Commemorating CP-1 at 80

Robert Rosner

My aim in writing this article is to tell a story, a story that has had a huge impact in my life, often in totally unanticipated ways. Just over 80 years ago, a momentous science achievement happened just across the street from my office at the University of Chicago, on 2 December, 1942; and in 2017, I was privileged to lead a faculty group from the University and Argonne National Laboratory to commemorate the 75th anniversary of that achievement. You might wonder: Why this curious choice of words – why “commemorate”, and not “celebrate” the event? In the following I will discuss that event, why we chose to call that anniversary a “commemoration”, and the myriad ways that this event has influenced the world we live in today.

The story I am about to tell you is about CP-1, Chicago Pile number 1, the experiment demonstrating that nuclear fission – the violent breaking apart of the nuclei of atoms – could be understood, and could be sustained and controlled. The experiment was conducted below the bleachers of our then football stadium, where our current main library, Regenstein Library, stands today. In large part, this story has been told previously many times, including by expositors who were key participants – such as, for example, Enrico Fermi – but there are aspects of this story that have not been widely discussed, and it is these that constitute the justification for my retelling.

The key initiator of this story was a series of experiments by two German chemists, Otto Hahn and Fritz Strassmann, and the theoretical explanation of these experiments – the discovery of nuclear fission – by the refugee Austrian physicist Lise Meitner and her nephew, Otto Frisch, and the subsequent experimental confirmation of the theory, all in 1938. What they showed is that if one bombarded uranium with neutrons, some of the uranium would split into a pair of daughter nuclei, such as xenon and strontium, or krypton and barium, releasing both a prodigious amount of energy and, on average, 3 additional neutrons. Frisch later related that a Danish colleague of his, Christian Møller, soon after pointed out to him the key implication, namely that these additional neutrons could lead to a chain reaction.

Leading physicists both in Europe and in the United States immediately realized that this discovery might allow for building a fearsome new weapon, and generated a visceral fear among scientists who – for good reasons – had escaped from the Nazis: the fear that Germany might achieve the building of such a weapon first. I think it is hard for us, today, to appreciate the depth of this fear that existed then. Lise Meitner – who was key to understand fission – was horrified about these implications of her own work, and refused to join the subsequent efforts to build a bomb, but others saw things differently. In particular, Leó Szilárd, a prominent Hungarian physicist who had also escaped the Nazis, pushed first the British, and then campaigned in the United States, to respond to the potential threat of a German atomic bomb. His key step (with the help of Eugene Wigner and Edward Teller) was to convince Albert Einstein to sign a letter to President Roosevelt (dated 2 August 1939) fig. 1, arguing that time was of the essence, and the threat enormous.

That letter succeeded in its goal – to get the United States government to start what eventually became the Manhattan Project. This was one of the first “big science” projects that served as a model for other megaprojects such as the NASA Apollo project to land humans on the Moon.

But at first, progress in the United States was very slow. In part, this was because physicists did not yet have a complete grasp of the science, and in part because the enormity of the threat, and the enormity of what had to be done, was not yet fully understood in Washington, and so the needed resources were not yet at hand.

In the meanwhile, the British had a far greater sense of urgency. By late 1939, physicists Otto Frisch and Rudolf Peierls – both Jewish refugees from Nazi Germany, and by that time living and working in Great Britain – had realized that U-235, the fissile form of uranium, was a far more likely candidate for constructing a fission bomb than the dominant form of naturally occurring uranium, U-238. They also realized that their estimate of the amount of fissile uranium necessary sustain a chain reaction – in the range of kilograms – meant that a fission bomb suitable to be carried on board an airplane was in fact attainable. Their memo led the British MAUD Committee in 1941 to urge the development of such a bomb. The British also understood that only the United States had at that time the potential human, financial, and infrastructure resources to actually carry out such a project, and lobbied fiercely for it in Washington. Thus, on October 9, 1941, President Roosevelt approved the start of what was to become the Manhattan Project – and with the Japanese attack on Pearl Harbor just 2 months later, on Dec. 7, 1941, and the American entry into World War II, the die was cast: With sufficient funds now available, the Manhattan Project started at Columbia University in New York City under the leadership of the Italian physicist Enrico Fermi.

The initial time table for demonstrating a sustained and controlled chain reaction using uranium was breathtakingly ambitious – Arthur Holly Compton, a Nobel Laureate and Professor of Physics and Dean of the Physical Sciences Division at the University of Chicago, was put in charge of bomb development, and was given two weeks to lay out the research plan that would lead to the building of the first atomic bomb; and on December 18, 1941, Compton proposed that, among other tasks, a controlled and sustained chain reaction using uranium be demonstrated by the beginning of October, 1942.

Compton also realized that the then-ongoing research on fission was too geographically spread – participating universities included Columbia and Princeton on the East Coast, Univ. of Chicago in the Midwest, and UC Berkeley on the West Coast. This fact, plus several key handicaps of the New York location – including a lack of sufficient space near the Columbia University campus and too close proximity to the Atlantic Ocean, thus possibly more vulnerable to sabotage – argued for finding a more convenient and safer central location for the project. Compton (fig. 2, right) clearly felt the urgency of moving forward – and was unafraid of exercising his authority: He declared that Chicago would serve as the central location of the initial science effort, basically for two reasons: its central location, minimizing travel impacts for participating scientists from both coasts; and the strong support given to the project by the University’s administration. As a result, the Manhattan Project moved from Manhattan to Chicago in early 1942, within the newly created Metallurgical Laboratory (the Met Lab) led by Compton and located in Hyde Park, the Chicago neighborhood in which the University of Chicago is located, across the street from where my office is today. Engineering that move took a great deal of diplomacy on the part of Compton – moving the project to Chicago clearly also meant moving Enrico Fermi (fig. 2, left), by far the most important physicist involved with the project, to Chicago as well. And a reluctant Fermi did in fact move his entire research team to Hyde Park; and moved his family as well, to a house not far from my own home, on University Avenue.

The tasks Fermi set for his team were deeply challenging: Could they confirm the critical mass estimates of Frisch and Peierls? Could they get a chain reaction going – and could they sustain it and control it? Urgency was still in the air, given the fears of German progress on their bomb, but the time schedule had been slightly relaxed by Compton: The controlled chain reaction should now be demonstrated by January of 1943, and a functional atomic bomb delivered by January 1945.

The plan to reach criticality, meaning the state of a sustained chain reaction, was iterative: Fermi and his colleagues were initially not sure how big the ultimate nuclear reactor would have to be in order to sustain a chain reaction. So they proceeded systematically, in a series of steps: The uranium would be layered among 20 pound chunks of graphite, the whole looking like a pile of black bricks – whence the name “pile” for the reactor. The uranium served as the fuel, that is, the source of both the neutrons and the nuclei that would be split by the neutrons; the graphite served as the moderator, meaning the material that could slow the neutrons down sufficiently so that they would be absorbed by the uranium. And the idea was to build a sequence of larger and larger such piles, and at each stage to monitor how many neutrons would be generated.

Now, Fermi had already started building such piles at Columbia, and in a critical bit of pure luck – or, perhaps more likely – a bit of genius on the part of Enrico Fermi, discovered what might have been a fatal flaw for the entire project. It turned out that at Columbia, the number of neutrons observed as the piles got bigger and bigger were much less than theory had predicted – and Fermi had the intuition that there was a problem – perhaps some sort of contamination – in the commercial graphite they were using. And indeed, in a lunchtime conversation between Fermi and Leo Szilard with representatives of the company supplying the graphite, it emerged that this graphite did have a contaminant, namely boron – and that this was hugely problematic because the physicists knew that boron was a superb absorber of neutrons. This fully explained the discrepancy between the observed and predicted number of neutrons – and as a consequence, all of the graphite subsequently provided to the Manhattan Project, including all of the graphite delivered to Chicago, were of a special purified form.

You might think that this issue of contaminated graphite was a bit of arcana that only physicists would find interesting – and you would be very wrong. It turns out that the Germans were, at the time, conducting similar experiments, but apparently did not realize that there was a contamination problem with commercial graphite – and decided that this was not the way to go, and instead chose to use heavy water – water that contained a heavier isotope of hydrogen, deuterium – as the moderator. This was a fateful step for the German nuclear effort because heavy water is far more difficult to obtain than graphite, and because the Allies were successful in both preventing German access to already existing heavy water supplies, and in severely damaging the facilities needed to produce the heavy water, principally in occupied Norway. Thus, by 20 February 1944, the German nuclear bomb effort had effectively come to an end.

But let us return to Chicago, and Fermi’s nuclear reactor pile. The target was to build a pile sufficiently large so that it could sustain a controlled nuclear chain reaction. This nuclear reactor would contain the key element uranium, in the form of 5.4 tons of uranium metal, and 45 tons of uranium oxide, as well as large amounts of graphite – 45,000 bricks of purified graphite, each brick weighing almost 20 pounds, which was needed to slow down the neutrons sufficiently so that they could split the uranium. It was truly going to be a pile – a pile of 360 tons of graphite, and just over 50 tons of uranium. This was to be the Chicago Pile number 1 (fig. 3).

The original location of this reactor was to be well outside the city of Chicago, but because the contractor hired to build the reactor failed to perform – their workforce went on strike, and so work on the reactor had come to a full stop – Enrico Fermi decided to simply build the reactor on campus, in the largest of the squash courts under the stands of the old Stagg Field, what was by then the defunct University football stadium. Who built it? Graduate students and young men hired from neighborhoods surrounding Hyde Park, working under the supervision of Fermi and his technical colleagues. All this was done in total secrecy – apparently the president of the University was not fully informed, and neither was the political leadership of the City of Chicago, including its mayor. Amazingly enough, one of those neighborhood boys was still alive during the 75th anniversary of CP-1 – Ted Petry, 17 years old when working for Fermi, was the last survivor of the people who built CP-1, and sadly passed in 2018.

I should also add that, quite aside from the work on CP-1, the University was host to a vast variety of other activities related to the bomb project, including a project involving the production and use of plutonium as an alternative to uranium as a fissile bomb material. A sense of the scale of what was going on right on campus during the war, consider that the workforce within the university’s Met Lab numbered over 2000 people by July 1944, thus completely overwhelming all other work being carried at the University at the time. Buildings housing the Met Lab on the campus occupied over 200,000 square feet, equivalent to just over 31⁄2 football fields; and the addition of the 124th Field Artillery Armory (which still stands just north of the university) provided another 360,000 square feet, or another 6 1/3 football fields of space. This was a simply enormous project.

So, how long did it take to build CP-1? 15 days, working in two 12-hour shifts. In other words, the work continued non-stop, until the Pile was completed. And in the afternoon of the 2nd of December, 1942, after one failed start that morning, the experiment succeeded – the Chicago Pile number 1 went critical and a controlled and sustained chain reaction ensued at 3:25 pm, one month ahead of schedule (see fig. 4).

You may well ask at this juncture – What was the point of this experiment? It demonstrated that we understood the basic physics of nuclear fission, at a quantitative level sufficient to allow teams of physicists and engineers to design and build an atomic bomb.

And so they did ...

By late 1942, Los Alamos, New Mexico was selected as the site for the bomb design; two designs emerged in short order, one based on using uranium, the other using plutonium. The Met Lab outgrew the space allotted to it on campus, and so by early 1943, some of its activities moved to the suburban location where CP-1 was originally supposed to be located; that location served as the site for the design of new generations of reactors. A huge facility for separating out uranium-235 from the more common isotope uranium-238 was designed and built in Oak Ridge, Tennessee; and new reactors were built both in Oak Ridge and at the Hanford site next to Richland, Washington, the latter for producing plutonium. These reactors were all based on designs that originated in the Chicago Met Lab.

4 atomic bombs were built: 2 uranium bombs and 2 plutonium bombs – and one of the plutonium bombs, code-named Gadget, was the only one tested before deployment ... the uranium bombs were never tested before deployment.

The test of Gadget – an experiment called Trinity – occurred on July 16, 1945 at 5:30 in the morning, at what is today called the White Sands Missile Range, about 35 miles southeast of Socorro, New Mexico.

J. Robert Oppenheimer, the leader of the bomb effort at Los Alamos, recalled his immediate reaction to seeing the explosion – a line from the “Bhagavad-Gita”, the Hindu sacred text, flashed through his mind: Now I am become death, the destroyer of worlds. And indeed that singular event marked the first time in human history that we fashioned a weapon with the capability to eliminate all human life on Earth.

What about the remaining 3 bombs? Two of the bombs were used ... on Japan – the first and last time that atomic bombs have been used in warfare. And one was kept in reserve ... and never used.

An important aside to the story I am telling you is that Nazi Germany surrendered unconditionally on the 7th of May, 1945, thus ending the war in Europe. In other words, the first ever deployment of an atomic bomb occurred just about 3 months after the country that originally motivated the American nuclear bomb project had already surrendered.

What then led the United States to continue the atomic bomb project, and to deploy two of the bombs? The answer was, in short, the desire to end the war faster – to persuade the remaining Axis power, Japan, that further resistance was futile, and to avoid the loss of American lives if an invasion of the Japanese home islands had to be carried out.

But how to deploy them turned out to be highly controversial.

Many options were presented and discussed about how the power of the atom bombs could be demonstrated – for example, deploying one of the bombs off shore in the vicinity of Tokyo, thus ensuring that the Japanese leadership directly witnessed the destructive power of these weapons. But in the end, the decision was made to use them on 2 medium-sized cities: Little Boy, a uranium bomb, was exploded over Hiroshima on August 6, 1945, and Fat Man, the last of the plutonium bombs, was exploded over Nagasaki on August 9, 1945.

Japan surrendered 6 days later, on 15 August, 1945. Was Japan’s surrender driven by the deployment of these two bombs? Why drop two bombs – why was the first bomb not sufficient? These questions engendered additional controversial issues – because the USSR declared war on Japan on August 8, 1945, just a day before the second bomb was dropped on Nagasaki. As you can imagine, the notion that the Soviet entry into the conflict in Asia might have contributed to Japan’s surrender was anathema to those that saw the use of atomic bombs as the reason for the Japanese surrender ... and there are some that have argued that one of the U.S. goals was to end the war quickly enough so as to prevent the USSR from gaining too much advantage in the Japanese war theater. These are controversies that remain contentious even today, and I do not have an easy answer to these questions.

But let us turn the clock back again a bit, return to the Trinity test that demonstrated the destructive power of these weapons, and ask how the participants felt about what they had witnessed. We already know how the leader of the bomb project, Oppenheimer, felt – namely a deep foreboding. I think it is fair to say that the others present at the time of the Trinity test had mixed reactions: In a later interview, Oppenheimer was quoted as saying “We knew the world would not be the same, a few people laughed, a few people cried, most people were silent.” So while there was elation that Trinity had worked, and that the incredible effort that had been mounted succeeded in its goals, in an amazingly short time span, others began to worry about a future in which atomic bombs were a reality – and that future had just arrived ... So the elation was balanced for many of those present by a “but” ... and for the balance of this paper, I would like to focus on this “but” ... it is this “but” that led the University of Chicago to refer to the events of the 75th anniversary as a commemoration, and not a celebration.

Here are a few questions one might ask oneself at this point: What was the reaction of the scientists who had worked in the Manhattan Project – and knew what it was all about – at certain key moments:

• First, when the question of how to target Japan was being discussed?
• Second, when Germany surrendered, and the atomic bombs had not yet been deployed in combat?
• Third, after two of the atomic bombs had been dropped on Hiroshima and Nagasaki?

The historical record shows that opposition to deployment of atomic bombs had already been building among the Manhattan Project scientists before the Trinity test, especially here at the University of Chicago. Certainly by late 1944 and early 1945, a number of different suggestions had been made to demonstrate the power of atomic bombs without targeting either civilian or military populations. And many were horrified and spoke out against further work on nuclear weapons after Hiroshima and Nagasaki – they had not expected the bombs to be used on civilian targets, and had argued against that, right from the start.

I will return to these issues in a moment, but it is important to understand the full context of those times. By then, both the Axis powers and the Allies had already cast aside any reluctance to attack civilian targets: the Germans in their attacks on English cities early in the war; the Japanese in their infamous Nanking Massacre in December of 1937, well before their Pearl Harbor attack; and the Allies in their carpet bombing of German and Japanese cities, which led to enormous firestorms whose casualties were – amazingly enough – comparable to the losses resulting from the atomic bombs.

Nevertheless, the sheer scale of destruction resulting from a single bomb, and the long-lasting legacies of radiation sickness and radioactive contamination that follow from the explosion, made the atomic bombing uniquely horrific.

Finally, the ultimate irony of the targets chosen was not lost on anyone: While the bombs were developed in response to fears about possible German atomic weapons, in fact they were used on the Japanese, who were not thought to have had any efforts in this direction – and as one can imagine, this raised all sorts of additional questions about possible underlying racism in the decision processes that led to the bombing.

So now let us return to Chicago, and more specifically ask how Chicago scientists viewed what had transpired in New Mexico, and what they did.

University of Chicago scientists had already by the summer of 1944 foreseen that some of the long-range consequences of their work would be far from benign – in correspondences to Professor Compton, the head of the University’s Met Lab, they foresaw the great benefits to be gained by exploiting nuclear physics but also the dangers of a future nuclear arms race.

These concerns led Prof. Compton to appoint a committee, chaired by another Chicago Nobel Laureate, Prof. James Franck, to develop a report to be delivered to the Truman Administration, outlining their concerns. The deliberations of this committee were held in secret; and much of the writing was done by Eugene Rabinowitch, a physicist we will shortly encounter again. The report that emerged from these discussions, now referred to as the Franck Report, was sent to Secretary of War Henry Stimpson in June 1945. It was amazingly prescient about the future:

• It recognized that the secrecy that had enveloped the Manhattan Project could not be maintained forever;
• It envisaged a nuclear arms race, starting as soon as the secrets leaked out; and
• It recognized that equilibrium between contending nations owning atomic bombs could only be established once their respective arsenals were sufficiently large that any attack could and would be met with devastating retaliation. This concept is known today as mutually assured destruction, or MAD, and had in fact been the driver behind American and USSR nuclear doctrine since the start of the Cold War.

Finally, the Report argued that the American bombs not be used in warfare, and offered instead two alternatives: first, that the United States offer a demonstration – at some to be determined isolated location – to an assembly of representatives of all the United Nations, with the aim of internationalizing control of nuclear weapons right from the outset; second, that the United States simply continue keeping the existence of atomic bombs a secret, with the advantage that the U.S. would always have a head start in atomic bomb development, even should the secret leak out.

The Franck Report was of course unsolicited. Why was it written? Because, as Glenn Seaborg, one of the participants in these discussions and a signer of the Report, put it: “By an accident of history, we were among a very few who were aware of a new, world-threatening peril, and we felt obligated to express our views.”

What was the reaction in Washington, DC? We know that the Report was discussed by the so-called Interim Committee, a body appointed by President Truman to advise on the possible deployment of the atomic bombs, on June 21, 1945. We do have evidence that the opinions expressed in this Report were at the time unpopular, and unwelcomed, in Washington, DC. And we know that the Interim Committee reported to President Truman that the use of the bombs was unavoidable. And so they were used.

The failure of the Franck Report to influence the use of our atomic bombs was of course deeply disappointing to the participants, and by the end of the war, a number of Chicago scientists involved with the Manhattan Project decided to organize a means of opening up to the general public discussions about nuclear science, and nuclear weapons in particular. Led by the aforementioned Eugene Rabinowitch and the physicist Hyman Goldsmith, this group founded the Atomic Scientists of Chicago, an organization that soon morphed into the Bulletin of the Atomic Scientists, starting publication in December 1945.

While some may not have heard of the Bulletin, I suspect most readers have heard of the Doomsday Clock, which the Bulletin runs; it is located right here on our campus, on 60th Street, in the same building as the Harris School of Public Policy. And this is one of my own connections to this history: I was a member, and then chair, of the Science and Security Board of the Bulletin, a Board that discusses and decides on the movement of the Doomsday Clock minute hand as an informal way of signaling how dangerous the world is, as determined by a group of nonpartisan experts. Set at 7 minutes to midnight at its birth in 1947, it Is currently at 90 seconds to midnight ... the furthest from midnight it has ever been was in 1991, at the end of the Cold War, when it was reset to 17 minutes before midnight. Why have I participated? Because of my expertise in areas relevant to the Bulletin, and my sense that this participation is a payback for the opportunities I have been given as an immigrant to the United States.

The Chicago founding scientists of the Bulletin, together with likeminded scientists and topical experts drawn from around the world, aimed to push back against the further use of nuclear weapons, to ensure civilian – not military – control over the atomic weaponry, and to direct nuclear research in the direction of civilian applications, such as in the realms of medicine (for example, the use of radioisotopes to battle cancer tumors) and electricity generation. And the Bulletin has in fact had a powerful role to play in the history of nuclear weapons – for example, it served as a major international forum for discussions about nuclear nonproliferation and arms control in the 1950s through the 1970s, discussions that ultimately led to the Treaty on the Non-Proliferation of Nuclear Weapons, or the NPT, which entered into force in 1970. While the Bulletin is not, and never was, a part of the University of Chicago – it is an independent 501(3) non-profit organization – it has maintained close connections to us, both by virtue of the involvement of University faculty in its various activities – indeed, President Hutchings was a major financial supporter of the Bulletin at its birth – and because it is located right here in Hyde Park. More recently, the Bulletin has added a focus on other instances in which human scientific and technological progress has led to conditions that threaten human welfare on this planet – obvious examples include anthropogenically-driven climate change and the confounding potential threats posed by emerging new technologies. Thus, it has over the past decade served as a forum for discussions on the science underlying climate change, on the means by which climate change might be mitigated, and on the mechanisms by which humankind might adapt to climate change. Again, as we all know, these are topics that are politically charged, and as before, the Hyde Park spirit lives on: We believe in forthright debate, and in airing all of the issues, all done with the aim of advancing informed public policy decisions.

But what about the Met Lab, and all those folks who worked on CP-1 and its successors? The push here in Chicago for exploiting nuclear physics for civilian use also resulted in a re-direction of the Met Lab away from weapons research – this push was formally instantiated by the Jeffries Report (also commissioned by Compton), which strongly recommended this path for the Met Lab, and sent to Washington by Compton on November 18, 1944.

These efforts did bear fruit: On July 1, 1946, the Met Lab morphed into the first American National Laboratory, Argonne National Laboratory (fig. 6), located some 25 miles south-west of Hyde Park, and managed since then by the University for the Federal Government – and that is my other connection to this story, since I was Argonne’s chief scientist and then lab director from 2002 to 2009.

One month later, on August 1, 1946, President Truman signed the McMahon Atomic Energy Act, which formally transferred control of atomic energy to the civilian sector, and founded the civilian-led Atomic Energy Commission – the AEC – that is the ultimate parent of today’s U.S. Department of Energy. Most profoundly, it placed all the wherewithal to design and build nuclear weapons into the hands of a civilian federal agency, not the military.

Argonne is a civilian national lab, and does not do any weapons research. For the first 30 years of its existence, it focused on the civilian applications of nuclear energy, designing most of the existing types of light water reactors operating around the world. It was also heavily involved in the science and engineering related to dealing with nuclear waste; and even contributed to the American nuclear navy: The first nuclear submarine, the Nautilus (fig. 7), used a eactor designed by Argonne engineers. Nuclear medicine was powerfully influenced by the Manhattan Project since the deleterious biological effects of radiation were recognized early on, and it should therefore not be surprising that the Atomic Energy Commission funded the creation of the Argonne Cancer Research Hospital in 1948, located right here in Hyde Park; aims included the study of producing medically useful radioisotopes, using such isotopes in treating cancer, and carrying out research on tissue damage resulting from exposure to radiation. While Argonne has continued its research in the domains it first focused on – nuclear and particle physics – its scientific and technological focus has of course continued to evolve, and today its research programs additionally deal with all manners of energy production, not just nuclear, as well as with computational and material sciences, from the basics of energy storage to the molecular structure of biological materials, and a variety of engineering issues, such as improved transportation technologies.

What lessons can we draw from all this?

Here are my candidates:
Perhaps the most important lesson is that as scientists we strive to – and need to – speak truth to power: We speak up when we believe it is important to do so; we vigorously defend our views, even if, in fact, especially if, they are unpopular or politically inconvenient. And we get involved in issues of the day when we believe we have the expertise to add value to the ongoing discussions, especially if the issues involved are related to, or are an outgrowth of research we have been conducting. That is, we hold ourselves responsible and accountable for the consequences of our work as academics – we do not see ourselves as locked up in an ivory tower, removed from society.

Second, we believe that such involvement can lead to positive changes. Thus, Argonne National Laboratory stands as an exemplar of how a concerted effort by involved scientists and engineers can turn swords into plowshares, morphing a weapons program into a civilian research program that aims to improve the human condition. And the Bulletin of the Atomic Scientists, founded originally by Chicago Manhattan Project personnel, early on provided a forum for discussions of international control of nuclear weapons – a position that was subsequently enshrined in international agreements such as the Nuclear Non-proliferation Treaty (NPT) and the Comprehensive Test Ban Treaty.

Thus, when we remember the events of 2 February 1942, we indeed commemorate, but do not celebrate, the successful experiment to achieve and control nuclear fission. Commemorating reminds all of us of both the good and the bad that flowed from that portentous moment when CP-1 became critical; and I hope they will also serve as a reminder of the lessons I have just discussed.

So, you might wonder at this point, what does all this have to do with me personally? It has viscerally affected how I see my role as a teacher at my university. I not only see myself as an instructor of physics and astrophysics, but also as a teacher who drives his students to

• Think deeply about what they are doing, to never blindly accept arguments from authority, and to always question;
• Consider the consequences of their work;


• Be active – not passive – in responding to issues that matter to them – to speak out, and not hold back, especially when such issues threaten societal well-being.

It is useful to remember that the authors of the Franck Report were not asked for their advice by the U.S. Federal Government. They volunteered their advice, unsolicited, because – as Glenn Seaborg put it – “By an accident of history, we were among a very few who were aware of a new, world-threatening peril, and we felt obligated to express our views.” It is my hope my readers feel same obligation, even when the moment is not quite as momentous as that encountered by the Franck Report scientists.