Bruno Rossi

Bruno Benedetto Rossi was born on April 13, 1905 in Venice, Italy. His father, Rino, was an electrical engineer and had taken part in the electrification of Venice. Rossi was educated at home until he was 14, after which he attended ginasio (gymnasium) and liceo (high school) in Venice. He began his university studies at the University of Padua and finished his laurea (doctorate) at the University of Bologna in 1927. In 1928 Rossi took a job as an assistant at the Physics Institute of the University of Florence. Initially Rossi was at a loss to find a project to work on with the limited resources of the institute, but after reading a paper on cosmic rays, Rossi began studying them and developed an improved instrument, called a coincidence circuit, allowing him to study them. The instrument consisted of two Geiger counters, one mounted above the other, where metal plates could be inserted in between. By varying the type and thickness of the metal plates Bruno could determine the penetrating power of the cosmic rays.

Cosmic rays are charged atomic particles that bombard the Earth originating from the supernovas of large stars and in smaller amounts from active galactic centers. The surface of the Earth is protected from these charged particles by the Earth's atmosphere and magnetic field, although some reach the Earth's surface. Life on Earth would not survive were it not for this protection. Initially these particles were believed to be a form of electromagnetic radiation, but in 1927 Jacob Clay measured the amount of rays detected as he voyaged from Netherlands to Java and reported that the amount of rays hitting the Earth's surface changed with latitude with a minimum at the equator. This demonstrated that the "rays" were not photons and must be charged particles that were deflected by the Earth's magnetic field.

In 1932 Rossi became a professor of experimental physics at the University of Padua. In 1938 he was dismissed from his professorship because he was Jewish. After  a brief stays at the Bohr Institute in Copenhagen and University of Manchester, Rossi emigrated to the United States where he took a position at Cornell University in 1940. In 1943 Rossie joined the Manhattan Project in Los Alamos, New Mexico where he was co-chair, with Hans Straub, of the "detector group", which was responsible for designing detectors used by the scientists developing the atomic bomb.

In 1946 Rossi took a professorship at the Massachusetts Institute of Technology at the new Laboratory of Nuclear Science. At MIT Rossi focused on studying newly discovered subatomic particles. Rossi focused on developing detectors that could be launched into space to study cosmic rays that are not affected by the Earth's atmosphere and magnetic field. Rossi retired in 1970, but continued teaching. Awards won by Rossi include the Rumford Prize from the American Academy of Arts and Sciences (1976), the Elliot Cresson Medal from the Franklin Institute (1974) and the National Medal of Science (1985). Rossi was also awarded honorary doctorates from the Universities of Palermo, Durham, and Chicago.

Rossi died on November 21, 1993, suffering a cardiac arrest.


References:

Clark, George W.; "Bruno Benedetto Rossi: 1905-1993"; in Biographical Memoirs Vol. 75 (1997) National Academy Press

Clark, George W.; "The Contributions of Bruno B. Rossi to Particle Physics and Astrophysics"; Retrieved from: http://www.brera.unimi.it

Bruno Rossi Wikipedia Entry




 

Hannes Alfven

Hannes Olof Gosta Alfven was born on May 30, 1908 in Norrkorping, Sweden. His parents, Johannes and Anna-Clara Alfven were both practicing physicians, his mother being one of the first women in Sweden to practice medicine. Alfven recorded that one of the events that kindled his interest in astronomy and astrophysics was his receiving at an early age the gift of a popular book on astronomy by French astronomer Camille Flammarion. The other was his membership in his school's radio club. As part of club activities young Alfven built radio receivers and without a nearby radio station in Norrkorping, and the one in Stockholm to faint to be received, Alfven was thrilled to hear the notes of music coming out the atmospheric noise and identifying as coming from Aberdeen, Scotland.

After high school Alfven entered the University of Upsala where he studied mathematics, theoretical and experimental physics. He went on to complete his doctorate at Upsala, doing his dissertation on "ultra-short electromagnetic waves". At a time when many others were studying nuclear physics, Alfven demonstrated his independent thought by going on to study electronics and astronomy. After finishing his doctorate in 1934, Alfven remained at the University of Upsala as a lecturer in physics. In 1937 he became a research physicist at the Nobel Institute. In 1940 he was appointed Professor of the Theory of Electricity at the Royal Institute of Technology. He was appointed Professor of Electronics in 1945 and Professor of Plasma Physics in 1963. In 1967 he moved to the University of California at San Diego as a visiting professor.

In 1933, as a graduate student, Alfven published a theory of the origin of cosmic rays in Nature. The term cosmic ray is a misnomer. Cosmic rays are particles (almost 90% of them are protons) that travel through space. In 1937 Alfven proposed that there was a galactic electromagnetic field that caused cosmic rays to move in spiral patterns and because of this they are observed as coming from all directions. He argued that if plasma pervaded the galaxy and the plasma carried an electrical charge, it would create a magnetic field pervading the galaxy. At the time Alfven's suggestion of a galaxy wide magnetic field was dismissed, and it was not until 1950s that the electromagnetic acceleration of cosmic rays was accepted and it was not observed until the 1970s.

For most of Alfven's career because of his unorthodox ideas he was forced to publish in journals without large circulations. Interplanetary space was largely thought to be a good vacuum, disturbed only by occasional comets. This view was largely accepted because it looked that way when viewed by telescopes which only observe in the visual region of the electromagnetic spectrum. Alfven's proposal of electromagnetic currents could not be observed and thus they were dismissed.

Alfven's most well known discovery was the discovery of Alfven waves, proposed in a 1942 paper in Nature. Alfven waves, in plasma, are oscillations of ions and the magnetic field. At first Alfven's proposal was discounted and it was not until after a seminar given by Alfven in 1948 at the University of Chicago with the famous physicist Enrico Fermi in the audience, after which Fermi was seen to nod his head and heard to remark "of course", that Alfven waves were accepted. Alfven was awarded the Nobel Prize in Physics in 1970 "for fundamental work and discoveries in magnetohydrodynamics with fruitful applications in different parts of physics".

Other awards won by Alfven include the the Gold Medal from the British Royal Astronomical Society in 1967, the Franklin Medal from The Franklin Institute in 1970, the Lomonosov Medal from the USSR Academy of sciences in 1971, and the Bowie Medal awarded by the American Geophysical Union in 1988. The European Physical Society awards the Hannes Alfven Prize annually for outstanding contributions to plasma physics.

Alfven retired in 1991 and returned to his native Sweden.

Alfven died on April 2, 1995.

References:

Falthammer, Carl-Gunne;"Hannes Alfven" at the European Geophysical Society website (www.egu.eu)

Falthammer, C-G. and Dessler, A.J.; "Hannes Alfven" at alfvenlab.kth.se

Hogan, James P.; "Kicking the Sacred Cow"; Bean Books, 2004

Perrat, Anthony; "Dean of Plasma Dissidents"; The World and I (1988)p.190-197 found online at public.lanl.gov

Hannes Alfven Nobel Biography

Hannes Alfven Wikipedia Entry