is partly what is called the cosmic background radiation. The key to the thermonuclear bomb has come to be in the use of this largely X-ray radiation, as we shall see. Most of the energy in a fission bomb is in this radiation and nothing travels faster, certainly not the fission fragments or the neutrons.

In October 1950, the General Advisory Committee, with Oppenheimer as Chairman, visited Los Alamos to check on progress with the Super. He had offered to resign after his advice was over-ruled but that offer was rejected. There was much to consider as Teller was pushing for the establishment of a second nuclear laboratory to concentrate on the thermonuclear bomb. The Committee reviewed the Ulam and Fermi calculations but were enthusiastic about the George test, 3

as it would give some reliable results about the possibility of fusion. Teller appeared before the Committee but he had no new ideas. Teller was bitter and testified that the George test might show the Super to be impossible, in which case the laboratory could continue its research. But if the test showed that the Super was indeed possible, he thought that the laboratory was not strong enough to exploit what he called a triumph. There was considerable annoyance at what was called Teller’s autocratic and temperamental behaviour. Ulam-Fermi calculations had shown that the project was not ready for the crash programme that Teller had pushed so assiduously. Ulam’s calculations were reinforced by the first ENIAC calculations, even before the more powerful MANIAC machine was ready. The situation looked bleak for Teller and rather more hopeful for the world.

I understand that the following information is difficult but it is what makes these horrible weapons work. It is not crucial to understand for anyone to understand the devastation they can cause.

Ulam gave up working on this and set to work on improving the reliability of fission bombs, to make the best use of the still rare plutonium and U235. He came up with the idea of a staged explosion. Set off a fission bomb. The number of X-rays, neutrons and fission fragments generated is beyond enormous, with densities comparable to a solid, which is several grams per cubic centimetre. They are so hot they are a gas, but a gas, with density generally one one-thousandth of a solid, to be several thousand times denser is really quite remarkable. Ulam thought that this hugely dense gas could then compress, could squeeze, a second fissionable material, thereby causing it to explode. This was, in fact, the key insight to greatly increasing the bomb yield. This process could be repeated indefinitely. But then he thought this compression could also be used for the thermonuclear fusion process. This was an even more crucial key insight.

Ulam told Teller of this idea and then Teller added a new component to it. Ulam’s idea was to use the shock of material objects to compress the D-T mixture. But Teller understood that, in these new fission bombs with a levitated core, the temperatures were much higher than they had been in the original Fat Man bomb. That bomb was not very efficient in the use of the plutonium with only a few percent of the material actually fissioning. The bomb blew itself apart before much of it could fission. There were X-rays produced but they did not go very far as there was so much material around in the explosion that the X-rays were quickly absorbed. In other words, the bomb was not very transparent to the huge number of X-rays produced as we saw in the Slide. But these new bombs were much more efficient and much more transparent. The number of X-rays was huge and they travelled faster than the material particles of Ulam’s design. The apparent density of the radiation was again so high it was comparable to solid materials. It’s not easy to think of som many X-rays in a small space that the number is equivalent to the number of atoms in the same size of a piece of iron. But that caused Teller to think, why not use the radiation for compression rather than the materials flying out. The X-rays get there quicker and speed counts. This idea is called radiation implosion and is used in all such weapons now. Ulam’s idea of using compression from the fission bomb is really revolutionary. Teller’s substitution of radiation for material particles seems to me less revolutionary. Yet Teller went out of his way to deny Ulam any credit and always claimed that he alone was the “Father” of the H-bomb. The people at Los Alamos at the time noticed and remarked that Teller basically never spoke to Ulam after their original discussions and used almost every occasion to deny Ulam any credit for the idea. You can probably tell that I am not very fond of this man.

Teller did clearly add a very original idea. The deuterium-tritium mixture begins to “burn,” a poor term but there’s not a really better one, it is, of course, very very hot, hundreds of millions of degrees. As hot things do , it expands. It is in a container so it expands in all directions, outward and inward. Teller considered a rod or pipe in the middle with plutonium in it. The expanding gas from D -T then compressed the pipe, called the Sparkplug. It then becomes critical and fissions. This starts expanding, trapping the D-T gas between expanding toward the centre and being pushed

4

outward. This makes it react even better. The D -T reaction generates neutrons of fairly high energy, 14 MeV. These neutrons are energetic enough to fission U238 so the D -T gas mixture is surrounded by a shell of this uranium. The Sparkplug increases the yield of the bomb.

Teller’s reputation was sufficiently bad that his new ideas were greeted with considerable scepticism and it took some time for them to be accepted. His response was to denigrate his colleagues at Los Alamos and lobby in Washington for his second laboratory, dedicated solely to thermonuclear work.

Discussion of these ideas had to be put on hold by the upcoming Greenhouse test shots at Eniwetok. These were aggressive steps en route to a successful H bomb design. The first of these was the Greenhouse Dog, in May 1951. This was a production, levitated model equivalent to 81 kilotonnes. But it gave new impetus to the sparkplug idea in the George shot.

SLIDE 2, 3, 4 Slide of the George shot. Done at night.

This test was set for May 1951 and the bomb was on a tower similar to that for the original Fat Man back in 1945 at Alamogordo. It yielded the largest amount up to that time, 225 kilotons. It made a fireball more than a kilometre in diameter. It completely vaporised an 80 metre high steel tower laden with 250 tonnes of equipment. 200 kilotonnes came from the fission reaction, using the improved levitated core principle. The remaining 25 kilotonnes of explosive power came from about 20 grammes of deuterium and tritium, which is about the weight of 3 or 4 sheets of plain paper. The deuterium tritium interaction also creates quite high energy (fast) neutrons. These are then capable of fissioning the U238 tamper, adding yet more energy to the weapon. Greenhouse Item was set off a few days later with a tiny amount of the D -T gas at the centre. It was over 45 kilotonnes about twice what a non-boosted bomb would have made.

The AEC had a new Chairman, Gordon Dean, and he decided that the results of these tests required a serious review of the work on thermonuclear explosions. It was clear that the Greenhouse tests showed that a fission bomb could ignite a possible fusion bomb. He asked Oppenheimer, as head of the GAC to organise the review, and it was held in June 1951 in Princeton. Teller came, albeit reluctantly. Moreover, his description of the meeting differed substantially from the description of any other person who attended, including all the AEC Commissioners and all members of the GAC. The bickering, as reported by the AEC Chairman, was finished and a plan was now in place. This included also producing Lithium Deuteride. This material is a solid and it created the tritium for the fusion process. The use of this material, if it worked, meant that liquid deuterium was not necessary and thus a deliverable weapon could be made. There was no discussion of the morality of building such a massively destructive weapon. Fermi and Rabi had condemned the original Super idea as an evil thing.

Oppenheimer wrote

“It is my judgement in these things that when you see something that is technically sweet, you go ahead and do it and you argue about what to do about it only after you have had your technical success. That is the way it was with the atomic bomb.”

Slide 5 this quoteWhy technical promise should decide questions of politics and morality was never explained. Of course, he well knew that Soviet scientists were just as capable of making this weapon, and that the world would be a safer place if it had proved impossible. Both he and Hans Bethe realised that it

5

was now quite likely to succeed and therefore that the Russians could also do it. So it was better, they assumed, if the US got it first. Also, of course, the Korean War was raging at the time, the political situation relative to the Soviets was increasingly paranoid. and people were genuinely frightened.

Teller left the meeting with the feeling that shadowy forces were at work to thwart his dream of the bomb and these forces were centred around Oppenheimer. He was not completely alone in these feelings. William Borden was still the chief counsel to the Congress’s Joint Committee on Atomic Energy and he believed that Oppenheimer was a Soviet spy. He consulted with Lewis Strauss, who was already deeply suspicious of Oppenheimer. Back at Los Alamos, Teller spoke with the Director, Norris Bradbury, and offered to stay at the lab if he were given administrative control over the thermonuclear programme. Bradbury offered him an Assistant Directorship, remarking that Edward could argue vehemently with concepts, some of which were really good, but basically impossible to translate into hardware. He changed ideas almost daily. Things with him were always very black, or very white and never grey. Bradbury also said that, had he given that job to Teller, two thirds of his division leaders would quit, would refuse to work with Teller.

The final straw for Teller was that Marshall Holloway was appointed to run the programme, a man who was very competent but whom Teller hated. And so Teller quit the lab and left the project, assuming that Los Alamos would never succeed in making this thing work. He was, of course, very wrong.

In September 1951, the US detected the second Soviet bomb explosion, which they called Joe 2. This was a much improved weapon following Joe-1, the identical Fat Man copy from 1949. A third bomb, Joe-3, was air dropped in October and this led to the first Soviet production bomb. By 1953, the Soviet military had such weapons. Meanwhile, at Los Alamos, Holloway organised what was called the Panda Committee or the Theoretical Megaton Group. Before he left Los Alamos, Teller argued for a full-blown test of the radiation implosion bomb, the Ulam-Teller idea. He argued for July 1952 but Holloway insisted on late October, a full year away. July was summer and monsoon season and the technical requirements were such that July was likely too soon in any case. Again, Teller’s impatience was highly impractical.

One question the Group had to consider was what fuel to use. The choices were liquid deuterium, Lithium deuteride, and deuterated ammonia. The latter two were good materials, Lithium deuteride a solid at room temperature and deuterated ammonia a liquid. But no one was completely confident that they understood these materials well enough to be sure they would work satisfactorily. Moreover, Lithium deuteride required Li6, an isotope only 7% of normal lithium. How long such a separation process would take was also not known. So liquid deuterium, which was the best understood material, was the best choice. The trouble is that it is a gas at room temperature and not dense enough. To make it a liquid, it needed to be cooled to its boiling point which is 23.5 K or about -250o C. Refrigerators to reach such astonishingly cold temperatures did exist but storing and transporting such liquid was a serious problem.

The device would be large. It needed much more work and new ideas than just the Teller-Ulam concept. All of this was done at Los Alamos, despite Teller’s misgivings about the lab. It needed a fission bomb at one end and the smallest such bomb then in existence was over a metre in diameter. It needed a thick container to make sure the deuterium had a real chance to “burn” before everything vaporised. The bomb was a big container of liquid deuterium, with a fission bomb at one end and a stick of plutonium in the middle of the deuterium to act as the sparkplug.

SLIDE 6 Mike, first simplified

6

In the first, simpler slide, we can see the big tank of liquid deuterium, the material whose fusion would be the thermonuclear reaction. You can see the thick steel container, the circular fission bomb and the lead lining of the steel, meant to keep the X-rays from leaving the container.

But they were concerned that there were not enough X-rays generated and so provision to make even more was included. The density of X-rays was equivalent to a reasonable metal density, that is, about 5 gm/cm3, which is huge. Yet it was not considered enough to compress the deuterium, especially along the entire length of the liquid. They decided to increase the number of X-rays. The way to do that was to line the lead with another material. It would get so hot that the material would be ionised, which means the electrons would be completely stripped from their nuclei. These electrons would then re-combine with their nuclei and that would release X-rays in doing so. There was then the choice of material to use. Using a dense material would mean the ionisation would take some time and there were only millionths of a second. That was too slow. So they lined the lead with plastic, polyethylene and that worked. You can see this in

SLIDE 7, Detailed Mike drawingThe major problem was the liquid deuterium however. A temperature of -250 C is really cold and maintaining that was a serious problem. A physicist named James Dewar invented the solution in 1898 when he made a highly improved version of a thermos bottle. Not only did he invent refrigerators for making liquid air and even liquid hydrogen, but he made these Dewar flasks, as they came to be called, to store the liquid.

The biggest expert in low temperature physics at that time was Peter Kapitza. He had, of course, developed much of this technology when at Cambridge but he had carried that knowledge back to Moscow where he was forbidden to leave. This caused considerable concern in the American weapons community.

In 1946, an MIT physicist named Samuel Collins had developed a better liquefier than Kapitza’s. This was then used for the liquefaction of the deuterium. Another physicist, Joseph Wechsler, developed an improved Dewar flask for liquid storage. Deuterium gas would be shipped to Eniwetok and Collins’s cryostats would liquefy it on site. It would be stored in Wechsler’s Dewar flask. It was a technically complex and expensive idea but it worked.

A fission bomb blows itself apart before it can fully fission. The Nagasaki bomb’s plutonium was bigger than a grapefruit but only a golf ball size actually fissioned. Enough, of course, to kill 70,000 people. But a fusion bomb, a hydrogen bomb, can be as big as desired, just by adding more deuterium and tritium. That makes it ever more horrible.

Los Alamos estimated the yield between one and ten Megatonnes, but with the possibility of exceeding 50 Megatonnes. The most likely value was 5 Megatonnes. The Nagasaki bomb was almost 20 Kilotonnes, at least 500 times smaller. The test was scheduled for 1 November, 1952. The explosion turned out to be 700 times the Hiroshima explosion.

The construction of a hydrogen bomb, this new and insanely powerful weapon, had strong political and social implications as well, of course. Teller had left Los Alamos because he was not appointed to head the new bomb project. He had lobbied for a second lab to be constructed and it was finally approved in July 1952. Originally set at Berkeley, it was moved inland to Livermore California, where it is still in existence. Teller was, however, not made Director here either. But he felt it was “his” lab.

7

Three people who were not enthusiastic about the hydrogen bomb, Oppenheimer, James Conant and Lee DuBridge, were not reappointed to the General Advisory Council to the AEC. They were replaced by people much more enthusiastic about the new weapon. But those opposed to this new weapon saw this moment as the last opportunity to negotiate some sort of moratorium on thermonuclear weapons. Oppenheimer, Vannever Bush, Hans Bethe, James Conant all lobbied for at least a postponement of the Mike test. Especially as it was scheduled on November 1, 1952. This was a Presidential election year, and that is always scheduled on the first Tuesday in November, which was the 4th. So the test of the most powerful weapon ever imagined was to take place three days before an election. There was considerable pressure to postpone the test. Truman had decided not to run again and the race was between Dwight Eisenhower and Adlai Stevenson. The General won of course, and the bomb was detonated on the first. There was considerable sympathy for postponing the shot but it went ahead on schedule.

After the end of World War II, the US had designated the Eniwetok atoll and the Bikini atoll, some 300 km east, as testing grounds for atomic weapons. All inhabitants had been “removed.” The military was there in tremendous force with nine thousand personnel (and two thousand civilians), more than 80 aircraft including 26 B-29s and 2 B-36s, the largest plane in existence. The Navy had several destroyers and an aircraft carrier at sea, with a large fleet of smaller craft, quite the armada. Of all the islands in the atoll, the bomb was to be placed on Elugelab, the northernmost of the islands. The prevailing winds would blow the radiation out to sea. There were more than 500 monitoring stations on thirty islands around the site. A wooden tunnel 2.5 m square and 2.75 km long was built from the site and filled with helium balloons. This was designed to measure the neutron and gamma radiation from the blast without attenuation by the air. It was meant to measure the timing of the fission phase and the rise of the fusion reaction. All personnel were put on board ships so no one was left on any of the atoll’s islands. A momentary power failure changed the firing sequence by half as second but at 7 Hours, 14 minutes, and 59.4 seconds, the shot was initiated and the world was changed for the worse.

SLIDE 7 point out the parts.The amount of money and the investment of human ingenuity was very large. The use of polyethylene for the rapid creation of a plasma in order to increase the number of X-rays generated, the lead walls for containment of the explosion for a few extra microseconds, the uranium, U238, surrounding the deuterium and a thin gold lining of the uranium to reflect X-rays back into the deuterium. The uranium casing served several functions. It gave a few extra microseconds for containment before it vaporised. When it did so, some parts moved inwards but some also outwards of course and, by Newton’s 3rd Law, created an extra inward recoil pressure on the deuterium. Finally, because the neutrons created in fusion are of very high energies, the U238 will fission as well, a fission which needs a much higher energy neutron than U235. Lots of ingenuity.

A few millionths of a second after the ignition signal, X-radiation from the furiously hot fission fireball, temperatures hotter than the centre of the Sun, penetrated the polyethylene shield, heating it to a plasma of individual nuclei and electrons. The recombination of these electrons with nuclei generated enormous numbers of more X-rays which flooded onto the vaporising uranium pusher, driving the uranium inward even as it was liquifying and vaporising. This inrushing material encountered the very cold liquid deuterium, started to heat and compress it. As the deuterium was squeezed to thermonuclear temperatures and with a large flux of neutrons as well, the compression and neutrons fell upon the spark plug at the centre. The squeezing of the sparkplug is called implosion and that caused the plutonium sparkplug to fission so that the deuterium was trapped between compression from both outside and inside. The X-radiation from the fissioning sparkplug further heated the compressed deuterium, causing the deuterium nuclei to fuse, past the electrostatic 8

repulsion barrier and close enough, some thousand million millionth of a metre, to experience the nuclear or strong force. The temperature went from -250 C to 100 million C in microseconds!

SLIDE 8 Drawings of the process of fusionThis nuclear force is 137 times stronger than the electrical repulsion and causes numerous nuclear reactions to take place. Here is a list of the physical process taking place. There are many more such processes than in a fission bomb and very much more energy is released.

SLIDE 9 Physical processes.Fission also yields significant energy but, again, the fissioning core will blow itself apart before the fissioning of all the material. In this thermonuclear device, all of it will fuse yielding enormous amounts of energy. Bombs can be made as large as desired just by adding more such containers of deuterium as shown in this figure.

SLIDE 10 Multistage bombAll of the shown reactions contributed to the Mike explosion. Once the explosion broke through the thick steel casing, it expanded in seconds to a blinding white fireball, more than 5 km across. In contrast, the Hiroshima fireball was 150 metres across. The fireball also created every known element in the universe, as well as several artificial elements well beyond uranium. Two elements, isolated from the debris following the test, were the rare and unstable elements 99 and 100, with 99 and 100 protons and many isotopes. These were call 99Es254 and 100Fm257, called Einsteinium and Fermium. The wings of an observing B-36 at some 25 km from ground zero were almost instantly heated by 35 C. Within five minutes, the fireball reached a height of over 40 km with a stem of about 13 km across. Eventually the stem reached 50 km wide with a canopy of about 170 km. Radioactive mud fell, followed by heavy radioactive rain. The island, Elugelab, caught fire, turned, red, slowly shrank and within six hours had disappeared. It had been completely vaporised, leaving a crater nearly 2 km across and some 60 metres deep. It had been nearly 2 km wide. It filled with seawater. Animals and vegetation from surrounding islands also disappeared. Not a living thing was found on an island five km away. even fish looked as if they had been dropped into a hot pan, skin seared off.

SLIDE 11 Elugelab before and afterThe yield of this bomb was 10.4 Megatonnes of TNT equivalent, nearly 1000 times more powerful than the Hiroshima bomb. The neutrons generated were ten million times greater than a supernova explosion of a star. This blast would have obliterated all five boroughs of New York City.

SLIDE 12 Bomb over ManhattanA small amount of tritium had been used in this bomb. And tritium was also used as a booster for boosted fission weapons. It had been thought that large amounts of tritium would be needed and, to that end, large reactors had been built at a new plant in Savannah river South Carolina to produce it. But the Mike test had shown that large amounts of tritium were not necessary as tritium could be produced from the lithium deuteride. These large new reactors were then turned to increased production of plutonium to replace the Hanford Washington plants. They could also produce the small amounts of tritium used for the boosted fission weapons. The result of this was a large

9

decrease in the cost of producing hydrogen bombs, not particularly an outcome “devoutly to be wished”.

Edward Teller had left Los Alamos and thus was not in the Pacific for the test. He was, of course, hugely interested. He was at the University of California in Berkeley and in the basement of the Geology building. California has, of course, many earthquakes and there was a very sensitive seismograph in the building. At exactly the scheduled time, a shock wave travelled thousands of miles through the Earth to Berkeley. It took about twenty minutes and the size of the tremor indicated a very big explosion. Teller sent out telegrams, claiming paternity, with the statement “It’s a boy.” The new director of the Livermore lab, Herbert York, said that this marked “a moment when the course of the world suddenly shifted from the path it had been on to a more dangerous one. Fission bombs, destructive as they might have been, were thought of as being limited in power. Now, it seemed, we had learned how to brush even those limits aside and to build bombs whose power was boundless.”

SLIDE 13, York’s quoteThe course of history was now changed, but not in the direction of decisive US advantage that the H-bomb enthusiasts had fantasised. The reason, of course, is that physics cannot be kept secret. The way in which the universe works is open to all who are interested. Once it was clear that a given process was possible it never took long for people to make it a reality!

Things were humming along very well in Beria’s little nuclear empire. There had been two successful nuclear tests. One had been an identical copy of Fat Man, just to be sure that it would work. But the second, Joe 2 as the Americans called it, was detonated in September 1951, a full year earlier than Mike and it was a greatly improved weapon. It had a levitated core and was tritium boosted and yielded 38 kilotonnes. A month later, Joe 3, a 42 kilotonne weapon, was dropped from an airplane, proving that the Soviets now had deliverable weapons. This badly frightened the Americans and helped create the panic that led to the Ivy test series, of which Mike was the most significant.

The success of the nuclear bomb programme led to much more freedom for the scientists involved in the laboratory at Sarov. They were able to listen to the BBC and their library had a subscription to the US journal Bulletin of the Atomic Scientists, which had been started by Leo Szilard. Farther east, at Chelyabinsk, the reactors were producing large amount of U235 and Pu239. Most physical labour was done by prisoners but Beria promised them a year off their sentences for every two years worked. They were never informed of the existence or dangers of radiation and, of course, most of them did not live to finish out their sentences.

By 1952 the Soviets were working on the sloika or layer cake design of a fusion bomb which meant that they were not yet aware of the Teller-Ulam design. With Fuchs no longer in the programme, their espionage was not as effective. They were stunned by the Mike shot and its magnitude which they only heard about second hand when various US servicemen wrote letters home about their experience. Some of these made their way into the papers and, of course, the Soviets read them. They did not have the sniffer airplanes that the US had and so they tried to analyse snow samples from Siberia. But the various isotopes they needed to detect had short lifetimes and were decayed by the time they collected the snow.

At the end of February 1953, Stalin had a major stroke and it took him several days to die. Even as he lay dying a major power struggle for succession began, focused primarily on Georgi Malenkov and Lavrenti Beria. Beria started giving orders, one of which was a liberalisation of the conditions in East Germany. There had been thousands of East Germans fleeing to the West and Beria’s 10

change brought workers into the streets, started riots and the Soviets had to put down the disorder with tanks and troops.

Considerable intrigue went on in the Politburo of course and Nikita Khrushchev rallied Malenkov, Molotov, Bulganin and other Politburo members to overthrow Beira, whom all hated and feared. We must stop killing each other, was their collective decision, with the exception of Beria. He was arrested at a Politburo meeting in June 1953, and sent to prison. His organisation, the NKVD, was carefully controlled, with troops in the streets of Moscow. Beria was tried in secret in December, found guilty of course, and shot in the head in a secret cell underground. His body was burnt on the spot. When his records were opened in the summer of 1953 his entire nuclear infrastructure, Sarov, Chelyabinsk and Semipalatinsk, came to light and greatly surprised the Politburo. Nevertheless they obviously understood the importance and continued the considerable support for the programme.

By 1953 the Cold War was creating considerable fear and paranoia in the US. People in the Soviet Union had no idea of what was happening so there was little protest there. But in the US, the trial of Julius and Ethel Rosenberg attracted huge attention. David Greenglass was tried and sentenced to fifteen years in prison. Morton Sobell was sentenced to thirty years but, in April 1951, Julius and Ethel Rosenberg were sentenced to death. This was peculiar, vindictive, and indicative of the paranoid atmosphere of the time. They were convicted of espionage where the sentence was not death. Death was the sentence for treason and they were not convicted of treason. But paranoia and fear were in the air and the judge, Julius Kaufman, was keen to be promoted to the Supreme Court, which he never was. After considerable discussion in the Eisenhower administration, the sentence was upheld. Their deaths were scheduled for June 1953, despite the fact that they had two young children. Tens of thousands of protest letters were sent to the White ouse. The FBI was hoping that one or both of them would decide to confess, which they refused to do. They were both electrocuted on the evening of June 18, 1953.

July 1953 was the date scheduled for the Russian test of the sloika at Semipalatinsk. It was to be a tower shot as so many test on both sides were. The Soviet scientists had just got a copy of the US government publication, Effects of Atomic Weapons. This made them aware of the problems of radioactive fallout and the town of Semipalatinsk was only a few tens of kilometres from the test site. The test would require the evacuation of the entire city to prevent dangerous fallout from landing on civilians. It took quite some time and the test was set for 12 August, 1953. This bomb, Joe-4 as the Americans called it, was less powerful than boosted fission weapons the US possessed. The Americans analysed the fallout and realised that this bomb was similar to the Teller alarm Clock design, so that the Soviets had not come upon the Teller-Ulam solution. This Soviet approach was identical to that of the UK and of France and a dead end. This fact, that the US held a significant advantage over the Soviets should have comforted these burgeoning Cold warriors, but it did not.

Several distinguished scientists in the US, Teller of course, but also John von Neumann and John Wheeler actually believed that the Soviets were either very close to the US in weapons technology or actually ahead. Wheeler wrote “If we had started our effort in 1946 instead of 1950, I see no good reason why we could not have been four years ahead of where we are now.” This despite the fact that the Teller-Ulam design did not exist in 1946. This was clearly stated by a more reasonable statement by I. I. Rabi who said that “we could not have undertaken a major thermonuclear programme until we had some good idea of how to proceed. In my judgement, these ideas did not appear before 1950.” These profound differences of opinion were related to their different weighing of the deterrent value of such weapons. That they are a deterrent may be seen from the fact that North Korea continues to exist due to its possession of such weapons. They may be militarily useless because of their enormous destructive ability, but they are politically invaluable. Eisenhower wrote “This would be a deterrent - but if the contest to maintain this relative position

11

should have to continue indefinitely, the cost would either drive us to war - or into some form of dictatorial government. In such circumstances, we would be forced to consider whether or not our duty to future generations did not require us to initiate war at the most propitious moment that we could designate.”

SLIDE 14The anxiety was intense and needed to be alleviated. There was a scapegoat conveniently to hand.

12