James Franck

James Franck was born on August 26, 1882 in Hamburg, Germany. His father was a banker and his mother came from a family of rabbis. Franck attended Wilhelm Gymnasium in Hamburg and was not a brilliant scholar, only barely passing his high school final examinations. After high school he went to the University of Heidelberg, where he was to study law and economics, so that he could take a place at his father's firm. Franck was interested in science and took classes on chemistry and geology. At Heidelberg he met Max Born and the two became lifelong friends. With the help of Born he was able to persuade his father to let him study science and in 1902 he moved to Berlin where he studied physics under Emil Warburg and Paul Drude at the University of Berlin. He finished his PhD under Warburg in 1906, completing a thesis on the movement of ions in gaseous discharges.

After briefly working in Frankfurt-am-Main Frank returned to Berlin to work as an assistant for Heinrich Ruben, where he studied the structure of the electron shells of atoms and molecules, using atomic collisions. In 1911 Franck became a lecturer at the University of Berlin and when World War I broke out he enlisted and served as a private. In the war he was wounded, awarded the Iron Cross, first class, and then was promoted to lieutenant, despite his Jewish heritage. After his promotion he was assigned to a chemical warfare unit led by Fritz Haber, where he became Haber's assistant. After the war, at Haber's suggestion, Franck took a job at the Kaiser Wilhelm Institute of Physical Chemistry and in 1918 he became the head of the physics department.

Franck worked with Gustav Hertz and they studied the nature of electron collisions with atoms. From this work they were able to demonstrate the quantized nature of energy from electron transitions in atoms. In 1900 Max Planck had hypothesized that the energy emitted by excited atoms (atoms with electrons above their ground or lowest energy states) come in discrete amounts. When excited electrons fall back to their ground states they emit energy in the form of electromagnetic radiation. Because there are distinct electronic orbitals around the nucleus when electrons transition between these their emissions only come at certain wavelengths that depend on which orbitals the electrons transition between. Franck and Hertz's experiments were the first experimental demonstration of the quantized nature of electronic transitions. For these experiments Franck and Hertz were awarded the 1925 Nobel Prize in Physics.

In 1920 Franck moved to Gottingen where he was a professor of experimental physics at the Physical Institute. Franck's laboratory in Gottingen became a center for study of atomic and molecular physics and many important physicists studied there. In 1933, when the Nazis came to power in Germany, Franck moved to Baltimore, Maryland, where he was the Speyer Professor of Physics at Johns Hopkins University. He then spent a year in Copenhagen, Denmark, where he was a guest professor. In 1935 he returned to Johns Hopkins as a physics professor. He stayed at Johns Hopkins until 1938, when he moved to the University of Chicago, becoming a professor of physical chemistry. During World War II Franck was the director of the Chemistry Division of the Metallurgical Laboratory, which was part of the Manhattan Project. In 1945 he served as the chairman of the committee that produced the Franck Report, a document signed by several prominent physicists urging the United States Government not to use the atomic bomb on Japan and predicting the arms race. He became a professor emeritus at the University of Chicago in 1947, but continued doing research with the Photosynthesis Research Group until 1956.

Other honors won by Franck include the Planck Medal from the German Physical Society in 1951, the Rumford Medal in 1955 from the American Academy of Arts and Sciences for his work on photosynthesis and election as a foreign member of the Royal Society of London in 1964.

Franck died suddenly while on a brief trip to Gottingen on May 21,1963, at the age of 81.


References:

Rice, Stuart A. and Jortner, Joshua; "James Franck 1882-1964"; National Academy Press; 2010

James Franck Nobel Biography

James Franck Wikipedia Entry

Felix Bloch

Felix Bloch was born on October 23, 1905 in Zurich, Switzerland.  His father, Gustav Bloch was a wholesale grain seller in Zurich.  He entered public elementary school at age 6 and initially had trouble in school because he spoke Swiss German with an accent different than those of his peers.  In 1918 he began attending gymnasium run by the canton of Zurich.  Young Bloch excelled in mathematics and science and in 1924 he passed his "matura" an exam that allowed him to go on to an institution of higher learning.  Initially planning to study engineering he entered Federal Institute of Technology in Zurich.  After a year he changed his mind and began to study physics and continued at the same institution, graduating in 1927.

After graduating he went to the University of Lepzig, where he studied under Werner Heisenberg, completing his Ph.D. in 1928.  His doctoral thesis introduced the concept of Bloch waves to explain the behavior of electrons in crystals, developing the theory of metallic conduction.  After finishing his doctorate he took a tour of the various centers of experimental physics in Europe working for Wolfgang Pauli at the University of Zurich, Niels Bohr in Copenhagen, and Enrico Fermi in Rome, before returning to the University of Lepzig as a lecturer in physics.  In 1933, soon after Hitler came to power in Germany, he emigrated to the United States, taking a position at Stanford University in Palo Alto, California.  Bloch became Stanford's first professor of theoretical physics in 1939.  During World War II he worked on nuclear power at Los Alamos Nuclear Laboratory and on ways to interfere with radar at Harvard University.  After the war he returned to Stanford.

Bloch is most famous for his work developing the theory of nuclear induction and magnetic resonance.  Atoms that have an uneven number of protons and/or neutrons have an intrinsic magnetic moment and angular momentum.  This is called spin.  When placed into a magnetic field nuclei will emit electromagnetic radiation, as their spin lines up with the magnetic field.   The frequency of this emission depends on the strength of the magnetic field and the isotope.  By measuring these emissions it is possible to determine the chemical structure in which the atom resides.  This technique is used by chemists to determine the structure of compounds and it is used in medical imaging and is called magnetic resonance imaging, or MRI (the name was changed to remove the word "nuclear").  For his discovery of nuclear magnetic resonance Bloch won the Nobel Prize for physics in 1952, which he shared with Edward Mills Purcell who developed the theory simultaneously.

In 1952 Bloch became the first director of CERN, the European Organization for Nuclear Research, and he formulated its early policies regarding atomic research.  Because as director he had little time for research he returned to Stanford a year later.  In 1965 he served as president of the American Physical Society.

Bloch died on September 10, 1983.


Bibliography:

Hofstader, Richard; "Felix Bloch"; Physics Today (1984)37:115-116

Hofstader, Richard; "Felix Bloch: 1905-1983" in Biographical Memoirs Vol. 64; National Academy Press; 1994

Felix Bloch Nobel Biography

Felix Bloch Wikipedia Entry

C. T. R. Wilson

Charles Thompson Rees Wilson was born of February 14, 1869 in Glencorse a parish near Edinburgh, Scotland. His father was a sheep farmer who died in 1873, when Wilson was 4. His mother moved the family to Manchester, where with the help of an older brother from his father's previous marriage he was educated at a private school and then Owen's College, which is now the University of Manchester. At Owen's college he studied biology, making a study of beetles and hoping to become a medical student. Though he failed a scholarship test for Christ College, Cambridge he was awarded a scholarship at Sidney Sussex College, Cambridge where he became interested in the physical sciences, studying chemistry and physics.

In 1894 he was studying cloud formations at Ben Nevis, an observatory on the highest point in Scotland and he observed the coronas, the rings of color that form around the sun when it shines through clouds, and "glories", colored rings surrounding shadows cast upon clouds. Interested in this phenomena, he returned to Sidney Sussex and attempted to reproduce them in the laboratory, by rapidly expanding moist, dust free air. As the air expands the temperature drops and when it reaches the dew point the water vapor in the air condenses. Wilson noticed that water droplets formed in the air and he suspected that this was caused by water condensating on ionic nuclei. This prediction was verified when Wilson's "cloud chamber" was exposed to the newly discovered x-rays. The massive increase in water droplets after x-ray exposure coincided with the observation that air was made conductive by x-rays, which produced ions in the air.

This was the birth of the cloud chamber, a device which allows for the photographic recording of the paths of ionizing, nuclear particles. When ionizing nuclear particles fly through the air they colide with air molecules, producing ions. These ions can be observed in the cloud chamber because of the water that condenses on them. The water droplets form paths that can be observed and photographed. Cloud chambers have been used to record a number of nuclear phenomena. Wilson used his cloud chamber and in 1911 was the first person to observe and record the paths of alpha and beta particles and electrons.

For his invention of the cloud chamber Wilson shared the 1927 Nobel Prize in physics with Aurthur Compton. He was elected to the Royal Society in 1900. Other honors received by Wilson include the Copley Medal in 1935 and the Franklin Medal in 1929. After his retirement he moved to Edinburgh and then moved to the village of Carclops, close to this birthplace.

He died, surrounded by his family, on November 15, 1959.

References:

"Profile: C.T.R. Wilson" The New Scientist; (1959)5:348-349

C.T.R. Wilson Nobel Biography

Charles Thompson Rees Wilson Wikipedia Entry

Lester Halbert Germer

Lester Halbert Germer was born on October 10, 1896 in Chicago, Illinois and lived most of his childhood in Canastota, New York. He graduated from Cornell University in 1917. After graduation he joined Bell Labs and then served in World War I as a fighter pilot, earning a citation from General Pershing. After the war he returned to Bell Labs and finished his Ph.D. at Columbia University in 1927.

At Bell Labs, Germer initially worked as an assistant to Clinton Davisson. In April of 1925 Davisson and Germer began working on an experiment studying the diffraction of electrons off of a nickel surface. At first their results were similar to results obtained four years earlier. Then suddenly the results changed. Looking for an explanation for the change they cut open the vacuum tube containing the nickel target. With the help of microscopist F. F. Lewis they observed that the crystalline surface of the nickel target had changed due to extreme heating. They believed that the change in their results was due to the change of the crystalline surface of the nickel target.

They performed a similar experiment in 1927, after Davisson had attended a conference where Louis-Victor DeBroglie's hypothesis about the wave nature of matter was presented. When electrons of known velocity were used to bombard the nickel surface at a 45 degree angle they observed that the diffraction of the electrons obeyed Bragg's Law, which relates the wavelength of diffracted x-rays with the lattice spacing of the target and the angle of diffraction. This was the first proof of DeBroglie's particle wave hypothesis. For this work Germer and Davisson were awarded the Elliot Cression Medal in 1931 (Davisson shared the 1937 Nobel Prize in Physics with George Thompson, who preformed a different experiment confirming DeBroglie's hypothesis four months later).

DeBroglie's hypothesis, that matter, like electromagnetic radiation, has a wave like nature is one of the more surprising revaluations that came with the development of quantum mechanics. In his doctoral thesis DeBroglie hypothesized that the wavelength of matter is dependant on its mass and velocity and that the wavelength is equal to Planck's constant divided by the momentum (p=mass*velocity) of the matter (wavelength=h/p).

After this experiment Germer continued working at Bell Labs, studying the use of this technique to determine the structure of surfaces, work that eventually led to the development of the electron microscope. In addition to his work at Bell Labs, Germer was also an avid rock climber. On October 3, 1971, one week before his 75th birthday, Germer died of a massive heart attack while he was rock climbing.

References:

Lieter, Daryll J. and Lieter, Sharon; "A to Z of Physicists"; Infobase Publishing; 2003

MacRae, Alfred U.; "Lester H. Germer"; Physics Today(1972)25:93-97

Lester Germer Wikipedia Entry

Prince Louis-Victor de Broglie

Prince Louis-Victor de Broglie was born in Dieppe, France on August 15, 1892., the younger son of Victor Duc de Broglie and Pauline d'Armaille. The history of the de Broglie family included service to the French crown for which the head of the family was granted the hereditary title of "Duc" (Duke) by Louis XIV and the German title of "Prinz" (Prince) for service to Austria during the Seven Years War. All of de Broglie's early education was provided by private tutors. In 1906 he was sent to Lycee Janson de Sailly where he spent three years completing his secondary education. De Broglie then went to the Sorbonne where he initially studied history, intending to take a job in the diplomatic service, earning a degree in 1910. Unsatisfied with his studies in the liberal arts de Broglie began studying theoretical physics.

De Broglie graduated with a degree in physics in 1913. Thereafter, as required by French law, de Broglie enlisted in the military. De Broglie served for the duration of the First World War, from 1913 to 1919. In his initial posting he was sent to a fort at Mount Valerien, where he was given very little to do and it was a difficult time for him. Later, with the influence of his brother Maurice, who had succeeded his father as Duc, de Broglie was posted to a radio station at the Eiffel Tower working as an electrician. De Broglie found this posting much more satisfying as it allowed him experience working with electrical equipment, which would serve him well in his scientific career.

After leaving the French service de Broglie worked with his brother Maurice, also a theoretical physicist, taking advantage of the laboratory built by his bother at the family mansion in Paris. At the time physicists thought of matter as being composed of particles and light was thought of as a wave-like phenomena. Albert Einstein, in his description of the photo-electric effect had demonstrated that light can behave both as a particle and a wave. Influenced by Einstein, de Broglie proposed that matter also has a dual nature, as both a particle and a wave. He proposed that the wavelength of matter is equal to Planck's constant divided by the momentum of the particle (wavelength h/p). This is true for all matter, small particles like electrons and large objects such as bullets or cars. Because of the momentum term in the wavelength equation (p) is equal to the mass of an object multiplied by its velocity (p=m*v) the wavelength gets shorter the more massive an object is and it is only for small particles that the wavelength has any practical effect. Using this insight for his doctoral thesis, his committee was unsure of the validity of his ideas and so passed his thesis on to Einstein who wholeheartedly agreed with the work. De Broglie was granted his doctorate in 1923.

De Brolie's insight into the wave nature of matter gave rise to a field of physics called wave mechanics. An electron, traveling around a nucleus, must have a wave pattern that is stable, where the length of the orbital is an integer number of wavelengths long. Erwin Schrodinger used de Broglie's theory of particle waves to work out the solutions to the wave equation that showed the behavior of an electron in a hydrogen atom and these equations agreed with experimental data.

For his discovery of the wave nature of matter de Broglie was awarded the Nobel Prize in physics in 1929. After completing his doctorate de Broglie gave a series of lectures at the Sorbonne, and was appointed professor of theoretical physics at the Poincare Institute in 1926. In 1932 he was appointed chair of theoretical physics at the Sorbonne where he taught until 1962.

De Broglie died on March 19, 1987.


References:

"Biography of Prince Louis-Victor de Broglie the Nobel Prize in Physics 1929" at debroglie.poldow.com

Prince Luis de Broglie Nobel Biography

Luis de Broglie Wikipedia Entry

Niels Bohr

Born on October 7, 1885, Niels Bohr won the Nobel Prize in physics in 1922 for proposing a structure for the atom and his work in quantum mechanics.

Before Bohr physicists knew that the structure of an atom consisted of a small dense nucleus orbited by electrons. Earnest Rutherford in 1911 published the results of an experiment in which alpha particles emitted by the decay of radium were used to bombard a thin piece of gold foil. The results of the experiment showed that a small amount of the alpha particles were deflected and did not penetrate the gold foil. Rutherford hypothesized that these alpha particles were deflected by the small, hard nuclei of the gold atoms. This led him to propose that atoms were composed of small nuclei surrounded by orbiting electrons that orbited the nuclei in a similar manner to the way planets orbit stars. This model is sometimes called the planetary model (wikipedia entry).

In 1913 Niels Bohr proposed a model for atomic structure where:

1. Electrons orbit nuclei only in certain orbits: orbits set at discrete distances from the nucleus.

2. Electrons can change orbitals, but in doing so they must either absorb (when moving to a higher orbital, further from the nucleus) or emit energy (when moving to a lower orbital, closer to the nucleus).

3. The frequency of the light emitted by an electron changing orbitals is related to the period of the orbital.

The emission of light by electrons falling back into lower orbitals can be seen in neon lights. A gas, sealed in a tube is electrified, causing electrons (normally staying in the lowest energy levels) to move to higher energy levels (higher orbits). When they fall back to their lower, ground state they emit light. This is how neon lights work, and each gas emits a different spectrum giving each gas a distinct color.

For his work determining the structure of atoms, Neils Bohr is our Dead Scientist of the Week for the week of October 4-10, 2009.

References:

Neils Bohr Wikipedia Entry

Bohr Model, Wikipedia Entry

Carpi, Anthony, Vision Learning, Atomic Structure II