GC: n

CT: Exploring the nature of the atom.
Uranium was discovered in 1789 by Martin Klaproth, a German chemist, and named after the planet Uranus.
Ionising radiation was discovered by Wilhelm Rontgen in 1895, by passing an electric current through an evacuated glass tube and producing continuous X-rays. Then in 1896 Henri Becquerel found that pitchblende (an ore containing radium and uranium) caused a photographic plate to darken. He went on to demonstrate that this was due to beta radiation (electrons) and alpha particles (helium nuclei) being emitted. Villard found a third type of radiation from pitchblende: gamma rays, which were much the same as X-rays. Then in 1896 Pierre and Marie Curie gave the name 'radioactivity' to this phenomenon, and in 1898 isolated polonium and radium from the pitchblende. Radium was later used in medical treatment. In 1898 Samuel Prescott showed that radiation destroyed bacteria in food.
In 1902 Ernest Rutherford showed that radioactivity as a spontaneous event emitting an alpha or beta particle from the nucleus created a different element. He went on to develop a fuller understanding of atoms and in 1919 he fired alpha particles from a radium source into nitrogen and found that nuclear rearrangement was occurring, with formation of oxygen. Niels Bohr was another scientist who advanced our understanding of the atom and the way electrons were arranged around its nucleus through to the 1940s.
By 1911 Frederick Soddy discovered that naturally-radioactive elements had a number of different isotopes (radionuclides), with the same chemistry. Also in 1911, George de Hevesy showed that such radionuclides were invaluable as tracers, because minute amounts could readily be detected with simple instruments.
In 1932 James Chadwick discovered the neutron. Also in 1932 Cockcroft and Walton produced nuclear transformations by bombarding atoms with accelerated protons, then in 1934 Irene Curie and Frederic Joliot found that some such transformations created artificial radionuclides. The next year Enrico Fermi found that a much greater variety of artificial radionuclides could be formed when neutrons were used instead of protons.
Fermi continued his experiments, mostly producing heavier elements from his targets, but also, with uranium, some much lighter ones. At the end of 1938 Otto Hahn and Fritz Strassmann in Berlin showed that the new lighter elements were barium and others which were about half the mass of uranium, thereby demonstrating that atomic fission had occurred. Lise Meitner and her nephew Otto Frisch, working under Niels Bohr, then explained this by suggesting that the neutron was captured by the nucleus, causing severe vibration leading to the nucleus splitting into two not quite equal parts. They calculated the energy release from this fission as about 200 million electron volts. Frisch then confirmed this figure experimentally in January 1939.
This was the first experimental confirmation of Albert Einstein's paper putting forward the equivalence between mass and energy, which had been published in 1905.

S: WNA - http://www.world-nuclear.org/info/current-and-future-generation/outline-history-of-nuclear-energy/(external link) (last access: 24 November 2015)

N: 1. Word composed by the word-forming element α, not and τομον, a cutting. From Greek atomos, which means "uncut, indivisible". It is an ancient term of philosophical speculation (in Leucippus, Democritus), revived 1805 by British chemist John Dalton. Term and definition standardized by ISO in 1997.
2. Atoms contain three sub-atomic particles called protons, neutrons and electrons. The protons and neutrons are found in the nucleus at the centre of the atom. The nucleus is very much smaller than the atom as a whole. The electrons are arranged in energy levels around the nucleus.
The number of electrons in an atom is always the same as the number of protons, so atoms are electrically neutral overall. Atoms can lose or gain electrons. When they do, they form charged particles called ions:
  • if an atom loses one or more electrons, it becomes a positively charged ion
  • if an atom gains one or more electrons, it becomes a negatively charged ion
3. Atoms are tiny units that make up all matter in the universe. Energy is what holds the nucleus together. There is a huge amount of power in an atoms dense nucleus. In fact, the power that holds the nucleus together is officially called the "strong force.
Nuclear energy can be used to create electricity, but it must first be released from the atom. In nuclear fission, atoms are split to release the energy.
4. Atomic absorption is a process involving the absorption by free atoms of an element of light at a wavelength specific to that element, or put more simply, it is a means by which the concentration of metals can be measured.
In Atomic Spectrometry, emission, absorption and fluorescence, energy is put into the atom population by thermal, electromagnetic, chemical and electrical forms of energy and are converted to light energy by various atomic and electronic processes before measurement. Atomic Absorption Spectrometry is useful not only for the identification but also the quantitative determination of many elements present in samples. The technique is specific, in that individual elements in each sample can be reliably identified and it is sensitive, enabling small amounts of an element to be detected down to around 1μg g-1 (1ppm) i.e. one part in one million using straightforward flame procedures. The absorption of energy by atoms follows well known physical laws which provide us with a basis for quantitative analytical chemistry.
5. Cultural Interrelation: We can mention A Boy And His Atom: The World's Smallest Movie (2012) by IBM and The Martian (2015) by NASA.

S: 1. OED - http://www.etymonline.com/index.php?term=atom(external link) (last access: 24 November 2015); TERMIUM PLUS - http://goo.gl/7VSPHZ(external link) (last access: 27 November 2015). 2. BBC - http://www.bbc.co.uk/education/guides/z44xsbk/revision/3(external link) (last access: 24 November 2015). 3. National Geographic - http://education.nationalgeographic.org/encyclopedia/nuclear-energy/(external link) (last access: 24 November 2015). 4. THERMOSCIENT - http://goo.gl/j7U8Xc(external link) (last access: 24 November 2015). 5. IBM - http://www.research.ibm.com/articles/madewithatoms.shtml#fbid=sRz_mg8tdIX(external link) (last access: 27 November 2015); NASA - https://www.nasa.gov/feature/nine-real-nasa-technologies-in-the-martian(external link) (last access: 27 November 2015).


CR: absorption, adsorption, electron (EN), ion (EN), lepton (EN), linear accelerator, molecule, muon (EN), neutrino (EN), nitrogen dioxide, nitrogen oxide, nuclear energy, proton (EN), quark (EN), synchrotron, X-rays.


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