The life of Enrico Fermi: phase three
Early morning, November 10, 1938. The telephone ringing so early that morning has a special sound: sudden, unexpected, strident and peremptory. That’s how Laura, Fermi’s wife, remembers that day. In fact, it was she who answered the phone…
(first female voice, Fermi’s wife)
“Hello? Professor Fermi’s house.”
(second female voice – secretary)
“Hello, I would like to let you know that Professor Fermi will be called by telephone from Stockholm this afternoon at six.”
(first female voice)
“Enrico, wake up! They’re going to call you from Stockholm tonight at six!”
Fermi understands immediately; a phone call of this kind can only mean the Nobel prize. But there’s no time for rejoicing. The trip to Sweden is the chance to implement a plan Fermi has been working on for months with great secrecy for fear that the regime won’t let him go: to leave Italy and emigrate to the United States of America. The Racial laws have been passed and the fascist regime is becoming more dangerous every day. Fermi’s wife, Laura, is in fact, Jewish and her father, even though a retired Italian Navy admiral, would die in a concentration camp.
The hours pass with unbearable slowness until the much awaited phone call arrives. The secretary of the Royal Swedish Academy of Sciences is on the line. He announces to Fermi the awarding of the prize and reads the motivation.
(second male voice) “To Professor Enrico Fermi of Rome for his identification of new radioactive elements produced by neutron bombardment and for his discovery made in relation to this work on nuclear reactions effected by slow neutrons.”
The die is cast: Sweden will be only a stop along the way towards the United States of America. In spite of their scientific successes, the survival of Fermi’s group in the cultural and political climate of fascist Italy has become ever more difficult due to the lack of adequate research opportunities and financing; the passage of the anitsemitic laws removes even the most elementary of civil rights from Italian citizens of Jewish origin. Not only is Fermi’s wife Jewish but so are some of the Boys including Bruno Pontecorvo and Emilio Segrè. So, at the station on December 6, the day of departure for Sweden, there are only Rasetti and Amaldi with his wife, Ginestra. The send-off can only mean one thing: the end of an era. Besides, the group of Via Panisperna had been dwindling lately anyway both for personal and academic reasons: Majorana had died in the spring of 1938 and others had left Italy.
When the film of the Nobel prize award ceremony was shown in Italy, Fermi was harshly criticized for his supposedly unpatriotic attitude: he hadn’t worn the Italian academic uniform and hadn’t given the fascist salute. Italian authorities didn’t know yet that Enrico, Laura and their two children, Giulio and Nella, had already left on a ship bound for New York; officially they were leaving for a 6-month sabbatical but the intention was to move permanently. And it was exactly during those fateful days that a group of German physicists made a sensational discovery …
Francesco Guerra talks about the atomic pile
The first “nuclear reactor”
December 2, 1942, Enrico Fermi, working underneath the stadium at the University of Chicago, pulls off an exceptional feat, that of producing a self-sustaining, controlled nuclear chain reaction. Remember that Fermi had arrived in the US at the beginning of 1939 after having been awarded the Nobel prize in Stockholm in December. In New York his colleagues tell him that a few weeks before, Otto Hann and Fritz Strassmann in Berlin had discovered a completely new phenomenon, nuclear fission: slow neutrons hitting the nucleus of uranium, splitting it into two pieces and liberating a huge amount of energy. All over the world a race begins, in France, England, the US but also in Germany, to search for practical ways of putting to work this gigantic quantity of energy liberated by nuclear fission.
With his experimental reactor, the so-called CP-1 (Chicago Pile Number One) Fermi would be the first to demonstrate this amazing feat.
To create a chain reaction there are some enormous hurdles to overcome from a practical standpoint. First of all, there are two uranium isotopes, uranium 238 and uranium 235. This second isotope represents a tiny percentage of natural uranium and it’s the one best adapted to fission. So it’s necessary to produce appreciable quantities of it. Besides, a chain reaction is possible because during fission, other neutrons are liberated that can split other atoms and so on, producing a self-sustaining reaction. Unfortunately, the neutrons thus produced are fast neutrons and they have to be decellerated. So a substance is needed that slows them down. Fermi used graphite. The slowed-down neutrons can then produce other fissions and set off the chain reaction.
It’s a very critical situation, very delicate, because all material inside the pile absorbs neutrons and if too many neutrons are absorbed the chain reaction obviously shuts down. Fermi’s main competition came from Werner Heisenberg in Germany, who had very clear ideas about how to do the work because he had read Fermi’s articles and was perfectly familiar with them; but he was working under very difficult circumstances from an industrial point of view. Beyond that, in spite of the totalitarian character of the Nazi regime, management was very bad because it consisted of many separate projects. So, at the end, Fermi was able to apply chain reactions to practical use and Heisenberg never managed it.
There are many applications for chain reactions. Given the times, the first were of course, military. Uranium rods exposed to the intense flow of neutrons produced in a reactor undergo a nuclear transmutation and are transformed into an element that doesn’t exist in nature: plutonium, number 94 in the periodic table of the elements. This element has the property of being highly fissionable and so can be used for nuclear weapons as unfortunately happened. There are, however, other applications and Fermi had already understood that perfectly back in 1934.
The intense neutron flow turns the reactor into a source of neutrons that are perfect for studying the interaction between neutrons and the atomic nucleus. What’s more, it can produce nuclear transmutation of other elements that create isotopes useful for medicine: typically, iodine 131, for example, is produced when tellurium is irradiated by a flow of neutrons; this can be utilized on a large scale for medical purposes, in particular for the thyroid. Other radioactive isotopes are used as tracers in metabolic or chemical reactions.
Thus Fermi’s nuclear reactor immediately offered some extremely interesting applications. A few years would have to pass before the use of reactors in the production of electrical energy. In this speech Enrico Fermi explains the importance of the atomic age:
“Uranium is the basic material of the atomic age. It’s estimated that the uranium deposits currently known around the world can furnish sufficient energy to last many thousands of years, energy that will be available to all the peoples of the world since the atom is international and no single nation or group of nations hold a monopoly on uranium or atomic science or atomic reactors.
The atomic age began as a result of studies carried out by various scientists in Italy, France, England, the United States, Denmark, Germany as well as other countries; the spirit of cooperation continues today as demonstrated by the research agreement on nuclear energy between Norway and Holland, with its headquarters in Oslo, and the European Organization for Nuclear Research, known as CERN, in Geneva that promotes the research and scientific knowledge of the different European nations that are its members. They work together following a coordinated research plan and have access to equipment that no one nation alone would be able to furnish.
The results of this research are made available to everyone. For example, radioactive isotopes produced in England, the US, Canada and elsewhere are used all over the world in hospitals, industry and agriculture in places as different as Finland and New Zealand. The development of nuclear energy plants is becoming a reality in a growing number of countries. Delivery of isotopes grows daily. In the United States alone, the consignment of isotopes jumped from 1,900 in 1947 to more than 11,000 in 1953.
The atomic age is only 12 years old and we’re just beginning: we’re only stepping through the doorway now towards the benefits that will come from the work of hundreds of thousands of technicians in the atomic field.”