You could cover the steel with lead. That would make it more opaque, so it couldn't give a pressure pulse that quickly. That at least would keep you from getting down to the steel. But even the lead, the surface of the lead, would blow off. So then we covered the lead with plastic — with polyethylene. That was low-Z, just CH2 [i.e., carbon and hydrogen]. From a time point of view, the radiation ionization of the heavy materials with all that shielding would be so late that it would have zilch effect on the overall system.
The polyethylene would function as their plasma generator as well.
A fission implosion bomb used a tamper to smooth out its high-explosive shock wave and to hold the core assembly together by inertia a few microseconds longer to allow a few more chain-reaction generations to occur, increasing the efficiency of the explosion. The Sausage secondary also needed a tamper. It would function not only as a tamper, to hold the secondary together, but also as a pusher, to transfer the energy from the hot, ionized polyethylene plasma into the liquid deuterium. The cylindrical pusher would be cast of thick, heavy pieces of U238, the largest uranium castings made up to that time. X rays from the fission primary would heat the plastic that lined the outer Sausage casing. The resulting hot plasma would reradiate longer-wavelength X rays inward from all sides toward the thick uranium pusher. These X rays would heat the surface of the pusher so hot that it would ablate: boil vaporized uranium off its outer surface. To every action there is an equal and opposite reaction: the ablating vapor would function as burning fuel ejecting from the nozzle of a rocket functions, accelerating the pusher shell inward and rapidly compressing the liquid deuterium to fusion-ignition temperatures. But the Sausage pusher would serve another important function as well. It would serve as an additional source of fuel, soaking up the high-energy neutrons that the thermonuclear reactions would generate that would otherwise escape the explosion and go to waste, neutrons energetic enough to fission U238 and contribute significantly to the overall yield.
It was this thick, heavy U238 assembly that surrounded the deuterium dewar suspended within the Mike casing; the floating, nitrogen-cooled intermediate shield looked at its inner surface. That inner surface posed a problem cryogenically, Wechsler explains. “Oxidized uranium is pretty damned black, about the worst thing you could use in a cryogenic environment. We made the whole actual secondary right here, including the [thermal-] radia-tion shield parts, the sparkplug assembly and the big uranium pusher parts. Those castings were all made at the old Sigma Building” at the opposite end of the Los Alamos Tech Area from the S building where the Sausage's Brobdingnagian schematic drawing was laid out. “Cast here, machined here, inspected here, everything.” To deal with uranium's high emissivity, Wechsler says, they decided to cover the inner surface of the uranium pusher with a coating that would serve as an additional radiation shield, like the silvering on a thermos bottle. The Boulder NBS laboratory had measured the absorptivities of sixty different metallic surfaces. The least absorptive, it found, was gold.
“In the old days,” Wechsler comments, “sign painters used gold leaf for signs. They'd buy this really, really thin leaf, so thin that when you hold it, it almost feels as if it will float away.” Gold leaf is made by layering gold foil squares between sheets of parchment, wrapping the stack in a sheepskin and beating the sheepskin with a hammer. The finished leaves, less than a thousandth of a millimeter thick — thin enough to see through — are then trimmed into three-inch squares and repacked between sheets of tissue paper in books of twenty-five sheets each. “We got a sign painter,” Wechsler continues. “We brought this guy over to Sigma and he glued gold leaf on the inner surface of every one of those uranium pusher sections. It was bubble-free. It was smooth, like a gold mirror.”
The fission sparkplug, mounted on a column in the middle of the deuterium dewar, was a plutonium device, cylindrically imploded. It included a chamber for tritium gas to boost the sparkplug yield; a line ran out through the end of the tank for loading the tritium, a few grams. “The problem of plutonium behavior at liquid hydrogen temperatures” had never been faced before, Mark comments, “and there were plenty of problems with plutonium even at room temperature.”
The Panda Committee estimated that the Mike device would yield one to ten megatons, with the remote possibility that it might go as high as fifty to ninety megatons. The likeliest yield estimated was five megatons, the equivalent of ten billion pounds of TNT. That was as much as all the explosives used during the Second World War. Steel, lead, waxy polyethylene, purple-black uranium, gold leaf, copper, stainless steel, plutonium, a breath of tritium, silvery deuterium effervescent as sea-wake: Mike was a temple, tragically Solomonic, evoking the powers that fire the sun.
Wechsler looks over an old photograph from June 1952, when the Mike team assembled the Sausage secondary at Los Alamos. “That's a convoy. That was a convoy coming down from Boulder with three dewars loaded with liquid hydrogen. There's an old ‘49 Pontiac in front. We still had old cars then, we didn't buy new cars for the government every year. This was 1952 and our lead car was a ‘49 Pontiac.” They trucked liquid hydrogen to Los Alamos to do a full cryogenic secondary assembly; the ordinary hydrogen would substitute for the more valuable deuterium. The transport dewars were so good that the cooling systems did not have to be turned on even once between Boulder and Los Alamos, but the liquid hydrogen stratified within the tanks — cooler at the bottom, warmer at the top — with a worrisome build-up of pressure. “One of the engineers said, Drive the damned thing around the block and it will slosh. So, hell, we drove around the block and the pressure dropped right down. We kept those things around for about a week and a half and ran the equipment a little bit and never had to vent anything.”
The whole secondary assembly would be suspended within the Mike casing with stainless-steel cables and supported on springs. “The main tubes leading into the assembly were set up with bellows,” Wechsler notes, “little bellows in the lines so that things could move a little bit. The secondary didn't have to be perfectly centered. It's not a true implosion system like the primary, where convergence is so critical. If the thing is a little off, you're talking about tremendous pressure. What we needed to make sure was that, in the period of time before it went off, we had everything stable. We did a lot of monitoring. We had a lot of thermocouples and we had thermistors and we had strain gauges. We did physical measurements here when we did the trial fill.” They did the trial fill at DP Site, where Los Alamos produced plutonium metal, bomb cores and initiators, away from the main Tech Area. “We did the full cool-down to liquid hydrogen, ran it for about a day and a half and measured everything so we could calibrate all the gauges that we were going to use.” The first cool-down revealed problems with the cryogenic assembly. After last-minute modifications, Wechsler's team did a second, successful cool-down in July.
The week of July 14, American Car and Foundry assembled the six-by-twenty-foot Mike casing in Buffalo with a dummy primary and secondary inside a mock-up of the building that would house it — known as a shot cab — at Eniwetok. Mike was never put together in its entirety in the United States. The casing, disassembled again into a set of big rings, and the primary and secondary components went off to Eniwetok aboard the USS
After resisting Edward Teller's drive for a second weapons laboratory for nine months, Gordon Dean finally capitulated at the beginning of July 1952. Teller had rallied the Air Force to his cause; the military service had threatened to open its own laboratory if the AEC refused. Ernest Lawrence supported Teller's proposal and arranged to house the new organization temporarily within his Radiation Laboratory at Berkeley. (“Lawrence believed Edward,” Bradbury explains the collaboration. “Simple as that. Why not? Edward could sell refrigerators to Eskimos.”) It would soon move inland to Livermore, California, to a former Second World War air base which Luis Alvarez had converted to develop the monumental linear accelerator, now abandoned, that was supposed to breed U233 from thorium to bolster the US atomic-bomb stockpile. Not Teller but young Herbert York would be Livermore's first director, and its first responsibilities would be thermonuclear diagnostic studies. Despite Lawrence's support, York writes, Teller almost aborted the new project before it began:
Teller… found the vagueness of the AEC's plans for the Livermore laboratory entirely unsatisfactory. As a result, in early July he told Ernest Lawrence, Gordon Dean, myself, and others that he would have nothing further to do with the plans for establishing a laboratory at Livermore… Intense negotiations were resumed among all concerned. Within days, these led to a firm commitment on the part of Gordon Dean that thermonuclear weapons
