April
Important historic dates in science

April 30: Cosmic rays generate electricity
In 1939, the first electric power generated by cosmic rays was produced at the Hayden Planetarium, New York City.

April 29: Nuclear power plant
In 1957, the first military nuclear power plant was dedicated in Fort Belvoir, Virginia.

April 28: Arthur L. Schawlow
(Born May 5, 1921: Died April 28, 1999)
American physicist who was a corecipient (with Nicolaas Bloembergen of the U.S. and Kai Siegbahn of Sweden) of the 1981 Nobel Prize for Physics for his work in developing the laser and in laser spectroscopy.

April 27: Philip Hauge Abelson
(Born April 27, 1913: Died August 1, 2004)
Philip Hauge Abelson was a U.S. physical chemist who proposed the gas diffusion process for separating uranium-235 from uranium-238 which was essential to the development of the atomic bomb. In collaboration with the U.S. physicist Edwin M. McMillan, he discovered a new element, later named neptunium, produced by irradiating uranium with neutrons. At the end WW II, his report on the feasibility of building a nuclear-powered submarine gave birth to the U.S. program in that field. In 1946, Abelson returned to the Carnegie Institution and pioneered in utilizing radioactive isotopes. As director of the Geophysics Laboratory of the Carnegie Institution (1953-71), he found amino acids in fossils, and fatty acids in rocks more than 1,000,000,000 years old.

April 26: Arno Penzias
(Born April 26, 1933)
Arno Allan Penzias is a German-American astrophysicist who shared one-half of the 1978 Nobel Prize for Physics with Robert Woodrow Wilson for their discovery of a faint electromagnetic radiation throughout the universe. Their detection of this radiation lent strong support to the big-bang model of cosmic evolution.

April 25: Manhatten project
In 1945, the new U.S. President, Harry S. Truman was briefed on the status of the atomic bomb project. Within 24 hours of Roosevelt's death on 12 Apr 1945, Truman had been told briefly about the atomic bomb project by Secretary of War Henry Stimson. In this more extensive briefing on 25 Apr, Stimson, with General Groves's assistance, gave Truman information that the uranium-235 gun design had been frozen, but sufficient uranium-235 would not be accumulated until around 1 Aug. Enough plutonium-239 would be available for an implosion assembly to be tested in early July; a second would be ready in August.

April 24: Hendrik Anthony Kramers
(Born December 17, 1894: Died April 24, 1952)
Dutch physicist who, with Ralph de Laer Kronig, derived important equations relating the absorption to the dispersion of light. He also predicted (1924) the existence of the Raman effect, an inelastic scattering of light. Kramer's work covers almost the entire field of theoretical physics. He published papers dealing with mathematical formalism of quantum mechanics, and others on paramagnetism, magneto-optical rotation, ferro-magnetism, kinetic theory of gases, relativistic formalisms in particle theory, and on theory of radiation. His work shows outstanding mathematical skill and careful analysis of physical principles.

April 23: Max von Laue
(Born October 9, 1879: Died April 23, 1960)
German recipient of the Nobel Prize for Physics in 1914 for his discovery of the diffraction of X rays in crystals. This enabled scientists to study the structure of crystals and hence marked the origin of solid-state physics, an important field in the development of modern electronics.

April 22: Fritz Strassman
(Born February 22, 1902: Died April 22, 1980)
German physical chemist who, with Otto Hahn and Lise Mietner, discovered neutron-induced nuclear fission in uranium (1938) and thereby opened the field of atomic energy used both in the atomic bomb for war and in nuclear reactors to produce electricity. Strassmann's analytical chemistry techniques showed up the lighter elements produced from neutron bombardment, which were the result of the splitting of the uranium atom into two lighter atoms. Earlier in his career, Strassmann codeveloped the rubidium-strontium technique of radio-dating geological samples.

April 21: Sir Edward Appleton
(Born September 6, 1892: Died April 21, 1965)
Sir Edward (Victor) Appleton, was an English physicist, born in Bradford, who won the Nobel Prize for Physics in 1947 for his discovery of the so-called Appleton layer of the ionosphere, which is a dependable reflector of radio waves and as such is useful in communication. Other ionospheric layers reflect radio waves sporadically, depending upon temperature and time of day.

April 20: Radium
In 1902, Marie and Pierre Curie isolated one gram of radium, the first sample of the radioactive element. They had refined it from eight tons of pitchblende ore.

April 19: Albert Wallace Hull
(Born April 19, 1880: Died January 22, 1966)
American physicist who independently discovered the powder method of X-ray analysis of crystals (1917), which permits the study of crystalline materials in a finely divided microcrystalline, or powder, state. His first work was on electron tubes, X-ray crystallography, and (during WW II) piezoelectricity. In the 1920's, he studied noise measurements in diodes and triodes. In the 1930's, he also took interest in metallurgy and glass science. His best-known work was done after the war, especially his classic paper on the effect of a uniform magnetic field on the motion of electrons between coaxial cylinders. He also invented the magnetron (1921) and the thyratron (1927), and other electron tubes with wide application as components in electronic circuits.

April 18: Albert Einstein
(Born March 14, 1879: Died April 18, 1955)
German-American physicist who developed the special and general theories of relativity and won the Nobel Prize for Physics in 1921 for his explanation of the photoelectric effect. Recognized in his own time as one of the most creative intellects in human history, in the first 15 years of the 20th century Einstein advanced a series of theories that proposed entirely new ways of thinking about space, time, and gravitation. His theories of relativity and gravitation were a profound advance over the old Newtonian physics and revolutionized scientific and philosophic inquiry.

April 17: Harriet Brooks
(Born January 1, 1876: Died April 17, 1933)
Canadian nuclear physicist who was probably the first to observe the recoil of the atomic nucleus as nuclear particles were emitted during radioactive decay. During the years 1901-05, she contributed much to the new science of radioactivity. Working with Rutherford, she measured the rate at which radium released radon (and other gases) into the air. They demonstrated that the diffusion of the emanations of radium both behaved like a a gas, and that this gas had a high (over 100) molecular weight. Rutherford credited her work identifying the release of radon as crucial to developing his theory of the transmutation of one element into another. She died at the age of 56, from leukemia or a like disease related to radiation exposure.

April 16: Sun Approach
In 1976, the Helios-B rocket made the closest approach to the sun at 27 million miles. (The earth is 93 million miles from the sun.) This was a U.S.-German project.

April 15: Emory Leon Chaffe
(Born April 15, 1885: Died March 8, 1975)
U.S. physicist known for his work on thermionic vacuum (electron) tubes.

April 14: Telescope
In 1611, the word "telescope" was first used in public by Prince Federico Cesi at a banquet held by the pioneer scientific society, the Academy of Linceans (or Lynxes, of which he was a founder). It was held to honour Galileo, on a grand hillside estate. After Galileo showed the guests the satellites of Jupiter, other celestial marvels, and even an inscription on a building three miles away. Although the name was announced by Cesi to christen Galileo's instrument, the word telescopio (in Italian) was perhaps devised by a Greek poet-theologian who happened to be present from Greek words* (tele = far and scopeo = see). In 1625, another Lincean, Giovanni Faber of Bamberg (1574 - 1629) coined the analagous word microscope.

April 13: Stanislaw M. Ulam
(Born April 13, 1909: Died May 13, 1984)
Polish-American mathematician who played a major role in the development of the hydrogen bomb at Los Alamos. He solved the problem of how to initiate fusion in the hydrogen bomb by suggesting that compression was essential to explosion and that shock waves from a fission bomb could produce the compression needed. He further suggested that careful design could focus mechanical shock waves in such a way that they would promote rapid burning of the fusion fuel. Ulam, with J.C. Everett, also proposed the "Orion" plan for nuclear propulsion of space vehicles. While Ulam was at Los Alamos, he developed "Monte-Carlo method" which searched for solutions to mathematical problems using a statistical sampling method with random numbers.

April 12: Marie Curie's discoveries announced
In 1898, Marie Curie observed a meeting of the French Academy of Sciences, where one of her teachers, Prof. Gabriel Lippmann announced her discovery of substances much more radioactive than uranium. Working since Dec 1897, she had verified that the radiant activity of various compounds was directly related to the amount of uranium present, irrespective of its solid, powdered, or wet state. She assayed innumerable metals, salts, and minerals. When working with pitchblende and charcolite she discovered that some compounds of thorium were even more active than uranium. She emphasized that both uranium and thorium had high atomic weights and suggested that the radiant activity was an atomic property, for it was independent of the physical or chemical state of the radioactive element. She also announced the probable presence in pitchblende of a new element endowed with powerful radioactivity.

April 11: Halley's Comet
In 1986, Halley's Comet made its closest approach to Earth this trip, 63 million kilometers (39 million mi), on its outbound journey. Many observers were disappointed because the famous comet was barely visible to the naked eye. Some years are simply better than others, as in 1066 when the comet was so bright that it terrified millions of Europeans. Comet Halley isn't officially scheduled to visit Earth again until 2061 when it returns on its 76-year orbit. This comet's closest known approach to the Earth was 3 million miles on 10 Apr 837 AD). Its perihelion (the closest point to the Sun) occurred earlier in the year, on 9 Feb 1986, when it was 88 million km (55 million mi) from the Sun, between the orbits of Mercury and Venus.

April 10: Sir John Leslie
(Born April 10, 1766: Died November 3, 1832)
Scottish physicist and mathematician who first created artificial ice. His practical scientific investigations led to his book Experimental Inquiry Into the Nature and Propagation of Heat (1804), dealing with the fundamental laws of heat radiation. Leslie gave the first correct description of capillary action (1802) and invented many instruments, most notably an accurate differential air thermometer, and also a hygrometer, a photometer, the pyroscope, atmometer and aethrioscope. In 1810, he devised a method of obtaining very low temperatures, by evaporating water in a receiver evacuated with an air-pump but containing a drying agent. His mathematical works include texts on geometry, trigonometry and The Philosophy of Arithmetic.

April 9: William Prout
(Born January 15, 1785: Died April 9, 1850)
English chemist and biochemist noted for his discoveries in atomic weights. He is best known for formulating Prout's hypothesis (1815) which states that the atomic weights of all elements are exact multiples of the atomic weight of hydrogen. At that time the atomic weight of hydrogen was taken to be 1.0, the hypothesis implied that all atomic weights would be whole numbers. In 1818, he isolated urea and uric acid for the first time. In 1920, the proton was named after Prout.

April 8: Sunspot
In 1947, the largest sunspot group recorded was observed on the sun's southern hemisphere. Its size was estimated at 7 billion square miles, or an area of 6100 millionths of the Sun's visible hemisphere. Sunspots are areas of somewhat cooler surface than the surrounding solar gases, and appear as dark spots on the solar surface. Astronomers measure the sizes of sunspots as millionth fractions of the Sun's visible area. Typically, a big sunspot measures 300 to 500 millionths, whereas the entire surface area of the Earth is only 169 millionths of the solar disk.

April 7: Atomic electricity
In 1959, the first atomic generated electricity was produced at Los Alamos Scientific Laboratory, New Mexico. The experimental model used a "plasma thermocouple" in the reactor instead of a fullscale turbine, and produced merely enough electrical power for a light bulb.

April 6: Russian nuclear accident
In 1993, in Russia, a huge radioactive cloud was released from an explosion of a tank of radioactive waste at the secret military facility at Tomsk 7. Located in the Russian wilderness, 1700 miles east of Moscow, it was the worse nuclear accident, thought not the only one, since the incident at Chernobyl in April, 1986. A week later, delegates at a meeting in Tokyo from the world's richest nations, agreed to give urgent help to Russia for problems with nuclear waste, obsolete nuclear missile warheads, and aging nuclear reactors.

April 5: Robert Oppenheimer
In 1963, the U.S. Atomic Energy Commission gave the Fermi Award to J. Robert Oppenheimer for research in nuclear energy. Oppenheimer was the chief scientist of the Manhattan Project during WWII that created the atomic bomb. Later, he opposed the more destructive hydrogen bomb development and his security clearance was revoked (1954). Nine years later, a wiser U.S. government awarded Oppenheimer the prestigious Fermi Award, "For contributions to theoretical physics as a teacher and originator of ideas, and for leadership of the Los Alamos Laboratory and the atomic energy program during critical years." The actual presentation of the medal and $50,000 was made December 2, 1963 by President Lyndon B. Johnson.

April 4: Sir William Crookes
(Born June 17, 1832: Died April 4, 1919)
British chemist and physicist noted for his discovery of the element thallium and for his cathode-ray studies, fundamental in the development of atomic physics.

April 3: Space nuclear power
In 1965, SNAP 10A, the first nuclear reactor in space, was launched from Vanden berg Air Force Base, Calif. It was activated by a signal from scientists on earth about four hours later, and generated 500 kilowatt-hours of power during its life, providing electrical power for a 1 kgf ion engine. While its ground version lasted 10,000 hours without problems, the orbiting reactor was shut down by an electrical failure in another of the satellite's systems after 45 days in operation. It is still orbiting the earth. SNAP stands for Systems for Nuclear Auxiliary Power. Although the Soviet Union has flown many nuclear reactors in space, the SNAP-10A is the only one flown by the United States.

April 2: Photo of sun
In 1845, H.L. Fizeau & J. Leon Foucault took the first photograph of the Sun.

April 1: Lev Davidovich Landau
(Born January 22, 1908: Died April 1, 1968)
Soviet physicist who worked in such fields as low-temperature physics, atomic and nuclear physics, and solid-state, stellar-energy, and plasma physics. Several physics terms bear his name. He was awarded the 1962 Nobel Prize for Physics for his theory to explain the peculiar superfluid behaviour of liquid helium at very low temperature (2.18 K). Landau's further contributions are partly reflected in such terms as Landau diamagnetism and Landau levels in solid-state physics, Landau damping in plasma physics, the Landau energy spectrum in low-temperature physics, or Landau cuts in high-energy physics.

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