Stephane Groueff: Now you said that you had some opening remarks?
William J. Sturm: Yes. In terms of what you would have said and what your colleagues have said you are interested in, it occurred to me to note that pretty generally insofar as the things that were done at Chicago are concerned—they were done by physicists. That is to say, they were not done by technologists. They had to be their own technologists of necessity under these particular circumstances. Perhaps as physicists, too, they are not the most skilled technologists. They might be the most ingenious, but they are not skilled. Plus the attitude that at least I sensed or felt was that a group of people—physicists—came together here under these circumstances to do this job, which job they would never, in the normal course of events, have been associated with.
The job that we had, I suppose, would be specified as producing quantities of plutonium by producing the machine based on the nuclear chain reaction to do this. This was all solved in principle before the group assembled, but now it is a matter of doing them. And I do not know that to the level of producing the first chain reaction whether we in the physics section had to solve particularly outstanding technological problems.
Robert G. Nobles: Is this your impression—
Sturm: As far as our group, our group, being the one that worked with [Enrico] Fermi starting late in ’41 and through ’42, and then on to the time in late ’42 when the chain reaction started—our problems were not technological.
Groueff: They were theoretical?
Sturm: Well, I am sorry. I supposed you would call the specification of high purity carbon and the calculation of the nature of the impurities tolerable in uranium on the basis of neutron cross sections and so on, which were physical—in a physicists’ context—to apply these physics concepts to actual systems. It probably is a technological thing.
What I mean to say is that we did not—well, maybe we did—we did have to produce new materials, or insist on them.
Nobles: We had to insist in the instance you mentioned in the graphite.
Nobles: And there our problem was just keep insisting for more and more purer and purer graphite. I wonder if the people who made the graphite would not have some interesting problems to talk about. They probably did not even know why.
Groueff: Because it had never been required before, this purity, both for graphite and uranium, of course.
Nobles: Yeah, yeah.
Sturm: I recall being sent to Mallinckrodt Chemical in St. Louis with a list of specifications for uranium that they wanted. Fermi had figured it out on an ordinary piece of paper and pencil. I went there thinking, “I am a physicist, I do not know chemistry.” So I went into the plant. They were sort of expecting me. I told them what we want. I could not tell them why exactly but we wanted this many tons of this uranium, and that was happy just as an industrial thought.
When I produced the specifications to a Dr. Keiger there, who was a lower level, I was then ushered into Mr. Mallinckrodt’s office because of these specifications. Mallinckrodt read them and looked and said to me, “You know that there has never been an industrial chemical made to this purity?”
“No, I do not know this.” But I had my orders, which is to insist that it be done to this purity and in that sense they had to produce it.
We later, in this particular case, had to devise special tests to make sure that they were pure. So in that sense, we pressed industrial technology.
I think our biggest problem was physicist-type ingenuity, solving our problems on the field, calculating things with the exponential series of experiments for many months and calculating from one to the other what change do you want to do to optimize the multiplication and so on.
Groueff: How were you organized? For instance, you worked in a group of physicists under whom? Fermi?
Sturm: Fermi, but then he had another set of group leaders and there were – well, [Walter] Zinn was one, [George] Weil, [Herbert] Anderson. And of course, for a while, Anderson. Later [Albert] Wattenberg. I do not know if he was at that time, at the same chain reaction. I think he was just a member of the group. But there were three fellows. And there was Wilson, who had an electronics group. They were just making instruments.
Groueff: So each group had a special assignment?
Groueff: And there was a physicist and there were also—
Sturm: These were all physicists.
Groueff: Yeah, physicists. Fermi was the leader of the group?
Sturm: Yes, yes.
Groueff: And from administration point of view, everybody was under [Arthur] Compton, no?
Sturm: Yes, yes.
Groueff: And [Norman] Hilberry acted as assistant to Compton?
Sturm: Yes, he was at one time—I am not sure where he was.
Groueff: But I mean, he was mostly in the administrative at that time?
Groueff: Where did [Leo] Szilard fit in that?
Nobles: Oh, he had a special—
Sturm: There were a group of theorists. Now under Fermi, mostly they were experimentalists or theorists at various times under various people, at one time under [Eugene] Wigner. [John] Wheeler was there for a while. Others, [Robert] Christy and—
Groueff: Under Fermi?
Sturm: No, these were theorists, they worked for the most part, simply under Wigner.
Groueff: I see.
Sturm: Szilard was in that general area, although I think – oh, he had a group. He had Feld, Bernie Feld was in his group, and [Julius] Ashkin.
Groueff: But later, I think he was working mostly under heavy—he wanted to invent some special kind of cooling.
Sturm: This was his property. He was more or less a free wheeler of sorts. That is, he would specialize in ingenious new ideas, not always greatly successful. I recall his coming into our lab one day and wanting to know some particulars about the formation of certain fission product abundances, which we may have been able to get from—I had a little geometry, we were making some fissions.
He was examining at that time the possibility of making permanent light sources by having the radiation active fluorescent material to see about making little devices which were meant to be light sources. Well, I do not think that one was very successful but he was always coming up—
Groueff: Always coming with some new idea?
Sturm: New ideas.
Groueff: But by temperament and by job, he did not fit the exactly in this sort of strict organizational chart now?
Sturm: He was not a line man.
Groueff: But your group was under Fermi, which was different from Wigner’s group?
Sturm: Yes, yes. The Fermi/Wigner level consulted and formed plans of action, and so on. But beyond that, there were experimental things to do. We were experimentalists.
Groueff: And they were mostly on the theoretical side and you were more on the experimental?
Groueff: And Fermi was mostly experimental, or both?
Sturm: Well, he was both, yeah. I remember we had one Christmas—I do not know if you recall this. A group of people presented one of these large slide rules that they use in classes to demonstrate—you know, six feet long, big wide thing. A group of people would do a measurement on an exponential, and they would use this large slide rule and they would calculate, you see?
They would get an answer and Fermi would come in, and Fermi always had the five-inch size slide rule, and somebody played his part. They would get one answer with this machine, and Fermi would do like this, he got a different answer. So they would throw away their elegant answer and take Fermi’s little common answer.
The point being there, essentially, that Fermi was—well, he is a rare person in many ways. He was a physicist. You did not have to use adjectives. He was not a theoretical, he was not an experimentalist, he was not a nuclear physicist, he was not a high-energy physicist. He was a physicist. I think I have seen no man more highly cited, frequently cited, say in a field like solid state—I worked for some years in that field—than Fermi. Yet he never particularly worked in that field.
Nobles: He wanted astronomy?
Sturm: Yeah, I do not know of his field, particularly. I would not be surprised if some of his—
Groueff: One of the scientists told me, now modern physics progresses so fantastically, now everybody get so specialized that it is practically impossible to keep, even within your specialty. He said, “The last living man who grasped the whole field of modern physics was Fermi. And when he died after that, it would be impossible now for one man to grasp all the fields and all the intricacy of all fields in modern physics.”
Sturm: One would hope it would remain possible, but it is somewhat a hope. I think in no case, and perhaps at no time, in any period in the history of physics were there more than four or five such people alive simultaneously.
Nobles: You can only grasp so many different fields. He contributed—
Sturm: Yeah, yeah. Well, this would follow naturally.
Groueff: But so you would put him in a category by himself?
Sturm: Well, with others. I think Einstein is—
Groueff: No, I mean of the Manhattan Project people.
Sturm: Yeah, sure. He was the Chicago Manhattan Project conceptually and intellectually and drive.
Groueff: He was the leader—
Sturm: And he was it. There was no other. Everyone else was more or less a help, yes.
Groueff: Even Wigner? Wasn’t Wigner in a special category?
Sturm: I think Wigner was. Yes, yes, I would not be surprised. On the other hand, I think as far as this particular project goes—well, I think essentially he would be held, but a theorist is alone. When this is the goal, to make a practical thing, he is sort of helpless, alone—not that he could not have perhaps specified and so on.
Groueff: But Wigner would design, and Wigner’s group, the final model of the Hanford piles?
Sturm: I would not be surprised.
Groueff: Let’s proceed by sort of chronologic. At the beginning, the effort was to build the first pile at Stagg Field. All of you worked on that under Fermi?
Groueff: And Szilard and all those people worked with you—Wigner, [Glenn] Seaborg, everybody was working only on that?
Sturm: Yes, out of our labs. I may be forgetting something but that would seem to be the general goal.
Groueff: That was the main effort?
Sturm: Yeah. A lot of correlated work.
Groueff: And the principle of that was invented by Fermi and Szilard from this patent?
Sturm: I would think that probably this is true.
Groueff: So the idea was they gave the principle and all of the different groups were working on different aspects of building this new device, this new pile?
Groueff: And physically, where did you work? The Fermi group was in one building?
Sturm: Several, actually. Some were at the Eckert Hall, which is the mathematics building, the top story. We had offices and some labs there. We had labs in the Stagg Field. Let’s see, an electronics lab was in there in addition to the main exponential pile.
Nobles: What about Ryerson?
Sturm: Ryerson shops were used. I am not sure if we had any lab space there, particularly.
Nobles: I do not think we did.
Sturm: Not originally. Maybe after the first experiment.
Groueff: How many people were in the physics department, the physics division?
Sturm: How many up on the metallurgical list, that is a good start. There’s something like thirty or forty people were at the experiment.
Groueff: So you started with forty—
Sturm: No, this was after. We worked about a year at the university before we had a successful test.
Groueff: And now you are talking about the people present in the first—
Groueff: No, but how many people worked in the physics division?
Sturm: In fact I think I’d use that as a basis. At the time, December ’42, I could not quote an exact number, but in addition to those forty—I do not know if you want to count chemists, as well. If you count all of them, I do not know, it was 100, 150.
Nobles: There were many people that were not there on the list—
Groueff: But it was another 100, 150 people?
Sturm: I wouldn’t want to quote that exactly, you would have to look it up.
Nobles: You obviously had guards. Didn’t you have students helping with the moving of the graphite? They were not in on it, but they knew something was going on, but they were not in on it. They supplied muscle power. And guards and laborers, people in Ryerson Shop, and later on at the old brewery site.
Nobles: They were all at the shop, maybe they did not know what they were doing but they were making all of the—
Groueff: At the same time that you were solving the theoretical problems and some experimental problems, you scientists were building with your hands this pile, no?
Sturm: That’s right.
Nobles: Now how many exponential piles did they make? Thirty some, I have the number somewhere. The final pile was only the last one of many. They built these exponentials only part way and get readings, right?
Nobles: They would calculate—
Groueff: Only one was finished to have a critical mass.
Sturm: I can show you a typical exponential pile here. We have one in the next building. It’s made of the fuel and the graphite from the first reactor. But a typical exponential might be only six to eight feet square by eight or nine feet high—they were not that big.
Nobles: Then besides that, all the graphite that came in had to be tested by building it into signal piles.
Sturm: Did we test all of it?
Nobles: Not all of it, but representative.
Groueff: And the graphite was cut like bricks, no?
Sturm: Four inches by four inches by—
Nobles: Sixteen and a half, the bulk of them I would say were sixteen and a half.
Groueff: And those bricks were handled physically by you with your hands?
Nobles: Yes, by all means.
Groueff: Quite a messy thing, no?
Nobles: You would have to see it to believe it. I understand Wattenberg and a few new fellows that you would hardly get cleaned up. If you had took a day or two off, you would still come back with the graphite on your hands and your pores.
Groueff: Because it is black and also sort of greasy, no?
Nobles: That was one of our standard jokes that this is the cleanest dirt that any of us had ever been associated with.
Groueff: Because purity is a requirement?
Sturm: Yes, yes.
Groueff: And so you started building it like bricklayers do?
Groueff: Layer by layer, and put the slugs in the special holes?
Nobles: Well, in building the actual chain reactive pile, remember we had quite a problem of just wood construction, too, since it was built in the form of a simulated pseudo-sphere. It was started on a small base and then it went up and out. All of this had to be supported. I mean, the weight of all this—
Groueff: Oh, yeah. For slugs you used uncoated uranium oxide?
Sturm: Uranium oxide pressed, yes.
Groueff: Which came from Mallinckrodt or from different—
Sturm: Well, Ames, Iowa was making metal, Westinghouse was making metal. [Frank] Spedding from his labs. Someplace, Westinghouse Metal.
Groueff: So they would reach you here in the finished shape, like bars?
Sturm: Some were little cubes only so big. Some were cylinders, about three inches high by two inches diameter. At one stage, and I think even in the final reactor—of course, we took the metal in the center and the oxide on the outside. But even, I think perhaps at the stage of the final reactor, we did not have enough uranium in the single cylinder size.
I think we were building up a certain mass per unit cell of uranium metal by fabricating about a centimeter and a half cubes and putting so many of these and so many of these to make a cell unit. I am not sure whether the final reactor used that, or whether we, by that time, had enough uranium and metal within the cylinder.
We were hurting for metal so badly, I would not be surprised if—
Groueff: Who was telling you exactly how many? You had this kind of blueprint, no?
Sturm: Yes, by this time, it was a very simple instruction. But it depended on all of the thirty preceding exponentials, in which exponentials, one would modify the amounts of material—the spacing of material, originally—in order to evaluate certain parameters of this system. And these parameters would vary with the amount of uranium oxide or the uranium metal in the cell location, and the length of the cell, spacing the cell.
Once this was optimized, there is a maximum—that is, too much is bad, too little is bad. There was a just right. Once that is evaluated, that is a single number.
Groueff: So after that, it became like a routine?
Sturm: Yeah, you then just put so much in every cell.
Groueff: But who was in charge physically of the building?
Sturm: This is now the final reactor. Now there were two shifts. Somebody had the night shift and—
Nobles: [Walter] Zinn had one. And [Herbert] Anderson.
Sturm: Yeah, that is it.
Groueff: Zinn and Anderson. And Fermi was sort of supervising them?
Groueff: And all the others were contributing in different aspects?
Sturm: Well, at this stage, one had passed through—if you are speaking on the construction of the final reactor, this was—
Nobles: I think in that stage, everybody shifted.
Sturm: Everything, yes.
Sturm: Yes, including Compton.
Groueff: You became bricklayers.
Sturm: That is right.
Nobles: Bricklayers and carpenters and, well.
Groueff: And Fermi himself, too?
Sturm: Some, I imagine. I do not remember him doing an awful lot of it, but I am sure he did some of it. Compton was—
Nobles: Did anybody lay a cornerstone?
Sturm: No, I don’t think so. There might have been a first brick or something.
Nobles: The first brick, I had it for a while. Al sent it to me and he had saved it, so you know—
Sturm: Was that a first brick or a last brick?
Nobles: Well, the story that Al told me in the letter that he wrote me was that Fermi was present in the group who first swept the floor all up and got everything all in. So okay, now here is where we start and then somebody said, “Well, Enrico, why don’t you lay the cornerstone?”
And sort of half joking, he said, “Well, all right,” and laid it down.
Al remembered that. Al was there, too. Then he and Bob Johnson were working tearing down the pile because we were working out in Bayless building it up. So Al remembered that and he picked that last brick up and saved it. Everyone laughed at him but he saved that last brick. It was really never a very serious, ceremonialized thing.
Groueff: How many days did it take to build?
Nobles: Probably would have to go over the records. If it was recorded, it would be in Fermi’s report.
Groueff: Yeah, but it is a matter of weeks or days?
Sturm: No, no. Well, I do not know. I would guess between four days and ten days.
Nobles: Probably four hundred tons in there. Four hundred tons.
Sturm: We were taking these ordinary exponentials up and down at the rate of about one a day when we got going, and this was a volume five or six times as much.
Nobles: That was a three shift—
Sturm: But then we had all those wood shimming to do so.
Groueff: So you worked day and night?
Sturm: Yeah, there were two shifts.
Groueff: And the bricks arrived by truck in front of the stadium?
Nobles: By that time, most of the material was all there. Except for the lumber, they hauled lumber in.
Sturm: Yeah, it was the same stuff we had been using for all the thirty other piles.
Groueff: So it was stuck inside the courts?
Sturm: It was inside as far as I know. We did not get any last-minute, urgent delivery that we were waiting for. It was all on hand. It was a matter of deciding that we knew enough to proceed.
Nobles: We brought it in from that door on the south side where you had a ramp sticking out like a little dock. Remember, didn’t they bring your lift up into the right height—
Sturm: Into the room, yeah.
Nobles: Then you would wheel it in on a—
Sturm: When the reactor was below the dock level, we just shot it down on the slide.
Nobles: On that ramp. That shows on the model, I think.
Sturm: Later, we had to use it on—
Nobles: But I remember by this time, the people who had built all the piles developed techniques like just a plain old human chain where we would just even throw bricks up quite high. The fellow up above who was catching them, the brick would practically stop right in front of him and he would just reach down and—
Groueff: So you became very professional?
Nobles: At the time, everyone had a few fingernails smashed and toenails. We sort of took pride in our adroitness at evading the sliding blocks. I can remember the story that Al Rays tells. He said, “Well I do not know why anybody could get hurt because you are working beside this pile here.” And he says, “Pretty soon, say, something hits your face and you think, ‘Well, now that is a block falling. I will have to move my feet and get out of the way.’” [Laughter]
Groueff: But the pile was ready. Now, was it a coincidence that the first experiment happened the same day that this reviewing committee was in town? Or I think it was arranged—they needed a proof that the system would work?
Sturm: Well, I do not know. I do not know. I did not really work at these levels. But I would think that it would be a rather dramatic thing to do. I do not know that there was all that assurance that it was going to be successful, although I think that probably Fermi was pretty confident. We stopped short of the full size because the multiplication was extrapolated to be sufficiently high.
Groueff: And you did not finish the full size?
Sturm: We did not need to.
Sturm: It went critical before—
Groueff: You didn’t need it?
Sturm: No, it would have been too supercritical.
Groueff: I see. But were you all pretty confident that it would work?
Sturm: I would say Fermi was confident that it would work, and that speaks for all of us. We just took his word for it. There were counts being taken—inverse count rate data, you know. That was the first inverse multiplication—one over the count rate projecting down to final critical confirmation. And on that basis, it was all projected to operate successfully.
Groueff: There were not many fears of a big explosion and the whole city of Chicago flying in the air or things like that? Or you never knew?
Sturm: There was no such voiced fear. I do not know. I know that I did the calculation as to how much energy was in all of this stuff, but it was an amateur sort of a thing. I mean, to get it to explode was possibly difficult, actually, which we now know is difficult.
Groueff: But then you did not know, you were working with completely new materials and new science actually?
Nobles: No one knew very much at all about the temperature coefficient.
Sturm: No, no one would know about that necessarily.
Nobles: We did build one exponential pile. Remember the one where we insulated it with strip heaters all around it? That was one of the rather large ones right towards the end.
Sturm: Well, that would be related. I did not remember that until you told me. That would be a measurement of temperature coefficient—pretty valid.
Nobles: Went all around and screwed these long—
Groueff: You did not know that you would have a negative temperature coefficient?
Nobles: Well, that was the object for this one particular experiment, we had no idea.
Groueff: You did not know if it would be plus or minus. You were going to try to get it cooled, is that it?
Sturm: Well, that would be a measurement, a differential measurement. Indeed, we had done other work on heating uranium metal, for example, until it oxidized in furnaces—one heated it to see physically what it would do. What it did was expand grossly and it oxidized and became uranium oxide and it took up a considerably larger volume and so on and would become less efficient. The resonance escape probability would go down as a factor.
Nobles: Remember there was an experiment on the books planned for out at Bayless parking to build a block house. When they were going to build CP-2, they were going to let it run as far as it could go, and it was called a block house.
Sturm: Yes, this is probably the Zinn influence. The thing that finally terminated them, the borax experiment out in Idaho.
Groueff: What was the story about this blimp cover?
Sturm: Oh, yeah.
Nobles: They thought they might have to remove the nitrogen or the air from a large part of it; no one knew how close it would be to critical. So to do that, they proposed to enclose the whole thing in a big balloon, and the balloon would be, of course, supported by the structure itself, and it wouldn’t collapse. It reduced the pressure inside by pumping on it with these big vacuum pumps.
Groueff: So to do the whole experiment in more pressure or vacuum—
Sturm: Or to fill it with helium, which would not react.
Groueff: But you didn’t do it?
Sturm: We did not have to do it, no. But we have often thought about what the Goodyear Company, who made other blimps, thought about when they got the order for the cubicle blimp.
Groueff: But they didn’t know what it was for?
Nobles: They suggested it would not fly too well. [Laughter]
Sturm: Consistent with the fact that we did not have to build the whole sphere, you see, because we got enough reactivity early. We also did not have to evacuate the—
Groueff: So you did not use it, but it was physically there?
Sturm: It was there.
Nobles: It was physically there, and it was all up and one face was open. The front was just rolled up like a huge curtain and it was never lowered.
Groueff: But what you saw from this balcony there during the experiment was just this blimp? You could not see the—
Nobles: The back side.
Groueff: Did you see the pile at all?
Nobles: Then they put that structure in back, you know, that held the safety rod and a wooden frame going out with the track.
Unidentified Male: That went towards the balcony though.
Groueff: But the blimp was hiding the bricks?
Sturm: Yeah, this would be right, I guess. We fed it in from the other side.
Nobles: The only place you could see the bricks was from the—
Sturm: How about George Weil and his stick, and his rod?
Nobles: Those guys went up there on top on the backside. They went up the elevator with a can of sulfites in the back.
Sturm: No, George had a cadmium rod that was—
Unidentified Male: Well, he was standing on the—
Nobles: That was on the side with the balcony.
Sturm: They cut open a special hole? I do not remember about that, them cutting a hole.
Groueff: So the blimp was just there unused?
Sturm: It was an obstacle, basically, yeah, all along. We were much concerned, for example, if you dropped a tool down alongside this thing—a wrench or pliers or a hammer—when the thing were evacuated, it would pull it in tight, you see? And a tool would cut the balloon. So we were most particular not to drop tools.
Nobles: We did go around every once in a while and inspect to see that no one had fallen down. Because a man could go in between the curtain and the blimp cloth and the pile and go all the way around.
Groueff: And you could not remove it completely or it was already built in?
Nobles: The bottom was completely covered by the tons of materials. There was nothing you could do but just leave it there. Later it somehow got – I know that pieces of it were out at Site A.
Nobles: I wish I had a big square piece of that as an artifact, I don’t have any.
Groueff: Yeah, to see the color or the texture.
Groueff: Was there any authorization or permission asked from any authority, like university authorities, or Compton took it on himself?
Sturm: I do not know details here but it is my understanding that Compton arranged it with the authorities. For all I know, on his own responsibility, but I am not sure.
Groueff: But not with a city authority because you could not tell them?
Sturm: I do not know what one would do at that level. Well, I have a feeling not.
Groueff: Actually, you do not do that normally in experiments in chemistry or physics. You never ask permission, no?
Sturm: Yes, that is right. In addition to which it was done on university property and so on, so there would be no legal reason that you would perhaps have to consult them. The laws didn’t eliminate chain reactions.
Groueff: Now I have the descriptions of the day of the experiment and this is by Mr. [inaudible].
Sturm: [Inaudible] Al?
Groueff: Yes, [inaudible]. But what can we add now? I would like some personal feelings or souvenirs that you have of what you felt during the experiment. What was your job first? Were you among the spectators there or you have a job?
Sturm: Well, I had a job. Though the job diminished. I suppose now you refer to the time when one actually took the thing critical.
Sturm: It was finished, and it was just a matter of running it.
Sturm: Well, I do not know what—
Nobles: Well, there were very few of the people there who actually had a job to do. Some of them had jobs that—helping other people.
Nobles: I think everyone came dressed up in their good clothes wondering what they were expected to do, except that George [D.] Monk and [Robert E.] Bob Johnson were outside the door sitting on a load of graphite in case we needed another layer of deflecting, another layer—
Sturm: Of graphite.
Nobles: Somehow everyone forgot about them. They sat out there all the time.
Sturm: Yeah, they were outside—
Nobles: Right outside the door.
Groueff: Ready to bring in more graphite?
Nobles: Yeah, they had a skid load of graphite in case someone decided at the last moment that it would be nice to have another layer.
Groueff: So they did not see the experiment?
Nobles: No, they did not see the experiment.
Unidentified male: Tom Grill probably did not see either, because wasn’t he over in the tower?
Nobles: Tom Grill and Jerry were way down at the tower.
Groueff: Was this cadmium?
Sturm: Oh no, there was a remote control room, another control room, a duplicate set of instruments. It was a safety feature like the boys with the cadmium solution and Zinn zipped and the axe and the boys in the remote control room. I think actually, though, the operation basically was the withdrawing of rods step-wise as specified in detail by Fermi, done either by Fermi with his [inaudible] [00:53:51] control and his motorized rods, or by Weil, who would pull it out another six inches or whatever as requested by Fermi.
For the rest, it was a matter of reading instruments and interpreting these readings. Have you seen this birth certificate of the Atomic Age, the instrument readings?
Sturm: We have got it out there in case you do not have. But the point is the response to a change in rod position would be an exponential, either converging or diverging. Well, first, of course, converging. And from the time constant of the convergence, one could infer the state of criticality and the amount of sub-criticality, and these things were just withdrawn step by step.
This was the essential experiment. This was all that was going on. People were standing by safely, other people maybe to do special jobs, like the fellows in the halls, and maybe some people, for all I know, were reading radiation levels. Was [Carl] Gamertsfelder or anybody was watching ambient levels around?
Nobles: We had the two ion chambers up on the side. Somebody was watching them.
Sturm: This sort of thing. But they are all peripheral now to that experiment.
Nobles: [Herbert E.] Kubitschek was watching – what was he doing? He had a barometer? What was that for?
Sturm: Somebody talked about Kubitschek, I guess, maybe. Well, the concern here is, you see, you are now making changes. But what if the atmospheric pressure changes? Because we did not evacuate this pile. We pump in or pull out some nitrogen, and one would like to know if the reactivity changes, whether it correlates.
Nobles: The model, if you see it at the museum, will show a man on the balcony sitting there at a table and he has got a barometer. He is sitting there with an assistant or a partner. They are reporting to Fermi, no doubt.
Sturm: Yes. Well, Fermi did not actually write anything down, and this is where [inaudible] and I, and I think some others, too, were taking down these data and trying to calculate quickly from a slide rule or something.
Groueff: You were at the instruments?
Sturm: Yes, reading instruments, recording these data, and trying to relate them to the parameters of the exponentials and therefore to the state of reactivity of the system. Well, some of these things would come out as chart readings, some as numerical data as scalars and so on. You could get these constants from either source, and there were several sets of instruments. Even today in a reactor control problem, you do not rely on one set of instruments, there were a series. One was the graphical one, which is this birth certificate and by taking a couple of points and guessing where the zero level is and knowing how fast the chart is going, you would get some idea. Others of us worked from scalars and clocks and got the same data.
Groueff: But Fermi was the one who conducted the experiment?
Groueff: He was actually the only active man there, the others being mostly helpers or in case of accident.
Sturm: Yeah, that is the sort of thing.
Nobles: Actually, the day before, I think Fermi pretty well knew what was happening. Because remember many people were told the next day, “Well, do not come to work,” and so on.
All of us who had been building the thing, actually piling up graphite and so on were told, “Come back tomorrow.”
Groueff: I see.
Sturm: This could well be. I did not know about it.
Groueff: Because while you were building the pile, you worked for a few hours there and the rest of the time at your laboratories or your offices, no?
Groueff: Or entirely—
Nobles: As it approached completion, you know, we would put on a few layers. I think we even irradiated foils a couple of times during layers and then make essentially an exponential calculation and see what way – anyway, Fermi would calculate what is the K of this pile at this time and then the next few layers, do it again and calculate the change in K. As it approached one, then he could extrapolate and say “Well, so many more layers would do it.”
I think at night when we went home, we said, “We might have to put on one more layer or so.”
Sturm: I think the night shift under Anderson stopped at a predetermined state of affairs – the rods were in the reactor and so on. I think it was then estimated that it was now near enough to critical or at least as near to critical as Herb should take it at night. I was on the day shift, Fermi was on the day shift. So presumably then, when we came in in the morning, it was as Anderson left it. There was always some sort of doubt in some of our minds as to whether Herbie Anderson had taken it critical the night before, you see? You have to know Anderson—or you have to have known Anderson before he was ill to—this makes complete sense.
Groueff: What kind of man was he?
Sturm: He was an inquisitive man. [Laughter]
Groueff: So you were not sure whether his curiosity would have pushed him to—
Sturm: Pull out the rods just to see what would happen.
Nobles: It would not do any good to ask him because—
Sturm: Well, much later, only a couple years ago—Herb is now sort of more stable. No, he was quite stable. He was a man of unusual properties, which brought him to be Fermi’s right hand man. It is quite appropriate that he should be. But one of these properties was a great energy, great inquisitiveness, and great enthusiasm about this and his business.
Nobles: Maybe he is the real—
Sturm: No, no, no, I am now satisfied. I talked with him several times and he said no.
Groueff: But you would not have known if you did not, no? Unless an accident happened.
Sturm: No, if he did, he did not choose to tell anybody and there were no accidents. That is right.
Nobles: Knowing him, I am sure that with his regard of Fermi, that he knew that he could do it and he would not do it because he would want Fermi to.
Sturm: Right, agreed. But he may well have had an agonizing few seconds as he decided which course to take.
Nobles: I think this is a measure of the regard for Fermi on the part of many of these men who have told me that they had—it was not quite an awe but it was a profound respect for Fermi. I think this point you bring up is well taken. I do not think anybody wanted anybody but Fermi to have this.
Sturm: Yes, yes.
Nobles: But wouldn’t there have been some residual activity if it had been brought up to any—
Sturm: Well, yes, if he had gotten very far, there would be some fission product.
Nobles: They would have had some footprints.
Sturm: Well, yes, but the level of all these things was increasing as we put more fuel in, and toward the end, rapidly. I mean, one brick now made a much bigger effect than brick earlier.
Groueff: Could you describe in a few words the man Fermi was as a leader—the way he worked and some sort of the human side of it and his habits or some anecdotes about him during those early days? What kind of a leader was he? Was he very distant or was he very friendly?
Sturm: Oh no, quite friendly and quite willing to explain things and details to even such persons as myself. I was just a graduate student at the time. I did not have my graduate degree. No, he was very friendly and very approachable.
Nobles: It was always a great treat if you could happen to be lucky enough to be around at lunchtime and get in the crowd that went to lunch with Fermi, because the conversation around the dinner table was always scintillating. Fermi liked to talk, and people liked to challenge him with problems and, “What do you think about this, Enrico?” And he would always have something to say.
Groueff: Because he would have lunch with you, with the younger people in the cafeteria.
Nobles: Whoever was there, you know, “Let’s go to lunch.”
Groueff: I see.
Sturm: He was physics. He lived it; this was his business. His earlier group had the game Tu Lire, whatever it is in Italian. He had several groups from time to time but the Italian group always had this game, which they would play among themselves. Any man could challenge any other man on any subject in physics, and you could ask anybody any question in physics. And if the other man could not answer, you would win Tu Lire.
Groueff: They had that in Italy?
Sturm: That they have in Italy, yes. But this sort of spirit was on with his American group, as well. That is, one did these things, this is all that one lived for, more or less at this time—this all absorbing interest.
So how did Fermi lead, therefore, for this group? In no sense by having administrative meetings and saying, “This group will do this and this group this and you go there and you do this,” and so on. He was doing this and his short range lieutenants, the men nearest to him, would sense or ask what he needs doing and more or less clear the way. His leadership, it simply was just a sort of influence rather than a—
Groueff: He was doing the thing himself.
Sturm: Yes, but he was not overwhelming everybody. Everybody, in helping him, actually felt they were helping him. They were not demeaned or lessened. I mean, he was not overwhelmingly powerful above them. It was just a kind of a large group working as one, really, but with Fermi—
Nobles: Fermi says, “Now we need to come over this.” That would be the wording.
Groueff: Would people say, “Why should we?”
Sturm: They’d feel free to. You would feel free to, and you would be told why. Not in the sense of ordering but your thinking would be clarified. You would find out where you were making your mistake.
Groueff: And usually he would be right?
Sturm: Always, always. I do not think I ever—
Nobles: He was called “The Pope.”
Groueff: They were calling him the pope?
Groueff: So his authority was mainly based on his superiority in physics.
Sturm: Yes, yes.