Walking side by side along a deserted beach three days later, Oppenheimer and Compton briefly considered recommending that scientists go no further down the road that might lead to the superbomb.19
But the case for standing still did not win out. Compton and Oppie agreed that those at Berkeley should proceed with their calculations. They set a date of late September for a conference at the Met Lab to further investigate thermonuclear reactions.20
Back in Berkeley, meanwhile, the physicists at LeConte had gotten over whatever initial angst they felt about the Super.21 Bethe discovered that Teller’s earlier calculations had underestimated the effects of a fundamental process in physics—the manner in which the energy of a nuclear explosion is dissipated through radiation.22 Not only did radiative cooling keep the planet safe from incineration by hydrogen bombs, Bethe pointed out, but it probably made the hypothetical Super itself unworkable. Konopinski briefly rescued Teller’s thesis by proposing to light the deuterium with tritium, which has a lower ignition temperature. But Bethe seemingly knocked that theory flat, too.
By the time Oppenheimer returned from his meeting with Compton, the excitement over atmospheric ignition and the hydrogen superbomb had, in Serber’s words, “fizzled out.” For reasons of haste as well as secrecy, seminar participants did not bother drafting a final report.
Fatefully, what was left behind were two very different impressions of the conclusions that had been reached about the Super. Teller believed that his colleagues shared his optimism about the prospects for the weapon. For Bethe, Serber, and Oppenheimer, on the other hand, the Super was at best an interesting possibility—one worthy of further study, but only after the atomic bomb was already in hand.*
* * *
Oppenheimer informed Conant and the S-1 Committee of the prospective Super in late August. Conant passed the word along to Bush, who in turn alerted Secretary of War Henry Stimson.23 In his report to Conant, Oppenheimer described a superbomb even more fearsome than that imagined by Teller at Berkeley. Oppie wrote that igniting 2 to 3 tons of liquid deuterium would produce an explosion equal to 100 million tons of TNT, laying waste some 360 square miles and contaminating the area with lethal radioactivity for several days.
So startling and gruesome was this vision that his audience either was disbelieving or may have felt some obligation to tone it down. The Super that Conant described to Bush—a half ton of deuterium, equivalent to 100,000 tons of TNT, devastating some 100 square miles—was terrible enough, but less world shattering.24
The good news, if it could be called that, was that a very much larger and more powerful atomic bomb—“6 times the previous size,” Conant wrote—was thought necessary to ignite a thermonuclear explosion. While the focus remained upon building the fission weapon, Conant and the S-1 Committee agreed to give new priority to a heavy water plant under construction in British Columbia. Originally designed to provide the moderator for Fermi’s reactor, the facility would be used instead to produce deuterium for experiments connected with the Super.25
* * *
At the same time that he was reporting to Conant on the hydrogen bomb, Oppenheimer learned from Compton that the army had balked at granting him a security clearance.26 The OSRD appealed the case to the army provost marshal’s office, which overruled the earlier decision and granted Oppie another temporary clearance, pending “a further investigation of this individual.” From Chicago, Compton assured Oppie that his radical past “would not prove a bar to … further work on the program.”27
Lawrence, too, was having his own trouble with security officials. On September 1, 1942, an aide to Bush informed Ernest that the list he had given of people “who know of the new Oppenheimer work”—Berkeley’s summer seminar—appeared incomplete. Bush was particularly upset that a construction engineer working for the army had somehow learned of the superbomb. Pointedly, Bush instructed the aide to “again remind [Lawrence] that this subject is to be discussed with no additional people at this time.”28
In response, Lawrence asked Oppenheimer to put together a new list.29 Oppie divided the names into three categories and sent the list to Conant on October 12. Group A knew “the whole story,” Oppenheimer wrote. Group B had been involved in “technical calculations which do in fact concern the military applications.” Group C had only done computations “and have essentially no knowledge of what it is all about.”
Rossi Lomanitz’s name was in Group B.
* * *
Security was being tightened in part because the army was about to take over the bomb project. Bush and Conant had agreed that the Corps of Engineers would assume oversight for building the mammoth industrial complex necessary to produce the weapon. Early in the summer, the corps had selected a Boston-based construction firm, Stone and Webster, as primary contractor.
The army also scouted out “Site X,” some 56,000 acres of hardpan, woods, and scrub in a remote area near Oak Ridge, Tennessee. The Tennessee Valley Authority would provide electrical power and the Clinch River cooling water for the secret factories. In mid-June 1942, the army authorized creation of a new district in the corps, specifically to carry out the work of building the bomb. Two months later, the Manhattan Engineer District (MED) was officially established by the corps in New York.30
Although he welcomed the army’s involvement, Lawrence still hoped to keep electromagnetic separation under his control. As late as mid-August, he was urging Sproul to approve the purchase of a privately owned parcel of land above the Rad Lab for a pilot plant.31 But the recent shelling of an oil refinery in the Pacific Northwest by a Japanese submarine had persuaded military authorities that the West Coast was too vulnerable.32
Meeting in Berkeley on Sunday, September 13, the S-1 Committee approved $30 million for construction of both a pilot plant and a production facility. The latter would theoretically
