James Chadwick( English physicist, Nobel Prize in Physics, 1935)
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Biography James Chadwick
October 20, 1891, Mr.. - July 24, 1974
English physicist James Chadwick was born in g. Bollingtone, near Manchester. He was the eldest of four children of John Joseph Chadwick, owner of a laundry, and Ann Mary (Knowles) Chadwick. After graduating from the local primary school, he enrolled at the Manchester Municipal Secondary School, where distinguished achievements in mathematics. In 1908, Mr.. CH. enrolled in the University of Manchester, intending to study mathematics, but a misunderstanding with him interviewed on physics. Too modest to point out the mistake, he listened carefully to the questions he was asked, and decided to change specialization. Three years later he graduated with honors in physics.
In 1911, Mr.. CH. began graduate work under the guidance of Ernest Rutherford in the Physical Laboratory in Manchester. It was at this time, experiments on the scattering of alpha particles (which are considered as charged atoms of helium), . dropped through a thin metal foil, . Rutherford led to the assumption, . that the entire mass of the atom is concentrated in a dense positively charged nucleus, . surrounded by negatively charged electrons, . that, . is known, . have relatively low mass,
. CH. received a master's degree in Manchester in 1913, . and in the same year, . becoming the owner grants, . he went to Germany, . to study the radioactivity under the leadership of Hans Geiger (former assistant to Rutherford) in the State Physical-Technical Institute in Berlin,
. When in 1914. the First World War, W. was interned as a British citizen and more than 4 years spent in a camp for civilians in Rulebene. Although H. suffered from the harsh conditions, gnawing his health, he participated in a scientific society, founded by his companions in misfortune. This group has received support from some German scientists, including Walter Nernst, with which H. met, being interned.
W. returned to Manchester in 1919. Shortly before that Rutherford discovered that the bombardment of alpha particles (which are now viewed as a helium nucleus) can cause the disintegration of the nitrogen atom in the lighter nuclei of other elements. Several months later, Rutherford was elected to the post of director of the Cavendish Laboratory at Cambridge University, and he invited W. follow him. CH. received a scholarship to Uollestona Gonvill-end-Kayus College, Cambridge, and was able to work with Rutherford, while continuing to experiment with alpha particles. They found that the bombardment of nuclei often formed that, apparently, is the nuclei of hydrogen, the lightest of the elements. The nucleus of hydrogen carried a positive charge equal in magnitude to the negative charge of the electron, but have mass, about 2 thousand. times the mass of the electron. Rutherford later called it the proton. It became clear that the atom as a whole was electrically neutral, since the number of protons in its nucleus was equal to the number of electrons surrounding the nucleus. However, this number of protons have not agreed with the mass of the atoms, except for the simplest case of hydrogen. To resolve this discrepancy, Rutherford proposed in 1920. the idea that the nucleus may contain an electrically neutral particles, which he later called neutrons, formed compound electron and proton. An opposing view was that atoms contain electrons both outside and inside the nucleus and that the negative charge of nuclear electrons simply neutralizes the charge of the proton. Then the proton would give a full contribution to the total mass of the atom, and their total charge would be just so, to neutralize the charge of electrons surrounding the nucleus. While the assumption of Rutherford that there is a neutral particle, treated with respect, but there was no experimental confirmation of this idea.
W. received his doctorate in physics at Cambridge in 1921. and was elected a member of the Academic Council Gonvill-end-Kayus College. Two years later he became deputy director of the Cavendish Laboratory. Until the late 20-ies. he studied atomic phenomena such as the artificial disintegration of nuclei of light elements under the effect of bombardment by alpha particles and the spontaneous emission of beta particles (electrons). In this process, he pondered how could confirm the existence of a neutral particle Rutherford, but the crucial research that allowed it to have been held in Germany and France.
In 1930. German physicists Walther Bothe and Hans Becker discovered that the bombardment of some light elements by alpha particles resulting radiation, which has a special penetrating power, which they took for gamma-rays. Gamma rays for the first time became known as the radiation generated by radioactive nuclei. They had more than X-rays, penetrating power, because they have a shorter wavelength. However, some puzzling results, especially when, as a target for bombing used beryllium. The radiation in the direction of the incident flux of alpha particles have greater penetrating power than the inverse radiation. CH. suggested that beryllium emits a stream of neutral particles rather than gamma-rays. In 1932, Mr.. French physicist Frц╘dц╘ric Joliot and Irene Curie, folio, investigating penetrating radiation of beryllium, various absorbing materials placed between the bombarded beryllium and ionization chamber, serves as registrar of radiation. When a sink they took paraffin (a substance rich in hydrogen), we found an increase rather than decrease the radiation escaping from the paraffin. Checking led them to conclude that an increase in radiation due to the protons (hydrogen nuclei), knocked out of the paraffin by ionizing radiation. They suggested, . that eject protons from collisions with quanta (discrete units of energy) an unusually powerful gamma-ray, . just as electrons are knocked out by a collision with X-rays (Compton effect) in the experiment, . first conducted by Arthur X,
W. rapidly repeated and extended the experiment, . French pair held, . and found, . thick lead plate that does not have any noticeable effect on the emission of beryllium, . without weakening it and causing the secondary radiation, . an indication of its high penetrating power,
. However, the paraffin again gave an additional stream of fast protons. CH. made the test, which confirmed that this is indeed the protons, and determined their energy. Then he showed that by all indications, it is most unlikely that the collisions of alpha particles with beryllium can occur gamma-rays with sufficient energy to knock protons out of wax so fast. So he left the idea of gamma-rays, and focused on the neutron hypothesis. Accept the existence of the neutron, it showed that the capture of an alpha particle beryllium nucleus can form the nucleus of the element carbon, and released one neutron. The same thing he has done and with boron - another element which generates penetrating radiation when bombarded by alpha rays. Alpha-particle and the nucleus of boron join to form the nitrogen nucleus and a neutron. The high penetration power of neutron flux arises because the neutron has no charge and, therefore, the motion in a substance not influenced by the electric fields of atoms and interact with nuclei only in direct clashes. The neutron also requires less energy than the gamma-ray to knock out a proton, because it has great momentum than the quantum of electromagnetic radiation of the same energy. The fact that the radiation of beryllium in the straight direction is more intrusive, can be attributed to the preferred emission of neutrons in the direction of the momentum of the incident flux of alpha particles.
W. Rutherford also confirmed the hypothesis that the mass of the neutron should be equal to the mass of the proton by analyzing the energy exchange between neutrons and protons, knocked out of the matter as if we were talking about the collision of billiard balls. The energy is particularly effective because their masses are almost identical. He also examined the tracks of the nitrogen atoms subjected to collisions with neutrons, in the condensation chamber - a device, invented CH.T.R. Wilson. The vapor condenses in the condensation chamber along the electrified track, which leaves the ionizing particle in the interaction with the vapor molecules. Track is visible, although the particle and the invisible. Since the neutron has no direct ionizing effects, it should not be seen. CH. had to set the properties of a neutron on the track, leave the collision with the nitrogen atom. It turned out that the mass of the neutron by 1,1% higher than the mass of the proton.
Experiments and calculations done by other physicists, have confirmed the findings of Charles, and the existence of the neutron was quickly recognized. Shortly thereafter, Werner Heisenberg showed that the neutron can not be a mixture of proton and electron, and is uncharged nuclear particles - subatomic third, or the elementary particles from those that were open. The proposed H. proof of the existence of the neutron in 1932. radically changed the picture of the atom and paved the way for further discoveries in physics. There was a neutron and practical application as a destroyer of the atom: in contrast to the positively charged proton, he is not repelled when approaching the nucleus.
'For the discovery of the neutron' W. was awarded in 1935. Nobel Prize in Physics. 'The existence of the neutron fully installed, . - Said Hans Pleyel from the Royal Swedish Academy of Sciences in his speech at the ceremony, . - With the result that scientists have come to the new concept of atomic structure, . which is in better agreement with the distribution of energy within the atomic nuclei,
. It became obvious that the neutron form one of the building bricks, which make up the atoms and molecules, and hence the whole material universe. "
W. passed in 1935. at Liverpool University, to create a new Center for Nuclear Physics Research. In Liverpool he followed the modernization of university equipment and supervised the construction of the cyclotron - Installations for the acceleration of charged particles.
When in 1939. World War II began, the British government appealed to the V. asking whether it is possible a nuclear chain reaction, and he began using the Liverpool cyclotron explore this possibility. The following year he joined the Modovskogo Committee, . small select group of eminent British scientists, . which made the optimistic conclusions about the possibility of Britain to build an atomic bomb, . and became the coordinator of the pilot programs to develop atomic weapons in Liverpool, . Cambridge and Bristol,
. Later, however, Britain decided to join the U.S. nuclear weapons program and sent its scientists engaged in nuclear research, in United States. From 1943 to 1945. CH. coordinated the efforts of British scientists who worked on Manhattan Project (a secret program to create the atomic bomb).
W. returned to the University of Liverpool in 1946. Two years later he withdrew from active scientific work and headed Gonvill-end-Kayus College. In 1958, Mr.. He moved to North Wales with his wife Eileen, nee Stewart-Brown, whom he married in 1925. They returned to Cambridge in 1969, to be closer to his twin daughters. CH. died 5 years later in Cambridge.
In addition to the Nobel Prize, W. Hughes won a medal (1932) and Copley Medal (1950) Royal Society Medal of Merit of the U.S. government (1946), Medal of the Franklin Institute Franklinovskogo (1951) and the Guthrie Medal Physical Institute in London (1967 g.). Received a knighthood in 1945, he was the owner of 9 honorary degrees from British universities and was a member of many scientific societies and academies in Europe and the United States.