Difference between revisions of "First-Hand:Recollections of my Wartime and University Experiences in Nuclear Physics"
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Recollections of my Wartime and University Experiences
Submitted by Dean Edmonds, jr.
I begin by noting that the New York Worlds Fair that started in 1939 and was supposed to bring all nations together was in fact ended by the outbreak of World War II. I was just at the right age for this war, but was in no sense a patriot, wanted nothing to do with war, and thus went off to MIT immediately after my graduation from my prep school (Taft). My mother, who was a classics expert, would have preferred to see me at Harvard, and I probably would have gone there had it not been for the war. After all, Norman Ramsey was at Harvard. But I had done well in science and math at Taft, went off to MIT with no intervening vacation, and so hoped to be regarded as a great electronic genius who should be left in school "for the good of the country." 1943 was not a good year for the Allies, and the New York draft board was quick to see through my ruse. I was thus drafted after being at MIT for only two weeks. Get the picture of my being driven by the family chauffeur in our big limousine accompanied by my stoic father, my mother, who was holding back her tears with difficulty, and my governess (no kidding), who was French and thus responsible for teaching me that language, in which I am still fluent. We go to the Pennsylvania Station, where I hop out, say goodbye, and become a private in the Army of the United States (AUS) boarding a troop train headed for the reception center at Camp Upton, Long Island. I might note in passing that Camp Upton is now the Brookhaven National Laboratory and that many years later I was at BNL for a meeting and by chance stayed in the same building that had been my barracks when I was drafted.
After an eternity of processing, newly minted Private Edmonds was sent for basic training in an artillery company at the Field Artillery Replacement Training Center (FARTC) at Fort Bragg, North Carolina. Finally, on Christmas Eve, I was shipped to the newly formed 413th Field Artillery Group at Camp Gruber, Oklahoma. Although I and my fellow soldiers didn't know this on arrival, we quickly learned that this was not the 105-mm howitzer setup we'd been trained on but four battalions of mule-pack artillery. I kid you not! I'll never forget arriving at our new barracks with a brand-new sign out front proclaiming that we were the" 612th Field Artillery Battalion Pk" and wondering what the Pk stood for. That's right, it stands for "pack" and meant that we were now going to train for "mountain artillery," meaning that our weapons were 75-mm howitzers (the famous "French 75") to be carried on pack mules to emplacements that no motorized vehicle could reach. It took nine mules to carry one of these guns, so that part of our training was rapid disassembly and loading. I got so I could load a French 75 on nine mules in ten minutes! Then there'd be a march to the appointed location, where the guns would have to be unloaded, reassembled, and gotten into firing position. A gun company included four such howitzers and thus employed 36 mules plus an extra supply mule carrying ammunition. There was also a headquarters company, to which I was attached because it included the communications section equipped with transceivers adapted from Jeep installations which, as a supposed electronics genius who had fixed the company commander's car radio, I was assigned to keep operating. This wasn't difficult as the radios had very straightforward circuits using the then new miniature tubes such as the 6AU6, 6AT6, 12AX7, and 12AU7, which I already knew about. Thus the 12AX7 and 12AU7 appear to have 12-volt heaters, and indeed they do, but the heaters are in two sections that can be wired in parallel for operation from a 6-volt source. It should be noted that 6.3 volts was the standard heater rating for many tubes so that they could be run directly from the 6-volt storage batteries that most cars of that day, including Jeeps, had. A plate supply using the usual vibrator-power transformer-rectifier-filter setup to yield about 200 volts dc was mounted in a case that fitted under the radio, and one of my projects (as we had no wish to mount a storage battery on a mule) was to get rid of the contents of this case and substitute dry batteries a big lantern battery for the filaments and a couple of ponderous 90-volt B-batteries connected in series for plate power. I was provided with a mule to carry spare batteries and tubes, along with some rudimentary test equipment, and developed a special pack saddle for all this. My mule and I agreed (mules are very smart) on a non-aggression pact which stated that I would bring him (her? it? It's hard to tell with mules, as they can't reproduce) apples and sugar from the mess, and he promised not to kick me. I named him Flopso because he had floppy, fuzzy ears that were bigger than normal, even for a mule, and so Flopso the Maintenance Mule and I were often seen out on the range going from emplacement to emplacement in an effort to keep all stations on the air.
We learned a lot about mules from our battalion master sergeant, an old-time cadre man, who would greet us in the morning with a cheerful "Git down to de co-ral an' ketch up dese mules!" But one thing that didn't sink in was the fact that a pack mule is a pack mule and as such will not tolerate a rider. This became painfully obvious one day when the top brass was coming to inspect our outfit, and I had arranged with some pride to demonstrate our communications capability. I brought a mule, complete with transceiver, battery pack, and a big whip antenna sticking up from his back, on stage in front of the assembled officers. I had stationed a buddy with another radio at a simulated gun emplacement some distance off, the idea being to call him as if we were laying a gun battery there. On cue, I called "Niner Niner, this is Zero Zero, come in please!" and he responded right away with "Roger, Zero Zero, Niner Niner here, go ahead!"
Now I should have known what to expect. The Jeep radios had rather powerful loudspeakers so that everybody in the Jeep could hear what was going on over the engine noise. The mule therefore heard a human voice apparently coming from someone on his back and so began to suspect that he was being ridden. I saw his ears twitch but didn't think anything of it as I launched into my artilleryman's spiel and listened for Niner Niner's response.
"Battery adjust, shell HE, fuse quick!"
Niner Niner read back the instruction and the mule raised his head.
"Azimuth right two zero, elevation five zero!"
The mule's ears are now standing straight up, his forelegs splayed apart.
"Battery right, fire -------"
The mule, now convinced he had a rider, took off unceremoniously, bucking as he ran in an effort to throw off anything on his back, and leaving me standing there alone in front of the inspection team, holding my microphone with a bit of tom-off cable hanging down from it. There was an embarrassed silence, which I finally ended by saying in my best Missouri accent, "Ah guess ah better go ketch up mah mule."
I made myself scarce as fast as I could, but I didn't have to look far. My buddy at the simulated gun emplacement wasn't saying anything, and so the mule thought he'd got rid of his rider and was thus just standing there. But sure enough, even as I came up, the loudspeaker blared forth with "Zero Zero, come in please," and the mule took off again, swearing to himself, I'm sure, that this time he would not fail to unhorse (unmule?) the rash individual on his back. There was nothing to do but chase after him, but each time I got close, my man at the gun emplacement would try again for a response (any response!) from Zero Zero and would succeed only in driving my mule off on another run. This went on for some time, and I think I covered most of the state of Oklahoma before finally catching the mule, who now simply stood there quietly. He had found what I believe to be the only tree in the area and had bolted underneath it, presumably thinking that this would surely knock his rider off, and indeed it did, although not as planned. The tree broke off the whip antenna, effectively silencing my partner, and thereby allowing me to lead Zero Zero shamefacedly back to the corral. I was afraid there'd be all sorts of repercussions to my fiasco, but actually the inspectors were so amused by my performance that they gave our battalion a high rating, recommending only that the supply department provide headsets. Thus there was sort of a happy ending, but I'll never forget standing alone in front of that phalanx of officers as the communications mule disappeared over the horizon. In the words of the immortal W. S. Gilbert,
"That day ofsorrow, misery, and rage
I shall carry to the catacombs of ageWhen a yesterday has faded from its page!"
On the tablet of my mind
Anyhow, basic training was finally finished, our outfit was moved to Camp (now Fort) Carson, Colorado, and we were alerted for shipment overseas. But before shipping we were to have one more practice bivouac, this time up Cheyenne Mountain, which had then not yet been taken over by NORAD. There was, however a problem. There were ten feet of snow up there, but the supply department had been told we were going to the south Pacific and had thus issued us summer fatigues and a poncho. I did my best to keep warm cuddled up to Flopso but nevertheless managed to contract double pneumonia and pleurisy. Calling in sick when one is alerted for overseas duty just isn't done, but by the next morning I was in sufficiently bad shape that I had to be carried down the mountain and sent by ambulance to the Camp Carson station hospital, where I recovered fairly rapidly but not in time to be shipped to China with the 612th. It therefore appeared that I should let my parents know what had happened, but my choice of words in the letter I wrote was unfortunate. The phrase "in hospital for the moment" occurred, and my mother panicked. I don't know what strings my father had to pull, but Mother was on the next plane to Colorado Springs, from which she made valiant efforts to gain entrance to the hospital. This proved impossible, as I was in the isolation ward on account of the pneumonia. I found out about this when my doctor, who spoke with a foreign accent, visited me with a nurse, the epitome of a then well-known actress famous for being completely dead-pan. After looking me over he told her, "Ees mother, she luf heem! And heem? Ees a gold-a-breek! Nombre wan!" She didn't answer.
Goldbrick or not, I eventually got out of the hospital, had a visit with my mother, and reported for duty. Luckily someone had figured out that I was good at electronics, that the field artillery was not the place for me, and that I should be transferred to the Signal Corps. Consequently, although I went overseas, it was to Europe with the 66th Signal Battalion. Thus instead of a mule I had a so-called small-arms repair truck equipped with a signal generator, meters, and tools. We landed at Le Havre and moved up to a reception center near the French town of Cany-Barville just north of Fécamp. Centers like this for newly arrived replacement troops (remember, this is 1945, and the war is still on) were named for popular cigarette makes such as Camel, and the tent city we moved in to was called Camp Lucky Strike. From there we moved east behind the Normandy invasion, winding up at a small town called Bad Godesberg just south of Bonn in Germany. There we occupied a house at 13 Max Franz Strasse and dined in a fine mess hall that had been a Haus der Deutches Jugend (German youth meeting hall). We were pretty comfortable, but of course what everybody wanted was to go home. The armed forces was run very well in those days, and it was recognized that, I believe, this was the only time in the history of the United States that there had been a compulsory draft for military service. As a result, a point system was developed in which a soldier collected points that increased with his time in service and increased very rapidly if he were in combat. A signal company didn't see much combat, and so on VE Day none of us had enough points for discharge. Hence as the war in Japan was still going on, we were redeployed to the Pacific, and the 66th Signal Battalion proceeded to Marseille there to embark on a voyage through the Straits of Gibraltar, across the Atlantic, and through the Panama Canal. We were undoubtedly on our way to the planned invasion of Japan but were in the middle of the Pacific Ocean when the atomic bomb dropped. 1 can report that joy on our troop ship was unconfined. President Truman was our hero, and if we did have a complaint it was that in view of the carnage wrought by the first two bombs, he'd called off dropping the third one, which was intended for Kyoto. As it was, the atomic bomb probably saved my life, so that I have no patience with people who say we shouldn't have dropped it. 1 think, for example, it was Clinton who stopped the printing of postage stamps showing the bombing of Hiroshima lest our Japanese friends (sic) take offense, and one enraged citizen had a whole series of such stamps printed and sold. 1 bought a big set of them, and although of course they weren't valid for actual postage, 1 put one beside the regular stamp on every letter I mailed until 1 ran out.
The dropping of the bomb precipitated VJ day, and so we wound up on the Philippines instead of Japan. There I found that by reenlisting for a year I could go home at once and choose where I would be stationed. Although the picture of me reenlisting in the army is pretty ridiculous, I appeared otherwise to face a long stay occupying the Philippines. It turned out that our whole outfit was discharged shortly thereafter, but my deal wasn't so bad other than by delaying my return to MIT. I chose my station as Signal Corps headquarters at Fort Monmouth, New Jersey, where there were three electronics research laboratories. Squier Lab was located right on the post with the Evans and Coles laboratories some distance away. Evans specialized in radar, but more generalized electronic development went on at the Coles Signal Lab, so that I was assigned there. 1 was put in the countermeasures section to work on an interesting project which carried a big JAN (Joint-Army-Navy) number but consisted of one chassis and panel that contained a receiver, an exciter for a transmitter, and a control unit that set the transmitter frequency to duplicate whatever was being received. The point of such a setup was that in those days most radio communications from field stations were in Morse code. Thus if you transmitted a signal on the same frequency as one being received, you filled in the spaces between the dots and dashes so that the signal at the enemy station became just a continuous tone. I spruced up some of the existing circuits a little, but in field tests we found that an experienced operator could read the code anyway. It turned out that field transmitters had poorly regulated power supplies which gave the transmitted signal a quick initial frequency shift that was received as a click. A really good code operator could actually ignore the constant tone and read the clicks which preceded and followed every dot or dash. My contribution to the project was to design and build a random click generator which would insert a sprinkling of spurious clicks to confuse the listener. It worked very well, and I became known as Oer Klickmeister. The man in charge of all this was a civilian engineer named Morris Acker, whom we all called Morris Is-That-a-Fact Acker because you could tell him anything, even of it were that the moon was made of green cheese, and he'd always reply, "Is that a fact? Do you mean to tell me -----". I remember walking into the next-door office and finding a row of chairs lined up facing the blank wall. When I asked, I was told that the folks there were selling tickets for visitors to listen to Morris and me arguing.
The exciter in my unit was designed to drive a high-powered transmitter, and our countermeasures section included a group that operated one. There were three men in the group, and if you rattled off their last names as given on the door outside their lab you sounded as though you were reciting poetry. The names were Manamon, Carnevale, and Budenkaye, and some of us would sing this out before going in there. They operated a la-kilowatt transmitter, and one time when we were to be inspected by a general we conceived of a somewhat illegitimate way to impress him. The transmitter could be carried in an army truck and could therefore be located outside, where we directed its output to the building's exterior lights and the associated wiring. When we cranked it up to full power the lights flashed and the wiring blossomed with an array of arcs. The general, who was not an electronics expert, was duly impressed.
Finally, however, my year was up, I got discharged, and I could return to MIT. My two weeks there before being drafted had one good result, namely that my status was "leave of absence for service in the armed forces." Hence I didn't have to apply for admission but could simply come in and say my leave was over. I registered in Course 6, Electrical Engineering, because that's what I thought I was, but I was horrified at an orientation meeting where us newcomers were told we should take some business courses so that we'd know how to sell what we developed. Business courses were the last things I wanted, and so I rushed off to my advisor to complain. He turned out to be a very distinguished and very German MIT professor named Hans Mueller, who shook his head and replied to my story, "Ach, du bist ein Physiker!" And so I switched to Course 8, Physics, on the spot and have been "ein Physiker" ever since. I'll never forget Professor Mueller, who among other things, was a leading light of the MIT Radiation Laboratory. This was in a high-security building, and one day a guard challenged him as he was going to his office. He replied with "Ich gehen am Pysicalischer Arbeit!", whereupon the guard, assuming he was a spy and not realizing that an actual spy would hardly burst forth in German, arrested him. It took the Physics Department's combined efforts to get him out of jail!
I graduated from MIT in 1950 and would have stayed there for graduate school but was told that it was better to go to a different university for graduate work. Moreover, my father wanted me to attend Princeton because he liked the then head of the graduate school there, Hugh S. Taylor. It seems my father had picked him, as he was trained as a chemist, to be an expert witness in a patent suit involving the use of ethylene glycol as a catylist to promote the reaction forming automotive antifreeze. Taylor had had an audience with the pope at which he was somehow given the title of Your Excellency. As a result, whenever the lawyer opposing my father asked a question, Taylor would refuse to answer unless addressed as his excellency. This so unnerved the other side that my father won his case hands down, and so nothing would do but for me to attend Princeton under the aegis of Dean Taylor. An interesting sequel to this is that upon applying I got turned down. I showed this rejection to my father, but a few days later I got a letter from Princeton saying it had all been a mistake and I was accepted. I suspected that my father had had something to do with this, which seemed to be confirmed when I walked into the graduate school office and gave my name. I could see the secretaries whispering to each other and pointing as if to say "That's him!" Enough said!
I thought Princeton was a dreadful place where spoiled undergraduates blossomed in pink Cadillacs on dance weekends. But a notable exception to this was the Physics Department in Palmer Lab and the neighboring Math Department in Fine Hall. Most especially I came to admire two of the physics professors, R. H. Dicke, whom I was hoping to have as a thesis advisor, and D. R. Hamilton, who later became chairman of the department. Prof. Dicke was an amazing man, one of the few I've known who could function as a talented theoretician and at the same time invent a significant experiment and proceed to design and build the equipment himself. He was one of those people who somehow caused everything to start working properly the instant he walked into your laboratory. He was one of the authors of the Brans-Dicke theory, which proposed among other things to explain the precession of the perihelion of Mercury. We know that under the influence of an inverse-square-law force such as gravitation, satellites in orbit around a force center must follow an ellipse or a circle, which can be thought of as an ellipse whose distance separating the two foci has collapsed to zero. Most of the planets in our solar system have orbits that are nearly circular, but an outstanding exception is Mercury, whose orbit is quite elliptical. This means that the orbit extends out into space from the Sun, which is the force center and therefore one of the foci. The question is, which way from the Sun? What's the bearing from the Sun to the second focus and hence to the perihelion, defined as the point on the orbit furthest from the Sun? The answer is that it varies, the entire orbit rotating about the Sun, which is what precession means. It's not very fast, amounting to only a few minutes of arc per century, but its measurable, and Prof. Dicke proposed an answer. His idea was that the Sun, which looks to us like a sphere, has a surface that is quite irregular, and it is these deviations from true sphericity that cause the precession. He designed and built an apparatus that was essentially a big but very precise circular plate that he could orient to screen out the Sun's truly circular part, revealing only the deviations. It was hard to operate, and us students that tried to manage it christened it the Ill-Tempered Gravicord. The effort was brought to an end when Einstein, who was near Princeton at the Institute for Advanced Studies, showed that the precession came about due to a relativistic mass shift of Mercury at aphelion, the point on the orbit closest to the Sun. This occurs because the lever arm is shortest at aphelion, hence the planet's speed must increase to satisfy conservation of angular momentum for the orbital motion on which no torques act. The Brans-Dicke theory then rather passed away, but our admiration for Prof. Dicke did not, and I would have stayed at Princeton had it not been for a most unfortunate event. One of the Physics Department professors, a theoretician named David Bohm, had come under the scrutiny of the McCarthy Committee, which was making the rounds of the country's intellectuals at that time. Prof. Bohm had been a member of a communist cell group in the thirties when it was a popular thing to do, but the McCarthy Committee found nothing to be concerned about and moved on. Not so the Princeton administration. Parents and alumni started writing in demanding "Who is this Red teaching our sons?" and the Administration, instead of answering with a polite letter explaining that there was no problem, took the complaints seriously and fired Bohm, who did not yet have tenure. They said they would pay him to the end of his contract but that he was not to be found on campus and that any students who had contact with him would be summarily dismissed. As he had graduate students who were doing their doctoral theses with him, this created an impossible situation, and in view of my protests I was surprised that I subsequently got Q-clearance for some work at Oak Ridge, of which more later. I really couldn't stand Princeton after that, but one interesting matter developed before I left. I was in an analytical mechanics class of which Prof. Bohm had been the instructor, so that his dismissal left the class without a teacher. A visiting professor from England was called upon to fill in, and as he was a star ofthe famous (or infamous) British Tripos, we dreaded how he might direct the class. Actually he was a very good teacher, but the final examination was a monstrosity. It was a take-home because none of his problems could be done in the usual three-hour exam period. In particular, no. 3 had us all stumped. At first glance it appeared to be a straightforward problem in coupled systems consisting of a long string having a mass per unit length and carrying small balls each of mass m at intervals. The method of attacking this was given in our textbook, and we all followed it accordingly. The trouble was that it lead to an integral no one could solve. After a frustrating period, the honor system began to break down. You could tell the members of the class by their wan look, and you could hear furtive whispers in the corridor of"Did you get it?" and an answering "No, I didn't get it!" Soon the physics faculty became involved, and they couldn't get it either. Neither could the math faculty. The ultimate insult came one day when I found the integral chalked on one of the paths on the Princeton campus. Finally the examination period was over and our man from England came to collect our papers and do the answers on the blackboard. He walked in quite nonchalantly paying no attention to the assembled crowd, for not only were the class members present but all the other physics students, most of the math graduate students, and numerous members of the physics and math faculties had joined us to see the resolution. There was standing room only, and that stretched out into the corridor, Nevertheless, with quiet composure our Cambridge (1 think) professor stepped up to the blackboard and started in. First he did Problem 1, but we paid little attention, for we'd all gotten that. Likewise with Problem 2. Then of course came Problem 3, and we were amazed to see that he was following the textbook method just as we had. One heard whispers of"If he keeps going like that he's going to get it," for we all thought he would pull out some trick to avoid getting the integral. But he didn't! We thought "If he takes one more of these steps he'll have it!" And he did, and there it was, this impossible integral that had burned itself into our brains for the past month.
Now what? Still unperturbed, he steps up to the board saying, "And now, by the use of the usual Ansatz," and writes out the longest and most intricate trigonometric identity I'd ever seen. It ran all along the board and around onto a second board at the end of the room. It took me a week to prove that it really was an identity. But when substituted in, our monster integral fell apart into several smaller ones that were easily done and gave the solution to the problem showing that as you shook the end on the string a wave of varying velocity and hence wavelength propagated down it. We were all dumbfounded, and to this day if you ask an old-timer at Princeton about a problem in science he's likely to answer, "What you need is the usual Ansatz!" Many years later, when I had become a professor at Boston University, I held conference hours on Monday nights. As is usual, few people came, and so I was delighted one evening when three of my best students showed up. I assumed they wanted help with the homework, but they said no, they'd done all that.
"Great, so why are you here?"
"We want to talk about physics."
Of course nothing could please me more, so that we talked about physics for such a long time that they missed dinner. This was serious because they were on a dormitory plan that included meals, but the solution was easy. There was a very nice little restaurant near us on Beacon Street where I had dinner when teaching a night class, and so I simply took them there. We had a good meal and a bottle of Lam brusco, a sparkling red wine I found there and came to like. Our group grew with other good students that wanted to talk physics, and it was much better than the official physics club called Photon that anyone could join. Here the members suggested new ones and I appointed them. Moreover, questions were often asked that I couldn't answer, but I usually knew a faculty member who could. Thus when relativity came up I considered myself totally inadequate, but we had Prof. John Stachel in the department. He's an internationally known expert who had just returned from a leave to edit the Einstein papers at the Institute for Advanced Study in Princeton, and so I asked him if he would address our group. "And you get dinner!" I added. He accepted and gave a great talk from which I learned a lot about relativity myself. The only remaining trouble was that we didn't have a name, but that changed one evening when I was actually doing a homework problem and came out with an equation that had no ready solution. I was saying that the computer could handle it when I noticed one of our members sort of tentatively putting up his hand. This was a new appointee whose name, as best I could spell it, let alone pronounce it, was Hsieh. He was, as many brilliant Orientals are, very modest and polite, so that I considered his putting his hand up, even tentatively, quite an occasion. I called on him at once and he very humbly pointed out that if I made a certain substitution for the original unknown the solution could be worked out in closed form, along with our whole group was amazed, and I stood wondering how I could compliment him properly. And then I remembered: Pointing my finger I cried, "Mr. Hsieh, you are now a Hero of the Usual Ansatz!" Everyone clapped, and thereafter our group had its name: We became the Heroes of the Usual Ansatz. I wonder if it's still going today. I've retired and the members I knew back then have all graduated and gone on to rewarding careers. But I'll never forget Mr. Hsieh, the original hero.
After the David Bohm affair, when he left to become a distinguished professor in South America (The only time I know of when a talented intellectual has been forced to leave the United States for political reasons), I left to return to MIT. I called them to ask if they would take me back and they said they would. I wound up in J. R. Zacharias's molecular beam laboratory with such people as John King, who became an MIT professor himself, and Reiner Weiss, who now runs the Long Interferometric Gravitational Observatory (LIGO) near New Orleans. In addition, I met Len Herzog in the Chemistry Department who was interested in mass spectrometry and whom I came to know through the Gilbert-and-Sullivan society we were both members of. He was an expert in mass spectrometry by which isotopes of an element could be separated according to their mass but not by any chemical means as they are chemically identical. A typical mass spectrometer consists first of a source in which the sample is ionized so that it has a charge and can be accelerated to form a beam. This beam is directed into a perpendicular magnetic field, which makes the constituent particles move in a circular path. The radius of the circle depends on the particle mass, so that the lighter ones move in a smaller circle than the heavier ones and are thereby separated. A mass spectrometer involved a lot of electronics for power supplies and beam detection, and I came into the picture as the man who could design and build such stuff. Len and I worked so well together that we eventually formed a company, Nuclide Analysis Associates, to manufacture these instruments. That's how I came to visit the Oak Ridge National Laboratory, for although by the time I got there the gaseous diffusion process had long been established as the most efficient way to concentrate the rare isotope 235 of uranium, they wanted an analytical machine to measure the concentration achieved. You may remember that Oak Ridge was the site ofthe Manhattan Project, whose purpose was the separation of U235 from the common isotope U238 in order to make the first atomic bomb, which needed U235 because U238 doesn't fission very well. The ratio of these isotopes in the natural ore (pitchblende) is about 1 : 25,000 and their separation is an obvious application for a mass spectrometer. It's only necessary to put a receptor at the 235 position to collect that isotope with a purity approaching 100%. The only problem is that although millions of particles may enter the beam every second, these are atomic particles, so that getting a ponderable sample entails collecting a very large number such as Avogadro's, or about 1023 of them. According to a calculation I once made, it would take thirteen million years for a typical mass spectrometer to collect enough U235 to make that day's version of the atomic bomb. So what do you do? Well, you don't have thirteen million years, so you raise the beam current, which was Oak Ridge's initial attempt to obtain separation. What they produced was the so-called Calutron, a mass spectrometer on a grand scale. The brass can that housed the whole thing stood some seven feet high and was evacuated (remember, the whole works has to be under vacuum) by the most enormous oil diffusion pumps I'd ever seen. Brass is a poor material for a vacuum chamber, as it has a high vapor pressure at room temperature, but it was readily available, easy to work, and the lab was in a hurry. Despite the big pumps, a vacuum of only about 10-6 mm of Hg was the best obtainable, and there was enough residual gas to make the ion beam visible as a blue streak due to collisions along its path. The biggest pump was 32 inches in diameter and was involved in one of Oak Ridge's most gruesome but little publicized accidents. Leak testing was always a problem with the Calutron, and the accepted method of leak hunting at that time was to put a technician inside the can (there was plenty of room) and reduce the pressure slightly. Soapy water would then be sprayed on the exterior, and the man inside would look for bubbles with a flashlight. That's fine as long as all safety locks work, but nobody thought much about safety at the height of WWII. Here, then, was an accident waiting to happen, and one day it did. The huge pneumatically operated clapper valve that isolated the big pump from the main chamber accidentally opened, sucking everything in the chamber, including the unfortunate leak hunter, into the pump's boiling oil. I can't imagine a death on the battlefield worse than that.
The Calutron was reasonably successful, and several were made. An interesting feature of this project was the fact that copper was then in very short supply due to its use in ammunition, but silver is an even better conductor, and there was plenty of it stored as silver bullion at the government's Fort Knox. The cost of silver didn't apply in this case, and Fort Knox "loaned" a large amount to Oak Ridge, where it was drawn into wire with which to wind the Calutron's electromagnets. A beam current of approximately 5 milliamperes was achieved, and calculation shows that this would yield 0.04 grams per hour or about a gram after 24 hours of continuous operation. That's not a lot, but the purity is guaranteed, and Oak Ridge had more than one machine. However, the gaseous diffusion process, also developed at Oak Ridge, eventually won out over the Calutrons, largely because it was a continuous rather that a batch process. After all, when a Calutron had run for a while, you had to break vacuum, remove the selected isotope, and then pump down again, which took time and consumed a great deal of liquid air for the cold traps. A gaseous diffusion plant ran continuously, the raw material, which was usually uranium hexafluoride, being recycled over and over with the light isotope getting ahead of the heavy one until the desired level of purity was obtained. Considerable research had gone into raising the efficiency of this process, and you may recall that much of the resulting classified material was stolen by the notorious spy Klaus Fuchs. Nevertheless, Oak Ridge carried on, the gaseous diffusion system began turning out reasonably pure U235 in a steady stream, the Calutrons became obsolete, the war ended, and Fort Knox wanted their silver back. The great machines were accordingly dismantled, the magnets unwound, and I remember seeing the big brass vacuum cans cast aside in a long row in an Oak Ridge junk yard. Sic transit gloria mundis.
Back as a graduate student at MIT in Prof. Zacharias's molecular or more properly atomic beam laboratory, I started at once to learn the techniques involved. The history of atomic beam research goes back to the famous Stem-Gerlach experiment of 1925, which, curiously enough, was set up to prove that the then new theory called quantum mechanics was wrong. A beam of silver was formed in an oven with a small port through which a stream of vaporized silver atoms could be projected. OK, so this is no different from squirting water out of a garden hose and calling it a beam, and yes, you can call it that. The stream of water bends around under gravity, and the stream of silver atoms does too, but you don't notice it over the short distance to the detector because they're going much faster. There immediately arises the question of what you mean by a detector for silver atoms because an atomic beam is electrically neutral and therefore not amenable to detection by electronic means. That's why silver was chosen for the experiment, as the detector could then simply be a glass plate mounted at right angles to the beam. When silver deposited on it you had what amounted to an exposed photographic plate which could be developed by existing photographic means. Note also that the beam could not be deflected by a uniform magnetic field, but a non-uniform field could exert a net force due to the atom's dipole moment. In effect, the atom has a north and south pole slightly separated from each other and therefore subject to different field strengths in a non-uniform field. The magnet through which the beam passed instead of having plane, flat pole pieces had one that was pointed and the other concave in a rectangular shape to make the resulting field as non-uniform as possible. According to classical theory, the atomic dipole could point in any direction with respect to this field and could thus be deflected over a continuous range. The result on the photographic plate should then be a uniform smudge. Instead two distinct lines were observed, thus validating quantum mechanics but bringing in a new complication as the so-called "old" quantum mechanics extant at that time predicted three lines. This was because electron spin was then unknown, and the lowest angular momentum state of the valence electron had quantum number 1 which allowed three orientations, 1, 0, and -1, in an external field. The forthcoming "new" quantum mechanics showed the ground state of silver to be a so-called S state having zero angular momentum, the possibility of an actual atomic electron colliding with the nucleus having been removed, and the concept of electron spin, that is, of the electron having an intrinsic rotational angular momentum of its own, introduced. The spin had quantum number ½, so that its spin axis could point either up or down (projection ± 1 relative to the nucleus), thus giving rise to the two observed states. The idea of spin solved a lot of conundrums in atomic spectroscopy, and a famous lecture given, I believe, by Gamov, who liked to put some humor into his physics, was entitled "It might as well be spin!"
Atomic beam systems went on to be developed by I. I. Rabi at Columbia, Norman Ramsay at Harvard, and J. R. Zacharias at MIT. One of the first improvements made was the substitution of a better detector that would operate continuously without having to be removed from the apparatus to be read. The one that was generally adopted was the hot-wire detector consisting of a tungsten filament held perpendicular to the beam. It was heated by passing a current through it as if it were a filamentary cathode but only to red heat -not enough for electrons to be emitted through tungsten's very high work function. The element selected for the beam now became cesium rather than silver. Except for francium, a radioactive element we wanted no part of, cesium is the heaviest alkali, with that single valence electron sitting alone outside the inner core. It therefore has the lowest ionization potential of any stable element, so that when a cesium atom struck our hot wire, the tungsten surface would steal the valence electron and preferentially emit the atom as an ion. We now have a charged particle to deal with and can handle it by normal electronic means. The apparatus I inherited in Prof. Zacharias's laboratory had a small mass spectrometer following the the hot-wire detector to get rid of spurious ions, and the resulting signal was amplified by an electron multiplier. My apparatus, like all of the ones then extant, had two deflecting magnets in a row with a space between them in which a transition in the cesium hyperfine structure could be made to occur. Thus in the simple case of turning the valence electron over relative to the nucleus, a process nicknamed "flop" by atomic beamists, the atom's dipole moment would be reversed so that the second magnet would deflect the beam back on line, refocusing it on the detector. This was called "flop in,"and getting it would show that the transition in the C-region, as the space between the deflecting magnets (the A and B magnets) was called, had taken place. This lead to the atomic beam laboratory being called the flop house, which was amusing because our neighbor in Building 20 was the Communications Biophysics Lab that housed a poor cat who had electrodes implanted in its brain for their study of its response to audio signals. We were therefore known as the flop house next to the cat house. In my apparatus a C-magnet with flat pole faces to produce a uniform field was located in the C-region so that I could look at hyperfine transitions at high field, but for the atomic clock which was developed in both the Ramsey and Zacharias laboratories the zero-field transition was used. For a clock, the name of the game is precision, which in our case of an atomic transition means a sharp resonance at the transition frequency. The stimulating signal, which is needed, as the hyperfine energy levels are too close for a spontaneous transition, is applied over the length of the C-region, and quantum mechanics says that the resonance will get sharper as the time during which the atom is exposed to this radiation is increased. That means the time the atom spends in the C-region. This isn't long because the most probable velocity in the Maxwell-Boltzman distribution of cesium atoms in the beam is about 20,000 cm/sec, as the source has to be heated to some 80° C to form a reasonably intense beam in the first place. Thus lengthening the time in the C-region means lengthening that region, but there is a limit on how much you can do that. Remember, this is an atomic (i.e., neutral) beam for which focusing is not an option, although Hamilton at Princeton tried to make a focusing machine using specially shaped magnetic fields. It didn't work, and there was also the problem of maintaining a constant field over the entire length of the C-region even when that field is to be zero. Fortunately Ramsey showed this to be unnecessary if the stimulating radiation was applied not over the entire region but only in phase at the two ends, a condition easily met as the frequencies involved are in the microwave range. The intervening field then need only average to the desired value. The result was called "Ramsey Flop" and greatly simplified the clock's development. Zacharias then made a colossal attempt to slow the atoms down by aiming the beam vertically so that they'd be slowed by gravity. Under his direction Rainer Weiss presided over the building of a vertical atomic beam setup that was some 15 feet high and went through the ceiling into the room above that was conveniently vacated for him. Even 15 feet wasn't enough to stop most of the atoms, and so Zacharias tried to make an intense source whose beam would contain enough slow ones, the faster ones hitting the top of the apparatus and being trapped out with liquid air. Huge quantities of liquid air were required for the cold traps, and the entire vacuum chamber was made of stainless steel in an attempt to get the pressure down. I think even liquid helium was tried, there being a ready supply available from MIT's low temperature laboratory. The Zacharias source was an oven made of some refractory metal that wouldn't react with hot cesium and provided with an aperture about half an inch wide and two inches long to get the the concentrated beam out. Such an aperture obviously couldn't produce a directed beam, and so it was filled with hundreds of narrow channels formed by a Zacharias invention we called "crinkly foil." This was made by running a strip of thin stainless steel through a meshed pair of fine gears so that you got what looked like a length of miniature (and in this case metallic) corrugated paper. The narrow channels were formed by stacking alternate flat strips and strips of crinkly foil in the oven's aperture. The result seemed to meet the requirement of an intense and reasonably directed beam, but the "Big Clock" nevertheless didn't work. The idea was to have the slow atoms stop by gravity before hitting the can's top and falling back down through the C-region thus giving the transition a long time to take place. Note that there was no B-magnet, the A-magnet serving as the second deflecting magnet on the downward leg of each slow atom's round trip. Moreover, the exciting radiation, which, being in the microwave range, could be delivered in a waveguide, was applied in a single small cavity at the bottom of the C-region through which the beam passed on its way up and again on its way down. In-phase application of the RF both on the way in and on the way out of the transition region was thus guaranteed. The trouble was that there didn't seem to be any slow atoms. Finally, during a period when Prof. Zacharias was away, Ray Weiss undertook to solve the mystery by devising and building a velocity selector that he mounted in the beam path just above the source. It worked very well and gave a beautiful plot of the Maxwell-Boltzmann velocity distribution of the forthcoming atoms, but there was one peculiar feature: At about 1/6th of the most probable velocity, the curve abruptly dropped to zero. The question of why this happened has never been explained, although it is generally believed that the slow atoms were being knocked out of the beam by collisions with the huge number of fast ones coming up behind them. The Big Clock subsequently faded from the scene, but one of the more conventional apparatuses in the lab was modified by lengthening the C-region enough to give a very precise value for the hyperfine interval's frequency. The result was very close to the value accepted today, obtained in machines in which the beam is slowed down by an opposing laser beam and which are small enough to be flown in a satellite. The gravitational red shift has thereby been measured to great accuracy, and the second is now defined in terms of the zero-field cesium hyperfine interval at 9192.631770 Mhz. Note that an atomic definition has a big advantage over obtaining the standard from very precise crystal-controlled oscillators as was previously done. The crystals were ground to extreme precision, but the fact remains that if you want someone in a distant country to duplicate your standard, he must grind his crystal to exactly the same dimensions as yours and so is subject to the same machining tolerances. The advantage of an atomic standard is that atoms of the same type are identical the world over. No duplication of any physical characteristic is necessary. The MIT lab also produced a commercial version of the cesium atomic clock manufactured under Prof. Zacharias's direction by the National Company in Malden, Mass., a company well known to the radio amateurs in our group as the source of much-needed components such as ceramic tube sockets, tube shields, tank coils, and even IF transformers. Their version occupied a seven foot rack and had a 5-MHz output that was the primary source for the frequencies needed at the other apparatuses in the lab, including mine. I might add that I was also involved in developing the original laboratory version, which at first used a klystron to generate the 9192MHz needed for the cesium hyperfine transition. Some means was needed to control the klystron's output frequency by setting its high supply voltage with the low-voltage error signal from the servo system. I believe it was my colleague H.H.Stroke who thought up the idea of using what P. J. Angiolillo later called a static magnetron for this purpose (Am. J. Phys. 77, 1102, ). A static magnetron consists of a diode having a concentric cylindrical cathode and anode giving rise to a radial electron stream. If an axial magnetic field is now applied the stream bends around, and if the field is made strong enough it will miss the anode. Theoretically the diode current will drop to zero at this field, but for various reasons such as initial emission velocities, a practical static magnetron displays a characteristic curve suitable for controlling the klystron supply current with the error signal. Stroke and I had MIT's Research Laboratory of Electronics (RLE) make a simple diode in a cylindrical glass envelope on which we wound a coil to be driven by the servo system. Our setup worked pretty well but was never actually installed, as the final version of the Zacharias clock used a more-or-less conventional oscillator featuring the famous WE316 high-frequency triode. Our system was therefore greeted with his "Dim Viewer," a miniature coffin on which the lid would lift on such occasions to allow a corpse to rise up and stare balefully at the visitor. Nevertheless, Prof. Zacharias approved my thesis work, and I graduated with my doctorate in 1958.
Having graduated, I then had to find a job, and as luck would have it, the Cambridge Electron Accelerator (CEA), a joint MIT and Harvard project, was then under construction on the Harvard campus near the famous Glass Flowers museum, where they worried about damage from vibration due to the large distribution transformer at its center. The CEA was an electron synchrotron laid out in a ring close to a mile in diameter in a circular trench to stop the accompanying synchrotron radiation. The steering magnets were pulsed at 60Hz so that the regular city power line could be used, but that central transformer shook so badly that it had to be walled off with sound proofing. The man in charge was Prof. M. Stanley Livingston, who had been my registration officer at MIT, so that through him I got hired at the CEA .My job was to build the vacuum chamber, which consisted of curved sections of oval stainless steel pipe that fitted together to form the ring. When in the ring and under vacuum, each section could be outgassed by passing a heating current through it. Stainless steel is not a very good conductor so that it presented some necessary resistance to the heating current, but it wasn't enough. To raise it the pipe was sliced almost all the way through at intervals of about an inch and alternating from opposite sides to provide a long current path.The result was obviously anything but air tight, and so each section was covered with glass cloth which was then impregnated with epoxy and baked to form a hard, vacuum-tight, and low-vapor-pressure shell. The effort was successful, and the accelerator eventually came on line, but I was neither a machine operator nor a high energy physicist, and so it was time to look for the job I really wanted.
In those days, anyone looking for a job went to the New York meeting of the American Physical Society, so called because it was then actually held in New York city. It also took place at the end of January, which created a problem for some of us who wanted a break at Christmas too, but I went nevertheless. The headquarters hotel was the New Yorker, whose sixth floor became known as the flesh market because anybody who was hiring had a suite there. A list was posted in the lobby, and I noted that most of the outfits named on it were government-sponsored research organizations. But there was one notable exception. The Boston University Physics Department actually had a position open, the result, I gathered, of people leaving for Itek, one of the organizations mentioned above. This was not only a faculty appointment but was in Boston, where I lived at the time and thus wouldn't have to move. And so up I went to the little cubicle that was the BU "suite". Inside sat a little man with very bright eyes, the department chairman at the time. He was Prof. Robert S. Cohen, who held a doctorate in both physics and the History of Science and was serving as chairman because the former chairman had left. He and I had an instant rapport, so that the interview consisted of just one sentence: "You're hired!" Thus began not only a life-long friendship but my thirty years as a physics professor. Being much more of a teacher that a researcher, I was mostly concerned with the undergraduate courses and taught just about all of them in the course of my tenure. This included the special course we had for premedical students, which resulted in my chairing the premedical committee. Also included were the undergraduate laboratories, for which I wrote the textbook. In addition I became an assistant dean (causing much confusion with my name) assigned as advisor to students who had not declared a major and therefore had no departmental advisor. It was a delightful thirty years interrupted only briefly by a sabbatical year in Canada. Prof. William McGowan, an old friend who knew about my work at the CEA , invited me to the University of Western Ontario in London, Ontario, to work on the so-called microtron. A microtron is a small synchrotron, only a couple of feet in diameter and therefore not capable of anything like the energies of the big rings such as the CEA. It can be used as an injector for linear accelerators (LINACs) or as a source for the tangentially radiated synchrotron radiation, which can be used in various experiments instead of being thrown away as in the big machines. Funding for the UWO microtron had been supplied by the Canadian government to develop a source of a variable-energy beam to replace their well-known Co-60 source for cancer therapy. The advantage of the microtron was that the UWO version had specially-designed steering magnets that allowed the machine to operate over a range of energies rather than being limited to the one energy obtained from cobalt. In treating a deep-seated cancer, the beam energy could then be adjusted to maximize the energy deposition at the site of the cancer, thus minimizing the damage to surrounding healthy tissue. Chalk River, Canada's national laboratory, was also interested in the microtron as the injector for a planned linear accelerator, but nothing ever came of it. Eventually an Italian linac was purchased and installed in the hospital associated with the medical school at UWO. I was involved in this development, and an ironic consequence is that many years later my late wife Pamela was treated on the machine I had helped install. It is perhaps a shame that on that somber note I have reached the end of my tale, but such is the case. Hence in the words of my father the attorney, further deponent sayeth naught.