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Master 2 - NPAC 2009/10 Noyaux Particules Astroparticules Cosmologie (Le Noyau de l'Atome • Complement)

De Paris aHiroshima (1900-1945)

Miguel Marques LPC-Caen (France) [email protected]

De Paris aManhattan (1900-1939)

De Manhattan aHiroshima (1939-1945) PART II: THE MAKING OF THE BOMB

Emilio Segr´e: “In an enterprise such as the building of the atomic bomb, all the committees, the politicking and the plans would have come to naught if a few unpredictable cross sections had been different from what they are by a factor of two”.

Gil Elliot: “I see that as human beings we have two great impulses in us. One is to participate in life, which ends in the giving of life. The other is to avoid death, which ends tragically in the giving of death”.

C /2009/\De Paris aHiroshima" F.M. Marqu es(0/34) P A NPAC L E C N THORIUM & URANIUMS

’39 Feb Bohr: “It is a relief that we are now rid of those transuranians!” However, under bombardment U and Th can fission, but they can also capture the neutron at about 25 eV and : some transuranians were real!

Frisch: “Thorium did not respond to the magic of paraffin”. Below 1 MeV, only fissions... “Why should both Th(90)/U(92) ‘liquid drops’ have different responses to slow ?”

U235 was discovered in 1935, and measured to be 1/140 of Uranium by Alfred Nier in 1938. Bohr: “U235 must be responsible for slow-neutron fis- sion”. But why do they behave differently?

Changing odd to even number releases +1 MeV... ’39 Mar Fermi, Joliot, Szilard: Ra/Be+H2O+U Meitner and Frisch had calculated a 200 MeV gives “about 2 neutrons/fission”. slows output, but the input needed was 6 MeV : down neutrons below the U238 capture resonance at 25 eV, but it captures them too... The next com- {U238/Th232 + n}∗ ≈ +5.5 MeV mon material is graphite . If unsuitable, the “next +n U235 −→ { 236 }∗ ≈ +6.5 MeV best guess might be ”. Wigner, Szilard and Fermi meet Pegram: “We Any neutron at all would fission U235! must inform the US government”... C /2009/\De Paris aHiroshima" F.M. Marqu es(1/34) P A NPAC L E C N WAR BREAKS OUT

’39 Mar Teller: “We tried to convince Bohr, but he insisted that we would never succeed in produc- ing nuclear energy, and that secrecy must never be introduced into physics”. Bohr: “Separating large amounts of U235 can never be done, unless you turn the US into a huge factory ”.

’39 Apr Joliot in : ‘Number of neutrons liberated in the fission of U’! He finds 3.5/fission.

’39 Jul Szilard, Teller and Wigner worry about the Belgians selling U to Germany. Szilard re- Sep 1 But Hitler invades Poland. FDR appeals members that Einstein the belligerents to refrain from bombing civilians ! knows the Queen of Bel- “No theory of war can justify it”... gium... Wigner suggests ’39 Sep The Germans discuss the Physical Re- to send Einstein’s letter view of Bohr-Wheeler. Hahn argues that U235 through the State. Sachs: separation is almost impossible. Heisenberg dis- “These matters concern cusses a moderator for ‘U burner’ and separation the White House”. for bomb. Harteck considers layering U and mod- ’39 Aug Szilard and Sachs extend Einstein’s letter erator (like Fermi-Szilard), but using D2O . Bagge and wait for one hour with Roosevelt ... will measure slowing down of neutrons by D. The War Office takes over the KWI. C /2009/\De Paris aHiroshima" F.M. Marqu es(2/34) P A NPAC L E C N

’40 Feb Frisch wonders how much U235 should be separated. Following Bohr, Peierls assumes that, if U235 will fission whatever the neutron, the fission cross-section will be the geometric one:

MC(U235) ≈ 1 kg Smaller than a golf ball for Uranium! Peierls: “80 generations of neutrons (before U235 atoms were separated by the explosion) gave T as hot as the RC = f{ ρ , σsca , σcap , σfis } ⇒ MC interior of the Sun, pressures greater than the cen- ter of the Earth... we were staggered”. Frisch: ’39 Sep “100,000 Clusius tubes could produce 1 kg of U235 works on the cavity mag- in weeks”. netron... He has invited Frisch to work on ther- ’40 Mar Oliphant asks them to write it all down. mal diffusion with a Clu- “Memorandum on the properties of a radioactive sius tube, and Peierls on ‘super-bomb’ : a 5 kg bomb would be equivalent to an improvement of Per- several KT of dynamite... a byproduct of the explo- rin’s critical mass for- sion would be radiation, equivalent to 100 tons of mula. Plugging in the Radium, that would kill large numbers of civilians , cross-sections of natural making it unsuitable as a weapon for use by this U and unmoderated fast country... if Germany makes this weapon, it must neutrons leads to MC(U) be realised that no shelters are possible, the only of several tons... reply is a counter-threat ”... C /2009/\De Paris aHiroshima" F.M. Marqu es(3/34) P A NPAC L E C N HEAVY WATER

’40 Jan Heisenberg: “heavy water or graphite should work”. Harteck builds a Clusius tube and separates of Xenon. The world’s source of D2O is Norsk Hydro . Germany offers 120,000$ for all available stock (200 l) plus 100 l/month. They produce 10 l/month and want to know why!

’40 Feb Joliot wants the water. Dautry learns about the German offer and proposes to buy half the stock, but when the Norwegians hear what purpose the water might serve they volunteer the whole! The 26 cans of D2O reach Paris.

’40 Mar Nier sepa- rates a sample of U235 ’40 Apr Germany invades Norway and Denmark. with his spectrograph Bohr chooses to stay. Norsk Hydro becomes Ger- and sends it by letter man: they report to Harteck an expansion to in- to Dunning: he con- crease D2O production to 1.5 tons/year... firms that U235 is re- sponsible for the slow- ’40 Jun Kurchatov reports to Physical Review a neutron fission of Ura- rare spontaneous fissioning in U. “The complete nium! U235 fission lack of any American response to the discovery cross-section is about convinced the Russians that there must be a big 139 times higher... secret project under way in the US”.

C /2009/\De Paris aHiroshima" F.M. Marqu es(4/34) P A NPAC L E C N COMMITTEES

’40 Apr FDR has created the Uranium Commit- ’40 Jun Simon, a German emigr´e, proposes tee. Szilard: “But for months we heard nothing ‘ordinary’ diffusion : lighter gases diffuse faster. from Washington”. Four tons of graphite reach Columbia. Fermi: “The started looking like coal miners”. They obtain a small σcap(C) !

The Germans occupy Paris: they have the D2O factory, tons of U from Belgian Congo... and Jo- liot’s ! Failed test with U+H2O/paraffin.

’41 Jan Bothe measures σcap(C) at more than ’40 Jun : “America will enter the twice Fermi’s value: neutron-absorbing impuri- war sooner or later and we are not prepared”. He ties? Hopefully, Szilard/Pegram have asked Fermi proposes the NDRC , enlists Conant and absorbs to keep it secret: Germany abandons graphite ! the Uranium Committee. G.P. Thomson chooses ’41 Apr The Japanese Army authorizes Nishina’s MAUD as secret name for the British committee. research on atomic bomb at RIKEN. C /2009/\De Paris aHiroshima" F.M. Marqu es(5/34) P A NPAC L E C N PLUTO: THE GOD OF THE DEAD

’40 May Turner asks Szilard permission to send ’40 May McMillan-Abelson isolate a pure Ura- “Atomic energy from U238” to Physical Review: nium sample and demonstrate that the 2.3 day activity increases as the 23-min activity declines. 23994 Á β− [Pu] “Radioactive element 93 ” to Physical Review! 239 − 93 Á β [Np] ’41 Jan Seaborg 23592 23692 23792 23892 23992 [U] and Segr`e bom- (0.7%) (99.3%) bard 1 kg of UNH: “one α activity Szilard: “It might eventually turn out to be a very can be separated important contribution, keep it secret”. from all known elements: it must ’39 Feb McMillan is measuring the range of fis- be due to the new sion fragments: a stack of cigarette papers on a element 94 ”! layer of Uranium oxide, backed with filter paper, bombarded with slow neutrons. “Nothing interest- ’41 Mar They ing in the cigarette papers... but the filter paper un- separate less than der the stack showed something very interesting”: 1 µg of (93)239, two activities different from those of the fission and set it aside fragments that had recoiled away! until it decays to (94)239. They irradiate the sample with slow One of them (23 min) is U239, already identified neutrons and observe the fission of , by Hahn-Meitner-Strassmann. The other one is named for Pluto, the 9th planet... They calculate 2.3 days: the beta-decay of element 93? σfis(Pu) about twice that of U235! C /2009/\De Paris aHiroshima" F.M. Marqu es(6/34) P A NPAC L E C N OPERATION BARBAROSSA

’41 Mar Lawrence: “The British are ahead even Conant: “Only efforts likely to yield results within if we have the most, and the best of the world’s nu- months were worthy of consideration. Physicists clear physicists”. Bush forms a review group under talked about a new world, but I suggested that until : Nazi Germany was defeated all our energies should be concentrated on one immediate objective”. –! Radioactive dust, 1 year after . –! A power source, about 3 years after. ’41 Jul The asks the US to –! A bomb, U235 or Pu239, not before 1945. build a diffusion plant . Oliphant: “You have no right to work on power plants, you must concen- Bush moves to the OSRD, the NDRC to Conant. trate every effort on the bomb. It will cost 25M$ Jun 22 Hitler attacks the USSR : Blitzkrieg inva- and we don’t have the money, it is up to you!” sion “to crush Soviet Russia before winter”! ’41 Oct NDRC explosives expert, Kistiakowsky: “It can be made to work”. He convinces Conant, Oliphant convices Lawrence, who convinces Comp- ton... Bush carries the MAUD report to FDR.

Roosevelt wants to restrict nuclear-weapons policy to a small group under his authority: Vice Pres- ident Wallace, Secretary of War Stimson, Army Chief of Staff Marshall, Bush and Conant. No Congress, no scientists . A separate, secret state, mostly due to “fear of a thousand-year Reich made invulnerable with atomic bombs”...

C /2009/\De Paris aHiroshima" F.M. Marqu es(7/34) P A NPAC L E C N THE BOHR-HEISENBERG MEETING

’41 Sep Heisenberg layers D2O with U oxide and finds some neutron increase. He learns from von Weizs¨ackerthat a chain reaction in U will breed element 94. “We saw an open road ahead of us, leading to the bomb”... He decides to talk to Bohr!

’41 Oct Heisenberg and von Weizs¨ackerattend a scientific meeting in Copenhagen. Bohr receives him at his house. They take a walk.

Heisenberg : “Bohr was under surveillance, I tried to preclude putting my life into danger”. He asked if it was right for physicists to work on “the Ura- nium problem in wartime, leading potentially to grave consequences”. Bohr answered asking if a bomb really was possible. He answered that a “ter- Oppenheimer: “Bohr had the impression that they rific technical effort” would be needed, which he came less to tell what they knew than to see if Bohr hoped could not be realized in the present war. knew anything that they did not”. Peierls: “He had agreed to sup with the devil, and perhaps he found “Bohr was shocked , obviously assuming that I had that there was not a long enough spoon”. intended to convey to him that we had made great progress in atomic weapons. I tried to correct this Heisenberg passes to Bohr a drawing of the D2O false impression, but I did not succeed... I was very reactor he is working to build! Willing or not, he unhappy about the result of this conversation”. accelerates Allied efforts to build a bomb.

C /2009/\De Paris aHiroshima" F.M. Marqu es(8/34) P A NPAC L E C N TORA! TORA! TORA!

’41 Oct Compton goes on tour: Fermi estimates ’41 Dec Urey gaseous diffusion at Columbia, less than 50 kg for a bomb; Dunning makes progress Lawrence electromagnetic separation at Berkeley, with brass barrier diffusion; Wigner is afraid that Compton theoretical studies in Chicago... the Nazis make the bomb first; Seaborg plans a large-scale, remote-controlled plant for separating 94 from U... Lawrence brings Oppenheimer to work on “the destructiveness of the bomb”.

’41 Nov Bush delivers Compton’s report to FDR: “A fission bomb of superlative destructive power will result from bringing quickly together no more than 4 kg of U235 constrained in tamper”... OK!

Dec 7 The Japanese attack Pearl Harbor ! Ya- mamoto had studied at Harvard and knew US’s strength, but if war had to come he meant “to give a fatal blow to the enemy fleet at the outset”, hoping he could win a year. Torpedos had been modified for a shallower drop at Nagasaki ... C /2009/\De Paris aHiroshima" F.M. Marqu es(9/34) P A NPAC L E C N THE EXPONENTIAL PILES

’41 Sep Like the fast-neutron chain reaction in U235, the slow-neutron one on natural U needs a critical mass. Fermi proposes a series of sub- critical experiments: a ‘pile’ of 30 tons of graphite confining 8 tons of U oxide. He hires a football team to handle the 40 kg U cans! The 1st lattice leads to a ‘reproduction factor k’ of 0.87: “It was bad, but we had a firm point to start from”...

’42 Apr Before moving, Fermi reduces moisture (neutron absorption) to 0.03% and gets k=0.92! In Chicago, Compton takes over a squash court and Allison builds a smaller pile: k=0.94...

’42 May Fermi plans a full-scale chain-reacting pile when one of the piles indicates k=0.995: higher-quality graphite and pure U metal should push k above 1. Besides Betty Compton, none of the other wives is supposed to know about her hus- band’s work: they will find out after the war.

’41 Dec The projects are scattered at Columbia, ’42 Aug Fermi reports a probable k close to 1.04 ! Princeton, Chicago and Berkeley, no one wants to They work on control-rod design and vacuum prop- move: Compton chooses Chicago . New ‘Met Lab’. erties of cloth (exclude n-absorbing air). C /2009/\De Paris aHiroshima" F.M. Marqu es(10/34) P A NPAC L E C N OPERATION TYPHOON

’41 Oct Objective Moscow: “After 3 months of preparations, we finally have the possibility to crush our enemy”. But on Dec 6, at 50 km and −40 ◦C, Zhukov counterattacks across 500 km. For the first time the Blitzkrieg fails: 1 million casual- ties. Churchill: “The long war was certain”.

’41 Dec German economy has reached the lim- its of its expansion. Director of Reich military re- search: “The U studies can be justified only if there is a certainty of getting some benefit in the near fu- ture”. The War Office reduces their priority.

’42 Feb The Research Council invites G¨oring, Bormann, Himmler, Keitel, Speer... to a presen- tation. But they send the wrong program and no one comes! Basic knowledge of a Plutonium bomb is at hand, but money and materials are lacking.

’42 Jun Speer proposes “ larger than those in the US”. Heisenberg: “But do not count on a bomb for 3 or 4 years”. Speer: “Then continue to work on an Uranium motor” (the heavy-water pile)... The German bomb is over .

C /2009/\De Paris aHiroshima" F.M. Marqu es(11/34) P A NPAC L E C N FEAR

’42 Mar Bush: “We may be engaged in a race, but I have no indication of the enemy program”. Co- nant: “If we discard some methods now, we may be betting on the slower horse. And the Germans cannot be far behind since they started in 1939 with the same initial facts”. Time , not money, is be- coming the limiting factor.

’42 Jul Oppenheimer gathers together at Berkeley theoreticians. They let the H-bomb distract them: they name it the Super ! Bethe: “Fast-neutron fis- sion needed experiment more than theory”. Teller suggests the possibility that the bombs might ignite the Earth’s oceans or atmosphere and burn up the world! Bethe: “I very soon found some unjustified assumptions in Teller’s calculations”...

’42 Sep The program needs a stronger leader: ‘General’ Groves . He immediately solves the Project leaders are no longer allowed to fly. Szi- worst problems: buy Belgian Uranium, land for lard is convinced that authoritarian organization is ‘site X’... At the Met Lab: “There is no objection no way to do science . Fermi: “If we brought the to a wrong decision with quick results. If there is a bomb to them all ready-made on a silver platter, choice between two methods, one of which is good there would still be a 50% chance that they would and the other looks promising, then build both”! mess it up”. C /2009/\De Paris aHiroshima" F.M. Marqu es(12/34) P A NPAC L E C N PLUTONIUM

’42 Apr Seaborg must pull a dime of Pu out of 2 tons of U and highly radioac- tive fission products! Pu precipitates differently at different oxidation states : large number of oxidation- reduction cycles. To prove it at industrial-scale, he irradiates 150 kg batches of UNH for months. They use a quartz fiber to weigh: “Invisible mate- rial was being weighed with an invisible balance”!

Aug 20 “Today our microchemists isolated pure element 94 for the first time! Cunningham and Werner set about fuming a solution containing about 1 µg of Pu239 ... and the reduced 94 precip- itated free of carrier material. It is the first time that element 94 has been beheld by the eye of man”.

LIFE 1946

C /2009/\De Paris aHiroshima" F.M. Marqu es(13/34) P A NPAC L E C N CHICAGO PILE 1

’42 Nov The pile-building workers go on strike: Fermi proposes to Compton the squash court! They discuss the various hand and automatic control rods... Compton says ‘OK’ without informing the president of the University: he is risking a small Chernobyl in the midst of a crowded city!

The crews alternate layers of ‘dead’ graphite with layers of bricks drilled and loaded with Uranium pseudospheres. They have to line up the slots for the 10 Cadmium control rods, which are kept in- side and locked : only Anderson and Zinn have the keys. Better graphite reduces the originally de- signed 76-layer sphere to a 56/57-layer ellipsoid...

Dec 2 CP-1, unshielded and uncooled, has cost 1M$. Fermi has been matching its responses with his estimates, and is confident he will be able to control it when the chain reaction diverges. It looks like a black beehive : neutrons are its bees...

C /2009/\De Paris aHiroshima" F.M. Marqu es(14/34) P A NPAC L E C N THE LANGUAGE OF THE COUNTER

The last rod is removed step by step. Fermi notes – You’ll be interested to know that the Italian nav- the numbers. He asks that ZIP be slid in. To Weil: igator has just landed in the new world. “Take the control rod out 12 inches”. To Compton: – Is that so... Were the natives friendly? “This is going to do it”. k=1.0006 : 4.5 min later, – Everyone landed safe and happy. when it seemed that the anxiety was too much to bear, he ordered ‘ZIP in!’. Left uncontrolled for 90 Szilard: “Fermi and I stayed there alone. We shook min, it would have reached 1 Gwatt, after killing hands and I said I thought this day would go down everyone in the room and melting down... as a black day in the history of mankind”...

C /2009/\De Paris aHiroshima" F.M. Marqu es(15/34) P A NPAC L E C N THE

The US Army Corps of Engineers

’42 Nov Inland and isolated: • Los Alamos , weapons research • Oak Ridge, Uranium enrichment • Hanford, Plutonium production

C /2009/\De Paris aHiroshima" F.M. Marqu es(16/34) P A NPAC L E C N ROBERT OPPENHEIMER

“Emilio”, Fermi joked with Segr`e after visiting Berkeley, “I am getting rusty and old. I cannot follow the highbrow theory developed by Oppen- heimer’s pupils anymore. I went to their seminar and was depressed by my inability to understand them. Only the last sentence cheered me up; it was: ‘and this is Fermi’s theory of beta decay’.”

’42 Oct Oppenheimer: “We needed a central lab- oratory devoted wholly to the bomb ”. And Groves needs a leader. Lawrence and Compton have al- ready important roles, Urey is a chemist... Bethe: “He had no experience in directing a large group of people, he was a theorist, and he had no Nobel Prize to distinguish him”.

Groves: “His left-wing background was not to our “The notion of disappearing into the desert for an liking by any means”... He wants Oppenheimer indeterminate period and under military auspices anyway: “Others are very bright, good hard work- disturbed many scientists and their families”. ers. But he is a real genius ”. ’43 Feb Groves allows the new laboratory civilian ’42 Nov Oppie: “My two great loves are physics administration. The price: a guarded barbed-wire and desert country”. They will be combined at Los around the laboratory itself! Laura Fermi: “The Alamos. He begins recruiting: Bethe, Teller... European-born were unhappy, it reminded them of concentration camps”... C /2009/\De Paris aHiroshima" F.M. Marqu es(17/34) P A NPAC L E C N LOS ALAMOS

’43 Apr Serber delivers introductory lectures, the notes of which make the ‘’ , a document handed to all new arrivals. The young scientists finally learn the object of the project!

Produce a practical military weapon equal to 20,000 tons of TNT. The core would be a melon of U235 or an orange of Pu239, surrounded by a water- melon of U tamper! One km around the explosion would be uninhabitable for a time.

The problems: efficiency (more than one critical mass per bomb) and detonation (change k from less than 1 to more than 1). Predetonation by a pre- mature neutron, or postdetonation when the pieces separate and break, must be avoided: add initiator , a Ra/Be or Po/Be source...

’43 Mar Scientists and families arrive by train and car. Oppie has told them that this work will end the war to end all wars: the unit of measure- “Firing the core pieces together is the part of the ment for wasted hours is thus human lives ! job about which we know least”. C /2009/\De Paris aHiroshima" F.M. Marqu es(18/34) P A NPAC L E C N OAK RIDGE

’43 Oct UF6 corrosion: Nickel bar- riers, Nickel-plate all pipe interiors, invent Teflon! Thousands of diffu- sion tanks need a flat site, K-25 at the southwestern end of Oak Ridge.

They change the barrier design: Urey realizes that beating the Germans is no longer the goal and withdraws...

’43 May Build a ‘town’ for 20,000 workers, plus the Y-12 electromagnetic complex, plus the K-25 diffusion plant... Too close to Knoxville for Pu.

Lawrence designs the ‘’ , and arranges sev- eral of them around a large electromagnet in ovals: the racetracks (Alpha, plus 2nd stage Beta). The US is short of Copper for the electromagnets: they borrow 300M$ Silver from the US Treasury!

C /2009/\De Paris aHiroshima" F.M. Marqu es(19/34) P A NPAC L E C N FAR AWAY: HANFORD

’43 Feb Wigner designs the ‘reactor’: 8×11 m graphite cylinder (1,200 tons) on its side, pene- trated by 2,000 Al tubes filled with 200 tons of pure U slugs. High k makes water cooling practical!

After 100 days, 1/4,000 atoms are transmuted into Pu and the irradiated slugs are pushed out the back of the pile by loading new slugs in at the front. They fall into a deep pool of water that confines the short-lived fission-product activity. After 60 days, they are fished out for chemical separation.

’43 Oct Construction of 3 reactors begins. The irra- diated slugs are transported by rail to remotely operated separation plants. Groves: “We made certain that each member of the project un- derstood his part in the total effort; nothing more”. C /2009/\De Paris aHiroshima" F.M. Marqu es(20/34) P A NPAC L E C N OPERATION GOMORRAH

’43 Jul Bomber Command, order 173: “The to- tal destruction of Hamburg would achieve immea- surable results on German morale... very impor- tant in shortening and winning the war... At least 10,000 tons of bombs will have to be dropped to complete the process of elimination... Night attacks will be preceded and/or followed by heavy daylight attacks”. Explicit policy of mass destruction .

. .

Jul 27 A raging inferno : firestorm blowing at 240 km/h, 800 ◦C, people’s feet and hands stuck in the melted asphalt... 45,000 Germans, mostly old people, women and children, killed in one night.

Bombing of distant cities, out of sight and sound and smell, becomes generally approved...

C /2009/\De Paris aHiroshima" F.M. Marqu es(21/34) P A NPAC L E C N RADIOACTIVE DUST

’43 Apr Fermi proposes to Oppie that fission ’43 Nov American B-17’s attack Norsk Hydro products might be used to poison German food ! (already sabotaged in February) and shut it down. Oppenheimer: “I recommend delay until we can The Nazis want to transport the remaining D2O to poison food sufficient to kill 500,000 men”! Germany: Haukelid has to sink the ferry on his own! Is it worth it? “It is thought very important ’43 Aug Bethe-Teller: “Recent reports give indi- that the D2O shall be detroyed. Hope it can be cations that the Germans may be in possession of a done without too disastrous results. Greetings”. powerful new weapon, expected to be ready by Jan- uary”. It proved to be the V-1 and V-2 rockets. ’44 Sep Bohr is asking Roosevelt to Connant: “Extremely unlikely that a radioactive approach the So- weapon will be used against us”. But the British viet Union and to fear the German D2O pile might be used to breed openness . Churchill: radioactive isotopes for dusting London ... “The suggestion is not accepted. This new bomb is just go- ing to be bigger than our present bombs. It might be used against the Japanese”. To Cherwell: “How did Bohr come into this business? He says he corresponds with a Russian professor... Bohr ought to be confined ”!

C /2009/\De Paris aHiroshima" F.M. Marqu es(22/34) P A NPAC L E C N &

Cosmic-ray neutrons, too slow to fission U238, make the difference. Shielding out those neutrons will decrease: the bomb core purification needed, predetonation, the gun’s muzzle velocity, its length and weight... The 5-m bomb becomes a 2-m one: ‘’ becomes ‘Little Boy’ !

’43 Jun A plane that could carry a 5-m bomb? Except for the British Lancaster, all would require the bomb to be carried externally. The (too) new B-29 Superfortress requires considerable modifica- tion... They call the gun bomb ‘Thin Man’ and the implosion bomb ‘Fat Man’ , as though they were modifying a plane to carry Roosevelt and Churchill!

’43 Dec Segr`emeasures spontaneous fission in U and Pu, to determine how cleansed of impurities the bomb cores will have to be and how fast the gun will have to fire to avoid predetonation . At Los Alamos mesa, the rate is higher for U235!

C /2009/\De Paris aHiroshima" F.M. Marqu es(23/34) P A NPAC L E C N PLUTONIUM POISONS

’43 Nov The air-cooled, pilot-scale X-10 ’44 Sep The is ready at Hanford. reactor at Oak Ridge goes critical: first 5 Leona Marshall: “The U slugs were on the tons of irradiated U discharged from the pile. floor in solid wooden blocks... I teased Fermi saying it looked like a chain-reacting pile. ’44 Jul Gram quantities of Pu arrive at Fermi turned white and reached for his slide Los Alamos. The spontaneous fission rate of rule: after a few seconds he relaxed...”! X-10 Plutonium is much higher! The pile operates at high power for one 238U +1n −→ 239Pu hour... until the reactivity steadily decreases +2n · · · −→ 240Pu with time! By evening B pile dies... but the next morning it comes back to life! The rate for Hanford Pu would be higher: Wheeler: “B pile’s heavy breathing convinced they will not need to cleanse the Pu of im- me fission-product poisoning had occurred”: purities... but they cannot use a gun ! Even at 1 km/s the Pu bullet and target would melt 135 7 h 135 9 h 135 down and fizzle before they had time to join. I −→ Xe −→ Cs +1n −→ 136Xe Impossible to separate Pu239 from Pu240.

Oppenheimer: “Stop efforts to purify Pu and σcap=3 Mb ! “Xenon was an unexpected ex- concentrate on methods of assembly which do tra control rod: more reactivity was needed”. not require a low neutron background. Pri- ority to implosion ”. A Plutonium Fat Man ’44 Dec D pile goes critical with 1500 +500 “was the only real hope, and from current ev- channels, B pile follows. “Looks like a race idence not a very good one”... between a fat man and a thin man”... C /2009/\De Paris aHiroshima" F.M. Marqu es(24/34) P A NPAC L E C N THE DRAGON EXPERIMENT

’45 Mar Frisch runs subcritical experiments stacking blocks of U hydride (Lady Godiva acci- dent!). He wants to use a ‘guillotine’ to drop a block through a stack, that would form a critical mass for a split second! Feynman: “It will be like tickling the tail of a sleeping dragon ”.

’45 Jan Abelson was enriching U for the Navy by thermal diffusion since ’41! Groves builds the S-50 thermal plant to feed the :

Alpha Beta . 1% U −→ 10% U 258 g/d −→ 80% U 204 g/d U235 hydride should react more slowly than pure Bomb-grade U accumulates in a fortress! Armed metal... “It was as near as we could go toward an couriers transport them to Los Alamos, where atomic explosion ”! First evidence of an explosive Frisch leads the Critical Assemblies group. chain reaction: +2 ◦C/ms... C /2009/\De Paris aHiroshima" F.M. Marqu es(25/34) P A NPAC L E C N IMPLOSION LENSES

C /2009/\De Paris aHiroshima" F.M. Marqu es(26/34) P A NPAC L E C N INITIATOR: IMPLOSION TEST

“The chain reaction required 1/2 neutrons to start. ’45 May Several experiments lead to the choice of No one wanted to trust 1,000M$ of U or Pu to the initiator design, but however scarce Pu might spontaneous fission or a passing cosmic ray”! be, only a full-scale test can prove that it works. Building of a tower plus 3 shelters at 9 km... The challenge: design a Po/Be source of sufficient intensity that releases the neutrons only when needed... Relatively easy in Little Boy: separate Po and Be with bullet and target core.

In Fat Man, they have to be both at the center 210Po/Be of the core but ‘inert’ until the fraction of µs when Pu will be squeezed to maximum density!

Po210 is a soft metal . that emits 5000 times more α’s than Radium (the air around a pure sample glows with a blue light). The equivalent to 32 g of Ra, mixed with Be, will emit ≈ 108 n/s! But this is only: ≈10 n/ 0.1µs

C /2009/\De Paris aHiroshima" F.M. Marqu es(27/34) P A NPAC L E C N THE PACIFIC THEATER

A marine: “I whish we were fighting against Germans, they are human beings, like us. The Japs are like animals , you never see them until they are dead”... A historian, ex- marine: “Nip determination was attributed to ‘fanaticism’. In retrospect it is indistin- guishable from heroism”. In Burma, captured/dead Japanese is 1/120 (among Western armies is about 4/1)! Saipan’s mass suicide , Iwojima, Okinawa... The home islands will take a lot of killing.

’44 Nov The B-29’s practice diving turns to escape 16 km from the explosion and drop ‘pumpkins’ ! From the Marianas they bomb Japan for months. Air Force: “The entire population of Japan is a military target”...

Mar 9 334 B-29’s take off for Tokyo with 2,000 tons of incendiaries: 100,000 people die, 1 million lose their homes. For 10 days follow Nagoya, Osaka, Kobe, Nagoya again... LeMay: “Then we run out of bombs . Liter- ally”. C /2009/\De Paris aHiroshima" F.M. Marqu es(28/34) P A NPAC L E C N TRUMAN: ATOMIC BOMB?

Apr 12 Roosevelt dies . Some worry about the Stimson removes Kyoto ! He is outraged by mass continuation of the project... Harry Truman be- murder (Hamburg, Dresden, Tokyo...) and sug- comes President and within 24h learns from Stim- gests a demonstration. “Why? The number of son that “we are developing a new explosive of un- dead will be similar to that in fire raids!” But Op- believable destructive power” and from Byrnes that penheimer reminds that “the visual effect will be “it is great enough to destroy the whole world”! tremendous, as well as the radiation damage”.

FDR had asked for Soviet help in Yalta. Truman does not need them now (if the bomb works)! He postpones the Potsdam Conference until Jul 15...

’45 May Target Committee: Kyoto, Hiroshima, Yokohama, Kokura... Byrnes: “What have we got in exchange from the UK?” Szilard: “If we test and use atomic bombs, we will precipitate a race toward nuclear weapons and lose our military advantage”. Oppenheimer: “Scientists should be released to re- turn to their universities and basic science ”...

C /2009/\De Paris aHiroshima" F.M. Marqu es(29/34) P A NPAC L E C N

’45 May Bainbridge chooses a flat, deso- late site with good weather at 340 km south of Los Alamos: Jornada del Muerto .

’45 Jun Two small Pu hemispheres (5 kg) that become supercritical once the density doubles. The molds for the implosion lens segments begin to arrive: date moved from Jul 4 to 16. Physicists arrange a betting pool on the explosive yield!

’45 Jul The last segment does not fit! Due to different temperatures... Oppenheimer had asked Kistiakowsky to fire a Fat Man copy (without Pu) using rejected segments: the results predict Trinity’s failure ! But Bethe discovers that a perfect implosion would have lead to the same results...

Jul 16 Bainbridge is furious because Fermi scares the soldiers! Rabi: “It was raining cats and dogs, lightning and thun- der”. Wind blows at 50 km/h, the shot is delayed to 0530. Countdown begins ...

C /2009/\De Paris aHiroshima" F.M. Marqu es(30/34) P A NPAC L E C N DEATH: THE DESTROYER OF WORLDS

’45 Jul 16 0529:45

18.6 KT ! At Base Camp: “The blinding heat of a bright day on your face in the cold desert morn- ing”. Segr`e:“For a moment I thought it might set fire to the atmosphere, even if I knew it was im- possible”. The blast knocked Kistiakowsky down at S-shelter! Penney: “This weapon would reduce a city of 400,000 people to nothing ”... C /2009/\De Paris aHiroshima" F.M. Marqu es(31/34) P A NPAC L E C N URANIUM: HIROSHIMA

Aug 6 ‘’ (61+4 T) flies toward Hiroshima/Kokura/Nagasaki: weather reports condemn Hiroshima . ‘Little Boy’ is dropped at 0815...

...12.5 KT, 200,000 dead (54%). Groves:

– I’m very proud of you and all your people. – It went all right? – Apparently it went with a tremendous bang. – It’s been a long road. – Yes, and I think one of the wisest things I ever did was when I selected the director of Los Alamos. – Well, I have my doubts, General Groves.

C /2009/\De Paris aHiroshima" F.M. Marqu es(32/34) P A NPAC L E C N PLUTONIUM: NAGASAKI

Aug 7 Japan has not sued for peace... Marshall: “We did not take into account that the destruction would be so complete that there would be no com- munication with other cities for days”! The Army prints leaflets to threaten the Japanese people: Nagasaki will receive them on Aug 10! Drop scheduled on Aug 11, but weather is expected to be bad from Aug 10, and they want the Japanese to believe that they have a lot of bombs ...

Aug 9 ‘’ flies toward Kokura: the clouds condemn Nagasaki . A hole opens over a stadium: ‘Fat Man’ is dropped at 1102... 22 KT, 54% dead .

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C /2009/\De Paris aHiroshima" F.M. Marqu es(33/34) P A NPAC L E C N EPILOGUE

Aug 10 One ‘Fat Man’ will be ready on Aug 17 1952 The Teller-Ulam H-bomb is tested at full (plus three bombs in Sep and three more in Oct)! scale in the ”Ivy Mike” shot: 10.4 MT! Marshall: “It is not to be released without express authority from the President”. The USSR de- clares war on Japan and enters Manchuria...

Hirohito offers surrender accepting Potsdam, but keeping “the prerogatives of His Majesty as a Sovereign Ruler”. Byrnes disagrees! Stimson ad- vices Truman to accept. Hirohito announces capit- ulation on Aug 15 : “...the enemy has begun to use 1961 Sakharov’s Tzar Bomba : 50 MT... a new and most cruel bomb...”

1949 RDS-1, the ‘Soviet Fat Man’ : 22 KT.

1939 Hahn-Meitner did not ‘invent’ fission, they discovered it. Fission was there all along...

C /2009/\De Paris aHiroshima" F.M. Marqu es(34/34) P A NPAC L E C N