nations as well, the U.S. and the U.K. All this might occasion a complete break-up of the relations that we have been counting on to make the peace. There was no saying to what terrible lengths this whole thing might go.” The Canadians told the British about Gouzenko and called in the FBI.
Late in September, Mackenzie King flew to Washington to brief President Truman, whom he met in the White House Oval Office with Dean Acheson:
Narrated the incidents regarding [Gouzenko]… Told them of the extent of espionage in Canada. What we had learned about espionage in the United States. Mentioned particularly… information regarding the atomic bomb… Spoke of the [Vice-]Consul at New York who apparently had charge of the espionage business in the United States… What was thought to have gone from Chicago [i.e., the samples of uranium]. Also the statement that an assistant secretary of the Secretary of State's Department[20] was supposed to be implicated…
Confronted with these shocking revelations, writes King, Truman asked that “above all nothing should be done which might result in premature action in any direction.” For the time being the several security agencies involved would keep their secrets and set out their snares. Gouzenko's information in any case hardly shone glory on their guardianship of state secrets.
With the end of the war, David Greenglass received an early furlough. He and Ruth visited New York together in September and stayed in the cold-water flat in his parents’ building where David had lived before he was married. The morning after the couple arrived, David would testify, Julius Rosenberg dropped by:
He came up to the apartment and he got me out of bed and we went into another room so my wife could dress… He said to me that he wanted to know what I had for him… I told him “I think I have a pretty good description of the atom bomb.”… He said he would like to have it immediately, as soon as I possibly could get it written up he would like to get it… During this conversation he gave me $200 and he told me to come over to his house… He then left and I was there alone with my wife… My wife didn't want to give the rest of the information to Julius, but I overruled her on that… I said that “I have gone this far and I will do the rest of it, too.”… We went down — it was late in the morning — we had a combination breakfast and lunch, and I came back up again and I wrote out all the information and drew up some sketches and descriptive material… I would say about twelve pages or so.
“I did not want [David] to give the information to Julius,” Ruth Greenglass confirmed. “The bomb had already been dropped on Hiroshima and I realized exactly what it was and I didn't feel that the information should be passed on. However, David said that he was going to give it to him again.”
The description of the implosion bomb which David Greenglass passed to Rosenberg that afternoon was garbled, but it contained useful information. He collected it in the course of his work and by being observant. He described the “lens molds” — the high-explosive lenses — as “pentagonal” in shape, incorrectly reported that there were thirty-six lenses (there were thirty-two) and indicated that the detonators were fired by capacitators. Most valuably, he described a key feature of the small initiator at the center of the assembly that supplied a burst of neutrons to start the chain reaction: “cone-shaped holes…, the apex of each cone being toward the periphery of the beryllium.” In the initiator, at the appropriate moment, implosion mixed polonium210 with beryllium. Po210 is a powerful source of alpha particles, which easily dislodge neutrons from beryllium atoms. The cone-shaped holes in the initiator served to break the barrier of nickel plating between the polonium and the beryllium and improve their timely mixing. Their design took advantage of the Munroe effect, the principle on which the shaped charge is based that is used in such devices as armor-piercing rockets like the famous bazooka of the Second World War: a cone focuses a shock wave moving through such a configuration to an intensely penetrating highspeed jet. Applying the Munroe effect to initiator design was a direct outgrowth of the experiments with two-dimensional implosion and the studies of jets in which both Greenglass and Klaus Fuchs had participated. Initiator design, significantly, was one of the most difficult aspects of implosion development and effectively paced the plutonium implosion project. Greenglass had learned about the Munroe effect and shaped charges in conventional explosives during his training at Aberdeen. The cone configuration was an advanced design, different from the initiator used in the Trinity and Nagasaki Fat Man units. Its Los Alamos inventors patented it; the patent went jointly to experimental physicist Rubby Sherr and Klaus Fuchs.
But Greenglass recalled including even more valuable information in the handwritten pages he passed to his brother-in-law in September 1945. He described and supplied a rough sketch of an experiment, he said later, “which was concerned with the reduction of the amount of plutonium to be used in the atomic bomb.” It was also concerned with increasing the efficiency of the explosion. “This experiment… consisted of one sphere of uranium inside of a larger sphere of uranium with a large air gap between the two spheres and stilts to hold the inner sphere apart from the outer sphere. I informed Rosenberg that the air gap was used to increase the speed with which the outer sphere is imploded. I told him this would result in a greater explosion with the use of less plutonium… I made up portions of this experiment as one of my duties at Los Alamos.”
The experiment Greenglass described to Rosenberg concerned two important improvements in implosion design: levitation and the composite core. Hans Bethe explains:
The solid core clearly was very hard to compress. Originally we had wanted a hollow shell, but we didn't trust the symmetry [of the implosion with that arrangement]. Then we decided, yes, we could after all have a hollow shell, and if we had a hollow shell, it was useful to have the very center solid. So that the hollow shell was pasted on the [tamper], so to speak. And the core [at the center] had to be levitated. The question was, could you make thin enough wires [levitating the core within the shell] which were strong enough, so that they could survive transportation by plane and [being dropped as a bomb]. They had to be strong enough, and yet small enough — thin enough — so that they wouldn't disturb the spherical symmetry. Because the spherical symmetry is all- important. Only [if the symmetry of the implosion is maintained] do you get the increase in density, which you bank on. In addition to that, with the hollow construction, you can put a little more material in. You can put in more than a critical mass. Which again increases the yield. And then already in the last month of [the war], we invented the composite [core], plutonium in the center and uranium outside, which [results in] a great increase in the yield. Plutonium was much more expensive than separated uranium. Three times maybe. Therefore, we would get a much better arsenal by having the mixtures.
Levitation gave the imploding shell time to acquire momentum before it hit the core. Nuclear-weapons designer Theodore B. Taylor explained the principle to the writer John McPhee once without naming it: “The way to get more energy into the middle was to hit the core harder. When you hammer a nail, what do you do? Do you put the hammer on the nail and push?” The solid Fat Man core had been pushed; levitation hammered. And because it increased efficiency, levitation also made it possible to design bombs of smaller diameters than Fat Man, lighter weapons more easily transportable by plane. The composite core, as Bethe points out, used less plutonium and resulted in increased yield as well, both important advantages. (The core Greenglass described, with a uranium shell and a uranium center, was a substitute, probably of plentiful and non-chain-reacting natural uranium, used in implosion experiments.)
Greenglass asked Rosenberg why Harry Gold had contacted him in Albuquerque instead of Ann Sidorovich. “She couldn't make it,” Rosenberg told him unhelpfully.
Max Elitcher remembered Julius Rosenberg phoning him from Washington's Union Station that September as well and coming over for a talk. Rosenberg told Elitcher he was still in business even though the war was over; the Soviet Union still needed information on military technology, he said.
Harry Gold had met with Anatoli Yatzkov in Brooklyn in mid-August to prepare for the planned trip out to New Mexico in late September to rendezvous again with Fuchs. Since Yatzkov had told him that the information David Greenglass passed in June was valuable, Gold suggested meeting again with the young Army machinist as well. This time it was Yatzkov's turn to invoke protocol; Gold says the Soviet agent “told me that it would be inadvisable to endanger the trip to see Fuchs by complicating it with a visit to the Greenglasses in Albuquerque.”
