Bruno Benedetto Rossi (; ; 13 April 1905 – 21 November 1993) was an Italian
experimental physicist
Experimental physics is the category of disciplines and sub-disciplines in the field of physics that are concerned with the observation of physical phenomena and experiments. Methods vary from discipline to discipline, from simple experiments and o ...
. He made major contributions to
particle physics
Particle physics or high energy physics is the study of fundamental particles and forces that constitute matter and radiation. The fundamental particles in the universe are classified in the Standard Model as fermions (matter particles) an ...
and the study of
cosmic rays
Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...
. A 1927 graduate of the
University of Bologna
The University of Bologna ( it, Alma Mater Studiorum – Università di Bologna, UNIBO) is a public research university in Bologna, Italy. Founded in 1088 by an organised guild of students (''studiorum''), it is the oldest university in continuo ...
, he became interested in cosmic rays. To study them, he invented an improved electronic
coincidence circuit In physics and electrical engineering, a coincidence circuit or coincidence gate is an electronic device with one output and two (or more) inputs. The output activates only when the circuit receives signals within a time window accepted as ''at the ...
, and travelled to
Eritrea
Eritrea ( ; ti, ኤርትራ, Ertra, ; ar, إرتريا, ʾIritriyā), officially the State of Eritrea, is a country in the Horn of Africa region of Eastern Africa, with its capital and largest city at Asmara. It is bordered by Ethiopia ...
to conduct experiments that showed that cosmic ray intensity from the West was significantly larger than that from the East.
Forced to emigrate in October 1938 due to the
Italian racial laws, Rossi moved to Denmark, where he worked with
Niels Bohr
Niels Henrik David Bohr (; 7 October 1885 – 18 November 1962) was a Danish physicist who made foundational contributions to understanding atomic structure and quantum theory, for which he received the Nobel Prize in Physics in 1922. B ...
. He then moved to Britain, where he worked with
Patrick Blackett
Patrick Maynard Stuart Blackett, Baron Blackett (18 November 1897 – 13 July 1974) was a British experimental physicist known for his work on cloud chambers, cosmic rays, and paleomagnetism, winning the Nobel Prize for Physics in 1948. ...
at the
University of Manchester
, mottoeng = Knowledge, Wisdom, Humanity
, established = 2004 – University of Manchester Predecessor institutions: 1956 – UMIST (as university college; university 1994) 1904 – Victoria University of Manchester 1880 – Victoria Univer ...
. Finally he went to the United States, where he worked with
Enrico Fermi
Enrico Fermi (; 29 September 1901 – 28 November 1954) was an Italian (later naturalized American) physicist and the creator of the world's first nuclear reactor, the Chicago Pile-1. He has been called the "architect of the nuclear age" and ...
at the
University of Chicago
The University of Chicago (UChicago, Chicago, U of C, or UChi) is a private research university in Chicago, Illinois. Its main campus is located in Chicago's Hyde Park neighborhood. The University of Chicago is consistently ranked among the b ...
, and later at
Cornell University
Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to teach an ...
. Rossi stayed in the United States, and became an American Citizen.
During
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
, Rossi worked on
radar
Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
at the
MIT Radiation Laboratory
The Radiation Laboratory, commonly called the Rad Lab, was a microwave and radar research laboratory located at the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts. It was first created in October 1940 and operated until 31 ...
, and he played a pivotal role in the
Manhattan Project
The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...
, heading the group at the
Los Alamos Laboratory
The Los Alamos Laboratory, also known as Project Y, was a secret laboratory established by the Manhattan Project and operated by the University of California during World War II. Its mission was to design and build the first atomic bombs. Ro ...
that carried out the
RaLa Experiment
The RaLa Experiment, or RaLa, was a series of tests during and after the Manhattan Project designed to study the behavior of converging shock waves to achieve the spherical implosion necessary for compression of the plutonium pit of the nuclear we ...
s. After the war, he was recruited by
Jerrold Zacharias
Jerrold Reinach Zacharias (January 23, 1905 – July 16, 1986) was an American physicist and Institute Professor at the Massachusetts Institute of Technology, as well as an education reformer. His scientific work was in the area of nuclear physics ...
at MIT, where Rossi continued his pre-war research into cosmic rays.
In the 1960s, he pioneered
X-ray astronomy and space
plasma
Plasma or plasm may refer to:
Science
* Plasma (physics), one of the four fundamental states of matter
* Plasma (mineral), a green translucent silica mineral
* Quark–gluon plasma, a state of matter in quantum chromodynamics
Biology
* Blood pla ...
physics. His instrumentation on
Explorer 10
Explorer 10 (also known as Explorer X or P14) was a NASA satellite that investigated Earth's magnetic field and nearby plasma. Launched on 25 March 1961, it was an early mission in the Explorer program and was the first satellite to measure th ...
detected the
magnetopause
The magnetopause is the abrupt boundary between a magnetosphere and the surrounding plasma. For planetary science, the magnetopause is the boundary between the planet's magnetic field and the solar wind. The location of the magnetopause is d ...
, and he initiated the rocket experiments that discovered
Scorpius X-1
Scorpius X-1 is an X-ray source located roughly 9000 light years away in the constellation Scorpius. Scorpius X-1 was the first extrasolar X-ray source discovered, and, aside from the Sun, it is the strongest apparent source of X-rays in the sky. ...
, the first extra-solar source of
X-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...
s.
Italy
Rossi was born to a Jewish family in
Venice
Venice ( ; it, Venezia ; vec, Venesia or ) is a city in northeastern Italy and the capital of the Veneto Regions of Italy, region. It is built on a group of 118 small islands that are separated by canals and linked by over 400 ...
,
Italy
Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical re ...
. He was the eldest of three sons of Rino Rossi and Lina Minerbi. His father was an electrical engineer, who participated in the
electrification
Electrification is the process of powering by electricity and, in many contexts, the introduction of such power by changing over from an earlier power source.
The broad meaning of the term, such as in the history of technology, economic histor ...
of Venice. Rossi was tutored at home until the age of fourteen, after which he attended the
Ginnasio
''Gymnasium'' (and variations of the word) is a term in various European languages for a secondary school that prepares students for higher education at a university. It is comparable to the US English term '' preparatory high school''. Bef ...
and the
Liceo
The Gran Teatre del Liceu (, English: Great Theatre of the Lyceum), known as ''El Liceu'', is an opera house in Barcelona, Catalonia, Spain. Located in La Rambla, it is the oldest running theatre in Barcelona.
Founded in 1837 at another loca ...
in Venice.
After beginning his university studies at the
University of Padua
The University of Padua ( it, Università degli Studi di Padova, UNIPD) is an Italian university located in the city of Padua, region of Veneto, northern Italy. The University of Padua was founded in 1222 by a group of students and teachers from B ...
, he undertook advanced work at the
University of Bologna
The University of Bologna ( it, Alma Mater Studiorum – Università di Bologna, UNIBO) is a public research university in Bologna, Italy. Founded in 1088 by an organised guild of students (''studiorum''), it is the oldest university in continuo ...
, where he received a
Laurea
In Italy, the ''laurea'' is the main post-secondary academic degree. The name originally referred literally to the laurel wreath, since ancient times a sign of honor and now worn by Italian students right after their official graduation ceremony ...
in Physics in 1927.
His thesis advisor was
Quirino Majorana
Quirino Majorana (28 October 1871 – 31 July 1957) was an Italian experimental physicist who investigated a wide range of phenomena during his long career as professor of physics at the Universities of Rome, Turin (1916–1921), and Bologna (192 ...
,
who was a well-known experimentalist and an uncle of the physicist
Ettore Majorana
Ettore Majorana (,, uploaded 19 April 2013, retrieved 14 December 2019 ; born on 5 August 1906 – possibly dying after 1959) was an Italian theoretical physicist who worked on neutrino masses. On 25 March 1938, he disappeared under mysteri ...
.
Florence
In 1928, Rossi began his career at the
University of Florence
The University of Florence (Italian: ''Università degli Studi di Firenze'', UniFI) is an Italian public research university located in Florence, Italy. It comprises 12 schools and has around 50,000 students enrolled.
History
The first universi ...
, as assistant to
Antonio Garbasso
Antonio Garbasso (16 April 1871 – 14 March 1933) was an Italian physicist and National Fascist Party politician. He was the 14th mayor and the 1st podestà of Florence, Kingdom of Italy.''Antonio Garbasso: la vita, il pensiero e l'opera scientifi ...
, who had founded the University's Physics Institute in 1920.
It was located in
Arcetri
Arcetri is a location in Florence, Italy, positioned among the hills south of the city centre.
__TOC__
Landmarks
A number of historic buildings are situated there, including the house of the famous scientist Galileo Galilei (called ''Villa Il Gio ...
, on a hill overlooking the city. When Rossi arrived, Garbasso was
Podestà
Podestà (, English: Potestate, Podesta) was the name given to the holder of the highest civil office in the government of the cities of Central and Northern Italy during the Late Middle Ages. Sometimes, it meant the chief magistrate of a city ...
of Florence, appointed by
Benito Mussolini
Benito Amilcare Andrea Mussolini (; 29 July 188328 April 1945) was an Italian politician and journalist who founded and led the National Fascist Party. He was Prime Minister of Italy from the March on Rome in 1922 until his deposition in 194 ...
's
fascist government of Italy.
However, he brought to the Institute a group of brilliant physicists which included
Enrico Fermi
Enrico Fermi (; 29 September 1901 – 28 November 1954) was an Italian (later naturalized American) physicist and the creator of the world's first nuclear reactor, the Chicago Pile-1. He has been called the "architect of the nuclear age" and ...
and
Franco Rasetti
Franco Dino Rasetti (August 10, 1901 – December 5, 2001) was an Italian (later naturalized American) physicist, paleontologist and botanist. Together with Enrico Fermi, he discovered key processes leading to nuclear fission. Rasetti refused ...
before they
moved to Rome, as well as
Gilberto Bernardini
Gilberto is the Iberian and Italian version of the originally Norman-French given name '' Gilbert'', used in Italian, Portuguese and Spanish languages. In Galician, it's spelled Xilberto or Xilberte. ''Gilbert'' is ultimately derived from the Ger ...
,
Enrico Persico, and
Giulio Racah
Giulio (Yoel) Racah ( he, ג'וליו (יואל) רקח; February 9, 1909 – August 28, 1965) was an Italian–Israeli physicist and mathematician. He was Acting President of the Hebrew University of Jerusalem from 1961 to 1962.
The crater ...
.
In 1929, Rossi's first graduate student,
Giuseppe Occhialini
Giuseppe Paolo Stanislao "Beppo" Occhialini ForMemRS (; 5 December 1907 – 30 December 1993) was an Italian physicist who contributed to the discovery of the pion or pi-meson decay in 1947 with César Lattes and Cecil Frank Powell, the latter ...
, was awarded the doctoral degree.
In search of pioneering research, Rossi turned his attention to
cosmic rays
Cosmic rays are high-energy particles or clusters of particles (primarily represented by protons or atomic nuclei) that move through space at nearly the speed of light. They originate from the Sun, from outside of the Solar System in our own ...
, which had been discovered by
Victor Hess
Victor Franz Hess (; 24 June 188317 December 1964) was an Austrian-American physicist, and Nobel laureate in physics, who discovered cosmic rays.
Biography
He was born to Vinzenz Hess and Serafine Edle von Grossbauer-Waldstätt, in Waldstein ...
in manned balloon flights in 1911 and 1912. In 1929, Rossi read the paper of
Walther Bothe
Walther Wilhelm Georg Bothe (; 8 January 1891 – 8 February 1957) was a German nuclear physicist, who shared the Nobel Prize in Physics in 1954 with Max Born.
In 1913, he joined the newly created Laboratory for Radioactivity at the Reich Physi ...
and
Werner Kolhörster
Werner Heinrich Gustav Kolhörster (28 December 1887 – 5 August 1946) was a German physicist and a pioneer of research into cosmic rays.
Kolhörster was born in Schwiebus (Świebodzin), Brandenburg Province of Prussia. While attending the U ...
, which described their discovery of charged cosmic ray particles that penetrated of gold.
This was astonishing, for the most penetrating charged particles known at the time were
electrons from radioactive decay, which could penetrate less than a millimetre of gold. In Rossi's words, it
Rossi coincidence circuit
In 1954,
Bothe was awarded the Nobel Prize in Physics "for the coincidence method and his discoveries made therewith" for a method of assessing coincident events he implemented prior to 1924. However, his implementation of this method was very cumbersome, for it involved visual correlation of photographed pulses. Within a few weeks of reading his paper with Kolhörster, Rossi invented an improved electronic
coincidence circuit In physics and electrical engineering, a coincidence circuit or coincidence gate is an electronic device with one output and two (or more) inputs. The output activates only when the circuit receives signals within a time window accepted as ''at the ...
, which made use of
triode vacuum tubes.
The Rossi coincidence circuit has two major advantages: it offers very precise temporal resolution and it can detect coincidences among any number of pulse sources. These features make it possible to identify interesting events that produce coincident pulses in several counters. These rare events stand out even in the presence of high rates of unrelated background pulses in the individual counters. The circuit not only provided the basis for electronic instrumentation in nuclear and particle physics, but also implemented the first electronic
AND circuit, which is a fundamental element of the
digital logic
A logic gate is an idealized or physical device implementing a Boolean function, a logical operation performed on one or more Binary number, binary inputs that produces a single binary output. Depending on the context, the term may refer to an id ...
that is ubiquitous in
modern electronics
''Modern Electronics'' was a hobbyist magazine published from October 1984 to March 1991. It became ''Computer Craft'' in April 1991 and the name changed again to ''MicroComputer Journal'' in January 1994. Modern Electronics, Inc. was owned by CQ ...
.
At the time, an improved tubular version of the original
Geiger counter
A Geiger counter (also known as a Geiger–Müller counter) is an electronic instrument used for detecting and measuring ionizing radiation. It is widely used in applications such as radiation dosimetry, radiological protection, experimental ph ...
, invented by
Hans Geiger
Johannes Wilhelm "Hans" Geiger (; ; 30 September 1882 – 24 September 1945) was a German physicist. He is best known as the co-inventor of the detector component of the Geiger counter and for the Geiger–Marsden experiment which discover ...
in 1908, had just been developed by his student
Walther Müller
Walther Müller (6 September 1905, in Hanover – 4 December 1979, in Walnut Creek, California) was a German physicist, most well known for his improvement of Hans Geiger's counter for ionizing radiation, now known as the Geiger-Müller tube.
W ...
. These
Geiger–Müller tube
The Geiger–Müller tube or G–M tube is the sensing element of the Geiger counter instrument used for the detection of ionizing radiation. It is named after Hans Geiger, who invented the principle in 1908, and Walther Müller, who collaborated w ...
s (GM tubes or counters) made possible Bothe's investigations. With Occhialini's help in the construction of GM tubes, and with the aid of a practical coincidence circuit, Rossi confirmed and extended the results of Bothe, who invited him to visit
Berlin
Berlin ( , ) is the capital and largest city of Germany by both area and population. Its 3.7 million inhabitants make it the European Union's most populous city, according to population within city limits. One of Germany's sixteen constitue ...
in the summer of 1930. Here, with financial support arranged by Garbasso, Rossi collaborated on further investigations of cosmic ray penetration. He also studied
Carl Størmer's mathematical description of the trajectories of charged particles in the
Earth's magnetic field
Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the Sun. The magnetic f ...
.
On the basis of these studies, he realised that the intensity of cosmic rays coming from eastward directions might be different from that of westward ones. From Berlin, he submitted the first paper suggesting that observations of this east–west effect could not only confirm that cosmic rays are charged particles, but also determine the sign of their charge.
Rome conference
In the fall of 1931, Fermi and
Orso Mario Corbino
Orso Mario Corbino (30 April 1876, Augusta – 23 January 1937, Rome) was an Italian physicist and politician. His younger brother was Epicarmo Corbino.
He served as the minister for education in 1921 and as the minister for economy in 1921. H ...
organized in Rome an international conference on
nuclear physics
Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions, in addition to the study of other forms of nuclear matter.
Nuclear physics should not be confused with atomic physics, which studies the ...
, which was sponsored by the
Royal Academy of Italy
The Royal Academy of Italy ( it, Reale Accademia d'Italia, italic=no) was a short-lived Italian academy of the Fascist period. It was created on 7 January 1926 by royal decree,See reference . but was not inaugurated until 28 October 1929. It was e ...
. Fermi invited Rossi to give an introductory talk on cosmic rays. In the audience were
Robert Millikan
Robert Andrews Millikan (March 22, 1868 – December 19, 1953) was an American experimental physicist honored with the Nobel Prize for Physics in 1923 for the measurement of the elementary electric charge and for his work on the photoelectric e ...
and
Arthur Compton
Arthur Holly Compton (September 10, 1892 – March 15, 1962) was an American physicist who won the Nobel Prize in Physics in 1927 for his 1923 discovery of the Compton effect, which demonstrated the particle nature of electromagnetic radia ...
, both of whom had won the Nobel prize in physics, in 1923 and 1927, respectively.
During the 1920s, Millikan, who is famous for his
oil drop experiment
The oil drop experiment was performed by Robert A. Millikan and Harvey Fletcher in 1909 to measure the elementary electric charge (the charge of the electron). The experiment took place in the Ryerson Physical Laboratory at the University of Chi ...
, made extensive measurements of the mysterious radiation discovered by Hess. He coined the name "cosmic rays" and proposed that they were
photons
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they alway ...
created by the
fusion
Fusion, or synthesis, is the process of combining two or more distinct entities into a new whole.
Fusion may also refer to:
Science and technology Physics
*Nuclear fusion, multiple atomic nuclei combining to form one or more different atomic nucl ...
of hydrogen in interstellar space. He was not pleased by the presentation of evidence that most observed cosmic rays are energetic charged particles. Later, Rossi wrote:
Compton, who is famous for the
Compton effect
Compton scattering, discovered by Arthur Holly Compton, is the scattering of a high frequency photon after an interaction with a charged particle, usually an electron. If it results in a decrease in energy (increase in wavelength) of the photon ...
, had a more positive reaction, for he told Rossi later that the talk had motivated him to begin his own research on cosmic rays.
Rossi curve
Immediately after the Rome conference, Rossi carried out two experiments that led to a significant advance in the understanding of cosmic rays. Both involved triple coincidences of pulses from three Geiger counters; but in the first, the counters were aligned and separated by blocks of lead, while in the second, they were placed in a triangular configuration such that all three could not be traversed by a single particle travelling in a straight line. Results from the first configuration demonstrated the existence of cosmic-ray particles capable of penetrating of lead.
With the second configuration enclosed in a lead box, the results showed that some cosmic rays interact in lead to produce multiple secondary particles. In an extension of the second experiment, he measured the rate of triple coincidences as a function of the amount of the lead above the counters. A plot of this rate against thickness, which came to be known as the Rossi curve, showed a rapid rise as the lead layer was increased, followed by a slow decline.
These experiments showed that ground-level cosmic rays consist of two components: a "soft" component which is capable of prolific generation of multiple particle events, and a "hard" component which is capable of traversing great thicknesses of lead. At the time, the physical nature of both was a mystery, for they did not yet fit into the growing body of knowledge about nuclear and particle physics.
Late in 1931, Rossi arranged for Occhialini to work in the
Cavendish Laboratory
The Cavendish Laboratory is the Department of Physics at the University of Cambridge, and is part of the School of Physical Sciences. The laboratory was opened in 1874 on the New Museums Site as a laboratory for experimental physics and is named ...
at the
University of Cambridge
, mottoeng = Literal: From here, light and sacred draughts.
Non literal: From this place, we gain enlightenment and precious knowledge.
, established =
, other_name = The Chancellor, Masters and Schola ...
with
Patrick Blackett
Patrick Maynard Stuart Blackett, Baron Blackett (18 November 1897 – 13 July 1974) was a British experimental physicist known for his work on cloud chambers, cosmic rays, and paleomagnetism, winning the Nobel Prize for Physics in 1948. ...
, whom he had met in Berlin.
With the aid of the new technique of electronic coincidence, Occhialini helped Blackett develop the first counter-controlled
cloud chamber
A cloud chamber, also known as a Wilson cloud chamber, is a particle detector used for visualizing the passage of ionizing radiation.
A cloud chamber consists of a sealed environment containing a supersaturated vapour of water or alcohol. ...
, with which they confirmed
Carl Anderson's discovery of the
positron
The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. It has an electric charge of +1 '' e'', a spin of 1/2 (the same as the electron), and the same mass as an electron. When a positron collides ...
and deduced that the positive electrons are produced in association with negative ones by
pair production
Pair production is the creation of a subatomic particle and its antiparticle from a neutral boson. Examples include creating an electron and a positron, a muon and an antimuon, or a proton and an antiproton. Pair production often refers specific ...
.
Up to 23 positive and negative electrons were observed in some events, which were clearly related to the showers of Rossi's soft component.
Padua
In 1932, Rossi won a competition for an academic position in an Italian university, and was appointed professor of experimental physics at the University of Padua. Soon after Rossi arrived, the
rector
Rector (Latin for the member of a vessel's crew who steers) may refer to:
Style or title
*Rector (ecclesiastical), a cleric who functions as an administrative leader in some Christian denominations
*Rector (academia), a senior official in an edu ...
asked him to oversee the design and construction of Padua's new Physics Institute. Although this task diverted his attention from research and teaching, he complied willingly, and the institute opened in 1937.
East-West effect
In spite of this distraction, Rossi was able to complete, in 1933, an experiment on the east–west effect that he had begun before leaving Arcetri. Because this effect is more prominent near the equator, he organised an expedition to
Asmara
Asmara ( ), or Asmera, is the capital and most populous city of Eritrea, in the country's Central Region. It sits at an elevation of , making it the sixth highest capital in the world by altitude and the second highest capital in Africa. The ...
in
Eritrea
Eritrea ( ; ti, ኤርትራ, Ertra, ; ar, إرتريا, ʾIritriyā), officially the State of Eritrea, is a country in the Horn of Africa region of Eastern Africa, with its capital and largest city at Asmara. It is bordered by Ethiopia ...
, which was then an Italian colony on the
Red Sea
The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; T ...
at a
latitude
In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...
of 15° N.
With Sergio De Benedetti,
he set up a "cosmic ray telescope", which consisted of two separated GM counters in coincidence, whose axis of maximum sensitivity could be pointed in any direction. It soon became apparent that cosmic ray intensity from the West was significantly larger than that from the East. This meant that there was a larger influx of positive primary particles than of negative ones. At the time, this result was surprising, because most investigators held the preconceived notion that the primaries would be negative electrons.
Just as Rossi left Eritrea, he received news of two observations of a similar east–west effect. These were published in the ''Physical Review''. One was by Thomas H. Johnson,
and the other was by Compton and his student,
Luis Alvarez, who reported observations at
Mexico City
Mexico City ( es, link=no, Ciudad de México, ; abbr.: CDMX; Nahuatl: ''Altepetl Mexico'') is the capital and largest city of Mexico, and the most populous city in North America. One of the world's alpha cities, it is located in the Valley o ...
, where the latitude is 19° N.
Because others had carried out the first experimental exploitation of his important idea of 1930, Rossi was disappointed, but published his results immediately after returning to Padua.
Later, with Frederick C. Chromey, Alvarez and Rossi patented a "Vertical Determination Device", which made use of cosmic ray telescopes.
In Eritrea, Rossi discovered another phenomenon that would become a principal theme of his postwar cosmic ray research:
extensive cosmic ray air showers. The discovery occurred during tests to determine the rate of accidental coincidences between the Geiger counters of his detector. To assure that no single particle could trigger the counters he spread them out in a horizontal plane. In this configuration, the frequency of coincidences was greater than that calculated on the basis of the individual rates and the resolving time of the coincidence circuit. Rossi concluded that:
In 1937, Rossi became acquainted with Nora Lombroso, the daughter of
Ugo Lombroso, a professor of physiology at the
University of Palermo
The University of Palermo ( it, Università degli Studi di Palermo) is a university located in Palermo, Italy, and founded in 1806. It is organized in 12 Faculties.
History
The University of Palermo was officially founded in 1806, although its ...
, and Silvia Forti. Her grandfather was the renowned physician and criminologist
Cesare Lombroso
Cesare Lombroso (, also ; ; born Ezechia Marco Lombroso; 6 November 1835 – 19 October 1909) was an Italian criminologist, phrenologist, physician, and founder of the Italian School of Positivist Criminology. Lombroso rejected the establis ...
, and her aunts,
Gina Lombroso and
Paola Lombroso Carrara, were well known Italian writers and educators. In April 1938, Bruno and Nora married and set up a household in Padua.
Although Rossi avoided politics, some of Rossi's associates were active opponents of the
fascist
Fascism is a far-right, Authoritarianism, authoritarian, ultranationalism, ultra-nationalist political Political ideology, ideology and Political movement, movement,: "extreme militaristic nationalism, contempt for electoral democracy and pol ...
state. For example, he mentored
Eugenio Curiel
Eugenio Curiel (11 December 1912 – 24 February 1945) was an Italian-Jewish physicist, a prominent figure of the Italian resistance movement. He was awarded a gold medal (posthumously) for military valour.
Life
Eugenio Curiel was the first o ...
, who became a member of the
communist party
A communist party is a political party that seeks to realize the socio-economic goals of communism. The term ''communist party'' was popularized by the title of ''The Manifesto of the Communist Party'' (1848) by Karl Marx and Friedrich Engels. A ...
, while completing a degree at Padua. Later, in 1943, Curiel joined the resistance in Milan, and in 1945, was assassinated by soldiers of the
Republic of Salò
The Italian Social Republic ( it, Repubblica Sociale Italiana, ; RSI), known as the National Republican State of Italy ( it, Stato Nazionale Repubblicano d'Italia, SNRI) prior to December 1943 but more popularly known as the Republic of Salò ...
a German
puppet state
A puppet state, puppet régime, puppet government or dummy government, is a State (polity), state that is ''de jure'' independent but ''de facto'' completely dependent upon an outside Power (international relations), power and subject to its o ...
. Similarly,
Ettore Pancini, who received his ''
laurea
In Italy, the ''laurea'' is the main post-secondary academic degree. The name originally referred literally to the laurel wreath, since ancient times a sign of honor and now worn by Italian students right after their official graduation ceremony ...
'' under Rossi in 1938, spent the war years alternating between cosmic ray research and active participation in the
Italian resistance movement
The Italian resistance movement (the ''Resistenza italiana'' and ''la Resistenza'') is an umbrella term for the Italian resistance groups who fought the occupying forces of Nazi Germany and the fascist collaborationists of the Italian Social ...
s of Padua and Venice.
Because of these associations, and because both Rossis were
Jewish
Jews ( he, יְהוּדִים, , ) or Jewish people are an ethnoreligious group and nation originating from the Israelites Israelite origins and kingdom: "The first act in the long drama of Jewish history is the age of the Israelites""The ...
, they became apprehensive as Italy's
antisemitism
Antisemitism (also spelled anti-semitism or anti-Semitism) is hostility to, prejudice towards, or discrimination against Jews. A person who holds such positions is called an antisemite. Antisemitism is considered to be a form of racism.
Antis ...
grew under the influence of
Nazi Germany
Nazi Germany (lit. "National Socialist State"), ' (lit. "Nazi State") for short; also ' (lit. "National Socialist Germany") (officially known as the German Reich from 1933 until 1943, and the Greater German Reich from 1943 to 1945) was ...
. Eventually, as a result of
anti-Jewish laws
Anti-Jewish laws have been a common occurrence throughout Jewish history. Examples of such laws include special Jewish quotas, Jewish taxes and Jewish "disabilities".
Some were adopted in the 1930s and 1940s in Nazi Germany and Fascist Italy an ...
resulting from the
Manifesto of Race
The "Manifesto of Race" ( it, "Manifesto della razza", italics=no), otherwise referred to as the Charter of Race or the Racial Manifesto, was a manifesto which was promulgated by the Council of Ministers on the 14th of July 1938, its promulgation ...
, Rossi was dismissed from his professorship.
In his words:
Exile
With this setback, Rossi began an important phase of his career. He summarised this period in a memoir: "The Decay of 'Mesotrons' (1939–1943): Experimental Particle Physics in the Age of Innocence", which he presented in a symposium at
Fermilab
Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a United States Department of Energy national laboratory specializing in high-energy particle physics. Since 2007, Fermilab has been operat ...
in 1980.
On 12 October 1938, the Rossis left for
Copenhagen
Copenhagen ( or .; da, København ) is the capital and most populous city of Denmark, with a proper population of around 815.000 in the last quarter of 2022; and some 1.370,000 in the urban area; and the wider Copenhagen metropolitan ar ...
, where the
Danish
Danish may refer to:
* Something of, from, or related to the country of Denmark
People
* A national or citizen of Denmark, also called a "Dane," see Demographics of Denmark
* Culture of Denmark
* Danish people or Danes, people with a Danish a ...
physicist,
Niels Bohr
Niels Henrik David Bohr (; 7 October 1885 – 18 November 1962) was a Danish physicist who made foundational contributions to understanding atomic structure and quantum theory, for which he received the Nobel Prize in Physics in 1922. B ...
, had invited him to study. The couple had no intention of returning to Italy, and Bohr facilitated Rossi's search for a more secure position by sponsoring a conference attended by leading physicists. He hoped that one of them would find Rossi a job, and soon, Rossi received an invitation to come to the
University of Manchester
, mottoeng = Knowledge, Wisdom, Humanity
, established = 2004 – University of Manchester Predecessor institutions: 1956 – UMIST (as university college; university 1994) 1904 – Victoria University of Manchester 1880 – Victoria Univer ...
, where Blackett was developing a major center of cosmic ray research. After a pleasant two months in Denmark, Rossi and Nora arrived in
Manchester
Manchester () is a city in Greater Manchester, England. It had a population of 552,000 in 2021. It is bordered by the Cheshire Plain to the south, the Pennines to the north and east, and the neighbouring city of Salford to the west. The t ...
.
Manchester
Rossi's stay in Manchester was brief, but productive. At this time, a clear understanding of the soft component was available. In 1934,
Hans Bethe
Hans Albrecht Bethe (; July 2, 1906 – March 6, 2005) was a German-American theoretical physicist who made major contributions to nuclear physics, astrophysics, quantum electrodynamics, and solid-state physics, and who won the 1967 Nobel Prize ...
and
Walter Heitler
Walter Heinrich Heitler (; 2 January 1904 – 15 November 1981) was a German physicist who made contributions to quantum electrodynamics and quantum field theory. He brought chemistry under quantum mechanics through his theory of valence bond ...
published a quantitative description
not only of the production of electron-positron pairs by energetic photons, but also of the production of
photons by energetic electrons and positrons.
At Manchester, Rossi collaborated with Ludwig Jánossy on an experiment which demonstrated the correctness of the Bethe-Heitler theory of the second process, which had not yet been fully confirmed.
This experiment also introduced the technique of
anti-coincidence, which has become a ubiquitous feature of instruments for detecting and analyzing energetic particles.
By this time, cloud chamber observations had clarified the nature of the hard component. In 1936, Anderson and his student,
Seth Neddermeyer
Seth Henry Neddermeyer (September 16, 1907 – January 29, 1988) was an American physicist who co-discovered the muon, and later championed the Implosion-type nuclear weapon while working on the Manhattan Project at the Los Alamos Laborato ...
, discovered cosmic ray particles with mass intermediate between those of the electron and the proton,
which Anderson called "mesotrons". The mesotron subsequently became the known as the "μ meson",
which was shortened to "
muon
A muon ( ; from the Greek letter mu (μ) used to represent it) is an elementary particle similar to the electron, with an electric charge of −1 '' e'' and a spin of , but with a much greater mass. It is classified as a lepton. As wi ...
".
Just before the Copenhagen conference, Blackett suggested that observed variations of cosmic ray intensity with atmospheric temperature could be an indication that mesotrons are unstable,
and he held intense discussions with Rossi on this subject. As a result, Rossi left Manchester determined to confirm their decay and to measure the lifetime.
Chicago
With war looming over Europe, Blackett and others advised Rossi to leave Britain. Consequently, he wrote to Compton, who invited him to attend a summer symposium in
Chicago
(''City in a Garden''); I Will
, image_map =
, map_caption = Interactive Map of Chicago
, coordinates =
, coordinates_footnotes =
, subdivision_type = Country
, subdivision_name ...
, and hinted that a job might become available. In June 1939, the Rossis sailed for
New York
New York most commonly refers to:
* New York City, the most populous city in the United States, located in the state of New York
* New York (state), a state in the northeastern United States
New York may also refer to:
Film and television
* '' ...
, where they were greeted by Fermi and his wife
Laura, who had also left Italy because of the racial laws. After a brief reunion with the Fermis, the Rossis were offered a ride to Chicago by Bethe. They gratefully accepted, and arrived at the
University of Chicago
The University of Chicago (UChicago, Chicago, U of C, or UChi) is a private research university in Chicago, Illinois. Its main campus is located in Chicago's Hyde Park neighborhood. The University of Chicago is consistently ranked among the b ...
in mid-June 1939.
Mesotron decay
Immediately after a symposium session on mesotron instability reached a consensus that more definitive observations were needed, Rossi and Compton began to plan an experiment. Because the intensity of the hard component increases with altitude, while the density of air decreases, Compton suggested that the investigations should be carried out on
Mount Evans
Mount Evans is the highest peak in the Mount Evans Wilderness in the Front Range of the Rocky Mountains of North America. The prominent 14,271-foot (4,350 m) fourteener is located southwest by south ( bearing 214°) of Idaho Springs in Clear C ...
in
Colorado
Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of t ...
, where he had worked in the early 1930s, and where access to a research site at elevation is provided by the
Mount Evans Scenic Byway
The Mount Evans Scenic Byway is a National Forest Scenic Byway and Colorado Scenic and Historic Byway located in Clear Creek and Jefferson counties, Colorado, United States. The byway ascends to of elevation near the summit of Mount Evans, ma ...
, the highest paved road in North America. He urged Rossi to begin a series of experiments that summer, before snow blocked the road, and to help, enlisted two of his friends, Norman Hillberry and J. Barton Hoag,
and a student,
Winston Bostick. Rossi and his helpers hurriedly assembled equipment and loaded it onto a dilapidated bus that Compton borrowed from the Zoology department.
By this time, it was known that the main process by which mesotrons lose energy is ionisation energy loss, which is described by the
Bethe formula
The Bethe formula or Bethe-Bloch formula describes the mean energy loss per distance travelled of swift charged particles ( protons, alpha particles, atomic ions) traversing matter (or alternatively the stopping power of the material). For electro ...
, and is proportional to the mass per unit area of the layer of material traversed. If this were the only process, the intensity of the hard component passing through a layer of solid material would decrease by the same amount as in an equivalent layer of air. Rossi and his collaborators found that the decrease was significantly larger in the atmosphere than in a corresponding layer of solid carbon. Because the distance traversed in air was much larger than that in carbon, they interpreted this result as evidence for decay of the mesotron, and taking into account the effect of
relativistic time dilation
In physics and relativity, time dilation is the difference in the elapsed time as measured by two clocks. It is either due to a relative velocity between them ( special relativistic "kinetic" time dilation) or to a difference in gravitational ...
, estimated its mean life at rest as roughly 2 microseconds.
The next summer, Rossi returned to Mount Evans where he performed experiments near
Echo Lake at an elevation . With the use of anti coincidence techniques, the apparatus made it possible to measure the mean free path before decay of two groups of mesotrons with different average momentum. The results, published with David B. Hall, not only confirmed the proportionality between particle
momentum
In Newtonian mechanics, momentum (more specifically linear momentum or translational momentum) is the product of the mass and velocity of an object. It is a vector quantity, possessing a magnitude and a direction. If is an object's mass an ...
and the
mean free path
In physics, mean free path is the average distance over which a moving particle (such as an atom, a molecule, or a photon) travels before substantially changing its direction or energy (or, in a specific context, other properties), typically as a ...
of mesotrons before decay that is expected
on the basis of relativity theory, but also presented an improved estimate of the lifetime at rest: (2.4±0.3) microseconds.
These results and those of the previous year were not only the first to show definitively that mesotrons are unstable, but also the first experimental confirmation of the time dilation of moving clocks predicted by relativity theory.
Cornell
At Chicago, Rossi's position as
research associate
Research associates are researchers (scholars and professionals) that usually have an advanced degree beyond a Master's degree.
In some universities/research institutes, such as Harvard/Harvard Medical School/Harvard School of Public Health, the ...
was not permanent, and Compton was unable to secure him a better one. Consequently, he began a job search, during which he gave a seminar at
Cornell University
Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to teach an ...
, where coincidentally, death had created a vacancy in the Physics department. After Bethe suggested that Rossi should be invited to fill this position, he was appointed associate professor at Cornell. In the fall of 1940, after returning to Chicago from Colorado, the Rossis left for
Ithaca
Ithaca most commonly refers to:
*Homer's Ithaca, an island featured in Homer's ''Odyssey''
*Ithaca (island), an island in Greece, possibly Homer's Ithaca
*Ithaca, New York, a city, and home of Cornell University and Ithaca College
Ithaca, Ithaka ...
.
At Cornell, Rossi met his first American graduate student,
Kenneth Greisen, with whom he wrote an article, "Cosmic-Ray Theory", which was published in the
Reviews of Modern Physics
''Reviews of Modern Physics'' (abbreviated RMP) is a quarterly peer-reviewed scientific journal published by the American Physical Society. It was established in 1929 and the current editor-in-chief is Michael Thoennessen. The journal publishes re ...
and became known among cosmic-ray researchers as "The Bible".
During the summer of 1941, Greisen and physicists from
Denver
Denver () is a consolidated city and county, the capital, and most populous city of the U.S. state of Colorado. Its population was 715,522 at the 2020 census, a 19.22% increase since 2010. It is the 19th-most populous city in the Unit ...
and
Boulder
In geology, a boulder (or rarely bowlder) is a rock fragment with size greater than in diameter. Smaller pieces are called cobbles and pebbles. While a boulder may be small enough to move or roll manually, others are extremely massive.
In c ...
accompanied Rossi to Mount Evans, where they refined the knowledge of proportionality between mesotron momentum and lifetime before decay.
Greisen and Rossi also carried out experiments, which showed, in terms of processes documented in the "Bible", that not all particles of the soft component, could be produced by mesotrons of the hard component. They interpreted this as evidence for primary electrons or photons,
but it became evident later that the soft excess arises from the
decay of neutral pions.
After the 1941 expedition to Colorado, Rossi decided that the question of whether mesotrons decay had been answered. However, he was not satisfied with the precision with which the lifetime had been determined, for existing estimates depended on mesotron mass, which was not accurately known. To perform a more direct measurement, he designed apparatus to measure the time interval between the arrival of a mesotron in an absorber, where it stopped, and the emission of an electron when the mesotron decayed. To assist, he obtained the help of graduate student Norris Nereson. At the heart of their experiment, was a "chronometer", which was an electronic circuit that produced a pulse whose height was accurately proportional to the time interval, and which could be recorded by photographing an
oscilloscope trace.
This was the first
time-to-amplitude converter, another of Rossi's contributions to electronic techniques of experimental physics. With absorbers of lead and brass, the number of decays was plotted against time. These decay curves had the same
exponential form as those of
ordinary radioactive substances, and gave a mean lifetime of 2.3±0.2 microseconds,
which was later refined to 2.15±0.07 microseconds.
After the war, Rossi discovered that his Italian colleagues,
Marcello Conversi
Marcello Conversi (August 25, 1917 – September 22, 1988) was an Italian particle physicist. He is best known for his 1946 cosmic ray experiment where he showed that the "mesotron", now known as the muon, was not a strongly interacting partic ...
and
Oreste Piccioni
Oreste Piccioni (October 24, 1915 – April 13, 2002) was an Italian-American physicist who made important contributions to elementary particle physics during the early years of its history.
He was a graduate student of Enrico Fermi at the U ...
, had performed experiments very similar to his and measured a lifetime consistent with his result.
Looking back on what he called the "Age of Innocence", Rossi wrote:
Los Alamos
With the completion of his work on mesotrons, Rossi turned his attention toward the war effort. In 1942, while commuting from Ithaca to
Cambridge, Massachusetts
Cambridge ( ) is a city in Middlesex County, Massachusetts, United States. As part of the Boston metropolitan area, the cities population of the 2020 U.S. census was 118,403, making it the fourth most populous city in the state, behind Boston, ...
, he became a consultant on
radar
Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
development at the
Radiation Laboratory
The Radiation Laboratory, commonly called the Rad Lab, was a microwave and radar research laboratory located at the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts. It was first created in October 1940 and operated until 31 ...
of the
Massachusetts Institute of Technology
The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the ...
. Here, along with Greisen, he invented a "range tracking circuit", which was patented after the war.
In early July 1943, Bethe invited Rossi to join the
Manhattan Project
The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project w ...
. Within a month, he reported for duty at
Los Alamos Laboratory
The Los Alamos Laboratory, also known as Project Y, was a secret laboratory established by the Manhattan Project and operated by the University of California during World War II. Its mission was to design and build the first atomic bombs. Ro ...
. A few weeks later, Nora and their three-year-old daughter, Florence, joined Rossi in
Los Alamos, New Mexico
Los Alamos is an census-designated place in Los Alamos County, New Mexico, United States, that is recognized as the development and creation place of the atomic bomb—the primary objective of the Manhattan Project by Los Alamos National Labora ...
. The laboratory's director,
Robert Oppenheimer
J. Robert Oppenheimer (; April 22, 1904 – February 18, 1967) was an American theoretical physicist. A professor of physics at the University of California, Berkeley, Oppenheimer was the wartime head of the Los Alamos Laboratory and is often ...
, asked Rossi to form a group to develop diagnostic instruments needed to create the atomic bomb.
He soon realized that there already existed a group with a similar mission headed by the Swiss physicist
Hans H. Staub. The two decided to merge their efforts into a single "Detector Group". They were assisted by approximately twenty young researchers,
including
Matthew Sands
Matthew Linzee Sands (October 20, 1919 – September 13, 2014) was an American physicist and educator best known as a co-author of the ''Feynman Lectures on Physics''. A graduate of Rice University, Sands served with the Naval Ordnance Laborator ...
an "electronic wizard", who later earned a PhD under Rossi, and
David B. Nicodemus, whom Staub brought from
Stanford University
Stanford University, officially Leland Stanford Junior University, is a private research university in Stanford, California. The campus occupies , among the largest in the United States, and enrolls over 17,000 students. Stanford is consider ...
, who was an expert on particle detectors.
Fast ionization chamber
Bomb development called for large detectors of ionising radiation, whose response is proportional to the energy released in the detector and follows rapid changes in radiation intensity. From the Marie Curie#New elements, earliest research on radioactivity, radiation had been measured in terms of Ionisation, but existing Ionisation chambers were slow to respond to changes. To address this problem, Rossi and Staub carried out a careful analysis of the pulses that result when individual charged particles create ions within an ionisation chamber.
They realised that the high Electrical mobility, mobility of free electrons removed from ionised atoms means that the pulses produced by single particles can be very brief. With James S. Allen, Rossi found gas mixtures of high electron mobility and low Electron capture ionization, electron attachment.
On the basis of these investigations, Allen and Rossi invented the "fast ionisation chamber", which they patented after the war.
It was a crucial factor in the success of the Manhattan Project and became widely used in postwar research on particle physics.
RaLa experiments
In April 1944, the Manhattan project experienced a crisis, when Emilio G. Segrè, Emilio Segrè's group discovered that plutonium made in Nuclear reactors#Early reactors, reactors would not work in a gun-type fission weapon, gun-type plutonium weapon like the "Thin Man nuclear bomb, Thin Man". In response, Oppenheimer completely reorganised the laboratory to focus on development of an Nuclear weapon design#Implosion-type weapon, implosion-type weapon.
Rossi was enlisted to implement a method to test various weapon designs to arrive at one that produced an accurately symmetrical spherical implosion.
The tests measured changes of the absorption of gamma rays in a metal sphere as it underwent implosive compression.
The gamma rays were emitted by a pellet of the short-lived radioisotope Lanthanum-140 positioned in the center of the sphere. The term RaLa experiment is a contraction of Radioactive Lanthanum. As compression progressed, the rapid increase in absorption was detected as a decrease of gamma ray intensity recorded outside of the assembly.
The RaLa experiments revealed many pitfalls on the way to a successful implosion.
To understand problematic Jet (fluid), jets that plagued early implosion designs, other test methods were necessary, but the RaLa experiments played a primary role in the design of explosive lenses. In his history of the Los Alamos project, David Hawkins (philosopher), David Hawkins wrote: "RaLa became the most important single experiment affecting the final bomb design".
Trinity diagnostics
On 16 July 1945, an implosion-type plutonium device was detonated at the Trinity (nuclear test), Trinity site near Alamogordo, New Mexico. The code name for this device was "Trinity (nuclear test)#The Gadget, The gadget", and its design was very similar to the Fat Man weapon that was dropped on Atomic bombings of Hiroshima and Nagasaki#Nagasaki, Nagasaki twenty four days later.
In preparation for Trinity, Rossi designed instrumentation to record gamma radiation during the chain reaction, whose duration was expected to be approximately 10 nanoseconds. Observations on this time scale were almost beyond the state of the art in 1945, but Rossi designed and built a large cylindrical ionisation chamber whose speed of response was adequate because its coaxial electrodes were separated by a narrow gap of only .
To record the signal, he installed a very fast oscilloscope, provided as a prototype by DuMont Laboratories, in an underground bunker several hundred feet from the Gadget, where it was photographed. To bring the signal to the oscilloscope, he devised an oversized coaxial cable, coaxial transmission line, whose inner conductor was made smaller as it went from chamber to oscilloscope. Because this configuration enhanced the signal reaching the oscilloscope, there was no need for amplification. To confirm this surprising behaviour, Rossi consulted with Harvard professor Edward Mills Purcell, Edward Purcell.
A few days after the test, Rossi went into the darkroom with Fermi, and before the newly developed film was dry, they were able to compute the initial growth rate of nuclear activity, which was crucial information for future weapons development. Of three attempts to measure this rate at Trinity, Rossi's was the only one that was fully successful.
MIT
With the success of the Manhattan Project and the Radiation Laboratory, MIT moved into a new era of "Big science#Development, big science" funded by the US government.
MIT's expansion in nuclear physics was spearheaded by Jerrold R. Zacharias, who went to Los Alamos late in the war, and recruited Viki Weisskopf and Rossi as MIT professors.
Rossi left Los Alamos for Cambridge on 6 February 1946.
Within the new Massachusetts Institute of Technology School of Science#Laboratory for Nuclear Science, Laboratory for Nuclear Science, headed by Zacharias, Rossi was delegated to create a cosmic ray research group at MIT. To help, he recruited four young scientists who had been at Los Alamos as PhD candidates: Herbert Bridge, Matthew Sands, Robert Thompson and Robert Williams. Two who had been in the Radiation Laboratory also came to work with him: John Tinlot and Robert Hulsizer. All six were more mature than typical graduate students, for they had several years of wartime research experience. Consequently, they were paid a stipend similar to that of a postdoctoral researcher, which was funded by the Office of Naval Research and enabled them to support families during their graduate studies.
For this new phase of his activities, Rossi made a fundamental change of approach. In his words:
Elementary Particles
With the discovery of the pion in 1947, the search for new elementary particles became a popular research topic.
By operating fast ionization chambers within a cloud chamber, Herbert showed that the bursts of ionization they recorded were primarily produced by relatively low energy cosmic rays, whose nuclear interactions typically involve the ejection of several Spallation, heavily ionising nuclear fragments. On the basis of this effect, he and Rossi demonstrated that the behaviour of these interactions is similar to that of penetrating showers.
Rossi's group focused on the use of cloud chambers to study their properties and interactions. In 1948, with the aid of a multi-plate cloud chamber in which lead plates alternated with aluminium ones, Gregory, Rossi and Tinlot showed that the source of the electromagnetic component of cosmic ray interactions was predominantly energetic photons, rather than electrons.
This result confirmed Oppenheimer's suggestion of 1947 that neutral pions are produced in interactions, along with charged ones, and that this component arises from their rapid decay into photons.
To study the new elementary particles, Bridge and Martin Annis operated a large rectangular multi plate cloud chamber at Echo Lake.
This investigation provided the basis for a 1951 PhD thesis by Annis, supervised by Rossi. The next year, these authors, with another student of Rossi's, Stanislaw Olbert,
showed how to derive information on particle energies from measurements of their Scattering#Single and multiple scattering, multiple scattering. This added another way to use cloud chambers to measure the properties of elementary particles.
In early 1953, with Bridge, Richard Safford and Charles Peyrou, Rossi published results of a comprehensive cloud chamber study of the elementary particles that became known as kaons.
Peyrou was a visitor from at the École Polytechnique, where he had obtained an accurate value of the muon mass in 1947,
and Safford was Rossi's student.
Bagnères-de-Bigorre conference
By 1952, a bewildering "zoo" of elementary particles had been reported, with various masses, decay schemes, nomenclature and reliability of identification. To deal with this situation, Blackett and Leprince-Ringuet organized an International Cosmic Ray Conference at Bagnères-de-Bigorre in 1953.
According to James Cronin, "this conference can be placed in importance in the same category as two other famous conferences, the Solvay Conference#Fifth Conference, Solvay congress of 1927 and the Shelter Island Conference of 1948."
Leprince-Ringuet asked Rossi to give a summary of new information presented at the conference and to propose nomenclature for the new particles. Before the conference, in response to the latter assignment, Rossi circulated a suggestion that particles with mass smaller than that of a neutron be designated by small Greek alphabet, Greek letters and those with larger mass be designated by capital Greek letters. In his talk, on 11 July 1953, he reported that conference results, which he had compiled with the aid of Powell and Fretter,
were consistent with this scheme, which was commonly used afterwards.
A highlight was Leprince-Ringuet's declaration in his closing talk that: "...in the future we must use particle accelerators." With the 3 GeV Cosmotron already in operation at Brookhaven National Laboratory, this declaration reflected a consensus among the participants.
As a result, Rossi's group began to wind down their cloud chamber experiments. However, in 1954, Bridge, Hans Courant, Herbert DeStaebler, Jr. and Rossi reported on an unusual event in which a stopping singly charged particle decayed into three photons whose energies totaled more than the proton rest energy. This is the signature of an antiproton annihilation.
The next year, a group led by Owen Chamberlain and Emilio Segrè detected antiprotons,
for which they were awarded Nobel Prize in Physics in 1960.
Extensive air showers
By the time of the Bagnères-de-Bigorre conference, Rossi had already turned his attention toward the astrophysical implications of cosmic ray phenomena, particularly extensive air showers. After Rossi's recognition, in Eritrea, that these events exist, they were extensively studied by Pierre Victor Auger, Pierre Auger,
and by Williams.
At this time, the extremely fast response of the newly developed scintillation counters offered a new way to study the structure of air showers. To do this, Rossi enlisted his student, George W. Clark, who completed a PhD in 1952, and Piero Bassi, who was a visitor from the University of Padua. Because solid scintillating material was unavailable, they decided to use terphenyl dissolved in Petroleum ether, benzine, which is an efficient Liquid scintillation counting, liquid scintillator. With the aid of three counters deployed on the roof of the MIT Physics building during the winter of 1952/53, they found that shower particles arrived within only one or two meters of a disk, which travels at nearly the speed of light in the direction of the shower axis.
This result showed that scintillation counters can not only determine of the arrival times of shower disks at many detectors spread over a large area, but also to estimate the number of particles striking each detector. These capabilities combine the "fast-timing" method of determining shower arrival directions with the density sampling method of determining their size and the location of their axes.
Agassiz experiment
With this progress, Rossi's group began a major experiment that could measure both primary energies and arrival directions of extensive air showers. Participating in this effort were: George Clark, William Kraushaar,
John Linsley, James Earl, and Frank Scherb. Kraushaar came to MIT from Cornell in 1949, after earning his PhD under Kenneth Greisen. With the support of Professor Donald Howard Menzel, Donald Menzel who was director of the Harvard College Observatory, Rossi's group deployed fifteen liquid scintillators, of area on the wooded grounds of the observatory's Oak Ridge Observatory, Agassiz station. The signals were brought on cables to a Quonset hut, where they were displayed on fifteen Oscilloscope, oscillographs and recorded photographically.
Shortly after the experiment began to record shower data, lightning ignited the flammable liquid of one of the counters. Local firemen quickly extinguished the resulting fire before it spread to nearby trees, which were soaked with rain water. Because the trees played an essential role in suppressing atmospheric convection that would degrade telescopic observations, Harvard and MIT carried out tense negotiations, until an elaborate system of fire protection was installed, and the experiment was allowed to resume.
To eliminate the threat of fire, Clark, Frank Scherb and William B. Smith created a "factory" that made nonflammable plastic scintillator disks, whose thickness was and whose diameter was approximately .
After a switch to plastic in the late spring of 1956, the experiment ran continuously. Its findings were reported in Nature (journal), Nature
and the Physical Review.
The most important results were summarized by Rossi as:
As the Agassiz experiment came to an end, the group realized that observations near the equator and in the southern hemisphere were needed to extend their conclusion that air shower arrival directions are nearly isotropic. Consequently, Clark, in collaboration with Vikram Sarabhai, ran his smaller experiment at Kodaikanal, India, at a latitude of 10° N, and confirmed the absence of anisotropies.
Later, at the suggestion of Ismael Escobar,
the Agassiz equipment was moved to El Alto, La Paz, El Alto at 4200 meters on the Altiplano, Bolivian plateau at 16° S. Here, Clark, Escobar and Juan Hersil found no anisotropies, but they showed that the structure of air showers at their maximum development is different from that at sea level.
Volcano Ranch experiment
The maximum energy of a particle recorded by Agassiz experiment, 10
19 electron volt, is close to energies beyond which charged particles can not be confined to the Disc (galaxy), galactic disc by typical interstellar magnetic fields of 10
−5 Gauss (unit), gauss. A detector array of very large dimensions is needed to detect showers of these energies. John Linsley agreed to take on responsibility for building such an array.
He came to MIT in 1954 from the University of Minnesota, where he completed a PhD under Edward P. Ney. Soon, he was joined by Livio Scarsi, whom Rossi had recruited from Occhialini's group at the University of Milan.
Because no large enough tract of open land was available near Boston, the array was constructed on a semi-desert property known as''Volcano Ranch'', about west of Albuquerque, New Mexico, at an altitude of . During 1957 and 1958, Linsley and Scarsi deployed 19 scintillation counters, which used fluorescent plastic disks similar to those of the Agassiz detectors, except that each counter incorporated four disks viewed by four photomultipliers. Initially the area of the array was 2.5*10
6 m
2, which is to be compared with Agassiz's 10
5 m
2, but in 1960, after Scarsi had returned to Istituto Nazionale di Fisica Nucleare, Milan, Linsley spread the detectors over an area of 10
7 m
2.
Results from the Volcano Ranch experiment showed that the cosmic-ray intensity decreases smoothly with energy from 10
17 - 10
18 electron volt.
and that primaries in this range arrive isotropically.
Of particular significance was the detection of a single particle whose energy of 10
20 electron volt is larger than the maximum that could be contained in the galactic disc by galactic magnetic fields.
Particles of these energies can only originate in the galactic halo or from Extragalactic cosmic ray, beyond the galaxy, and their existence is not consistent with the Greisen-Zatsepin-Kuzmin limit.
Space Plasma Research
On 4 October 1957, the Soviet Union launched the first Satellite, artificial Earth satellite, Sputnik 1. This event began the Sputnik crisis, a "wave of near-hysteria"
among a surprised American public.
In response, the U.S. government increased funding for the National Science Foundation, and in 1958, created both the NASA, National Aeronautics and Space Administration (NASA) and the DARPA, Advanced Research Projects Agency, which was renamed the Defense Advanced Research Projects Agency (DARPA) in 1972.
On 4 June 1958, two days after legislation creating NASA was introduced, Detlev W. Bronk, chairman of the National Academy of Sciences, met with the heads of these three agencies to create a new advisory body, the Space Science Board, to provide advice for the expansion of space research and to make sure that funding of fundamental science would be properly emphasized.
![Explorer 10](https://upload.wikimedia.org/wikipedia/commons/e/ee/Explorer_10.jpg)
The Board convened for its first meeting on 27 June 1958. Only four members were already engaged in space research: Rossi, Leo Goldberg, John Alexander Simpson, John Simpson, and James Van Allen.
Rossi formed a subcommittee which included Thomas Gold, Philip Morrison and biologist Salvador Luria, who agreed that investigations of plasma in interplanetary space would be desirable. Consequently, Rossi decided to turn his group's efforts towards its study.
With Herbert Bridge, Rossi designed and tested a plasma probe based on the classical Faraday cup. However, to enhance the instrument's response to positively charged protons and to suppress its response to Photoelectric effect, photoelectrons produced by sunlight, four grids were deployed within the cup. A key innovation was a modulating voltage applied to one of the grids, which converted the signal into an alternating current, proportional to the proton flux and uncontaminated by any contribution of photoelectrons.
After intense lobbying of Homer E. Newell, Jr., Homer Newell, NASA's deputy director of space flight programs, Rossi secured a flight opportunity on
Explorer 10
Explorer 10 (also known as Explorer X or P14) was a NASA satellite that investigated Earth's magnetic field and nearby plasma. Launched on 25 March 1961, it was an early mission in the Explorer program and was the first satellite to measure th ...
, "Goddard Space Flight Center, Goddard's first home-grown satellite".
The unannounced goal was to hit the moon, but after launch on 25 March 1961, the satellite went into a highly elongated orbit around Earth, whose Apsis, apogee, at 70% of the distance to the moon, was well short of this goal.
Nevertheless, during 52 hours of data recorded by the MIT probe before battery power ran out, Rossi's group found a transition between two distinct regions around earth. Near earth, there were fairly strong and well organised magnetic fields, but no indication of interplanetary protons. At 22 earth radii, the spacecraft entered a region where magnetic fields were weaker and more irregular, and where a substantial flux of protons was observed coming from the general direction of the Sun. On several occasions during the rest of the flight, this flux disappeared and then reappeared again, which indicated that the spacecraft was flying close to the boundary between the two regions and that this boundary was moving irregularly.
Eventually, this boundary became known as the
magnetopause
The magnetopause is the abrupt boundary between a magnetosphere and the surrounding plasma. For planetary science, the magnetopause is the boundary between the planet's magnetic field and the solar wind. The location of the magnetopause is d ...
.
Under Bridge and Rossi, the MIT space plasma group included Frank Scherb, Edwin Lyon, Alan Lazarus, Alberto Bonnetti, Alberto Egidi, John Belcher and Constance Dilworth, who was Occhialini's wife.
Its Faraday cups have collected data on plasma throughout the solar system: near Earth on Orbiting Geophysical Observatory, OGO-1, OGO 3 and IMP 8,
in Outer space#Cislunar space, interplanetary space on WIND (spacecraft), WIND, and in the Heliosphere and Heliosphere#Heliosheath, Heliosheath on Voyager 1 and Voyager 2.
X-Ray astronomy
![X-Ray Explorer Satellite](https://upload.wikimedia.org/wikipedia/commons/8/8a/X-Ray_Explorer_Satellite.jpg)
As a consultant to American Science and Engineering, American Science and Engineering, Inc., Rossi initiated the rocket experiments that discovered the first extra-solar source of
X-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...
s,
Scorpius X-1
Scorpius X-1 is an X-ray source located roughly 9000 light years away in the constellation Scorpius. Scorpius X-1 was the first extrasolar X-ray source discovered, and, aside from the Sun, it is the strongest apparent source of X-rays in the sky. ...
.
Rossi was made Institute Professor at MIT in 1966.
Retirement
Rossi retired from MIT in 1970. From 1974 to 1980 he taught at the University of Palermo. In retirement he wrote a number of monographs, and a 1990 autobiography, ''Moments in the Life of a Scientist'', which was published by Cambridge University Press. He died from a cardiac arrest at his home in Cambridge on 21 November 1993. He was survived by his wife, Nora, daughters Florence and Linda and son Frank.
He was cremated, and his ashes are in the graveyard of the church of San Miniato al Monte, which overlooks Florence and the hill of Arcetri.
Honors and awards
Awards
* Wolf Prize in Physics for his role in the development of X-ray astronomy (1987)
* National Medal of Science (1985)
* Rumford Prize award of the American Academy of Arts and Sciences for "discoveries concerning the nature and origins of cosmic radiations" (1976)
* Elliott Cresson Medal (1974)
* Gold Medal of the Italian Physical Society (1970)
* Doctors ''honoris causa'' from the universities of Palermo, Durham, and Chicago
Honors
* Elected to the American Academy of Arts and Sciences (1948)
* Elected to the United States National Academy of Sciences (1950)
* Elected to the American Philosophical Society (1959)
Legacy
* Rossi X-ray Timing Explorer, a NASA satellite X-ray observatory launched in 1995.
* Bruno Rossi Prize of the High Energy Astrophysics division of the American Astronomical Society.
* There is an endowed chair named in honor of Bruno Rossi at MIT. It is currently held by Prof. Claude R. Canizares.
Books
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References
External links
Oral history interview transcript with Bruno Rossi on 21 July 1976, American Institute of Physics, Niels Bohr Library & ArchivesCosmic Ray Observations in Eritrea: Research Notes of Bruno Rossi, 1933
{{DEFAULTSORT:Rossi, Bruno
1905 births
1993 deaths
Scientists from Venice
University of Bologna alumni
University of Florence faculty
University of Padua faculty
University of Chicago faculty
Cornell University faculty
20th-century Italian astronomers
Jewish astronomers
20th-century Italian physicists
20th-century Italian Jews
Jewish physicists
Manhattan Project people
People from Los Alamos, New Mexico
National Medal of Science laureates
Particle physicists
Fellows of the American Physical Society
Wolf Prize in Physics laureates
University of Palermo faculty
Cosmic ray physicists
Members of the United States National Academy of Sciences
Jewish Italian scientists
Recipients of the Matteucci Medal
Italian emigrants to the United States
Members of the American Philosophical Society