Bruno Benedetto Rossi and the Cosmic Rays
The twentieth century has seen many great scientists who have made fundamental contributions to the knowledge of our world. A few of them are known to the general public: not always, in fact, a key finding was accompanied by a widespread reputation among the uninitiated. Albert Einstein and Marie Curie are perhaps cases more unique than rare, due not only to the versatility of their studies in explaining certain aspects of our sensible world but also to the personality traits of the German physicist or of the Polish scientist. Others were less lucky than their contemporaries from this point of view even though they have received important awards while they were still alive.
Bruno Benedetto Rossi belongs to the second group, but the bad luck, if we want to consider it in such a way, of being unknown to the general public was largely offset by the scope of its scientific insights.
Bruno Rossi will always be remembered as one of the pioneers in the study of Cosmic Rays, a mystery of nature understood thanks to many of his experiments, made with surprisingly simple means for those who are now accustomed to modern scientific laboratories. Not surprisingly, his 1940 article "Theory of Cosmic Rays", written with Kenneth Greisen for Reviews of Modern Physics, when Rossi was already in the United States, was immediately nicknamed "The Bible" and considered important even many years after its publication.
But let's order.
Rossi was born in Italy, in Venice, April 13, 1905 to a wealthy family in which the culture is at home. He did not attend elementary schools but is taught in the home. Teenager, he attended the grammar school, which at the time was considered the best prep school for those who would then deal with the University. He graduated in physics in Padua and in 1927 obtained a PhD at the University of Bologna.
The year 1928 sees Rossi in Florence, where, assistant to Antonio Garbasso, he gets involved in those Cosmic Rays that had been discovered a few years earlier by Victor Hess and which at the time are still a mystery.
It was assumed that, for example Cosmic Rays originate in space, perhaps by the fusion of hydrogen in space, as thought by Robert Millikan, but it was not known what they really were: intangible photons of light, electrically charged particles, particles subject to a natural decay. What exactly?
Rossi mastered well not only the mathematics needed to understand and describe natural phenomena but he was also a skilled experimenter thus improves a method of investigation due to the German Bothe. He invented a device that allows him to get a more precise time resolution and revealed events from multiple sources thanks to a new version of Geiger counters, became available recently. It is the well known coincidence circuit of Rossi, which is nothing else than the first working prototype of the AND circuit, well known in computer science and that will have a great fortune even in nuclear physics research.
In 1930 Rossi is in Berlin for some time and here he deepens Bothe's studies about the trajectories of charged particles in the Earth's magnetic field. He makes his way into his personal belief that Cosmic Rays are charged particles and not immaterial photons of light.
In 1931, Rossi tooks part in the international conference in Rome on Cosmic Rays: there are, among others, Arthur Compton and Robert Millikan.
Rossi is young, 26 years old, Millikan already a little getting on in years and firmly believes that Cosmic Rays are only photons. Rossi defends his thesis with a passion that is not pleasing to the old American while Compton has more possibilities and understands that it is the young Italian to be right. Sparks between scientists: things that happen.
The years 1931-1938 are full of commitments and satisfaction for Bruno Rossi: he continues his researches and moved to Padua, where he oversees the construction of the new Institute of Physics even today seat of the degree course. He leaves for Asmara, in Eritrea then Italian colony, where he discovered and studied the East-West Effect, even if he cannot be the first to communicate his discovery to the scientific community.
The East-West Effect is a predominance of positively charged particles of the negatively charged in the flow of Cosmic Rays. Rossi also discovers the existence, in this flow, of two components: a harder and more energetic, able to pass through large thicknesses of lead and a softer and less energetic, but easily dimming capable of giving rise to secondary showers.
In April of 1938 married Nora Lombroso but already in September of the same year the two must flee Italy because of the racial laws promulgated by the fascist government: both spouses are, in fact, of Jewish origin.
The pair find hospitality in Denmark, hosted by Niels Bohr in Copenhagen, then in England, visitors in Manchester to Blackett, their colleague and friend. The war now raging across Europe and spouses Rossi finally repaired in New York in 1939, hosted by Enrico Fermi and his wife.
Rossi does not have an official academic position in the United States but also continues his research on Cosmic Rays and some elementary particles related to them, mesons and pions, also providing a reliable estimate of the average life of the meson ų, corrected for relativistic effects.
The stay in America will have irreversible effects on the life of Bruno Rossi. As he writes in his biographical notes, because of the racial laws he found himself suddenly without a homeland and a stranger in his own home. America welcomed him, perhaps not disinterestedly, but at least he's not haunted: in the change, was Italy to lose something.
In 1943, Rossi joined the Manhattan Project and his experience with detectors and coincidence circuits is of paramount importance in the war effort.
In particular, the ionization chambers were the detectors perfected by him which allowed the construction of the plutonium bomb after it was clear that the critical mass in plutonium could not be reached as in uranium. And it was still one of Rossi's ionization chambers, a super-fast model, the only able to read the burst of gamma rays given off during the explosion test at Trinity Site, where the first atomic bomb in human history detonated.
Years later, during the Reagan presidency, Rossi served his participation in the Manhattan Project strongly rejecting, but in vain, the space shield that the United States were preparing to develop.
The years after the war see Rossi as Professor at MIT in Boston, intent to resume research on Cosmic Rays and the new elementary particles that were going to find out. He participates in numerous international conferences, endorses research on Cosmic Rays through the use of artificial satellites and on the fundamental components of matter through the use of particle accelerators. On the other hand, those years were very intense for the entire scientific community.
Rossi leaves MIT in 1970. Since 1974 he teaches Physics in Italy but not in Padua: at the University of Palermo, where he remained until 1980.
Bruno Benedetto Rossi came to America as a refugee but already with a solid reputation as a scientist. This reputation was further consolidated thanks to the researches that took place in his new adopted country and thanks to his remarkable skills as a teacher. Many of Rossi's students embarked the academic career and became later estimated researchers. He never received the Nobel Prize, though certainly deserved it for the quality and quantity of his studies but he benefited the same of other awards such as the Wolf Prize and the National Medal of Science.
He died at age 88 at his home in Cambridge, Massachusetts, in 1993.