I ragazzi di via Panisperna (The Boys of Via Panisperna)

Hiroshima in 1945 following its devastation by  history's first nuclear attack.
Hiroshima in 1945 following its devastation by history’s first nuclear attack.

I have been often drawn to the beautiful aspects of nuclear physics and yet appalled by some of its applications in the realm of war and politics. Did practising scientists, specifically those who initiated the nuclear revolution, experience moral dilemmas?  By probing into the lives of such pioneers, the so-called boys of Via Panisperna (I ragazzi di via Panisperna), I found among them an entire gamut of attitudes and ensuing fates.

Who the Ragazzi Were 

From left to right, D'Agostino, Segré, Arnaldi, Rasetti  and Fermi. Not shown are Mjorana and Pontevarvo, who like many others experienced radically different fates.
From left to right, D’Agostino, Segré, Arnaldi, Rasetti and Fermi. Not shown are Majorana and Pontevarvo, who like the rest experienced radically different fates.

In autumn of 1926, Enrico Fermi moved to University of Rome’s Physics Institute of Via Panisperna. There he assembled a group of collaborators with a complementary set of theoretical and experimental skills. First came Franco Rasetti and eventually Emilio Segré, Edoardo Amaldi, Bruno Pontecorvo and Oscar D’ Agostino. Ettore Majorana helped with theoretical issues. Author and cosmologist João Magueijo says the institute was a kind of kindergarten for geniuses, giving them free reign over the nature of their work.  In their playtime they made geeky bets on who had the quickest differential equation-solving abilities. Someone once threw a chair at another over a debate about the nature of solar fuel.

The Boys’ Science

At first, Fermi’s group investigated spectroscopy and the Raman effect. But in the early 1930s it was clear that the study of the atomic nucleus was a much more promising research avenue. Aside from Fermi, according to Franco Rasetti, he and Amaldi were most convinced of it. Consequently, various members of the group temporarily went abroad to learn experimental techniques in nuclear physics. Latecomer D’Agostino, a southerner originally from Avellino, had worked at the Radium Institute, where Irene Curie, daughter of Marie Curie, and her husband Julot-Curie later (in 1934) bombarded light elements like aluminum with alpha particles, transforming the reactant’s atomic number and in the process, creating a radioactive nuclide.

Curie

A few months earlier, and before international publication, Fermi’s group had developed the theory of beta decay, another mechanism that led to the increase of atomic number and hence to the age-old alchemist dream of transmuting elements.betaDecay In fact, one of the members, Majorana(Maiorana in Italian) had proposed the existence of the neutron before Chadwick’s discovery. Unlike the others, he had not ignored the overall +1 spin of the nitrogen nucleus, which could not result from what was presumed to be an odd sum of nuclear particles ( an assumed 14 positives plus 7 negatively charged intranuclear negative particles.). Majorana even realized that there had to be some unknown strong force holding the nuclear particles together. But despite Fermi’s urging, the brilliant but unambitious Majorana refused to publish his ideas. And although the antineutrino formed by beta decay wasn’t detected until decades later,  the Via Panisperna boys included the particle in their beta decay theory to secure the energy, momentum and spin conservations involved in the transformation of neutron to proton.

They made two fundamental contributions to understanding beta decay and neutrinos. (1) Fermi, with the help of others, developed the golden rule ( an ironic name, given what eventually happened to the citizens of Hiroshima and Nagasaki) which applies to atomic transitions in their original field of study, spectroscopy, and to nuclear decay. The rule relates the likelihood of a transition to the coupling strengths between final and initial states (Matrix element) and to the number of ways that such a transition can occur (final states’ density).

goldenFermi
from http://hyperphysics.phy-astr.gsu.edu/

(2) Majorana came up with a relativistic wave equation, similar to Dirac’s which had predicted antimatter, but specifically for uncharged masses such as the neutrino. He proposed that the antineutrino and neutrino are the same particle, transforming into each other by flipping the orientation of their spin state.

In the following spring of 1934 , Fermi thought that the best way to produce artificial radioactivity was to use neutrons as bullets. Since they were electrically neutral they would not experience Coulombic repulsion from the protons.  After several unsuccessful attempts, he got a positive result using fluorine and aluminum with  radon-beryllium as a source of neutrons. Alpha particles emitted by radon are absorbed by the beryllium which turns into carbon with emission of a fast neutron.

beryllium_neutron

Realizing the potential of this discovery, Fermi began a systematic study with his group. Within months, 50 new species of radioactive nuclides were formed by firing neutrons at them. In October of that same year, Fermi and his collaborators realized that if the neutrons were slowed down by a medium like water, they would spend more time interacting with the nucleus and would become about 100 times more effective in inducing nuclear reactions.

The group’s  intense work on neutron physics continued, but at the end of 1935, the group broke up. Rasetti went to America, Pontecorvo to Paris, and Segré was appointed as a professor in Palermo, Sicily. Fermi and Amaldi continued their research, discovering the resonant absorption of neutrons by certain nuclei. At that point, Fermi formulated the theory behind the slowdown of neutrons, which included much of the mathematics that would serve as the basis of the theory behind nuclear reactors.

Different Decisions and Fates

At the end of 1938, shortly after the implementation of Fascist racial laws in Italy, Fermi went to Stockholm to receive the Nobel Prize for his contributions to neutron physics. While in Sweden, he had stirred an uproar in the Italian media by not using the Fascist salute at the ceremonies. Coupled with the fact that his wife was Jewish, it persuaded Fermi not to return to Rome but to emigrate to America.

Soon after his arrival in the U.S., Hahn and Strassmann announced the discovery of uranium fission. Fermi immediately began the study of how neutrons were emitted in uranium fission and soon realized that it was possible to create a chain reaction that can produce energy on a macroscopic scale. Eventually the first nuclear fission reactor was created in Chicago in December of 1942, soon after Fermi had given his support to the Manhattan Project for use in nuclear war. After creating a new halogen, astatine, from 209Bi, his colleague Emilio Segré also joined the atomic bomb-creating-project as a team leader.

While Fermi and Segré surrendered nuclear science to the war effort, Franco Rasetti was in Canada, where he felt he would be less pressured by politics, an area he liked to avoid.

Rasetti, hiking in the Swiss Alps. He was an avid collector of Cambrian tribolites and wild flowers.
Rasetti, hiking in the Swiss Alps. He was an avid collector of Cambrian tribolites and wild flowers.

I never liked to discuss politics. In general, I never felt very strongly about controversial subjects.
I always preferred to talk about things like physics or the natural sciences, on which there can be
no different opinions.

Rasetti had left Italy to join the faculty at Quebec City’s Laval University, where he had created its first physics department. Even in Canada, the former Via Panispernia boy had been invited by the British to participate in secret war projects, but he refused on moral grounds.

pontecarvo
Bruno Pontecarvo, from the American Institute of Physics photographic archives of Emilio Segré.

Rasetti often asserted that physicists were uninterested in politics. Although he should be commended for not joining wartime applications of physics, he seemed to psychologically shut himself off from worldly realities. For instance, was he really unaware that Via Panisperna`s Bruno Pontecarvo had joined the Communist Party while working in France with Irene Curie and her husband, Joliot-Curie, a devoted communist? After Hitler’s invasion, Pontecarvo left for Texas and eventually became Rasetti’s colleague at Laval University.  But unlike Rasetti, Pontecarvo did not turn down the propositions of a Montreal-based British group, and he left the university to join secret war efforts in Chalk River in Ontario and then at Harwell. After going on a Mediterranean vacation with his family in 1950, he strangely moved with them to Scandinavia and eventually to Russia, where he spent the rest of his life. Based on the account by a top KGB defector, while working on nuclear projects, Pontecarvo had presumably worked as a Soviet spy. In his review of Frank Close’s book, Freeman Dyson points out, Pontecarvo may not have been a spy, but he was certainly spied upon by many others. Close thinks that Pontecarvo may have been blackmailed by Russians.

Recently, Close examined voluminous reports about Pontecorvo that are now accessible in the archives of the intelligence services of Britain, Canada, the United States, and Russia. These intelligence records never give any clear evidence that Pontecorvo was a spy, but they give abundant evidence that he was a person of serious concern to all four countries..

The author also argues that Pontecarvo’s decision to live in exile in a country with inferior research facilities ruined his career, a fate that could have been avoided if he had faced the charges. Two actual spies Allan Nunn May and Ted Hall fared better than he did; only one served jail time and both resumed their research. But I identify the pivotal point to be Pontecarvo’s decision to partake in military research while he was still a professor in Canada.

Unlike Pontecarvo, Majorana would not have joined any scientific war efforts if he had not disappeared mysteriously, months before Fermi received the Nobel Prize. The man who solved theoretical problems with far less sweat than the rest was also the only one of the boys, according to João Magueijo, who “acutely felt the limitations of science”.  Segré and Arnaldi had probably incorrectly surmised that their former colleague had committed suicide. On the last day he had been seen in Italy, he had withdrawn all his funds(the equivalent of $70 000) from the bank, not typical behavior from someone hellbent on killing himself. Given photographic evidence, Majorana seemd to have resurfaced in Venezuela in the 1950s. It’s likely that he quit physics and withdrew from an active role in society due to a combination of personal issues and from foreseeing the dire applications of nuclear science.

The Italian film  I ragazzi di via Panisperna, highlight the different approaches and personalities of Majorana and Fermi. They portrayed

Chi l'ha visto?--Who has seen him? An original ad announcing Majorana's disappearance on March 26, 1938
Chi l’ha visto?–Who has seen him? An original ad announcing Majorana’s disappearance on March 26, 1938

Fermi as being more of the experimenter and Ettore as “pure”, consistently “tense and beleaguered by the stimulus of a mysterious and genial intuition”.  Fermi was the pragmatic and more casual professor while Majorana was not only introverted but also more aware of the consequences that Via Panisperna discoveries imposed on the level of morality and human responsibility of scientists .

After the war, Oscar D’Agostino, the only chemist among the boys, investigated the effects of nuclear fallout. He realized that the isotope strontium 90 finds its way into vegetation and then into the bones of people and animals. Depending on concentration, beta decay, whose mechanism had been explained by them , can subsequently cause leukemia or cancer of the bones or surrounding tissues.

ESROEdoardo Arnaldi was the only other ragazzo di via Panespernia to have remained in Italy. After investigating cosmic rays and particle physics, he was the only group-member to have publicly raised concerns about military applications, specifically of space science. He wrote an open letter to a handful of eminent European administrators of science in 1959, which began the process leading to COPERS and the founding of ESRO, a precursor of the European Space Agency, a cooperative effort among countries ensuring peaceful space applications of science.

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