The Neutron and the Bomb, page 37
Chadwick’s responsibilities seemed to increase with no let up. His primary scientific focus was on the work being carried out in Liverpool, and he regularly informed the Maud Committee of work in progress there. At the end of June 1941, he listed a five-point programme of activity:61
1. Experiments on fission cross-sections, not quite finished.
2. Investigation of critical conditions for the bomb assembly by means of model assembly, probably by an optical analogy suggested by Frisch.
3. Investigation of the energy spectrum of fission neutrons. Some work on neutrons over 3 MV; may be important investigations under 3 MV.
4. Measure cross-section of separated 235U (awaited from the US).
5. Scattering of neutrons in uranium — more experiments may be necessary.
In addition, he continued to be in close touch with Powell in Bristol, constantly urging him to send results and warning that other things that Powell thought of pursuing ‘can and must wait’.62 He would write detailed letters to Powell, about once a fortnight, analysing data and making new suggestions. On 17 June 1941, he asked: ‘Can you send me any results about the scattering in uranium. We are waiting anxiously, and Pryce can get no further with some important calculations.’63 When Powell64 sent data on neutron cross-sections and the ratio of elastic to inelastic scattering (with the hopeful enquiry ‘is this the information you want?’), the results were eagerly devoured by Chadwick. He replied by return, thanking Powell for ‘something to be going on with’.65 He had expected the results for elastic scattering, but was surprised at the figure for total cross-section of uranium oxide, which was ‘considerably higher than our previous result’. Here was Chadwick practising his accustomed role as scientist and mentor, but he now had to deal as well with the French patents issue, and the stream of letters he received from Feather and others. There were also the site visits to the Cavendish and Birmingham, which were major undertakings, since he had insufficient fuel to drive there, and the railways were in chaos due to the mass transportation of troops and the disruption caused by bombing. He described one Saturday trip to Birmingham from Liverpool to Feather: ‘What a day. Eight hours railway with all the world on the move — platforms three or four deep.’66 In addition there were monthly progress reports from all the Cambridge scientists to vet, which he did with great diligence, unerringly spotting errors as well as opportunities for new advances. He was about to surpass all these efforts with a climactic burst of work which he would repeat periodically over the next few years, taking himself to the limits of his physical endurance.
At the meeting of the Maud Committee on 2 July 1941,67 G.P. Thomson reminded those present that a report on their activities was needed, and he presented a preliminary draft. Chadwick’s first reaction was that it was essential to keep the civil and military applications — the boiler and the bomb — entirely separate, which Thomson had not done. In this he was supported by Lindemann, who went further and would restrict the report to the bomb only; the ‘Prof.’ also warned against intruding into the political and economic aspects. Many committee members thought the report should clearly reflect their view that this was an essential weapon because of its unprecedented destructive power, and Chadwick stated as a corollary that steps should be taken to control all stocks of uranium forthwith. After debating these various amendments and points of emphasis, it was decided that Chadwick would be the best person to redraft the report.
He returned to Liverpool and immersed himself in the task of writing. He received some help from Frisch and would also show some draft passages to Rotblat for comment, when they were germane to his work. Rotblat42 realized that he was only seeing fragments of the whole, and that Chadwick was concealing as much as he could. As Chadwick30 wrote many years later in response to an enquiry: ‘If you will read Part 1 of the report, you will see that no-one else could have written it.’ Part 1 was a general statement on the use of uranium for a bomb, and in its economy of style and clarity, it is indeed typical of Chadwick’s writing. The dispassionate language does not disguise the chilling implications of the report’s contents, and reflects the absolute determination of the Maud Committee that this weapon should be available to the British in their struggle for survival.22
We should like to emphasise at the beginning of this report that we entered the project with more scepticism than belief, though we felt it was a matter which had to be investigated. As we proceeded we became more and more convinced that the release of atomic energy on a large scale is possible and that conditions can be chosen which would make it a very powerful weapon of war. We have now reached the conclusion that it will be possible to make an effective uranium bomb which, containing some 25 lb of active material, would be equivalent as regards destructive effect to 1,800 tons of T.N.T. and would also release large quantities of radioactive substances, which would make places near to where the bomb exploded dangerous to human life for a long period. The bomb would be composed of an active constituent (referred to in what follows as 235U) present to the extent of about 1 part in 140 in ordinary Uranium. Owing to the very small difference in properties (other than explosive) between this substance and the rest of the Uranium, its extraction is a matter of great difficulty and a plant to produce 2 1/4 lb (1 kg) per day (or 3 bombs per month) is estimated to cost approximately £5,000,000, of which sum a considerable proportion would be spent on engineering, requiring labour of the same highly skilled character as is needed for making turbines.
In spite of this very large expenditure we consider that the destructive effect, both material and moral, is so great that every effort should be made to produce bombs of this kind. As regards the time required, Imperial Chemical Industries after consultation with Dr Guy of Metropolitan-Vickers, estimate that the material for the first bomb could be ready by the end of 1943. This of course assumes that no major difficulty of an entirely unforeseen character arises. Dr Ferguson of Woolwich estimates that the time required to work out the method of producing high velocities required for fusing is 1-2 months. As this could be done concurrently with the production of the material no further delay is to be anticipated on this score. Even if the war should end before the bombs are ready the effort would not be wasted, except in the unlikely event of complete disarmament, since no nation would care to risk being caught without a weapon of such decisive possibilities.
We know that Germany has taken a great deal of trouble to secure supplies of the substance known as heavy water. In the earlier stages we thought that this substance might be of great importance for our work. It appears in fact that its usefulness in the release of atomic energy is limited to processes which are not likely to be of immediate war value, but the Germans may by now have realised this, and it may be mentioned that the lines on which we are now working are such as would likely to suggest themselves to any capable physicist.
By far the largest supplies of Uranium are in Canada and the Belgian Congo, and since it has been actively looked for because of the radium which accompanies it, it is unlikely that any considerable quantities exist which are unknown except possibly in unexplored regions.
The general overview went on to consider the method of fusing the weapon, its probable explosive effect, and the costs of the whole project. There was also a paragraph referring to the American efforts, the bulk of which, it was suggested, had been concerned with the production of energy and only to a much lesser extent with the bomb. There followed a long review of the technical evidence used to support the generalized statements of Part 1. As he had indicated he would at the last Maud meeting, Chadwick completely separated the bomb from the boiler, and the latter was presented as the second, shorter, part of the report. He completed the complex redrafting of the whole report in less than two weeks, despite being ‘busy on the State Bursary scheme’68 for the university, and when he finished said his mind was completely addled. He wrote69 to Feather on 16 July 1941:
I have been working about 20 hours per day, but now I have got off the reports both on bomb and boiler and today I have had a long discussion with G.P. [Thomson] and Peierls. With ten minutes to spare, I will attempt to answer your point.
At the end of August, he was exhausted and looking forward to a short holiday in the cottage in Wales. ‘I am hoping to go away tomorrow or Monday for a few days — a week, perhaps a day or so longer if I am not called to London. I shall be glad to put off the harness for I am feeling very down. I hope to get a little gentle fishing.’70
References (chapter 12)
1 Powell, C.F. and Fertel G.E.F. (1939). Energy of high-velocity neutrons by the photographic method. Nature, 144, 115.
2 Frank, F.C. and Perkins, D.H. (1971). Cecil Frank Powell, 1903-1969. Biographical memoirs of fellows of the Royal Society, 17, 541-55.
3 Powell, C.F., May, A.N., Chadwick, J. and Pickavance, T.G. (1940). Excited states of stable nuclei. Nature, 145, 893-4.
4 Chadwick, J. (16/5/40). Letter to N. Feather. Feather’s papers, CAC.
5 Chadwick, J. (17/6/40). Letter to N. Feather. Feather’s papers, CAC.
6 Oliphant, M.L. (1/6/40). Letter to J. Chadwick. CHAD I, 19/3, CAC.
7 Haworth, W.N. (4/6/40). Letter to J. Chadwick. CHAD IV, 2/10, CAC.
8 Chadwick, J. (11/6/40). Letter to W.N. Haworth. CHAD IV, 2/10, CAC.
9 Haworth, W.N. (1/7/40). Letter to J. Chadwick. CHAD IV, 2/10, CAC.
10 Chadwick, J. (2/7/40). Letter to W.N. Haworth. CHAD IV, 2/10, CAC.
11 Haworth, W.N. (30/7/40). Letter to J. Chadwick. CHAD IV, 2/10, CAC.
12 Chadwick, J. (1/8/40). Letter to W.N. Haworth. CHAD IV, 2/10, CAC.
13 Chadwick, J. (5/9/40). Letter to G.P Thomson. CHAD I, 19/7, CAC.
14 Haworth, W.N. (9/9/40). Letter to J. Chadwick. CHAD IV, 2/10, CAC.
15 Haworth, W.N. (7/3/41). Letter to J. Chadwick. CHAD IV, 2/10, CAC.
16 Chadwick, J. (24/6/40). Letter to G.P. Thomson. CHAD I, 19/7, CAC.
17 Churchill, W.S. (1949). The second world war: their finest hour, p. 570. Cassell, London.
18 Holt, J. (1988). Seminar on James Chadwick. University of Liverpool. See also Holt, J. (1994). Reminiscences and discoveries: James Chadwick at Liverpool. Notes and Records of the Royal Society, 48, (2), 299-308.
19 Chadwick, J. (24/2/40). Letter to N. Feather. Feather’s papers, CAC.
20 Oliphant, M.L. (22/6/40). Letter to J. Chadwick. CHAD I, 19/3, CAC.
21 Chadwick, J. (27/6/40). Letter to M.L. Oliphant. CHAD I, 19/3, CAC.
22 Gowing, M. (1964). Britain and atomic energy, 1939-1945, p. 64. Macmillan, London.
23 Hewlett, R.G. and Anderson, O.E. (1990). A history of the United States Atomic Energy Commission: the new world, p. 19. University of California Press.
24 Chadwick, J. (6/6/40). Letter to R.E. Peierls. CHAD I, 19/6, CAC.
25 Peierls, R.E. (12/6/40). Letter to J. Chadwick. CHAD I, 19/6, CAC.
26 Chadwick, J. (7/6/40). Letter to N. Feather. Feather’s papers, CAC.
27 Feather, N. (13/6/40). Letter to J. Chadwick. CHAD IV, 1/8, CAC.
28 Chadwick, J. (21/1/41). Letter to G.P. Thomson. CHAD I, 19/7, CAC.
29 Frisch, O.R. (1979). What little I remember. Cambridge University Press.
30 Chadwick, J. Undated papers CHAD II, 1/19 and CHAD III, 4/5, CAC.
31 Chadwick, J. (1/11/40). Letter to C. Darwin. CHAD I, 12/2, CAC.
32 Peierls, R.E. (1985). War. In Bird of passage, pp. 145-81. Princeton University Press.
33 Kurti, N. (1958). Franz Eugen Simon, 1893-1956. Biographical memoirs of fellows of the Royal Society, 4, 225-56.
34 Chadwick, J. (2/8/40). Letter to G.P. Thomson. CHAD I, 19/7, CAC.
35 Newton, J.O. (1992). Ernest William Titterton, 1916-90. Historical Records of Australian Science, 9, 167-85.
36 Simon, F.E. (19/2/41). Letter to J. Chadwick. CHAD I, 19/8, CAC.
37 Weiner, C. (1969). Sir James Chadwick, oral history. American Institute of Physics, College Park, Maryland.
38 Chief Constable of Liverpool (1947). Letter to J. Chadwick. CHAD II, 1/17, CAC.
39 Chadwick, J. (16/7/41). Letter to B.G. Dickins. CHAD I, 12/2, CAC.
40 Chadwick, J. (25/9/40). Letter to B.G. Dickins. AB, 1/21, PRO.
41 Chadwick, J. (21/1/41). Letter to B.G. Dickins. CHAD I, 12/2, CAC.
42 Brown, A.P. (1994). Interview with Joseph Rotblat, London.
43 McMillan, E. and Abelson, P.H. (1940). Radioactive element 93. Physical Review, 57, 1185-6.
44 Rotblat, J. (1985). Leaving the bomb project. Bulletin of the Atomic Scientists, Aug., 16-19.
45 Chadwick, J. (6/1/41). Letter to G.P. Thomson. CHAD I, 19/7, CAC.
46 Minutes of Maud Technical Sub-Committee (9/4/41). AB 1/347, PRO.
47 Goldschmidt, B. (1990). Atomic rivals. Rutgers University Press.
48 Feather, N. (15/12/40). Letter to J. Chadwick. CHAD IV, 1/8, CAC.
49 Chadwick, J. (20/12/40). Letter to N. Feather. Feather’s papers, CAC.
50 Feather, N. (26/12/40). Letter to J. Chadwick. CHAD IV, 1/8, CAC.
51 Chadwick, J. (31/12/40). Letter to N. Feather. Feather’s papers, CAC.
52 Feather, N. (6/1/41). Letter to J. Chadwick. CHAD IV, 1/8, CAC.
53 Chadwick, J. (5/5/41). Letter to G.P. Thomson. CHAD I, 19/7, CAC.
54 Chadwick, J. (6/5/41). Report on the experiments of Halban and Kowarski. CHAD I, 28/6, CAC.
55 Halban, H. (24/5/41). Letter to J. Chadwick. CHAD IV, 1/9, CAC.
56 Halban, H. (15/6/41). Letter to J. Chadwick. CHAD IV, 1/9, CAC.
57 Chadwick, J. (3/2/41). Letter to N. Feather. Feather’s papers, CAC.
58 Feather, N. (23/6/41). Letter to J. Chadwick. CHAD IV, 1/8, CAC.
59 Halban, H. (11/8/41). Letter to J. Chadwick. CHAD IV, 1/9, CAC.
60 Chadwick, J. (9/10/41). Letter to H. Halban. CHAD IV, 1/9, CAC.
61 Chadwick, J. (30/6/41). Letter to B.G. Dickins. CHAD I, 12/2, CAC.
62 Chadwick, J. (25/3/41). Letter to C. Powell. CHAD I, 19/2, CAC.
63 Chadwick, J. (17/6/41). Letter to C. Powell. CHAD I, 19/2, CAC.
64 Powell, C. (28/6/41). Letter to J. Chadwick. CHAD I, 19/2, CAC.
65 Chadwick, J. (1/7/41). Letter to C. Powell. CHAD I, 19/2, CAC.
66 Chadwick, J. (14/6/43). Letter to N. Feather. Feather’s papers, CAC.
67 Minutes of Maud Technical Sub-Committee (2/7/41). AB 1/347, PRO.
68 Chadwick, J. (14/7/41). Letter to N. Feather. Feather’s papers, CAC.
69 Chadwick, J. (16/7/41). Letter to N. Feather. Feather’s papers, CAC.
70 Chadwick, J. (30/8/41). Letter to N. Feather. Feather’s papers, CAC.
13 ~ Transatlantic travails
Several copies of the Maud Report were sent to the United States with the aim of fostering collaboration. One copy went to the inert Lyman Briggs, who as Oliphant1 subsequently discovered, locked the report in his safe without showing it to other members of his Uranium Committee. Fortunately, copies were also sent to an activist, Vannevar Bush — an inveterate inventor and academic engineer, who had persuaded President Roosevelt to place him at the head of the National Defense Research Committee (NDRC) in June 1940.2 By now he had become the director of a new, overarching, agency, the Office of Scientific Research and Development (OSRD). Bush had been succeeded at the NDRC by James B. Conant, an organic chemist, who had visited both Oxford and Cambridge in the early 1930s, when he found himself ‘on the point of becoming an Anglophile’.3 Bush and Conant were two middle-aged Yankees who had both spent a period working as government researchers in World War I before making successful careers as academic scientists in Boston: Bush had risen to become Dean of Engineering at the Massachusetts Institute of Technology before moving to Washington in 1939, and Conant was President of Harvard University. They were alarmed by events in Europe and were opposed to the United States’ isolationist stand; they seized on the Maud Report as a realistic opportunity for a scientific project which could be developed during the present war and which the United States could not afford to ignore. Although Bush and Conant recognized the quality of the British Maud Committee and the thoroughness of their report, they decided to subject the proposals to an independent scientific review by leading American experts under the auspices of the National Academy of Sciences to establish an incontrovertible basis for future progress.2
The first response to the Maud Report from America to reach London was from Charles Darwin, now Director of the British Central Scientific Office in Washington. He had previously written in early July 1941 to report his impressions of a meeting of the Briggs Uranium Committee, which he had attended. It had lasted over five hours with hardly a mention of the salient problem of isotope separation: ‘The plain fact is that they are very nearly stuck on that side’, was his verdict.4 In a handwritten letter dated 2 August 1941 to Lord Hankey (Chairman of the Cabinet Scientific Advisory Committee), Darwin5 allowed himself to bring up the morality of the enterprise, something which the Maud Committee had studiously avoided. He also said that he had recently been approached by Bush and Conant on the subject of atomic bombs, and there did seem to be the promise of movement. He thought that decisions needed to be made in government circles about the large expenditures involved, and raised the question whether such a weapon would ever be used:
Are our Prime Minister and the American President and the respective General Staffs willing to sanction the destruction of Berlin and the country round, when, if ever, they are told it could be accomplished at a single blow?
It appears to Bush and Conant, and I concur, that the time is ripe for a full examination of whether the whole business should be continued at all.
According to Darwin, Bush and Conant favoured a joint project between the two governments; he thought it ‘fairly clear’ that the plant would have to be built in the US or Canada. Darwin recommended that a small secret conference should be set up ‘with men of balanced judgement’; his suggestion for the British representatives were Chadwick, ‘who is an authority on the general subject of nuclear physics’, Professor Simon from Oxford, because of his expertise on isotope separation, and G.P. Thomson.
