Master 2 - NPAC 2009/10 Noyaux Particules Astroparticules Cosmologie (Le Noyau de l'Atome ² 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 di®erent 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 neutron bombardment U and Th can ¯ssion, but they can also capture the neutron at about 25 eV and beta decay: some transuranians were real! Frisch: \Thorium did not respond to the magic of para±n". Below 1 MeV, only Uranium ¯ssions... \Why should both Th(90)/U(92) `liquid drops' have di®erent responses to slow neutrons?" 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 ¯s- sion". But why do they behave di®erently? 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/¯ssion". Hydrogen 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- fU238/Th232 + ng¤ ¼ +5.5 MeV mon material is graphite . If unsuitable, the \next +n U235 ¡! f 236 g¤ ¼ +6.5 MeV best guess might be heavy water ". Wigner, Szilard and Fermi meet Pegram: \We Any neutron at all would ¯ssion 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 Nature: `Number of neutrons liberated in the ¯ssion of U'! He ¯nds 3.5/¯ssion. '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 O±ce takes over the KWI. C /2009/\De Paris aHiroshima" F.M. Marqu es(2/34) P A NPAC L E C N CRITICAL MASS '40 Feb Frisch wonders how much U235 should be separated. Following Bohr, Peierls assumes that, if U235 will ¯ssion whatever the neutron, the ¯ssion cross-section will be the geometric one: MC(U235) ¼ 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 = ff ½ ; σsca ; σcap ; σfis g ) MC interior of the Sun, pressures greater than the cen- ter of the Earth... we were staggered". Frisch: '39 Sep Mark Oliphant \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 di®usion 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 isotopes of Xenon. The world's source of D2O is Norsk Hydro . Germany o®ers 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 o®er 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... ¯rms that U235 is re- sponsible for the slow- '40 Jun Kurchatov reports to Physical Review a neutron ¯ssion of Ura- rare spontaneous ¯ssioning in U. \The complete nium! U235 ¯ssion 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' di®usion : lighter gases di®use faster. from Washington". Four tons of graphite reach Columbia. Fermi: \The physicists 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 cyclotron! Failed test with U+H2O/para±n. '41 Jan Bothe measures σcap(C) at more than '40 Jun Vannevar Bush: \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 ¯¡ [Pu] \Radioactive element 93 " to Physical Review! 239 ¡ 93 Á ¯ [Np] '41 Jan Seaborg 23592 23692 23792 23892 23992 [U] and Segr`e bom- (0:7%) (99:3%) bard 1 kg of UNH: \one ® 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 ¯s- be due to the new sion fragments: a stack of cigarette papers on a element 94 "! layer of Uranium oxide, backed with ¯lter paper, bombarded with slow neutrons. \Nothing interest- '41 Mar They ing in the cigarette papers... but the ¯lter paper un- separate less than der the stack showed something very interesting": 1 ¹g of (93)239, two activities di®erent from those of the ¯ssion 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 identi¯ed neutrons and observe the ¯ssion of Plutonium , 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 e®orts likely to yield results within if we have the most, and the best of the world's nu- months were worthy of consideration.