August 3, 2006
THE SECRET HANS
For the Celebration of the
100th Birthday of Hans Bethe
Aspen Center for Physics
August 4, 2006
Richard L. Garwin
I recount some early interactions I had with Hans, beginning in 1951. Hans had led the Theoretical Division at Los Alamos from 1943 to 1945, and despite his doubts about the hydrogen bomb, was willing to turn his talents to learning whether it could be done or not, which was his role when we interacted in the summer of 1951.
In May of 1951 my wife and I and our infant son went to Los Alamos for the second summer, where I would continue to work mostly on nuclear weapons. I was at that time an Assistant Professor at the University of Chicago and had spent the summer of 1950 at the Los Alamos Laboratory, sharing an office with my former professor and then colleague Enrico Fermi.
On first arriving in Los Alamos we were struck by the scent of the mesa. The mixture of dust and pine. To see from Los Alamos on the slopes of the Jemez Mountains to the Sangre de Cristo range some 20 miles to the east was an inspiration and a pleasure. On the not so rare day when Los Alamos was beneath a dark summer cloud, the Sangres in full sun were particularly striking, notably when the cloud covered most of the path over the valley that would otherwise have dimmed the contrast of the view by contributing a background of scattered light.
Perhaps like Cornell, the isolation of Los Alamos, even in 1950 and 1951, led to friendliness and an acceptance of newcomers that is rare in a community more tightly linked with its neighbors.
Because we had a 6-month-old baby in 1950, and I had a lot of work to do, I did not participate with Hans in his beloved mountain hikes, and thus totally missed this aspect of his being.
There was also the scent of the Lab's mission. This was no doubt a pale reflection of the spirit of the 1943-1945 era, and until the 1951 Teller-Ulam invention of the radiation implosion, the Los Alamos mission was not clear. The "Classical Super" occupied some in the Theoretical Division, but there was not all that much new about fission bombs, except for the dedication and inventiveness of Ted Taylor who by instinct and hard work made many innovations.
This was also the beginning of the struggle to limit strategic weapons and also to recognize that there were other security needs that could be better satisfied than by increasing enormously US capability to deliver nuclear destruction against the Soviet Union. Hence a combination of forces led to the creation of the US Air Force Tactical Air Command, and the spread of nuclear weapon technology to a vast array of new applications of the fission bomb, ranging from nuclear depth charges and nuclear-armed torpedoes on the one hand, to surface-to-air and air-to-air missiles armed with nuclear warheads. There were also atomic demolition munitions-- ADMs-- and weapons to be fired from artillery pieces or delivered by fighter-bomber aircraft against ground battlefield targets.
When I returned in 1951, and asked Edward Teller, another University of Chicago colleague, what was new and what I could do, he asked me to devise an experiment to confirm the principle of "radiation implosion," then very secret, that he and Ulam had invented that February.
For my research at the University of Chicago on experimental particle physics, I had built some liquid hydrogen and liquid deuterium targets for the 450-MeV proton beam of the new cyclotron there. So it was easy enough to contrive a large system that used both liquid hydrogen and liquid deuterium in order to implement the radiation implosion. Hans was at Los Alamos for about 2 months in 1950 and again in 1951 (and most of 1952), and in addition to his own analyses and contributions, in 1951 he chaired the Theoretical Megaton Group (TMG), to which my particular proposal was brought.
I attended only a couple of sessions, since I was not a member. As I recall, the room was packed with about 60 people, and my principal involvement was to present, probably in August 1951, my proposal for the large-scale test of the radiation implosion principle. I had designed a test that would use cubic meters of liquid hydrogen and liquid deuterium and that when tested November 1, 1952, would give yield of 11 megatons of high explosive equivalent. This was almost 1000 times the 13 kiloton yield of Hiroshima, the first of the only two nuclear weapons thus far used in warfare.
The enormous and speedy development effort under Marshall Holloway, to build the test weapon, MIKE, was an amazing achievement.
Hans did not permit his clear preference that the H-bomb be infeasible to interfere with his technical judgments on the path to build one. The radiation implosion concept provided a technically interesting approach, and opened the way for much work in the theoretical division.
Quite early, Hans recommended me to some of his other government involvements, so I soon began a friendship with Arthur Kantrowitz, although I did not contribute much practically to reentry body physics or design. I consulted for a couple of days for Convair in San Diego, which was very lucrative, since they paid the same fee whether I was traveling on the airplane or sitting in the Board Room with other worthies, including Hans, John Wheeler, von Karman, Edward Teller, and others, on a committee convened by Charles Critchfield, whom I had first met in Los Alamos in 1950.
I worked again with Hans to interpret the information that the United States gathered on the fourth Soviet nuclear explosion-- Joe-4-- in a 1953 paper coauthored also with Enrico Fermi and Lothar Nordheim, of which you can find on the web a heavily redacted three of the report's 49 pages. For many years, Hans led this important effort (the Bethe Panel) to divine details of Soviet weapons from the fragmentary information provided by the extensive seismic, acoustic, and radiochemical (air sampling) detection systems that the US created for this purpose.
I next encountered the secret Hans in the context of the President's Science Advisory Committee, to which I became a consultant about 1956 and pretty soon a member of the Strategic Military Panel, of which Hans was a stalwart member.
This was a highly technical panel, with capable people of every opinion, including Albert Latter, as I recall, and Dan Fink, as well as Murph Goldberger, myself, Hans, and Pief Panofsky.
Each year the Strategic Panel would assess the state of the Army's progress toward defense against nuclear-armed ballistic missiles, and would judge, "Not there yet." So we would write a Top Secret letter to the President from PSAC giving our judgment and analysis, and for the most part adding, "We realize that other than technical matters might be involved in the deployment of a missile defense." This was clearly the case in 1967 when Secretary of Defense Robert S. McNamara announced in his speech in San Francisco that despite all of the cogent arguments in the first 90% of his speech, the President Lyndon B. Johnson had decided to deploy a "light area defense" against ICBMs that might potentially be deployed by China-- a milestone not to be achieved for the next 11 years. Dubbed Sentinel, the proposed deployment had obvious fatal flaws that had been analyzed by the Strategic Panel.
The Sentinel program self-destructed because, contrary to the views of the experts, the American public feared nuclear-armed interceptors near their cities more than they feared nuclear-armed missiles attacking them. There is something to be said for that view.
It was clear, however, that electoral politics was being mixed with national security matters, and that as much as possible (while respecting official secrets) it was essential to inform the American public and the Congress, that after all had an important role in approving and funding such deployments. Accordingly, Hans and Murph Goldberger and I accepted when Gerard Piel, publisher of the Scientific American, asked us to participate in a national security panel at the Christmas 1967 AAAS meeting in New York City. And then Hans and I agreed to put in writing what we had said, resulting in our Scientific American article "ABM Systems" of March, 1968.
Any state considering the launch of nuclear-armed missiles against another country has every motivation to understand and to defeat the defensive system-- lessons that served us well when Hans and I and Kurt Gottfried were involved with the Star Wars program 20 years later. US presidents and congresses repeatedly fail to learn this lesson.
Hans and I were working together again in 1958 in Geneva, following the first 8-nation Conference of Experts June 1-August 21, of which he was a key participant. The negotiations for the Test Ban Treaty had started October 31, with a moratorium on nuclear testing that was to last a year, and on November 15 I came to Geneva as part of the US delegation to the 10-nation Conference on the Prevention of Surprise Attack. The sessions were held at the Palais des Nations of the United Nations, and the US delegations to both conferences worked on two successive floors of the Hotel du Rhone. My Surprise Attack delegation was not very busy, in view of the fact that by the end of the conference there was agreed only the title but not even the agenda of the conference. Despite that, an anecdote will illustrate the nature of our technical involvement in these weighty political matters.
The US delegation to the Surprise Attack Conference was trying to do its homework, covering all bases, so to speak, so we marshaled our technical resources to understand, for instance, the probability that an airfield in the Soviet Union escape detection from authorized reconnaissance flights, given a certain search area per day per flight, probability of cloud cover, and the like. Albert D. (Bud) Wheelon and I were working on this together and could do much of it analytically-- that is, with pencil and paper. President Eisenhower had earlier advocated an "open skies" policy of mutual aerial photoreconnaissance, and the Surprise Attack Conference addressed the same concerns.
As an experimental high-energy particle physicist who had been involved with Leon Lederman in 1957 with the experiment that demonstrated the nonconservation of parity in the decay of the pion and muon, I was quite familiar with the work at the European Nuclear Research Laboratory, CERN, just outside of Geneva. I knew also that they had a Ferranti Mercury computer, so one day Bud Wheelon and I went to CERN with the intent of putting our problem on the Mercury. Essentially we were going to use it as a glorified calculator, to evaluate various analytic forms including many factorials in numerator and denominator. We walked into one of the laboratories on the ground floor, and I introduced myself to a person working at the bench on some high-speed circuitry that I had published in 1950. The community of physicists was much smaller then, so it did not seem outlandish (to me at least) to ask the whereabouts of the Mercury and even as an interloper to gain access to the machine. We programmed it by punching 5-track teletype tape and received the printouts.
The first insight was that even electronic computers could not evaluate factorials of numbers like 100 or so, so we took a different approach and grouped the factors involved. We also used various approximations to the factorial, of course, which turned out to be good enough.
This contact with the CERN Mercury proved valuable a few weeks later, when the Test-Ban Conference of Experts was seriously involved in the question of detection of underground nuclear tests at distances of thousands of km from the explosion. I offered to do some calculations on the Mercury, modeling the response of a seismometer as a couple of springs and masses, and although I was not a member of that conference, I was asked to present my data in support of the US proposal to have seismometers with a maximum amplification of one million at a frequency of 1 Hz.
About two weeks later, the Test-Ban Conference was not making much progress, and so I was allowed to bring my wife, Lois, to sit in the back row so that she should see how these international technical negotiations were conducted. Imagine my surprise, when I heard my name mentioned by the head of the Soviet delegation, who was criticizing my calculation. I was rushed down to the table to respond.
The problem turned out to have been a different understanding of the words, which happened often enough to be both troubling and amusing. For instance, we had caught the Russian misinterpretation that "Seismic waves are reflected at national boundaries," which was spoken on our side in the preliminary discussions as "Seismic waves are reflected at discontinuities."
This time the misinterpretation was more subtle. The Soviets interpreted our proposal as stated above as "The seismometer was to have an amplification of no more than one million at a frequency of 1 Hz," leaving free what the maximum amplification actually would be and at what frequency. So the form of the recorded teleseismic wave form was, understandably, different in the Soviet mind than it was to us.
So I helped where I could with the test ban, with comparative analyses of the capability of US and Soviet seismometers to detect a distant nuclear explosion.
This was the time when the "big-hole decoupling" concept was introduced by Albert Latter and espoused by Edward Teller as a way of reducing the detectability (apparent explosive yield) of an underground nuclear explosion by detonating in a large cavity. Never mind that it would take a cavity 160 meters in diameter (some 500 feet) to gain the benefits of decoupling for a 70-kt nuclear explosion. Hans's initial reaction was that the concept was unsound in principle and that a change in the volume of the cavity would not reduce the seismic signal, but he soon did his own analysis and accepted the concept in principle. It played a big role in delaying a total test ban long past the 1963 Limited Test Ban Treaty that forbade tests in the atmosphere, in space, or in the waters of the world.
About ten years later on the Strategic Military Panel, we encountered another surprise, that the greatest vulnerability of our nuclear missile warheads to nuclear-armed interceptors in space could be the influence of soft (but intense!) x-rays on the skin of the vehicle. Some 80% of the energy of a nuclear explosion in space is emitted in few hundredths of a microsecond in the form of soft x-rays, which are absorbed in a very thin layer of the surface of an object, and if the object is close enough (perhaps 100 km) the surface blows off and, like a rocket, imparts a recoil momentum to the structure that can split a thin layer from the back of the structure and damage the contents. The remedy was in fact quite simple. Even assuming that one could not change the momentum contributed by the x-ray induced blow-off, one could eliminate the spall damage that it would produce. In fact, I can show you now the demonstration provided to our colleagues on the Strategic Military Panel. Here you have the flexible saw blade or a ruler, held against the table and bent up to store elastic energy. When I release the tip, you hear a resounding snap, and you can well believe that the palm of a hand placed under the blade or stick would receive a substantial bruise. The reason is that the momentum is removed from the blade in a short distance and hence time, and so the peak force is very large.
All one really needs to do, however, is to insert a material with a crushing pressure below the bruising pressure of the hand. This will, of course, take up a little distance (in this case about 5 mm) to stop the motion of the blade, but you will now be willing to put the remedy to the proof, and I show you here with my own hand that the slapping blade is now harmless.
In brief, we found a simple technical solution and these techniques were then deployed to protect our reentry vehicles.
One last "it was fun" episode of discovery aired in April 1983 at an Arms Control session of the Los Alamos National Lab's 40th anniversary celebration. Hans was invited to a panel with Edward Teller and Don Kerr (LANL director at the time) to discuss arms control, and made it a condition of his presence that I be on the panel as well. Hans and I had been involved quite separately in reviews of the Livermore nuclear weapons lab's program on an X-ray laser weapon powered by a nuclear explosive, which Teller was claiming would produce many lethal beams to destroy a whole flock of Soviet missiles in their boost phase of flight.
Hans was open-minded to a fault. He was always willing to listen, although people would sometimes misunderstand his welcoming "yes" for acquiescence, when it was only an indication that he had understood and that the person should proceed. His general view was that every idea deserved its day in court, and he was sometimes oblivious of the fact that others were neither so careful of the technical facts as he was, nor so careful to demarcate what they knew from what they only guessed or hoped.
Just before the April meeting, Hans and I recognized the simple but devastating fact that the proposed deployment of the non-existent X-ray laser was as a "pop-up" rocket interceptor that would need to reach an altitude of many hundreds of km in order to see over the curve of the Earth to project its X-ray beams at the Soviet missiles while they were still in their boost phase. The consequence was that the interceptors had to have the speed of ICBMs if their x-ray lasers were to counter the existing Soviet missiles with a boost time of 200-300 seconds. But if such a defense were to be built, it would be entirely feasible for the Soviets to build a new ICBM design that, at cost increase of about 5%, would reach ICBM speed in 100 seconds. The consequence would be that the US X-ray laser rocket would need to reach its firing point in half the time, and it would need not just "fast burn" of the same amount of rocket fuel but enough fuel to double its SPEED. Instead of a launch weight 50-100 times its payload, the interceptor would have a launch weight of 2500-10,000 times its payload. Hans and I agreed on a chart to be presented at the Panel discussion summarizing this analysis and pointing out that the X-ray laser weapon could not overcome the unfortunate fact that "The Earth is round."
Two years later, at a meeting in New York I encountered a Livermore physicist who still thought that a fast-burn ICBM could be countered by an X-ray laser on a fast-burn booster, having totally missed the point that the X-ray laser would need to have at least double the velocity and not just reach ICBM speed in a shorter time.
In the many days of meetings with the secret Hans, I discovered that he was the same as the everyday Hans-- the ideal colleague and friend.
For Hans, integrity was the word that came most often to my mind. He would do his calculation and compare it with those of others, and he would explain clearly the truth as he saw it, independent of where it led.
Among all with such independence and integrity, he did it for the longest time, and with unique style.