Henri Becquerel

Henri Becquerel was born on December 15, 1852 in Paris, France. He was born into a family of scientists. His grandfather, Antoine Cesar Becquerel, invented an electrolytic method for extracting metals from their ores and his father, Alexander Edmund Becquerel, a professor of applied physics was known for his work on solar radiation and phosphorescence. Becquerel attended the Ecole Polytechnique in 1872 and the Ecole des Pontes at Chaussees from 1874 to 1877 where he studied engineering. After graduation he worked as a engineer for the Department of Bridges and Highways. In 1876 he became an assistant teacher at the Ecole Polytechnique. In 1895 he became the chair of physics. He also worked as an assistant naturalist at the Museum of Natural History. When his father died in 1891 he assumed his position as the professor of physics at Museum of Natural History.

Becquerel's research covered a number of physics topics. His first work was the rotation of polarized light rays using magnets. Next he began researching phosphorescent materials following in the footsteps of his father. He studied phosphorescent materials by exposing them to sunlight and then exposing them to photographic plates. He was conducting an experiment with uranium. First he would expose it to sunlight and them place it in with a photographic plate. He noticed that the uranium fogged the picture produced. He found he could block the fogging by inserting coins between the uranium and the photographic plate. An experiment run on February 27 and 28, 1896. The weather was overcast when he exposed his uranium salts and so he expected only a faint fogging on the developed photographic plate. Instead he was surprised to find the fogging as severe as it would be from uranium exposed to the sun. This radiation produced by the uranium did not need to be illuminated with sunlight to be produced. The new rays that were produced by the uranium were named Becquerel rays.

Becquerel determined that the rays ionized gasses and could be bent by a magnetic field, unlike x-rays which had recently been discovered by Wilhelm Rontgen. Becquerel determined that the particles emitted by the uranium salts were identical to the electrons discovered by Joseph John Thomson. Becquerel named the particles beta particles. For his discovery of spontaneous radioactivity Becquerel shared the 1903 Nobel Prize in physics with Marie and Pierre Curie. Becquerel had given the breakdown products of his uranium salts to the Curies, who discovered polonium and radium in them. Other honors won by Becquerel include election to French Academy of Sciences in 1889. He was made an officer in the Legion of Honor in 1900.

Becquerel died on August 25, 1908.


References:

Steinman, Rebecca; "Henri Bequerel"; in Biographies of Atomic Scientists

Henri Becquerel Nobel Biography

Henri Becquerel Wikipedia Entry

Henry Kendall

Henry Way Kendall was born on December 9, 1926 in Boston, Massachusetts. His father was an industrialist and he had two siblings, a younger brother and sister. He grew up in Sharon, Massachusetts and attended Deerfield Academy in Deerfield, Massachusetts, graduating in 1945. As a child he had an intense curiosity for things mechanical, chemical and electrical. He attended the United States Merchant Marine Academy, and served on a troop transport ship in the north Atlantic during the winter of 1945-46. With the end of the World War II he enrolled in Amherst College, graduating with a bachelors in mathematics in 1950. After graduation he went to the Massachusetts Institute of technology where he earned his Ph.D. in physics. He did post-doctoral work at M.I.T. and Stanford university then returned to M.I.T. as a faculty member.

Kendall's research involved using particle accelerators to probe the make up of the atom. In the 1960s and 70s Kendall worked with Jerome Friedman and Richard Taylor scattering electrons off of protons, neutrons, duterons and other heavier nuclei. These experiments confirmed the existence of quarks, small, sub-nuclear particles that protons and neutrons are made of. Quarks take their name from a line in Finnegan's Wake by James Joyce, and come in two kinds, up quarks and down quarks. Protons are made up of two up quarks and one down quark and neutrons are made up of two down quarks and one up quark. For their work confirming the existence of quarks Kendall, Friedman, and Taylor were awarded the 1990 Nobel Prize in physics.

In a addition to his work in physics, Kendall was also an avid outdoorsman, mountain climber and scuba diver. In the 1960s Kendall served as an adviser to the United States Department of Defense. In 1969 he co-founded the Union of Concerned Scientists and served for many years as its chairman. The Union of Concerned Scientists is a non-profit group that advocates sensible environmental and sustainable agricultural policies. He was elected to the National Academy of Sciences in 1977 and was inducted into the American Alpine Club's Hall of Mountaineering Excellence in 2012.

He died on February 15, 1999 as the result of a scuba diving accident while exploring an underwater cave in Wakulla Springs State Park in Florida.


References:

Bjorken, James D., Friedman, Jerome I., Taylor, Gottfried, Kurt and Taylor, Richard B.; "Henry Way Kendal: 1926-1999"; National Academy Press; 2009

Kendall, Henry W., Nobel Autobiography

Kendall, Henry W. and Aasserud, Finn; "Oral History Transcript - Dr. Henry Kendall"; accessed at aip.org.

 Henry Way Kendall Wikipedia Entry

Patrick Blackett, Baron Blackett

Patick Maynard Stuart Blackett was born on November 18, 1897 in Kensington, London. His father Arthur Blackett was a stockbroker and he had two sisters, one older and one younger than him. Starting at the age of nine he attended Allen House preparatory school. During his youth he used a wooden shed in the family garden to make crystal radios and model airplanes. In 1910, just before he turned 13, Blackett began attending Osborne Naval College on the Isle of Wight where he began his training as a naval officer. In 1912 he began studying at Britannia Royal Naval College in Dartmouth. in 1914, with the outbreak of World War I, Blackett served on the HMS Carnarvon which took part in the Battle of the Falkland Islands and he served aboard the HMS Barham which took part in the Battle of Jutland. In 1918, with the conclusion of the war he resigned from the Royal Navy as a lieutenant and went to study mathematics and physics at Magdalene College, Cambridge, where he worked under Ernest Rutherford in the Cavendish Laboratory.

Blackett graduated from Magdalene College with a B.A. in 1921 and continued working for Rutherford for another ten years. In 1923 he became a fellow at Kings College and in 1924 he used a cloud chamber to record the transmutation of nitrogen into oxygen. A cloud chamber is a closed chamber saturated with water or alcohol vapor. When ionizing particles (alpha particles for example) are introduced they create ions. The vapor in the chamber condenses on these ions and the condensed liquid shows the path of the particle through the chamber. While in the Cavendish Laboratory Blackett used a cloud chamber to do experiements involving cosmic rays. From 1924 to 1925 he worked in the laboratories of James Franck in Gottingen, Germany studying atomic spectra. In 1932, working with Italian physicist Giuseppe Occhialini, he developed a cloud chamber with a geiger counter to trigger the camera.

In 1933 he became professor at Birkback College, at the University of London. Also in 1933 he confirmed Carl David Anderson's discovery of the positron. A positron is a positively charged electron, an anti-matter particle. Blackett also worked on annihilation, the collision of matter and anti-matter that produces gamma radiation. In 1937 he became the Longworthy professor at Victoria University in Manchester. While there he worked on a theory of the earth magnetism, hoping to use it to unify the forces of gravity and magnetism. Although he was unsuccessful his work led to the development of paleomagnetism, which was used to prove the existence of continental drift.

In 1935 he was invited to serve on the Tizard Committee, which recommended the installation of radar for air defense. During World War II he served on various defense committees and contributed to the invention of the Mark XIV bomb sight. In 1940 he was awarded the Royal Medal by the Royal Society. In 1948 he was awarded the Nobel Prize for his work on particle physics using cloud chambers. He was appointed chairman of the physics department of Imperial College at London in 1953 and he retired in 1963. Blackett served as an adviser to the post war Labor government and in 1964, at his advice, set up the Ministry of Science and Technology. Blackett was outspoken politically and frequently came under criticism for his socialist and anti-nuclear weapon views.

He died on July 13, 1974.


References:

Brown, Matt; "Patrick Blackett: From Cosmic Rays to International Development"; November 18, 2007; London Blog at blogs.nature.com

Nye, Mary Jo; Blackett: Physics, War and Politics in the 20th Century; Harvard University Press; 2004

Patrick Blackett Nobel Biography

Patrick Blackett 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

Ernest Orlando Lawrence

Ernest Orlando Lawrence was born in Canton, South Dakota on August 8, 1901, the son of Carl Gustavus and Gunda Lawrence. His parents were Norwegian immigrants and his father was superintendent of schools. He attended Canton High School and then St. Olaf College in Northfield, Minnesota. In 1919 he went to the University of South Dakota, working his way through college by selling kitchenware. Originally he studied for a medical career but switched to physics. He graduated in 1922 with a B.A. in Chemistry. He then went to the University of Minnesota where he earned an M.A. in physics in 1923. He then went to Yale finishing his Ph.D. in physics in 1925 completing a thesis on photoelectricity.

He remained at Yale for three more years as a National Research Fellow and assistant professor. In 1928 he left the relative comfort of his Yale position as an assistant professor to become an associate professor at the University of California Berkley. Two years later he became a full professor at Berkley, being the youngest professor at Berkley. In 1936 became director of the university's radiation laboratory. He remained at these positions until his death.

Lawrence's early research dealt with photoelectricity and the ionization potentials of gaseous metals. In 1929 he invented the cyclotron, a device which accelerates atomic particles without using high voltages. Cyclotrons use an alternating voltage to accelerate particles, and a perpendicular magnetic field holds the particles in a circular path so that they can re-encounter the accelerating voltage many times. Thus the particles are gradually sped up by multiple encounters with the accelerating voltage. Cyclotrons, because the accelerated particles move in a circular path, take up less space than linear accelerators. Cyclotrons are used to create non-naturally occurring elements by bombarding atoms with atomic particles to create larger atoms. Cyclotrons have also been used in medicine to bombard cancerous tumors with radioactive particles.

During World War II Lawrence worked to help develop the atomic bomb. His radiation laboratory actively took part in the research for the development of the bomb. A early proponent of electromagnetic separation of uranium isotopes he developed calutrons, a specialized type of mass spectrometer, to separate the isotopes. He also introduced J. Robert Oppenheimer into what would become the Manhattan Project.

In 1939 Lawrence won the Nobel Prize "for the invention and development of the cyclotron and the results obtained with it especially with regard to artificial radioactive elements." Other honors received by Lawrence include the Enrico Fermi Prize awarded by the U.S. Atomic Energy Commission in 1957 and the Sylvanus Thayer Award presented by the United States Military Academy. Element 103 (atomic number 103) is named Lawrencium after Lawrence.

In 1958 Lawrence was appointed by President Eisenhower to take part in the negotiations with the Soviet Union over and atomic weapons treaty. Despite suffering from colitis Lawrence decided to go to Geneva, to take part in the negotiations. Falling ill while he was in Geneva Lawrence was rushed back to America for medical treatment. Lawrence died one month later on August 27, 1958.

References:

Alvarez, Luis, "Ernest Orlando Lawrence"; in Biographical Memoirs (1970) National Academy Press

"A Few Important Events in Lawrence's Life" at lbl.gov

Ernest Lawrence Nobel Prize Biography

Ernest Lawrence Wikipedia Entry

James Chadwick

Born on October 20, 1891, James Chadwick won the Nobel Prize in Physics in 1935 for his discovery of the neutron.

In 1932 Chadwick discovered a nuclear particle that did not have any charge (one of his letters announcing the discovery can be found here). These chargeless particles, called neutrons, differ from the previously discovered protons in that they do not have any charge. Because they do not have any charge they can be combined with other nuclei without having to overcome electrostatic repulsion.

Atomic nuclei are composed of two different types of particles, protons and neutrons. They both have about the same mass (neutrons are slightly more massive than protons) but differ in the amount of electrostatic charge they carry. Protons carry a positive charge and neutrons have no charge. Because they are all positively charged protons repel each other and therefore it is difficult to add alpha particles (alpha particles have two protons) to a nucleus. A neutron has no charge and can be used to bombard a nucleus without having to overcome the electrostatic charge.

Chadwick also discovered that atomic number is determined by the number of protons that are found in a nucleus. This is now the definition of atomic number. What element a particular atom is is determined by the number of protons present in its nucleus. For example, 1 proton is hydrogen, two protons is helium, three protons is lithium, etc. A full list of atom:atomic number corespondences can be found on a periodic table.

Chadwick later work with particle accelerators contributed to the making of the atomic fission bomb.

For discovering the neutron James Chadwick is the Dead Scientist of the Week for the week of October 18-24, 2009.

References:

James Chadwick Wikipedia entry

James Chadwick Nobel biography

James Chadwick Answers. com biography