1—
A Fruitful Error
A Claim
The Laboratory's first sustained appearance on the international scene was the result of mixing heavy water with resonance acceleration. The mix gave rise to the false idea, which Lawrence defended resourcefully, that the deuteron is unstable. This hypothesis of deuteron disintegration had many unpleasant implications for nuclear theory. It therefore immediately excited incredulity and opposition in the wider world of physics. The persistence of the Laboratory in its error spread its reputation for sloppiness and forced others to make an important discovery; and it illustrated the strengths and the weakness of the Laboratory's style of teamwork centered entirely on Lawrence's research program.
Lewis and Lawrence first loosed deuterons into Livingston's 27-inch cyclotron in April 1933. Their expectation that "heavy protons" would be better projectiles than light ones was quickly fulfilled.[1] On May 3 Lawrence wrote his close colleagues—Boyce, Cooksey, and Oppenheimer—that "H-twotrons" blasted lithium into alpha particles with ranges in air of 8.2 cm and 14.8 cm, and knocked slow alpha particles from boron, magnesium, nitrogen,
[1] Lawrence to Poillon, 14 Apr 1933 (15/16A). The deuterons, at 1.3 MeV, came from H H ions accelerated to 2 MeV; Lewis, Livingston, and Lawrence, PR, 44 (1 Jul 1933), 55 (letter of 10 June).
and aluminum. The yield from lithium was ten times larger with deuterons than with protons. Lawrence hurried to capitalize on the new projectile and the new machine between the end of the term and early June, when he was to leave for vacation and teaching at Cornell. "I have been working night and day in the laboratory since class ended," he wrote Oppenheimer. "You will pardon me for dictating this. I am doing it while proctoring an examination. I am really trying to conserve time."[2]
Explaining the action of deuterons on lithium to Cockcroft, Lawrence supposed that the swifter alpha particles came from Li7 , according to Li(d,n)2a , and the slower from Li6 via Li(d)2a . A week later he changed his mind and identified the fast alpha particles with the disintegration of Li6 . Both processes, whichever was which, went well even with deuterons of modest energy. To coax alpha particles from aluminum, magnesium, and nitrogen, however, required energies above a million volts, well out of Cockcroft's range.[3] Every element bombarded with deuterons of such energies "disintegrated." It was time for a news release. The release: lithium, beryllium, boron, nitrogen, fluorine, aluminum, and sodium all suffered "transitions" at Berkeley; "at this rate of progress, one dares not guess what will be achieved in nuclear physics within a few years."[4] Within a few weeks the rate was retrograde; Lawrence still could not say for certain from which lithium the fast alpha particles came, nor whether anything else but nitrogen, and possibly beryllium and boron, disintegrated under bombardment by deuterons of 1.3 MeV.[5]
Then came an extraordinary find. Not stopping to resolve the problems they had raised, the Berkeley group found that every element gave off protons under bombardment by deuterons with more than 800 keV of energy. And more than that: the protons all
[2] Lawrence to Boyce (3/8), Cooksey (4/19), and Oppenheimer (14/9), all 3 May 1933; Lawrence to Boyce, 2 Feb 1933 (3/8), for Lawrence's summer plans.
[3] Lawrence to Cockcroft, 4 May 1933 (5/4); to Darrow, 10 May 1933 (6/9).
[4] Lawrence to Houtermanns, 12 May 1933 (8/11); Science service , 20 May 1933 (Lewis P), quote.
[5] Lewis, Livingston, and Lawrence, PR, 44 (1 Jul 1933), 55–6 (letter of 10 June), 317 (abstract for June meeting of the APS); Henderson also participated in the work. Cf. Lawrence to Cooksey, 2 June 1933 (5/4).
had the same range, 18 cm, irrespective of the material from which they came. "I am almost bewildered by the results," Lawrence wrote. But only almost. He reasoned that such homogeneous protons could scarcely come from so heterogeneous a set of elements, especially from the highly repulsive (to deuterons) nuclear charges of atoms as heavy as gold; and he declared that they must originate not in the targets but in the projectiles. "We have strong evidence that we have disintegrated the deuteron itself." So Lawrence wrote Bainbridge, asking for his latest values of the masses of H2 by return airmail.[6] The numbers were needed to calculate the mass of the neutron from the hypothesis of deuteron disintegration.
In the easiest hypothetical case, a deuteron of energy 1.33 MeV hits a gold nucleus, which is too heavy to be moved much by the blow and splits into an 18-cm proton and a neutron of unknown velocity. Lawrence's group had some shaky evidence that in the explosion of the deuteron, the constituents received equal momentum and energy. Now an 18-cm proton has an energy of 3.6 MeV; the kinetic energy produced in the explosion is accordingly (7.20 – 1.33)MeV = 0.0063 mass units. This, together with the masses of the proton and the neutron, must equal the mass of the deuteron, which Bainbridge had fixed at 2.0126 from his analysis of Lewis's water. The indicated arithmetic produced the startling answer, mn» 1.000. Thus was born the short-lived light Berkeley neutron.[7]
Lawrence's idea may be reconstructed from an improved calculation made after his return from Cornell and from later correspondence. The calculation rested on experiments by Henderson and Livingston, which seemed to show that the proton came off with all the kinetic energy of the deuteron and that a bombarding energy of 1.2 MeV, not 1.33 MeV, was enough to give protons of 18 cm. Therefore, in the explosion the proton gets 3.6 – 1.2 = 2.4 MeV and, to conserve momentum, the neutron does too. (The new numbers raised mn slightly, to 1.0006). The
[6] Quotes from, resp., Lawrence to Cockcroft, 2 June 1933 (5/4), and to Bainbridge, 3 June 1933 (2/20).
[7] Lawrence, Livingston, and Lewis, PR, 44 (1 Jul 1933), 56 (letter of 10 June); Bainbridge, ibid., 57 (letter of 14 June).
model: the deuteron tends to explode in the field of a nucleus at the place where it experiences the strongest force for the longest time, at rest at its closest approach. The neutron and proton receive equal and opposite momenta; in addition, the charged proton is pushed out by the electrostatic force of the nucleus, which returns to it the energy lost by the parent deuteron in penetrating to the place of its demise.[8]
Lawrence advertised the light neutron at a symposium held at Caltech in May 1933 in honor of Bohr. Always hoping for revolution, Bohr welcomed Lawrence's news as a "marvellous advancement." Millikan, the master of self-advertisment, praised Lawrence's work as "altogether extraordinary, and most intelligently announced."[9] On the way to Cornell Lawrence stopped at the Century of Progress Exposition in Chicago, where the American Physical Society held, on its own assessment, "perhaps the most important scientific session in its history." Aston, Bohr, Cockcroft, and Fermi, among others, were there as guests of the AAAS to help celebrate. In a special session on nuclear disintegration, Cockcroft discussed the blasting of light elements by his voltage multiplier, Tuve described the blasting of middling elements by his Van de Graaff generator, and Lawrence claimed the blasting of everything by the cyclotron. Bohr presented a public commentary, during which he wrapped himself up in the wave-particle duality and the microphone cord. It was not a hard act to follow. "It was much easier, and much more pleasant [wrote the reporter from Time ] to understand round-faced young professor . . . Lawrence . . . tell how he transmuted elements with deuton bullets."[10]
Lawrence stole the show. The New York Times 's correspondent, William L. Laurence, introduced his namesake as the proprietor of a "new miracle worker of science," which, when whirling deuterons, liberated about ten times the energy it was fed. "The newest developments give only an inkling of what lies in store for man when and if he finally succeeds in unlocking what
[8] Livingston, Henderson, and Lawrence, PR, 44 (1 Nov 1933), 781–2 (letter of 7 Oct); Darrow to Lawrence, 28 Nov 1933, and answer, 9 Dec 1933 (6/9); Boyce to Lawrence, 19 Feb 1934, and answer, 27 Feb 1934 (3/8).
[9] Childs, Genius , 199.
[10] PR, 44 (1933), 313–4; "Complementarity in Chicago," Time, 22 (3 Jul 1933), 40.
Sir Arthur Eddington calls the 'cosmic cupboard of energy'."[11] Lawrence explained that the cracking of the deuteron released a little of that vast store of atomic energy of which Aston had given an inkling in his famous overstatement that half a glass of water could drive the Mauretania across the Atlantic. According to the Laboratory's measurements and theories, the neutron weighed less than the sum of the weights of the proton and the electron, which Lawrence understood to be its constituents. Hence, according to the relativistic equivalence of mass and energy, the combination of a proton and an electron should yield energy. Here was another source—along with the disintegrating deuteron—of perpetual motion.[12] Lawrence did not bother readers of the Times with the worry that hydrogen atoms might, or rather should, collapse spontaneously to neutrons and blow the world apart.
A Doubt
Meanwhile the Cavendish Laboratory had started to project deuterons. Rutherford had been most eager to procure heavy water for his experiments even before the startling discovery of the efficacy of deuteron bombardment. When Fowler returned to Cambridge from Berkeley early in May 1933 without any, he was "nearly lynched," he told Lewis, who forthwith forwarded a protective ampule containing as much deuterium as Lawrence's group had used in their disintegration experiments. Rutherford promised through Fowler not to hurry any results he might obtain into print, "so as to give Lawrence plenty of chance to get in first."[13] He received the news that deuterons had smashed atoms of lithium, nitrogen, magnesium, and beryllium. It reminded him of better times and of the Maori warrior on his baronial shield. "I should like to congratulate Lawrence and his colleagues for the
[11] Seidel, Physics research , 381, from William L. Laurence, "New 'gun' speeds breakup of atom: 'Deuton's bullet frees ten times its own energy,' scientists are told," New York Times (20 June 1933), 1. By our count the factor was five (7.2/1.33) for the deuterons that disintegrated; it is, of course, scarcely worth mentioning in comparison with Laurence's exaggerations.
[12] Laurence, "Neutron 'weighed' by Prof. E.O. Lawrence, proves lighter than its component parts," New York Times (24 June 1933), 1.
[13] Fowler to Lewis, 9 May 1933, and Lewis to Rutherford, 15 May 1933 (Lewis P).
prompt use they have made of the new club to attack the nuclear enemy. . . . These developments make me feel quite young again."[14]
Rutherford hurled his clubs from a proton accelerator that had been made for him by Oliphant to follow up the experiments of Cockcroft and Walton. This accelerator may stand as a symbol of Rutherford's methods in contrast with Lawrence's. Rather than go to higher energies than Cockcroft and Walton had reached, Rutherford opted for lower; theirs could attain 800 kV, his only 200 kV. He wanted to examine the thresholds of proton-induced nuclear reactions, identify the products, and estimate yields as functions of the energy of bombardment. To achieve his purposes, he directed that his new machine have a large proton current; a directive so well executed that Oliphant and Rutherford had for their experiments about 1,000 times the single microamp of Cockcroft and Walton's early experiments.[15]
The Oliphant-Rutherford accelerator, though short on energy, was by no means the cheap, jerry-rigged contraption of string and sealing wax dear to Cavendish mythology.[16] Metropolitan-Vickers designed, built, and contributed the oil-diffusion pump that created the vacuum, which was produced and maintained with the help of Apiezon oils and greases; the accelerating system incorporated the voltage-multiplier circuit perfected by Cockcroft and Walton with the help of Metro-Vick's engineers and a 100-kV transformer bought from Metro-Vick at what Rutherford thought the extravagant price of 85 pounds; and the detectors, which recorded the ionization created in a special chamber by the disintegration products, used a linear amplifier, thyratron tubes, and a purely electronic counting system then just invented at the Cavendish by C.E. Wynn-Williams and his co-workers.[17] The Cavendish was then far ahead of Berkeley in electronics and vacuum technology and in integrating the work of academic
[14] Rutherford to Lewis, 30 May 1933 (Lewis P).
[15] Rutherford to Hevesy, 3 Apr 1933, in Eve, Rutherford , 370; Oliphant and Rutherford, PRS, A141 (1933), 259–81, in Rutherford, CP, 3 , 329–50.
[16] Crowther, Cavendish , 242–4, and Cockburn and Ellyard, Oliphant , 49–50, both relying on Oliphant.
[17] Oliphant and Rutherford, PRS, A141 (1933), in Rutherford, CP, 3 , 330–4; Allibone in Hendry, Cambridge physics , 158–9, 161–2, 169; Wynn-Williams in ibid., 142–7; Hendry, ibid., 114–9.
physicists and industrial engineers.
By February 1933 Oliphant and Rutherford were extending Cockcroft and Walton's results, provoking the disintegration of lithium with protons of only 100 kV. "It is a great show! But who would have thought that anything would happen at 100,000 volts, except perhaps Rutherford?"[18] In June, about the time the heavy water came to hand, they presented an account of their work on proton disintegration. They found that lithium's threshold stood at 20 kV and boron's at 60 kV; that beryllium's could not be determined because of its very small yield; and that in elements heavier than boron, except for a trace at fluorine, even the most energetic protons available, at 200 kV, did not stimulate disintegration. Oliphant and Rutherford traced apparent reactions in heavy metals such as gold to disintegration of boron impurities from the glass walls of their pyrex discharge tube.[19] This was an important warning. Lawrence did not heed it: he was too busy running through the periodic table, too eager to accept the astounding, to take the time to track down subtle effects.
When he ran Lewis's water against lithium, Oliphant detected particles of 13.2-cm range, which he identified with Berkeley's particles of 14.8 cm. "The Professor seems very happy."[20] Soon Oliphant and Rutherford confirmed the existence of rays that penetrated to 8.2 cm, which they showed to be alpha particles with the maximum energy possible in the reaction Li7 (d,n)2a .[21] Walton informed Cockcroft, then visting the Laboratory, of the good general agreement of Cambridge's results with Berkeley's. Cockcroft found himself curiously placed: he sat in the camp of one of his competitors while his partner, Walton, sat in the other. He decided that the most attractive subject for them was the prolific 18-cm proton, which Oliphant and Rutherford could not excite and Lawrence's company could not stop to study. "We ought to be able to get many of these [Cockcroft advised Walton]
[18] Fowler to Bohr, 15 Feb [1933], in Hendry, Cambridge physics , 107.
[19] Oliphant and Rutherford, PRS, A141 (1933), in Rutherford, CP, 3 , 335–7, 343, 349–50; Rutherford to Hevesy, 3 Apr 1933, in Eve, Rutherford , 370.
[20] Dee to Cockcroft, 10 Jun 1933 (CKFT, 20/4), quote; Rutherford to Boyle, 28 Jul 1933, in Eve, Rutherford , 374.
[21] Dee to Cockcroft, 7 Jul 1933 (CKFT, 20/7); Oliphant, Kinsey, and Rutherford, PRS, A141 (1933), 722–33, in Rutherford, CP, 3 , 354–6, 358–60.
and I hope you will be able to [borrow] some of the Professor's
The Cavendish work, and Rutherford's congratulations to Lawrence on the "fine reward for his labour in developing his accelerated [!] system," pleased the Berkeley group and probably helped to harden their belief in what Lewis called "the most important discovery so far[:] the essential instability of the H2 nucleus and the low mass of the neutron." Cockcroft was also pleased at the confirmation obtained using the Oliphant-Rutherford accelerator. That had given him the hope that with the Cockcroft-Walton machine it would be possible to detect the 18-cm protons, for which Lawrence gave a threshold of 700 kV. "If so [Cockcroft wrote Rutherford] it [sic] will find a whole lot more work to be done with the present apparatus."[23]
To make all this work possible, the Cavendish required a steady supply of heavy water. Rutherford detailed a visitor, Paul Harteck, from the Kaiser-Wilhelm-Institut für Chemie, to the task. The Cavendish apprentice system in this respect paralleled Berkeley's: Harteck had been told to help with electronic counters, but was reassigned because of his knowledge of chemistry when Rutherford decided to domesticate the manufacture of deuterium. The change did not please Harteck. "I must take on the production of heavy water at the wish of the high Lord," he wrote his patron, K.F. Bonhoeffer. "If you know anything [about it], write me soon, for with the Lord everything must go very quickly. . . . You must hurry, since heavy water evidently seems to be no rarity in America."[24] The gift from Lewis took the heat off Harteck, who had not succeeded. An application to Lewis for information elicted a full answer that did not help; and by the end of June,
[22] Walton to Cockcroft, 20 June 193[3] (CKFT, 20/35); Cockcroft to Walton [24 June 1933] (ER).
[23] Lewis to Rutherford, 12 Jul 1933, and Cockcroft to Rutherford, 22 Jul 1933 (ER).
[24] Harteck to Bonhoeffer, 28 Apr and 12 May 1933 (Harteck P). Cf. Harteck and Streibel, Zs. anorg. und allgem. Chemie, 194 (1930), 299.
Harteck could only imagine that there was some trick to the business that had been withheld from him. Rutherford then lost half the original sample. Had Lewis then turned off his water, the Cavendish deuteronomers would have been out of business until the end of October, when Harteck managed to make enough heavy water at sufficient concentrations for their needs.[25]
There was already good reason to worry that Berkeley water did not give the same results in England as at home. Walton and Dee saw only a few 18-cm protons, nothing like the profusion the Berkeley group had reported. "I noticed Lawrence's views about the nature of these tracks," Rutherford wrote Lewis at the end of July, "but we are at the moment not inclined to view with favour the conversion of a deuton into a neutron of mass about 1. However, it is too early to take definite views."[26] The principal parties then relaxed for the summer, to prepare for more definite views in the fall.
The Error
At Berkeley preparation included improvements in the cyclotron, which made possible production of 0.02 µA of 3 MeV deuterons, and curing "vacuum troubles and other misfortunes" that kept the machine down for most of September.[27] When the streams began to flow, they called forth showers of neutrons from everything they hit, a confirmation most agreeable to the minds, but also threatening to the bodies, of the cyclotroneers.[28] (The Laboratory was so full of stray neutrons that an investigator quirky enough to have tested the fillings in his teeth might have discovered artificial radioactivity.) Another set of doubters then
[25] Harteck to Lewis, 4 June, and Lewis to Harteck, 23 June 1933 (Lewis P); Harteck to Bonhoeffer, 9 and 28 June 1933 (Harteck P); Rutherford to Lewis, 27 Jul, 10 Aug, 21 and 30 Oct 1933 (Lewis P); Cockcroft to Rutherford, 23 Aug and 29 Sep 1933 (ER). Imperial Chemical Industries had trouble with the plant it built not long after Harteck got his first heavy droplets; Fowler to Lewis, 3 Feb 1934 (Lewis P).
[26] Darrow to Lawrence, 11 Oct 1933, Livingston to Darrow, 20 Oct 1933, and Lawrence to Darrow, 20 Nov 1933 (6/9); Rutherford to Lewis, 27 Jul 1933 (Lewis P).
[27] Lawrence to Cooksey (5/4) and to Tuve (3/32), 23 Sep 1933.
[28] Lawrence to Barton, 28 Sep 1933 (2/25), to Beams, 4 Oct 1933 (2/26), and to Tuve, 9 Oct 1933 (3/32); Lewis to Rutherford, 5 Oct 1933 (ER).
entered the game. Richard Crane, a junior collaborator of Lauritsen's at Caltech, came to Berkeley, collected some heavy water, dribbled it on a beryllium target in Lauritsen's machine, and got "enormous quantities of neutrons." That was of course most gratifying, "in entire agreement with our expectations," Lawrence wrote Cockcroft, "though the precise interpretation is as yet ambiguous." The point of imprecision was whether Crane's neutrons came from the disintegration of the beryllium target or of the deuteron projectile. In either case, however, Lawrence thought that Crane's evidence favored a value of the neutron mass close to unity.[29]
Once the cyclotron returned to work, Livingston and Henderson found quantitative evidence of the deuteron's instability. They counted the number of "disintegration" protons (some 40,000 per minute registered in their ionization chamber) and then the number of "recoil" protons reported by the same chamber when covered with a wax-coated lead screen (12/min.). Their previous estimate of the probability of the conversion of neutrons to protons in wax suggested that 40,000 neutrons would make around 12 protons. Hence neutrons and protons appeared in equal numbers, which would be necessary if they came from the breakup of deuterons. They realized that this agreeable agreement had "profound theoretical implications" through its relevance to the value of the neutron mass, which they set at 1.0006. Their report, signed also by Lawrence, appeared on November 1.[30]
At Cambridge preparation included completing reports for the Solvay conference to be held in Brussels at the end of October. Cockcroft had responsibility for reviewing particle accelerators and Chadwick for the state of knowledge about neutrons. Lawrence contributed by sending Cockcroft information about the cyclotron and by bringing his latest evidence for disintegration to the Solvay meeting in person. The invitation to attend, at his own expense for travel, was a great honor; Lawrence was but the eighth American so distinguished since the conferences began in 1911
[29] Quotes from, resp., Lawrence to Tuve (3/32) and to Cockcroft (5/4), 23 Sep 1933.
[30] Livingston, Henderson, and Lawrence, PR, 44 (1933), 782; Lawrence to Tuve, 9 Oct 1933 (3/32); Lawrence to R.C. Gibbs, 9 Feb 1933 (9/16), on Henderson.
and the only one in 1933. He declared himself "surprized and tremendously pleased,"[31] though the invitation came very late, some six weeks before the meeting (he owed it to Peter Debye, a member of the Solvay scientific committee, who had visited Berkeley the previous summer and taken a fancy to the Sloan x-ray tube).[32] Lawrence went to this most august of physicists' gatherings (fig. 4.1), the first international meeting he had ever addressed, to correct the opinions of Chadwick, Cockcroft, and Joliot, who also had a candidate for the neutron mass. "I particularly want to make some rather extensive remarks on Cockcroft's report."[33]
Fig. 4.1
McMillan's apparatus for studying the absorption of gamma rays by various
materials. The rays scatter at right angles to the proton beam from the target
and enter through the mica window. McMillan, PR, 46 (1934), 868.
[31] Lawrence to Cockcroft, 2 Jun and 16 Sep 1933 (4/5); to Beams, 16 Sep 1933 (2/26); and to Swann, 28 Sep 1933 (17/3), quote.
[32] Lawrence to Cooksey, 5 Oct [1932] (4/19); Debye to Langevin, 8 Oct 1932 and 16 Sep 1933 (Langevin P, "Solvay 1933").
[33] Lawrence to Langevin, 4 Oct 1933 (Langevin P, 75). Each participant was asked to state the points in others' reports on which he wished to speak; Bethe to Langevin, 10 Oct 1933 (Langevin P, "Solvay 1933").
Cockcroft ended his report with an unenthusiastic review of Berkeley work. He accepted the alpha particles from the bombardment of lithium and presented the data about the 18-cm protons, but declined to entertain the hypothesis of disintegration. "It is rather superfluous to discuss further the nature of the transformations with proton emission until we have more experimental information." And how to get the information? From improved Cockcroft-Walton machines. The weak current the cyclotron brought to the target, one-thousandth the flux from the "direct" Cambridge method, might well wash out the advantage of the greater efficacy of its faster particles. "Our present information does not suffice for prediction."[34]
Lawrence's extensive comments centered on the cyclotron method and its latest achievements—hydrogen-molecule ions of over 5 MeV, deuterons of 3.6 MeV, a promise of protons at 3.5 MeV, evidence of the disintegration of heavy hydrogen in the fields of target nuclei, and numbers that made the neutron's mass unity. These last remarks made Lawrence himself the object of a bombardment. Heisenberg observed that if disintegration occurred in the electric field of a nucleus, the yield should decline for heavy targets since the deuteron's penetration, and hence the rate of change of force on it, must decrease with increasing atomic number (Z ); for (very) high Z the field would appear to the deuteron to change adiabatically and produce no disintegration at all. That being the case, added Bohr, we might suppose that the deuteron splits after entering a nucleus; but then the speed of the ejected proton should increase with atomic number, like the nuclear Coulomb field, contrary to Lawrence's results.[35]
Then came the experimentalists. Rutherford said that he had found no neutrons from lithium under deuteron bombardment. Chadwick reaffirmed the value of the neutron mass at between 1.0067, which he deduced from the hypothetical reaction B11 (a ,n)N14 , and 1.0072, which he had deduced from Li7 (a ,n)B10 . Joliot and Curie came forward with a neutron still heavier than Chadwick's. Their careful examination of decay products of
[34] Cockcroft, Solvay, 1933, 50–5; cf. Oliphant, PT, 19:9 (1966), in Weart and Phillips, History , 181.
[35] Solvay, 1933, 71, 72.
alpha-bombardment of boron and other light elements had disclosed quantities of positive electrons along with neutrons. They supposed that these particles came away simultaneously, according to the reaction B10 (a ,ne+ )C13 , and constituted when together the familiar proton. In place, therefore, of Chadwick's initial conception, that n = p + e– , they now proposed p = n + e+ . So much, and much more, was tied up in the question of the neutron mass. Calculations based on the transmutation of B10 made mn = 1.012. This big mass had the advantage of accounting for the stability of the hydrogen atom, since it prevented the spontaneous union of its proton and electron into a neutron; but it made the decay of the neutron into a proton, electron, and neutrino energetically possible.[36] The only difficulty that Joliot and Curie saw with their fat neutron was the conflicting experience in Berkeley. They were prepared to compromise: "It is not impossible that it will be necessary to suppose the existence of neutrons with different masses," theirs being the elementary one and Lawrence's a condensed combination of the elementary with an electron-positron pair.[37]
Lawrence responded to these challenges by invoking suppositious gamma rays, whose inclusion in the energy balance would lower the neutron mass. Chadwick denied the gammas and insisted, against Joliot and Curie, that the neutrons came from the more plentiful isotope B11 , with the mass he had assigned them. After this exchange the theorists could only feign hypotheses and await the outcome of the squabble.[38] As perhaps no one outside France expected, victory eventually fell to Joliot and Curie.
[36] Solvay, 1933, 77, 101–2, 155–6; Curie and Joliot, CR, 197 (1933), 237 (17 Jul 1933), in Oeuvres , 417–8; Langevin, "Rapport sur les titres et travaux de M. Frédéric Joliot" (Langevin P, 73/2); Pauli to Joliot, 1 Feb 1934, in Pauli, Briefwechsel, 2 , 271.
[37] Joliot, Solvay, 1933, 156. This was to recur to the hypothesis of A. von Grosse, PR, 43 (1933), 143, who supposed neutrons of various masses to explain the energy spctrum in beta decay. Cf. Pauli to Heisenberg, 14 Jul and 30 Sep 1933, in Pauli, Briefwechsel, 2 , 185, 216.
[38] Solvay, 1933, 165–9; Pauli to Heisenberg, 17 Apr 1934, in Pauli, Briefwechsel, 2 , 316. Chadwick had wanted to talk about the mass and nature of the neutron (letter to Langevin, 13 Oct 1933, Langevin P), but, apparently, not to listen.
On his way back to Berkeley, Lawrence stuck his head into the Cambridge lions' den. Chadwick bared his claws, to such effect that his behavior needed explanation. It was found in the consideration that he had been the effective director of the Cavendish for some time and was too overworked to observe the niceties of philosophical combat. With the other lions, especially Cockcroft and Rutherford, who licked his chops over Berkeley's "broth of a boy," Lawrence got along well. They merely roared in a friendly way against the hypothesis of deuteron disintegration and pointed their paws at the possibility that Lawrence had contaminated his targets and tank.[39]
Back at home Lawrence mobilized Lewis and switched Livingston and Henderson from trying to withdraw a beam from the cyclotron to clearing up the enigma of the 18-cm protons. Livingston arranged a target holder that would make possible bombardment of many samples in succession to test possible contamination.[40] Working night and day through the Thanksgiving holiday, Lawrence and his group found the yield of protons from deuterons to be unaffected by their efforts to clean up their targets. "Perhaps before long the evidence will be such as to convince the most skeptical, including those at Caltech and even Chadwick."[41]
The Caltech team, Crane and Lauritsen, suggested several possible complications in the analysis of Berkeley's experiments (for example, that the neutron found in deuteron bombardment of lithium might come from Li7 (p)2a followed by Li7 (a ,n)B10 ), and could find no trace of the 18-cm protons.[42] Then Tuve's group, which had the only machine then capable of checking Berkeley's results above a million volts, entered the picture. Lawrence had visited the Carnegie Institution on the way back from Brussels. "I persuaded Tuve to investigate the origin of the 18 cm protons and
[39] Edward Pollard to Lawrence, 6 Dec 1933, and reply, 20 Dec 1933 (14/30); Lawrence to Cockcroft, 20 Nov 1933 (5/4); Cockburn and Ellyard, Oliphant , 74. Rutherford to Lewis, 30 Oct 1933 (Lewis P): "He is a broth of a boy, and has the enthusiasm which I remember from my own youth."
[40] Lawrence to Cockcroft (5/4), to Cooksey (4/19), and to Darrow (6/9), all 20 Nov 1933.
[41] Lawrence to Gamow (7/25), to Poillon (15/16A), and to Haupt (9/2), quote, all 4 Dec 1933.
[42] Crane and Lauritsen, PR, 44 (Nov 1933), 783–4 (letter of 14 Oct).
the hypothesis of the disintegration of the deuteron right away," Lawrence wrote Cockcroft. "I want to get the matter cleared up as soon as possible and it will be a great help if Tuve, with his independent set up, will investigate the problem."[43]
The experiments went forward everywhere at an American pace. Lewis prepared two samples of calcium hydroxide, one with ordinary and the other with heavy hydrogen. Under bombardment by 3 MeV deuterons the ordinary target showed nothing extraordinary, whereas the heavy target yielded a cornucopia of 18-cm protons. What could be clearer? The bombarding protons broke up the bound deuterons. Lawrence dispatched this "unambiguous proof of d[e]uton disintegration" to the Cavendish; "It would seem now that even Chadwick will agree."[44] The same message went to the East Coast, to Pollard at Yale ("these recent observations definitely rule out the possibility of impurities") and Beams at Virginia ("the deuton is energetically unstable and disintegrates into a proton and a neutron"); to all other physicists through the Physical Review ; and, of course, to the Research Corporation. "We have proved beyond any reasonable doubt that the deuton explodes when struck hard enough. . . . This first definite case of an atom that itself explodes when properly struck is of great interest, not only as a possible source of atomic energy, but especially because it is not understandable on contemporaneous theories. . . . [It] promises to be a keystone for a new theoretical structure."[45] The flaw in the hydroxide experiment, which we shall reveal in a moment, was no more subtle than the hint about cheap energy. So far did hope, ambition, impatience, and a need for benefactors drive Lawrence from the objectivity he would have claimed as the first virtue of the scientist.
When the Cambridge atom splitters returned from Brussels, they had a fountain of dilute heavy water and samples of almost
[43] Tuve to Lawrence, 30 Jan and 12 Sep 1933 (3/32); J.A. Fleming to Lewis, 9 May 1933 (Lewis P); Lawrence to Cockcroft, 20 Nov 1933 (5/4).
[44] Quotes from, resp., Lawrence to Walton, 20 Dec 1933 (18/1), and to Fowler, 28 Dec 1933 (7/12); Lawrence to Rutherford, 20 Dec 1933 (ER); Lewis, Livingston, Henderson, and Lawrence, PR, 45 (1933), 497.
[45] Lawrence to Pollard, 20 Dec 1933 (14/30), to Beams, 28 Dec 1933 (2/26), and to Poillon, draft enclosing report for the year 1933, 15 Dec 1933 (15/16A); Lewis, Livingston, Henderson, and Lawrence, PR, 45 (1934), 242–4 (rec'd 3 Jan).
pure deuterium created in their absence by the finally successful, and consequently now esteemed, Harteck. His achievement came in good time, since Lewis's still had run dry and he could supply nothing until just before the Solvay Congress.[46] Now, with sufficient stock to hand, Rutherford and a research student, A.E. Kempton, returned to the master's old game, let alpha particles from polonium plunge through deuterium gas (the inverse of deuterons on helium), and found no evidence of fast disintegration protons.[47] Cockcroft and Walton sent deuterons against copper and gold and likewise detected no protons.
In the middle of December, Rutherford gave a speech at the Royal Society summarizing the latest evidence. He and Oliphant had at last found neutrons from deuterons on lithium, and Lauritsen neutrons from deuterons on beryllium; but whereas everyone associated these neutrons with nuclear transformations, Lawrence plumped for what Rutherford dismissed in a letter to Bohr as an "exothermal nucleus," and, together with Livingston, offered very shaky evidence that ruled out the reaction Li7 (d,n)2a as the source of the Cambridge neutrons.[48] Another Cavendish man, D.E. Lea, countered the hypothesis of the deuteron's instability by ascribing the hard gamma rays he observed from wax irradiated by neutrons to the spontaneous, endothermic formation of deuterons.[49]
[46] Harteck to Bonhoeffer, 21 and 24 Oct, 5 and 24 Nov, 2 Dec 1933 (Harteck P); cf. "Discussion on heavy hydrogen," PRS, A144 (1934), 27 (Rutherford), 10–1 (Harteck); Lewis to Rutherford, 5 Oct 1933 (Lewis P).
[47] Rutherford and Kempton, PRS, A143 (1934), 724–30, in Rutherford, CP, 3 , 377–83.
[48] Rutherford, Nature, 132 (23 Dec 1933), 955–6; Oliphant, Kinsey, and Rutherford, PRS, A141 (1933), 722–33, in Rutherford, CP, 3 , 358; Lawrence and Livingston, PR, 45 (1934), 220 (letter of 3 Jan). "Exothermal nucleus" comes from Rutherford to Bohr, 3 Jan 1934 (ER). Lawrence and Livingston's evidence: there appeared to be too many neutrons in comparison with the number of alpha particles to agree with the supposed reaction.
[49] Lea, Nature, 133 (6 Jan 1934), 24. Lea's observations did concern deuteron synthesis, but not, as he thought, by direct action of the fast neutrons with the wax protons. Only after they have been slowed by collisions in the wax do the neutrons become very effective for making deuterons. Thus Lea, and Chadwick and Goldhaber, who questioned his results, missed the grand discovery of thermal neutrons later made by Fermi, who mentioned Lea's work. Goldhaber in Stuewer, Nuclear physics , 93–4, and in Hendry, Cambridge physics , 191–3; Fermi, CP, 1 , 757.
Lawrence sought protection behind his big gun. Your conclusions are "hardly justified," he told Cockcroft, since the Cavendish experiments had run at under 600 kV.[50] Beginning at 700 kV things became more interesting. Lauritsen had then recently found many neutrons from fast deuterons on beryllium, carbon, and even copper. That, Lawrence crowed to Livingston, amounted to unquestionable corroboration of their experiments. "Chadwick will have to come down off his high horse now." The word at the Laboratory was that Lawrence had "clinched his mass of the neutron—though the evidence [as Kurie rightly objected] is not as clear as I'd like to see." Why did Rutherford not find fast protons from alpha particles on deuterium gas?[51] Lawrence tried to convince the reigning theorist in the business, Gamow, whom he had met at the Solvay conference; Gamow found the fog of conflicting experimental findings too dense to penetrate and offered to "come to California and try to split nuclei by pure theory."[52]
The Fruit
The Cavendish experimenters instead resolved the matter by pure experiment. At the end of February 1934, Cockcroft reported that they had at last detected fast protons from deuteron bombardment of copper, iron, gold, and yttrium, at energies down to 200 kV. Also, and the eventual key to the problem: "Oliphant is getting queer results with H2 and H2 ." Oliphant and Harteck had made up targets like NH4 Cl containing heavy hydrogen. When bombarded with protons, the targets behaved as if constituted entirely of ordinary hydrogen. When shelled with deuterons, they gave off protons with a range of 14.3 cm, which the Cavendish researchers tacitly identified with Berkeley's 18-cm rays. And this irrespective of the deuterons' energy, as long as it exceeded 20 keV. At 100 keV the effect was too large for recording on the
[50] Cockcroft to Lawrence, 21 Dec 1933, and response to Cockcroft, 12 Jan 1934 (4/5).
[51] Livingston to Lawrence, 23 Jan 1934, and Lawrence to Livingston, 26 Jan 1934 (12/12); Kurie to Cooksey, 6 and 21 Mar 1934 (10/21).
[52] Lawrence to Gamow, 28 Dec 1933, and Gamow to Lawrence, 12 Jan 3[4] (7/25).
sensitive detector of the Oliphant-Rutherford apparatus, so great in fact that Oliphant and Rutherford at first ascribed it to a burst of x rays. Analysis of range and energy, confirmed by cloud chamber pictures, showed that the protons arose from the reaction d+d ® H3 +p. They also found the neutrons that Lawrence had advertised. Rutherford discerned their origin in the competitive reaction, d+d ® He3 n.[53] Oliphant broke the news gently. "We suggest very tentatively that your results may be explained as due to the bombardment of films of D and of D compounds. . . . I hope these results are of interest to you."[54]
The puzzle Lawrence started had therefore the simple solution of contaminated apparatus: deuterons stuck in the walls of the cyclotron chamber and in the targets gave the plentiful d-d reaction when bombarded by deuterons; the fast protons, apparently from everything, which had prompted the disintegration hypothesis, did in fact come from deuterons, not from the target, but in consequence of fusion, not disintegration. The accelerator men at Caltech and Carnegie also offered plentiful evidence that Berkeley's results came from synthesis of deuterons with pervasive contaminants. Lauritsen and Crane showed that the fast protons from deuterons on carbon came from C12 (d,p)C13 , an observation extended by Cockcroft and Walton to explain, as a consequence of oil films on metals, why deuterons appeared to knock protons from copper and tungsten. Tuve and Hafstad repeated all the Berkeley experiments with carefully controlled beams on immaculate targets and found that the Berkeley experimenters had got nothing right. With a chamber contaminated with deuterons, however, they had no trouble recovering Berkeley errors.[55] The demonstration with the hydroxide targets, which Lawrence had thought so convincing, also failed through ubiquitous deuterons.
[53] Cockcroft to Lawrence, 28 Feb 1934 (4/5); Oliphant to G.P. Thomson, 9 Mar 1934 (GPT, D/1), on Dee's confirmation with the cloud chamber; Dee, Nature, 133 (14 Apr 1934), 564; Oliphant, Harteck, and Rutherford, Nature, 133 (17 Mar 1934), 413, in Rutherford, CP, 3 , 364–5, expanded in PRS, A144 (1934), 692–703, in CP, 3 , 386–96; Cockburn and Ellyard, Oliphant , 53–5.
[54] Oliphant to Lawrence, 12 Mar 1934 (10/16).
[55] Lauritsen and Crane, PR, 45 (1934), 345–6 (letter of 15 Feb); Cockcroft and Walton, PRS, A144 (1934), 704–9, 717–9; Tuve and Hafstad, PR, 45 (1934), 651–3 (letter of 14 Apr).
As Lauritsen and Oliphant independently explained it to Lawrence: the proton beam playing on Ca(DH)2 liberated deuterons by collision or exchange; these deuterons then joined the bombardment and produced the 18-cm protons by d-d synthesis.[56]
The hunters horsed to catch the hare let loose from Berkeley were formidable: the Cavendish from the top down and the experienced teams and big machines at two of the best-endowed physics research institutes in the United States. Resolution of the conflicting results required very careful experiment in previously unexplored regions of multiple, competing nuclear reactions; and it required, and abetted, discovery of the occult d-d fusion process and the isobars of mass three. That detection and analysis of deuterium fusion was not so easy as its plentiful yield might suggest appears from the struggles of Otto Frisch, who proposed to Bohr that they build a big source of neutrons utilizing the d-d reaction. He had a machine available in December 1934. As late as the following March he had not detected a single neutron, although he commanded 60 kV, far above the threshold reported by Oliphant, Harteck, and Rutherford. He did succeed eventually, as did G.P. Thomson, who also had trouble reproducing the Cambridge results.[57]
In accordance with the social expectations of science, Lawrence confessed himself chagrined at the "stupidity" of his error, and Cockcroft softened the blow with the falsehood that "for a long time Rutherford and Chadwick were nearly convinced that you were right" and the truth that the experiments of Lawrence, Lewis, and Livingston had brought "an important enlargement of the field of nuclear research."[58] Lawrence diagnosed his stupidity as a consequence of the great productivity of the cyclotron, which
[56] Lawrence to Cockcroft, 14 Mar 1934 (5/4), and Lewis, Livingston, Henderson, and Lawrence, PR, 45 (1934), 497 (letter of 15 Mar), re Lauritsen's suggestion; Oliphant to Lawrence, 12 Mar 1934, and Lawrence to Oliphant, 5 June 1934 (10/16). Kurie to Cooksey, 16 Mar 1934 (10/21): "Lauritsen has thrown the final monkey wrench in the disintegration hypothesis."
[57] Frisch to Meitner, 25 Mar, to Bohr, 29 Jun, and to Rausch von Traubenberg, 28 Dec 1934; to Meitner and to his father, 10 Mar, and to Jacobsen, 5 Apr 1935; and to Meitner, 27 Oct 1937 (Frisch P); Thomson to Oliphant, 5 Mar 1935 (GPT).
[58] Quotes from, resp., Lawrence to Cockcroft, 14 Mar 1934, and Cockcroft to Lawrence [1934] (4/5), and Cockcroft and Walton, PRS, A144 (1934), 704.
discouraged "methodical, quantitative, measurements;" a healthy point of view that enabled him soon to dismiss the experiments that had prompted his error as "of the character of a preliminary survey."[59] He had persisted in his errors, however, in the face of warnings from many sides of the likelihood of contamination.[60]
This flouting of good advice and good procedure irritated some of Lawrence's closest associates. Tuve wrote Cockcroft: "From our own experiments we feel that the important issue is rather one of judgment and point of view rather than of the errors in technique which can give rise to such a situation." Lawrence had botched everything so badly that the corrective, as Tuve wrote in an internal report, "will be a difficult thing to present in public." Kurie wrote Cooksey: "The Englishmen are doing what seem at this distance to be clean experiments, but Ernest and Malcolm [Henderson] are too excited to go slowly." These expressions of disappointment appear to reflect a worry that Lawrence's way of doing science and his rising celebrity in the United States might compromise American physics just as it was assuming world leadership. Cockcroft agreed that Lawrence's style did not suit nuclear physics. "There is a real danger of the subject getting into a mess, and I feel that the only thing to do is to delay publication until we are reasonably sure."[61]
Tuve did not hide his irritation from Lawrence. Their different institutional settings and personal ambitions had become more important in determining their scientific ethos than their similar backgrounds and almost identical scientific interests. In the spring of 1934 Tuve advised Lawrence to withdraw his faulty claims formally, a step not only ethically sound but also useful to Tuve, who would be spared the obligation of a public exposé. Lawrence replied petulantly. In the summer of 1934 Tuve carried the attack
[59] Quotes from, resp., Lawrence to Rutherford, 10 May 1934 (ER), and to Beams, 13 Apr 1934 (2/26); Lawrence, PR, 47 (1935), 17; Oliphant, PT, 19:9 (1966), in Weart and Phillips, History , 182–4.
[60] E.g., in letters from Boyce, 23 Jan 1933 (3/8), Cockcroft, 30 Mar 1933 (5/4), and Fleming, 10 May 1933 (3/32).
[61] Tuve to Cockcroft, 18 Apr 1934, and Tuve, "Memorandum," 3 Apr 1934 (MAT, 5); Cockcroft to Tuve, 30 Apr 1934 (CKFT, 20/80), the latter also in Hartcup and Allibone, Cockcroft , 65; Kurie to Cooksey, 4 Mar 1934 (10/21). Cf. Beams to Lawrence, 7 Apr 1934 (2/26), and Tuve, Hafstad, and Dahl, PR, 48 (1935), 316, in Livingston, Development , 29.
to Berkeley, to a meeting of the American Physical Society. Either the hospitality or the prevailing genius of the place caused the secretaries who reported the discussions to nod: they attributed to Tuve the irenic solution that his and Lawrence's results could be brought into harmony by considering the different apparatus and energy with which they worked. Not a mention of contamination or haste. Tuve could not allow that to pass, since it implied that not Lawrence, but he, had been wrong. He therefore wrote to Science , which had published the irenic report, to point out that the Berkeley group had abandoned their major claims and withdrawn many of their results, "which have been sought for but not verified," and which, by confusing the subject, had "delayed some-what the examination of these questions."[62]
To recover his standing, Lawrence thought to make a few "precise and trustworthy measurements." The deuteron business brought home forcefully, he told Cockcroft, that most of the Laboratory's fast data had no value. Accordingly, Lawrence made an elaborate study of the excitation and decay products of the useful isotope radiosodium, a novelty whose discovery will occupy us presently. Up to the maximum energies he used (1.9 MeV), deuterons seemed to induce transformations in sodium in the amounts predicted by Gamow's theory. But continuation of the experiments to aluminum and to higher energies in collaboration with a new recruit to the Laboratory, a postdoc from Princeton named Edwin McMillan, who knew how to work exactly, showed excitation larger than Gamow allowed. The departure of their measurements from a theory that worked well for protons and alpha particles interested Oppenheimer and his student Melba Phillips, who had just finished failing to explain the curious rise of absorption beyond the series limit in Lawrence's old reliable measurements on the photoeffect.[63]
When a fast deuteron enters a heavy atom, Coulomb repulsion slows its proton and so increases the relative velocity of its constituents. Under these circumstances, the nucleus may capture the
[62] Tuve to Lawrence, 17 Apr 1934, and response, 20 Apr 1934 (17/34); Tuve to Darrow, 28 Jul 1934, and to Cattell, 4 Aug 1934 (MAT, 13/"lab. letters"); Ward, Science, 80 (20 Jul 1934), 49, and Tuve, ibid., 17 Aug 1934, 161–2, quote.
[63] Lawrence to Cockcroft, 14 Mar 1934 (5/4), and to R.W. Ditchburn, 13 May 1933 (6/16).
neutron. The released proton then makes an appearance in the world. Encouraged by this attractive possibility, which occurred to several physicists, Lawrence, McMillan, and another new postdoc, Robert Thornton from McGill, pushed on to silicon and copper. Their results agreed exactly with the calculations of Oppenheimer and Phillips for a binding energy of the deuteron—about 2 MeV—that agreed very well with values obtained from mass-energy balances in nuclear transformations as measured by others.[64] Here was a point for the underdog. "I am amazed at the agreement," Lawrence wrote Rutherford. And also incurable: with the new mechanism, deuterons with available energies might provoke nuclear reactions "much further up the periodic table than one could ever have hoped for."[65]
There was another point for Lawrence's side of the story. Maurice Goldhaber, an émigré research student at the Cavendish, suggested to Chadwick an idea for an experiment that he had brought from Berlin: the photodisintegration of the deuteron. Goldhaber recalled that Chadwick showed little interest in the matter until told that if successful it would give data from which the neutron's mass could be deduced.[66] Telltale protons announced the disintegration of deuterons in heavy water irradiated by the hardest photons then available, the gamma rays of 2.6 MeV from ThC", of which the Cavendish had a good supply. With a preliminary determination of the kinetic energy of the proton, Chadwick and Goldhaber had a value of the neutron's mass without making assumptions about the mass of complex nuclei:
mn = md – mp + Eg – 2Ep» 1.0081.
Their value, almost midway between Chadwick's and the Joliots', is close to the modern one (1.0085). Since the mass of the proton was known to be 1.0078, it followed that Chadwick's neutron was radioactive. Its decay was first observed in 1948.[67] The discovery
[64] Oppenheimer and Phillips, PR, 48 (1935), 500–2. Cf. Pollard to Lawrence, 6 Dec 1933 (14/30); Oppenheimer to Bethe, "27 Nov," and Fleming to Bethe, 7 June 1935 (HAB, 3).
[65] Lawrence, McMillan, and Thornton, PR, 48 (1935), 494; Lawrence to Rutherford, 17 Apr 1935 (15/34), quote; Lawrence, Ohio jl. sci., 35 (1935), 404.
[66] Goldhaber in Stuewer, Nuclear physics , 84–8, summarized in Goldhaber in Hendry, Cambridge physics , 190–1; Bethe to F.W. Loomis, 5 May 1938 (HAB, 3).
[67] Chadwick and Goldhaber, Nature, 134 (1934), 237, disconfirming Lauritsenand Crane, PR, 45 (1934), 550–2 (letter of 24 Mar), whose careful study of Li (d,n)2a had recovered Chadwick's earlier value (mn = 1.0068), and Curie and Joliot, Nature, 133 (12 May 1934), 721, whose review of (a ne ) reactions had confirmed their own value (mn = 1.010). Cf. Ladenburg, PR, 45 (1 Feb 1934), 224–5, and PR, 45 (1 Apr 1934), 495; Chadwick, Feather, and Bretscher, PRS, A163 (1937), 366–75, giving mn = 1.0090. Chadwick and Goldhaber, PRS, A151 (1935), 479–93, predicted the decay of the neutron; the first observations took place in reactor laboratories after World War II. Feld in Segrè, Exp. nucl. phys., 2 (1953), 217–8.
of the photodisintegration of the deuteron gave rise to a new branch of nuclear investigation, to which the Berkeley Laboratory, which preferred to shoot particles it could accelerate, contributed very little. For a time the (g ,n) reaction appeared to be a promising source of neutrons.[68]
And finally, a point to be dilated later, the discovery of the d-d reaction, although instigated by cyclotron experiments, did not much recommend cyclotrons to nuclear physicists. Certainly it helped confirm the opinion of Rutherford, who had outplayed Lawrence with beams ten or even a hundred times less energetic than Berkeley's, that the Cavendish had no need for a cyclotron. More generally, it made possible a cheap substitute for the energetic neutron beams that, for a brief time, had been the peculiar preserve of large accelerators. It was now only necessary to have a supply of heavy water and a Cockcroft-Walton or Van de Graaff that could develop 100 or 200 kV, and one had a copious current of fast neutrons almost equal in energy courtesy of the peculiar sociability of deuterons.[69]