Walter Bothe

Walter Bothe

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Walter Bothe was born at Oranienburg, Germany, on 8th January, 1891. He studied physics under Max Planck at the University of Berlin (1908-12) and obtained his doctorate in 1914.

Bothe fought in the First World War during the First World War and was taken prisoner by the Russian Army on the Eastern Front. He was not released until 1920.

He taught at the Physikalisch-Technische Reinsanstalt and in 1929 he showed that the cosmic rays bombarding the Earth are composed not of photons but of massive particles.

Bothe was appointed professor of physics at the University of Giessen (1930-32), the University of Heidelberg (1932-34) and director of the Max Planck Institute for Medical Research.

Walter Bothe, who won the Nobel Prize for Physics in 1954, died in 1959.

Walther Bothe's contributions to the understanding of the wave-particle duality of light ☆

It is little known that during the birth of quantum mechanics Walther Bothe (1891–1957) published from mid-1923 to the end of 1926, partly together with Hans Geiger (1882–1945), as many as 20 papers, all dealing with light quanta (photons). Around half of the publications (11) are of experimental nature the rest deal with theoretical problems. This paper presents Walther Bothe's experimental and theoretical contributions to the understanding of the particle-wave duality of light in the mid-1920s, for which the interplay between experimental and theoretical ideas plays an essential role.

Early years [ edit | edit source ]

In 1913, Bothe joined the Physikalisch-Technische Reichsanstalt (PTR, Reich Physical and Technical Institute today, the Physikalisch-Technische Bundesanstalt), where he stayed until 1930. Hans Geiger had been appointed director of the new Laboratory for Radioactivity there in 1912. At the PTR, Bothe was an assistant to Geiger from 1913 to 1920, a scientific member of Geiger's staff from 1920 to 1927, and from 1927 to 1930 he succeeded Geiger as director of the Laboratory for Radioactivity. Ώ] ΐ] Α] Β]

In May 1914, Bothe volunteered for service in the German cavalry. He was taken prisoner by the Russians and incarcerated in Russia for five years. While there, he learned the Russian language and worked on theoretical physics problems related to his doctoral studies. He returned to Germany in 1920, with a Russian bride. Α]

Upon his return from Russia, Bothe continued his employment at the PTR under Hans Geiger in the Laboratory for Radioactivity there. In 1924, Bothe published on his coincidence method. Then and in the following years, he applied this method to the experimental study of the nuclear reactions, the Compton effect, and the wave-particle duality of light. Bothe's coincidence method and his applications of it earned him the Nobel Prize in Physics in 1954. Β] Γ] Δ] Ε]

In 1925, while still at the PTR, Bothe became a Privatdozent at the University of Berlin, which means that he had completed his Habilitation, and, in 1929, he became an ausserordentlicher Professor (extraordinarius professor) there. Ώ] ΐ]

In 1927, Bothe began the study of the transmutation of light elements through bombardment with alpha particles. From a joint investigation with H. Fränz and Heinz Pose in 1928, Bothe and Fränz correlated reaction products of nuclear interactions to nuclear energy levels. Α] Β] Ε]

In 1929, in collaboration with Werner Kolhörster and Bruno Rossi who were guests in Bothe's laboratory at the PTR, Bothe began the study of cosmic rays. The study of cosmic radiation would be conducted by Bothe for the rest of his life. Β] Ε]

In 1930, he became an ordentlicher Professor (ordinarius professor) and director of the physics department at the Justus Liebig-Universität Gießen. That year, working with Herbert Becker, Bothe bombarded beryllium, boron, and lithium with alpha particles from polonium and observed a new form of penetrating radiation. In 1932, James Chadwick identified this radiation as the neutron. Ώ] ΐ] Α]

Heidelberg [ edit | edit source ]

Walther Bothe, Stuttgart, 1935

In 1932, Bothe had succeeded Philipp Lenard as Director of the Physikalische und Radiologische Institut (Physical and Radiological Institute) at the University of Heidelberg. It was then that Rudolf Fleischmann became a teaching assistant to Bothe. When Adolf Hitler became Chancellor of Germany on 30 January 1933, the concept of Deutsche Physik took on more favor as well as fervor it was anti-Semitic and anti-theoretical physics, especially modern physics, including quantum mechanics and both atomic and nuclear physics. As applied in the university environment, political factors took priority over the historically applied concept of scholarly ability, Ζ] even though its two most prominent supporters were the Nobel Laureates in Physics Philipp Lenard Η] and Johannes Stark. ⎖] Supporters of Deutsche Physik launched vicious attacks against leading theoretical physicists. While Lenard was retired from the University of Heidelberg, he still had significant influence there. In 1934, Lenard had managed to get Bothe relieved of his directorship of the Physical and Radiological Institute at the University of Heidelberg, whereupon Bothe was able to become the Director of the Institut für Physik (Institute for Physics) of the Kaiser-Wilhelm Institut für medizinische Forschung (KWImF, Kaiser Wilhelm Institute for Medical Research today, the Max-Planck Institut für medizinische Forschung), in Heidelberg, replacing Karl W. Hauser, who had recently died. Ludolf von Krehl, Director of the KWImF, and Max Planck, President of the Kaiser-Wilhelm Gesellschaft (KWG, Kaiser Wilhelm Society, today the Max Planck Society), had offered the directorship to Bothe to ward off the possibility of his emigration. Bothe held the directorship of the Institute for Physics at the KWImF until his death in 1957. While at the KWImF, Bothe held an honorary professorship at the University of Heidelberg, which he held until 1946. Fleischmann went with Bothe and worked with him there until 1941. To his staff, Bothe recruited scientists including Wolfgang Gentner (1936–1945), Heinz Maier-Leibnitz (1936 - ?) - who had done his doctorate with the Nobel Laureate James Franck and was highly recommend by Robert Pohl and Georg Joos, and Arnold Flammersfeld (1939–1941). Also included on his staff were Peter Jensen and Erwin Fünfer. Ώ] ΐ] Α] ⎗] ⎘] ⎙] ⎚]

In 1938, Bothe and Gentner published on the energy dependence of the nuclear photo-effect. This was the first clear evidence that nuclear absorption spectra are accumulative and continuous, an effect known as the dipolar giant nuclear resonance. This was explained theoretically a decade later by physicists J. Hans D. Jensen, Helmut Steinwedel, Peter Jensen, Michael Goldhaber, and Edward Teller. Α]

Also in 1938, Maier-Leibniz built a Wilson cloud chamber. Images from the cloud chamber were used by Bothe, Gentner, and Maier-Leibniz to publish, in 1940, the Atlas of Typical Cloud Chamber Images, which became a standard reference for identifying scattered particles. Α] Ε]

1st German Cyclotron [ edit | edit source ]

By the end of 1937, the rapid successes Bothe and Gentner had with the building and research uses of a Van de Graaff generator had led them to consider building a cyclotron. By November, a report had already been sent to the President of the Kaiser-Wilhelm Gesellschaft (KWG, Kaiser Wilhelm Society today, the Max Planck Society), and Bothe began securing funds from the Helmholtz-Gesellschaft (Helmholtz Society today, the Helmholtz Association of German Research Centres), the Badischen Kultusministerium (Baden Ministry of Culture), I.G. Farben, the KWG, and various other research oriented agencies. Initial promises led to ordering a magnet from Siemens in September 1938, however, further financing then became problematic. In these times, Gentner continued his research on the nuclear photoeffect, with the aid of the Van de Graaff generator, which had been upgraded to produce energies just under 1 MeV. When his line of research was completed with the 7 Li (p, gamma) and the 11 B (p, gamma) reactions, and on the nuclear isomer 80 Br, Gentner devoted his full effort to the building of the planned cyclotron. ⎛]

In order to facilitate the construction of the cyclotron, at the end of 1938 and into 1939, with the help of a fellowship from the Helmholtz-Gesellschaft, Gentner was sent to Radiation Laboratory of the University of California (today, the Lawrence Berkeley National Laboratory) in Berkeley, California. As a result of the visit, Gentner formed a cooperative relationship with Emilio G. Segrè and Donald Cooksey. ⎛]

After the armistice between France and Germany in the summer of 1940, Bothe and Gentner received orders to inspect the cyclotron Frédéric Joliot-Curie had built in Paris. While it had been built, it was not yet operational. In September 1940, Gentner received orders to form a group to put the cyclotron into operation. Hermann Dänzer from the University of Frankfurt participated in this effort. While in Paris, Gentner was able to free both Frédéric Joliot-Curie and Paul Langevin, who had been arrested and detained. At the end of the winter of 1941/1942, the cyclotron was operational with a 7-MeV beam of deuterons. Uranium and thorium were irradiated with the beam, and the byproducts were sent to Otto Hahn at the Kaiser-Wilhelm Institut für Chemie (KWIC, Kaiser Wilhelm Institute for Chemistry, today, the Max Planck Institute for Chemistry), in Berlin. In mid-1942, Gentner's successor in Paris, was Wolfgang Riezler from Bonn. ⎛] ⎜] ⎝]

It was during 1941 that Bothe had acquired all the necessary funding to complete construction of the cyclotron. The magnet was delivered in March 1943, and the first beam of deuteron was emitted in December. The inauguration ceremony for the cyclotron was held on 2 June 1944. While there had been other cyclotrons under construction, Bothe's was the first operational cyclotron in Germany. ΐ] ⎛]

Uranium Club [ edit | edit source ]

The German nuclear energy project, also known as the Uranverein (Uranium Club), began in the spring of 1939 under the auspices of the Reichsforschungsrat (RFR, Reich Research Council) of the Reichserziehungsministerium (REM, Reich Ministry of Education). By 1 September, the Heereswaffenamt (HWA, Army Ordnance Office) squeezed out the RFR and took over the effort. Under the control of the HWA, the Uranverein had its first meeting on 16 September. The meeting was organized by Kurt Diebner, advisor to the HWA, and held in Berlin. The invitees included Walther Bothe, Siegfried Flügge, Hans Geiger, Otto Hahn, Paul Harteck, Gerhard Hoffmann, Josef Mattauch, and Georg Stetter. A second meeting was held soon thereafter and included Klaus Clusius, Robert Döpel, Werner Heisenberg, and Carl Friedrich von Weizsäcker. With Bothe being one of the principals, Wolfgang Gentner, Arnold Flammersfeld, Rudolf Fleischmann, Erwin Fünfer, and Peter Jensen were soon drawn into work for the Uranverein. Their research was published in the Kernphysikalische Forschungsberichte (Research Reports in Nuclear Physics) see below the section Internal Reports. For the Uranverein, Bothe, and up to 6 members from his staff by 1942, worked on the experimental determination of atomic constants, the energy distribution of fission fragments, and nuclear cross sections. Bothe's experimental results on the absorption of neutrons in graphite were central in the German decision to favor heavy water as a neutron moderator. ⎞] ⎟] ⎠]

By late 1941 it was apparent that the nuclear energy project would not make a decisive contribution to ending the war effort in the near term. HWA control of the Uranverein was relinquished to the RFR in July 1942. The nuclear energy project thereafter maintained its kriegswichtig (important for the war) designation and funding continued from the military. However, the German nuclear power project was then broken down into the following main areas: uranium and heavy water production, uranium isotope separation, and the Uranmaschine (uranium machine, i.e., nuclear reactor). Also, the project was then essentially split up between nine institutes, where the directors dominated the research and set their own research agendas. Bothe's Institut für Physik was one of the nine institutes. The other eight institutes or facilities were: the Institute for Physical Chemistry at the Ludwig Maximilian University of Munich, the HWA Versuchsstelle (testing station) in Gottow, the Kaiser-Wilhelm-Institut für Chemie, the Physical Chemistry Department of the University of Hamburg, the Kaiser-Wilhelm-Institut für Physik, the Second Experimental Physics Institute at the Georg-August University of Göttingen, the Auergesellschaft, and the II. Physikalisches Institut at the University of Vienna. ⎡] ⎢] ⎣] ⎤]

Post WW II [ edit | edit source ]

From 1946, to 1957, in addition to his position at the KWImF, Both was an ordentlicher Professor (ordinarius professor) at the University of Heidelberg. Ώ] ΐ]

At the end of World War II, the Allies had seized the cyclotron at Heidelberg. In 1949, its control was returned to Bothe. Ώ]

During 1956 and 1957, Bothe was a member of the Arbeitskreis Kernphysik (Nuclear Physics Working Group) of the Fachkommission II "Forschung und Nachwuchs" (Commission II "Research and Growth") of the Deutschen Atomkommission (DAtK, German Atomic Energy Commission). Other members of the Nuclear Physics Working Group in both 1956 and 1957 were: Werner Heisenberg (chairman), Hans Kopfermann (vice-chairman), Fritz Bopp, Wolfgang Gentner, Otto Haxel, Willibald Jentschke, Heinz Maier-Liebnitz, Josef Mattauch, Wolfgang Riezler, Wilhelm Walcher, and Carl Friedrich von Weizsäcker. Wolfgang Paul was also a member of the group during 1957. ⎥]

At the end of 1957, Gentner was in negotiations with Otto Hahn, President of the Max-Planck Gesellschaft (MPG, Max Planck Society, successor of the Kaiser-Wilhelm Gesellschaft), and with the Senate of the MPG to establish a new institute under their auspices. Essentially, Walther Bothe's Institut für Physik at the Max-Planck Institut für medizinische Forschung, in Heidelberg, was to be spun off to become a full fledged institute of the MPG. The decision to proceed was made in May 1958. Gentner was named the director of the Max-Planck Institut für Kernphysik (MPIK, Max Planck Institute for Nuclear Physics) on 1 October, and he also received the position as an ordentlicher Professor (ordinarius professor) at the University of Heidelberg. Bothe had not lived to see the final establishment of the MPIK, as he had died in February of that year. ⎛] ⎦]

Bothe was a German patriot who did not give excuses for his work with the Uranverein. However, Bothe's impatience with National Socialist policies in Germany brought him under suspicion and investigation by the Gestapo. Α]

Timeline for the History of Nuclear Chemistry

In 1895, Wilhelm Röntgen studied cathode radiation, which occurs when an electrical charge is applied to two metal plates inside a glass tube filled with rarefied gas. Although the apparatus was screened off, he noticed a faint light on light-sensitive screens that happened to be close by. Further investigations revealed that this was caused by a penetrating, previously unknown type of radiation. X-ray radiation became a powerful tool for physical experiments and examining the body's interior. He received a Nobel Peace prize for his work with atomic physics and x-rays.

Henri Becquerel

In 1896, his previous work was overshadowed by his discovery of the phenomenon of natural radioactivity. When Henri Becquerel investigated the newly discovered X-rays in 1896, it led to studies of how uranium salts are affected by light. By accident, he discovered that uranium salts spontaneously emit a penetrating radiation that can be registered on a photographic plate. Further studies made it clear that this radiation was something new and not X-ray radiation: he had discovered a new phenomenon, radioactivity.

Pierre Curie

The 1896 discovery of radioactivity by Henri Becquerel inspired Marie and Pierre Curie to further investigate this phenomenon. They examined many substances and minerals for signs of radioactivity. They found that the mineral pitchblende was more radioactive than uranium and concluded that it must contain other radioactive substances. From it they managed to extract two previously unknown elements, polonium and radium, both more radioactive than uranium.

Marie Curie

She was a Polish and Naturalized-French physicist and chemist who conducted pioneering research on radioactivity. She was the first woman to win a Nobel Prize and the first person and only woman to win twice. She discovered that uranium rays caused the air around a sample to conduct electricity. She helped disprove that ancient assumption that atoms were indivisible.

Hans Geiger

He is known as the co-inventor of the detector component of the Geiger counter and for the Geiger–Marsden experiment which discovered the atomic nucleus. In 1911 Geiger and John Mitchell Nuttall discovered the Geiger–Nuttall law (or rule) and performed experiments that led to Rutherford's atomic model

James Chadwick

When Herbert Becker and Walter Bothe directed alpha particles (helium nuclei) at beryllium in 1930, a strong, penetrating radiation was emitted. One hypothesis was that this could be high-energy electromagnetic radiation. In 1932, however, James Chadwick proved that it consisted of a neutral particle with about the same mass as a proton. Ernest Rutherford had earlier proposed that such a particle might exist in atomic nuclei. Its existence now proven, it was called a "neutron".

Leo Szilard

He conceived the nuclear chain reaction in 1933, patented the idea of a nuclear reactor with Enrico Fermi, and in late 1939 wrote the letter for Albert Einstein's signature that resulted in the Manhattan Project that built the atomic bomb. He also helped to discover a means of isotope separation. This method became known as the Szilard–Chalmers effect, and was widely used in the preparation of medical isotopes.

Enrico Fermi

In 1934, he evolved the ß-decay theory, coalescing previous work on radiation theory with Pauli's idea of the neutrino. He demonstrated that nuclear transformation occurs in almost every element subjected to neutron bombardment. This work resulted in the discovery of slow neutrons that same year, leading to the discovery of nuclear fission and the production of elements lying beyond what was until then the Periodic Table. He helped direct the first controlled nuclear chain reaction.

J. Robert Oppenheimer

Oppenheimer was among those credited with being the "father of the atomic bomb" for their role in the Manhattan Project, the World War II undertaking that developed the first nuclear weapons used in the atomic bombings of Hiroshima and Nagasaki. As a scientist, Oppenheimer is remembered by his students and colleagues as being a brilliant researcher and engaging teacher who was the founder of modern theoretical physics in the United States.

Edward Teller and Stanislaw Ulam

The Teller–Ulam design is the technical concept behind modern thermonuclear weapons, also known as hydrogen bombs. The Teller–Ulam design was for many years considered one of the top nuclear secrets, and even today it is not discussed in any detail by official publications with origins "behind the fence" of classification.

Willard Frank Libby

Carbon is a fundamental component in all living material. In nature there are two variants, or isotopes: carbon-12, which is stable, and carbon-14, which is radioactive. Carbon-14 forms in the atmosphere when acted upon by cosmic radiation and then deteriorates. When an organism dies and the supply of carbon from the atmosphere ceases, the content of carbon-14 declines through radioactive decay at a fixed rate. In 1949 Willard Libby developed a method for applying this to determine the age of fossils and archeological relics. He also received a Nobel Peace Prize for his work in nuclear chemistry.

Walter Bothe, Physiker, Atomphysiker, D - undatiert

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Walther Wilhelm Georg Bothe

Walther Bothe was a brilliant German nuclear physicist who, in 1954, won the physics Nobel Prize with Max Born “for the coincidence method and his discoveries made therewith”.

His Early Life and Education

Walther Wilhelm Georg Bothe was born on the 8th of January, 1891 to Charlotte Hartung and Fritz Bothe, a merchant. He was from Oranienberg, a town in Brandenburg, Germany.

From 1908 to 1912 he studied physics, chemistry and mathematics at the University of Berlin. He continued his education and studied for a doctorate, under the brilliant physicist Max Planck, which he was awarded in 1914. His thesis concerned the molecular theory of refraction, reflection, dispersion, and extinction.

Career Path

During World War I, Bothe was a machine gunner in the German army. In 1915 was captured by the Russians and spent time in Siberia during his captivity. Being the consummate scientist, he chose to spend his time as a prisoner of war learning how to speak and read Russian and continued his research studies. He also found a wife.

Returning to Germany in 1920, with his Russian bride, Barbara Below, and he obtained a position at the radioactive laboratory of Physikalisch-Technische Reichsanstalt. He became director of the laboratory in 1927. Here he collaborated with Hans Geiger and made his most important discoveries.

During this time, Bothe was also a lecturer at the University of Berlin.

In 1931 he took a professorship at the University of Giessen and in 1934 he became director of the Physics Institute of the Max Planck Institute for Medical Research at Heidelberg, where he remained until his death.

Bothe also moved his work to the University of Heidelberg in 1934 and was a professor there from 1946 to 1957.

Major Achievements

Between 1923 and 1926 Bothe concentrated much of his work on the scattering of alpha and beta rays.

Bothe worked with Hans Geiger and together they researched the emission of electrons by x-rays to test Bohr’s quantum model of the atom. They used two Geiger counter tubes, one to detect the scattered x-rays and the other to detect the recoiling electrons, to study the coincidences of individual Compton collisions.

In 1924, Bothe then devised a coincidence circuit – this circuit was considered the first AND logic gate. Running several counters in coincidence enabled the scientists to calculate the angular momentum of a particle and thus they demonstrated that momentum and energy are conserved at the atomic level.

Four years later in 1929, Bothe researched the Compton Effect further and used the coincidence method again with Werner Kolhörster to establish the particle nature of cosmic rays. Their experiments showed that the rays were composed of gamma rays and high energy particles.

Bothe was also interested in the transmutation of elements and in 1930, with Herbert Becker, he obtained a never-before-seen form of radiation from beryllium that had been bombarded by alpha particles. This study led Sir James Chadwick to discover the neutron in 1932.

He supervised the construction of the first German cyclotron, a device that can accelerate particles (like protons) along a spiral path, which was completed in 1943.

During the Second World War he worked on nuclear energy research.

After the war, Bothe used the German cyclotron to produce radioactive isotopes for his medical studies.

In addition to numerous scientific articles, he published “Nuclear physics and Cosmic Rays” in 1948.

He was awarded the Max Planck medal in 1953.

Bothe received the 1954 Nobel Prize in Physics “for the coincidence method and his discoveries made therewith” together with Max Born.

Personal Life

Bothe married Barbara Below from Moscow in 1920 and they had two daughters.

He enjoyed vacationing in the mountains and would often paint using oils or watercolors. He was also an excellent pianist and he enjoyed listening to Beethoven and Bach.

Walther Wilhelm Georg Bothe died on 8 February 1957, aged 66 in Heidelberg, Germany.

NAACP Investigator

A 1916 graduate of Atlanta University, White worked in insurance before protesting cuts in funding for African American students in Atlanta. After starting a local chapter of the National Association for the Advancement of Colored People, he became a member of the organization&aposs national team in 1918, when executive secretary James Weldon Johnson selected White to be an assistant secretary.

White began investigating lynchings in the South, a terrifyingly regular occurrence. His appearance, paired with his Southern accent, meant he was able to obtain responses when he questioned politicians and suspected lynchers. The information he uncovered was then broadcast by the NAACP.

White looked into more than 40 lynchings and eight race riots, and each investigation was a dangerous endeavor. On one occasion in 1919, the fact that White was in fact an African American was discovered. Tipped off to the danger, he quickly fled town to avoid being attacked himself.

This Month in Physics History

By 1920, physicists knew that most of the mass of the atom was located in a nucleus at its center, and that this central core contained protons. In May 1932 James Chadwick announced that the core also contained a new uncharged particle, which he called the neutron.

Chadwick was born in1891 in Manchester, England. He was a shy child from a working class family, but his talents caught his teachers’ attention, and he was sent to study physics at the University of Manchester, where he worked with Ernest Rutherford on various radioactivity studies.

In 1914, Chadwick decided to travel to Germany to study with Hans Geiger. Unfortunately, not long after he arrived, WWI broke out and Chadwick ended up spending the next four years in a prison camp there. This did not entirely stop his scientific studies. To keep from being bored, he and some fellow prisoners formed a science club, lectured to each other, and managed to convince the guards to let them set up a small lab. Though many chemicals were hard to get hold of, Chadwick even found a type of radioactive toothpaste that was on the market in Germany at the time, and managed to persuade the guards to supply him with it. Using some tin foil and wood he built an electroscope and did some simple experiments.

After the war, Chadwick returned to England, where he finished his PhD in Cambridge in 1921 with Rutherford, who was then Director of Cambridge University’s Cavendish laboratory. Chadwick was able to continue to work on radioactivity, now with more sophisticated apparatus than tin foil and toothpaste. In 1923, Chadwick was appointed assistant director of Cavendish Laboratory.

Rutherford had discovered the atomic nucleus in 1911, and had observed the proton in 1919. However, it seemed there must be something in the nucleus in addition to protons. For instance, helium was known to have an atomic number of 2 but a mass number of 4. Some scientists thought there were additional protons in the nucleus, along with an equal number of electrons to cancel out the additional charge. In 1920, Rutherford proposed that an electron and a proton could actually combine to form a new, neutral particle, but there was no real evidence for this, and the proposed neutral particle would be difficult to detect.

Chadwick went on to work on other projects, but kept thinking about the problem. Around 1930, several researchers, including German physicist Walter Bothe and his student Becker had begun bombarding beryllium with alpha particles from a polonium source and studying the radiation emitted by the beryllium as a result. Some scientists thought this highly penetrating radiation emitted by the beryllium consisted of high energy photons. Chadwick had noticed some odd features of this radiation, and began to think it might instead consist of neutral particles such as those Rutherford had proposed.

One experiment in particular caught his attention: Frédéric and Irène Joliot-Curie had studied the then-unidentified radiation from beryllium as it hit a paraffin wax target. They found that this radiation knocked loose protons from hydrogen atoms in that target, and those protons recoiled with very high velocity.

Joliot-Curie believed the radiation hitting the paraffin target must be high energy gamma photons, but Chadwick thought that explanation didn’t fit. Photons, having no mass, wouldn’t knock loose particles as heavy as protons from the target, he reasoned. In 1932, he tried similar experiments himself, and became convinced that the radiation ejected by the beryllium was in fact a neutral particle about the mass of a proton. He also tried other targets in addition to the paraffin wax, including helium, nitrogen, and lithium, which helped him determine that the mass of the new particle was just slightly more than the mass of the proton.

Chadwick also noted that because the neutrons had no charge, they penetrated much further into a target than protons would.

In February 1932, after experimenting for only about two weeks, Chadwick published a paper titled “The Possible Existence of a Neutron,” in which he proposed that the evidence favored the neutron rather than the gamma ray photons as the correct interpretation of the mysterious radiation. Then a few months later, in May 1932, Chadwick submitted the more definite paper titled “The Existence of a Neutron.”

By 1934 it had been established that the newly discovered neutron was in fact a new fundamental particle, not a proton and an electron bound together as Rutherford had originally suggested.

The discovery of neutron quickly changed scientists’ view of the atom, and Chadwick was awarded the Nobel Prize in 1935 for the discovery. Scientists soon realized that the newly discovered neutron, as an uncharged but fairly massive particle, could be used to probe other nuclei. It didn’t take long for scientists to find that hitting uranium with neutrons resulted in the fission of the uranium nucleus and the release of incredible amounts of energy, making possible nuclear weapons. Chadwick, whose discovery of the neutron had paved the way for the atomic bomb, worked on the Manhattan Project during WWII. He died in 1974.

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Walther Bothe

Walther Wilhelm Georg Bothe 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 Physical and Technical Institute (PTR), where he remained until 1930, the latter few years as the director of the laboratory. He served in the military during World War I from 1914, and he was a prisoner of war of the Russians, returning to Germany in 1920. Upon his return to the laboratory, he developed and applied coincidence methods to the study of nuclear reactions, the Compton effect, cosmic rays, and the wave-particle duality of radiation, for which he would receive the Nobel Prize in Physics in 1954.

In 1930 he became a full professor and Walther Wilhelm Georg Bothe 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 Physical and Technical Institute (PTR), where he remained until 1930, the latter few years as the director of the laboratory. He served in the military during World War I from 1914, and he was a prisoner of war of the Russians, returning to Germany in 1920. Upon his return to the laboratory, he developed and applied coincidence methods to the study of nuclear reactions, the Compton effect, cosmic rays, and the wave-particle duality of radiation, for which he would receive the Nobel Prize in Physics in 1954.

In 1930 he became a full professor and director of the physics department at the University of Giessen. In 1932, he became director of the Physical and Radiological Institute at the University of Heidelberg. He was driven out of this position by elements of the deutsche Physik movement. To preclude his emigration from Germany, he was appointed director of the Physics Institute of the Kaiser Wilhelm Institute for Medical Research (KWImF) in Heidelberg. There, he built the first operational cyclotron in Germany. Furthermore, he became a principal in the German nuclear energy project, also known as the Uranium Club, which was started in 1939 under the supervision of the Army Ordnance Office.

In 1946, in addition to his directorship of the Physics Institute at the KWImf, he was reinstated as a professor at the University of Heidelberg. From 1956 to 1957, he was a member of the Nuclear Physics Working Group in Germany.

In the year after Bothe's death, his Physics Institute at the KWImF was elevated to the status of a new institute under the Max Planck Society and it then became the Max Planck Institute for Nuclear Physics. Its main building was later named Bothe laboratory. . more

Then & Now - The AdP section dedicated to the history of physics

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Tilman Sauer, Johannes Gutenberg University Mainz, Germany

Outgoing Founding Editors of Then & Now:

Dieter Hoffmann is Research Fellow at the Max Planck Institute for the History of Science (MPIWG) and adjunct Professor at the Humboldt University in Berlin (since 2014 retired). He graduated from Humboldt University in Physics where he earned his PhD and habilitation in History of Science in 1976 and 1989, respectively. From 1976 to 1990 he was a Research Fellow at the GDR Academy of Sciences, and subsequently at the Physikalisch-Technische Bundesanstalt, and a Humboldt Fellow at Stuttgart, Harvard, and Cambridge. His research is focused on the history of science and physics in the 19th and 20th century, in particular on biographies and institutional histories.
Christian Joas is the Director of the Niels Bohr Archive in Copenhagen, Denmark. After completing his PhD in theoretical physics at Freie Universität Berlin in 2007, he was a Postdoctoral Research Fellow at the Max Planck Institute for the History of Science and a Research Scholar at the Fritz Haber Institute of the Max Planck Society. From 2012-2017, he was Assistant Professor in the History of Science at LMU Munich’s History Department. His research focuses on the history of 20th century physics, especially on the genesis and applications of quantum mechanics, as well as on the history of processes of knowledge transfer in the modern physical sciences, e.g., between high-energy and condensed-matter physics, or between physics and chemistry.

Wilhelm Foerster's Role in the Metre Convention of 1875 and in the Early Years of the International Committee for Weights and Measures
Terry Quinn
Ann. Phys. (Berlin) 531, No. 5, 1800355 (2019)
(part of the special issue “The Revised SI: Fundamental Constants, Basic Physics and Units”)

Watch the video: Dont Starve Together: Constant Companion Walter Animated Short


  1. Adom

    You are certainly entitled

  2. Davison

    Test and niipet!

  3. Chigaru

    Yes, it seemed like that to me too.

  4. Anwealda

    It seems like a good idea to me. I agree with you.

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