It became clear from these experiments that there was a form of invisible radiation that could pass through paper and was causing the plate to react as if exposed to light. At first, it seemed as though the new radiation was similar to the then recently discovered X-rays. Further research by Becquerel, Ernest Rutherford, Paul Villard, Pierre Curie, Marie Curie, and others showed that this form of radioactivity was significantly more complicated. Rutherford was the first to realize that all such elements decay in accordance with the same mathematical exponential formula. Rutherford and his student Frederick Soddy were the first to realize that many decay processes resulted in the transmutation of one element to another.
History of discovery
Radioactive decay
Radioactive decay | History of discovery
Ernest Rutherford, Frederick Soddy Ernest Rutherford and his student Frederick Soddy Henri Becquerel Sorry. I cannot find the answer based on the context.
who was lise meitner?
user
She was an Austrian-Swedish physicist.
assistant
in which country did she live in her early days?
user
In the Leopoldstadt district of Vienna
assistant
any particular educational institution that she attended as a student?
user
University of Vienna
assistant
why did she have to flee from germany?
user
Because she lost her Austrian citizenship.
assistant
why?
user
Sorry. I cannot find the answer based on the context.
assistant
can you mention any of her contributions?
user
She completed the work on beta ray spectrum that she had begun with Hahn and Baeyer, and also her own study of the uranium decay chain.
assistant
could you please elaborate the last reaction?
user
It refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations - a.k.a. "radioactive cascade".
assistant
can you mention any health hazard caused by this decay?
user
The dangers are not immediately recognized.
assistant
who discovered this decay?
user
Subsequently, the radioactive displacement law of Fajans and Soddy was formulated to describe the products of alpha and beta decay.
Radioactive decay | History of discovery
It became clear from these experiments that there was a form of invisible radiation that could pass through paper and was causing the plate to react as if exposed to light. At first, it seemed as though the new radiation was similar to the then recently discovered X-rays. Further research by Becquerel, Ernest Rutherford, Paul Villard, Pierre Curie, Marie Curie, and others showed that this form of radioactivity was significantly more complicated. Rutherford was the first to realize that all such elements decay in accordance with the same mathematical exponential formula. Rutherford and his student Frederick Soddy were the first to realize that many decay processes resulted in the transmutation of one element to another.
Radioactive decay | History of discovery
Whilst at the Palmer Physical Laboratory at Princeton University from 1926–28, he discovered alpha decay via quantum tunnelling, together with Edward Condon and independently of George Gamow. In the early 1900s, radioactive materials were known to have characteristic exponential decay rates or half lives. At the same time, radiation emissions were known to have certain characteristic energies. By 1928, Gamow had solved the theory of the alpha decay of a nucleus via quantum tunnelling and the problem was also solved independently by Gurney and Condon. Gurney and Condon did not, however, produce the quantitative results achieved by Gamow in his work.
Ronald Wilfred Gurney | Radioactive decay processes
He found that a sample of this radioactive material of any size invariably took the same amount of time for half the sample to decay – its "half-life" (11½ minutes in this case). From 1900 to 1903, he was joined at McGill by the young chemist Frederick Soddy (Nobel Prize in Chemistry, 1921) for whom he set the problem of identifying the thorium emanations. Once he had eliminated all the normal chemical reactions, Soddy suggested that it must be one of the inert gases, which they named thoron (later found to be an isotope of radon). They also found another type of thorium they called Thorium X, and kept on finding traces of helium.
Ernest Rutherford | Scientific research
In the early 20th century, radioactive materials were known to have characteristic exponential decay rates, or half-lives. At the same time, radiation emissions were known to have certain characteristic energies. By 1928, Gamow in Göttingen had solved the theory of the alpha decay of a nucleus via tunnelling, with mathematical help from Nikolai Kochin. The problem was also solved independently by Ronald W. Gurney and Edward U. Condon. Gurney and Condon did not, however, achieve the quantitative results achieved by Gamow. Classically, the particle is confined to the nucleus because of the high energy requirement to escape the very strong nuclear potential well.
George Gamow | Radioactive decay
Radioactivity was discovered in 1896 by the French scientist Henri Becquerel, while working with phosphorescent materials. These materials glow in the dark after exposure to light, and he suspected that the glow produced in cathode ray tubes by X-rays might be associated with phosphorescence. He wrapped a photographic plate in black paper and placed various phosphorescent salts on it. All results were negative until he used uranium salts. The uranium salts caused a blackening of the plate in spite of the plate being wrapped in black paper. These radiations were given the name "Becquerel Rays". It soon became clear that the blackening of the plate had nothing to do with phosphorescence, as the blackening was also produced by non-phosphorescent salts of uranium and by metallic uranium.
Radioactive decay | History of discovery
Just a few weeks before Cockcroft and Walton's feat, another scientist at the Cavendish Laboratory, James Chadwick, discovered the neutron, using an ingenious device made with sealing wax, through the reaction of beryllium with alpha particles: Irène Curie and Frédéric Joliot irradiated aluminium foil with alpha particles, they found that this results in a short-lived radioactive isotope of phosphorus with a half-life of around three minutes: which then decays to a stable isotope of silicon They noted that radioactivity continued after the neutron emissions ceased. Not only had they discovered a new form of radioactive decay in the form of positron emission, they had transmuted an element into a hitherto unknown radioactive isotope of another, thereby inducing radioactivity where there had been none before.
Discovery of nuclear fission | Transmutation
It was not long before Fajans and Oswald Helmuth Göhring discovered it as a decay product of a beta-emitting product of thorium. Based on the radioactive displacement law of Fajans and Soddy, this was an isotope of the missing element, which they named "brevium" after its short half-life. However, it was a beta emitter, and therefore could not be the mother isotope of actinium. This had to be another isotope. Two scientists at the Kaiser Wilhelm Institute (KWI) in Berlin-Dahlem took up the challenge of finding the missing isotope. Otto Hahn had graduated from the University of Marburg as an organic chemist, but had been a post-doctoral researcher at University College London under Sir William Ramsay, and under Rutherford at McGill University, where he had studied radioactive isotopes.
Discovery of nuclear fission | Protactinium
Concurrent with the work of Rutherford, Geiger, and Marsden, the radiochemist Frederick Soddy at the University of Glasgow was studying chemistry related problems on radioactive materials. Soddy had worked with Rutherford on radioactivity at McGill University. By 1910, about 40 different radioactive elements, referred to as "radioelements", had been identified between uranium and lead, although the periodic table only allowed for 11 elements. Soddy and Kazimierz Fajans independently found in 1913 that an element undergoing alpha decay will produce an element two places to the left in the periodic system and an element undergoing beta decay will produce an element one place to the right in the periodic system.
Discovery of the neutron | Discovery of isotopes
De Pretto's paper discussed the radioactive decay of uranium and thorium and was the first to conclude that this decay was energy transformation from mass into energy. He also presented a hypothesis that the intense heat assumed to be in the center of the Earth (theory of central fire) was caused by the tremendous mass of the earth creating a massive radioactive core giving off heat and energy.
Olinto De Pretto | Radioactive decay
Radioactivity was discovered in 1896 by Henri Becquerel in uranium, and subsequently observed by Marie and Pierre Curie in thorium and in the new elements polonium and radium. In 1899, Ernest Rutherford separated radioactive emissions into two types: alpha and beta (now beta minus), based on penetration of objects and ability to cause ionization. Alpha rays could be stopped by thin sheets of paper or aluminium, whereas beta rays could penetrate several millimetres of aluminium. In 1900, Paul Villard identified a still more penetrating type of radiation, which Rutherford identified as a fundamentally new type in 1903 and termed gamma rays.
Beta decay | Discovery and initial characterization
This element is now named radon, the only one of the rare radioelements to be discovered in nature as a daughter of thorium rather than uranium. After accounting for the contribution of radon, Rutherford, now working with the British physicist Frederick Soddy, showed how thorium decayed at a fixed rate over time into a series of other elements in work dating from 1900 to 1903. This observation led to the identification of the half-life as one of the outcomes of the alpha particle experiments that led to the disintegration theory of radioactivity. The biological effect of radiation was discovered in 1903.
Thorium | Radioactivity
After James Chadwick discovered the neutron in 1932, Irène Curie and Frédéric Joliot irradiated aluminium foil with alpha particles, they found that this results in a short-lived radioactive isotope of phosphorus. They noted that positron emission continued after the neutron emissions ceased. Not only had they discovered a new form of radioactive decay, they had transmuted an element into a hitherto unknown radioactive isotope of another, thereby inducing radioactivity where there had been none before. Radiochemistry was now no longer confined to certain heavy elements, but extended to the entire periodic table. Chadwick noted that being electrically neutral, neutrons could penetrate the atomic nucleus more easily than protons or alpha particles.
Otto Hahn | Discovery of nuclear fission
They then attempted to separate these radioactive fractions further, to isolate a smaller fraction with a higher specific activity (radioactivity divided by mass). In this way, they isolated polonium and radium. It was noticed in about 1901 that high doses of radiation could cause an injury in humans. Henri Becquerel had carried a sample of radium in his pocket and as a result he suffered a highly localized dose which resulted in a radiation burn. This injury resulted in the biological properties of radiation being investigated, which in time resulted in the development of medical treatment Ernest Rutherford, working in Canada and England, showed that radioactive decay can be described by a simple equation (a linear first degree derivative equation, now called first order kinetics), implying that a given radioactive substance has a characteristic "half-life" (the time taken for the amount of radioactivity present in a source to diminish by half).
Nuclear chemistry | History
In 1934, Frédéric and Irène Joliot-Curie bombarded aluminium with alpha particles to effect the nuclear reaction + → + , and observed that the product isotope emits a positron identical to those found in cosmic rays (discovered by Carl David Anderson in 1932). This was the first example of decay (positron emission), which they termed artificial radioactivity since is a short-lived nuclide which does not exist in nature. In recognition of their discovery the couple were awarded the Nobel Prize in Chemistry in 1935. The theory of electron capture was first discussed by Gian-Carlo Wick in a 1934 paper, and then developed by Hideki Yukawa and others.
Beta decay | decay and electron capture
Radioactivity, which had overthrown the old calculations, yielded a bonus by providing a basis for new calculations, in the form of radiometric dating. Ernest Rutherford and Frederick Soddy jointly had continued their work on radioactive materials and concluded that radioactivity was due to a spontaneous transmutation of atomic elements. In radioactive decay, an element breaks down into another, lighter element, releasing alpha, beta, or gamma radiation in the process. They also determined that a particular isotope of a radioactive element decays into another element at a distinctive rate. This rate is given in terms of a "half-life", or the amount of time it takes half of a mass of that radioactive material to break down into its "decay product".
Age of Earth | Invention of radiometric dating
In 1896, Henri Becquerel discovered radioactive decay in a variety of chemical elements. Subsequently, the beta radiation from these decays was discovered to be the emission of a negatively charged particle. Later these particles were identified with the electron, discovered in cathode ray experiments by J. J. Thomson in 1897. This was connected with the theoretical prediction of the electromagnetic mass by J. J. Thomson in 1881, who showed that the electromagnetic energy contributes to the mass of a moving charged body. Thomson (1893) and George Frederick Charles Searle (1897) also calculated that this mass depends on velocity, and that it becomes infinitely great when the body moves at the speed of light with respect to the luminiferous aether.
Kaufmann–Bucherer–Neumann experiments | Historical context
The dangers of ionizing radiation due to radioactivity and X-rays were not immediately recognized.
Radioactive decay | Early health dangers
By the turn of the century, physicists had also discovered three types of radiation emanating from atoms, which they named alpha, beta, and gamma radiation. Experiments by Otto Hahn in 1911 and by James Chadwick in 1914 discovered that the beta decay spectrum was continuous rather than discrete. That is, electrons were ejected from the atom with a continuous range of energies, rather than the discrete amounts of energy that were observed in gamma and alpha decays. This was a problem for nuclear physics at the time, because it seemed to indicate that energy was not conserved in these decays.
Nuclear physics | History
This came with an annual salary of 5,000 marks. In addition, he received 66,000 marks in 1914 (of which he gave 10 per cent to Meitner) from Knöfler for the mesothorium process. The new institute was inaugurated on 23 October 1912 in a ceremony presided over by Kaiser Wilhelm II. The Kaiser was shown glowing radioactive substances in a dark room. The move to new accommodation was fortuitous, as the wood shop had become thoroughly contaminated by radioactive liquids that had been spilt, and radioactive gases that had vented and then decayed and settled as radioactive dust, making sensitive measurements impossible.
Otto Hahn | Discovery of radioactive recoil
In 1913, chemists Frederick Soddy and Kasimir Fajans independently observed that alpha decay caused atoms to shift down two places on the periodic table, while the loss of two beta particles restored it to its original position. Under the resulting reorganisation of the periodic table, radium was placed in group II, actinium in group III, thorium in group IV and uranium in group VI. This left a gap between thorium and uranium. Soddy predicted that this unknown element, which he referred to (after Dmitri Mendeleev) as "ekatantalium", would be an alpha emitter with chemical properties similar to tantalium. It was not long before Fajans and Oswald Helmuth Göhring discovered it as a decay product of a beta-emitting product of thorium.
Otto Hahn | Discovery of protactinium
He quickly realized that one of the half-lives closely matched the known 23-minute decay period of uranium-239, but the other half-life of 2.3 days was unknown. McMillan took the results of his experiment to chemist and fellow Berkeley professor Emilio Segrè to attempt to isolate the source of the radioactivity. Both scientists began their work using the prevailing theory that element 93 would have similar chemistry to rhenium, but Segrè rapidly determined that McMillan's sample was not at all similar to rhenium. Instead, when he reacted it with hydrogen fluoride (HF) with a strong oxidizing agent present, it behaved much like members of the rare earths.
Neptunium | Discovery
His group had responsibility for characterizing radioactive isotopes created by the fission of uranium and for developing a process for chemical separation of plutonium. In 1945 he was a member of the Clinton Laboratories team, with Jacob Marinsky and Lawrence E. Glendenin, that isolated the previously undocumented rare-earth element 61. Marinsky and Glendenin produced this element (later named "promethium") both by extraction from fission products and by bombarding neodymium with neutrons. They isolated it using ion-exchange chromatography. Publication of the finding was delayed until later due to the war. Marinsky and Glendenin announced the discovery at a meeting of the American Chemical Society in September 1947.
Charles D. Coryell | Introduction
Irradiating the natural stable isotope of aluminium with alpha particles (i.e. helium nuclei) resulted in an unstable isotope of phosphorus: Al + He → P + n. This discovery is formally known as positron emission or beta decay, where a proton in the radioactive nucleus changes to a neutron and releases a positron and an electron neutrino. By then, the application of radioactive materials for use in medicine was growing and this discovery allowed radioactive materials to be created quickly, cheaply, and plentifully. The Nobel Prize for chemistry in 1935 brought with it fame and recognition from the scientific community and Joliot-Curie was awarded a professorship at the Faculty of Science.
Irène Joliot-Curie | Research
These calculations were not particularly trustworthy. For example, he assumed that the samples had contained only uranium and no lead when they were formed. More important research was published in 1913. It showed that elements generally exist in multiple variants with different masses, or "isotopes". In the 1930s, isotopes would be shown to have nuclei with differing numbers of the neutral particles known as "neutrons". In that same year, other research was published establishing the rules for radioactive decay, allowing more precise identification of decay series.
Age of Earth | Arthur Holmes establishes radiometric dating
Studies of radiation and radioactive decay continued to be a preeminent focus for physical and chemical research through the 1930s, when the discovery of nuclear fission by Lise Meitner and Otto Frisch opened the way to the practical exploitation of what came to be called "atomic" energy.
History of physics | Radiation experiments
It later came to be known as radon. Rutherford identified beta rays as cathode rays (electrons), and hypothesised—and in 1909 with Thomas Royds proved—that alpha particles were helium nuclei. Observing the radioactive disintegration of elements, Rutherford and Soddy classified the radioactive products according to their characteristic rates of decay, introducing the concept of a half-life. In 1903, Soddy and Margaret Todd applied the term "isotope" to atoms that were chemically and spectroscopically indistinct but had different radioactive half-lives. Rutherford proposed a model of the atom in which a very small, dense and positively charged nucleus of protons was surrounded by orbiting, negatively charged electrons (the Rutherford model).
Discovery of nuclear fission | Radioactivity
The French scientists moved to Cambridge, where they conducted experiments that conclusively showed that a nuclear chain reaction could be produced in a mixture of uranium oxide and heavy water. In a paper written shortly after they arrived in England, Halban and Kowarski theorised that slow neutrons could be absorbed by uranium-238, forming uranium-239. A letter by Edwin McMillan and Philip Abelson published in the "Physical Review" on 15 June 1940 stated that this decayed to an element with an atomic number of 93, and then to one with an atomic number of 94 and mass of 239, which, while still radioactive, was fairly long-lived.
MAUD Committee | University of Cambridge
Enrico Fermi and his colleagues in Rome picked up on this idea, and began irradiating elements with neutrons. The radioactive displacement law of Fajans and Soddy said that beta decay causes isotopes to move one element up on the periodic table, and alpha decay causes them to move two down. When Fermi's group bombarded uranium atoms with neutrons, they found a complex mix of half lives. Fermi therefore concluded that the new elements with atomic numbers greater than 92 (known as transuranium elements) had been created. Meitner and Hahn had not collaborated for many years, but Meitner was eager to investigate Fermi's results.
Otto Hahn | Discovery of nuclear fission
Soddy and Kasimir Fajans independently observed in 1913 that alpha decay caused atoms to shift down two places in the periodic table, while the loss of two beta particles restored it to its original position. In the resulting reorganisation of the periodic table, radium was placed in group II, actinium in group III, thorium in group IV and uranium in group VI. This left a gap between thorium and uranium. Soddy predicted that this unknown element, which he referred to (after Dmitri Mendeleev) as "ekatantalium", would be an alpha emitter with chemical properties similar to tantalium (now known as tantalum).
Discovery of nuclear fission | Protactinium
In 1900 he became a demonstrator in chemistry at McGill University in Montreal, Quebec, where he worked with Ernest Rutherford on radioactivity. He and Rutherford realized that the anomalous behaviour of radioactive elements was because they decayed into other elements. This decay also produced alpha, beta, and gamma radiation. When radioactivity was first discovered, no one was sure what the cause was. It needed careful work by Soddy and Rutherford to prove that atomic transmutation was in fact occurring. In 1903, with Sir William Ramsay at University College London, Soddy showed that the decay of radium produced helium gas. In the experiment a sample of radium was enclosed in a thin-walled glass envelope sited within an evacuated glass bulb.
Frederick Soddy | Scientific career
in 1931, and his Ph.D. in 1933, writing his doctoral thesis on the "Radioactivity of ordinary elements, especially samarium and neodymium: method of detection" under the supervision of Wendell Mitchell Latimer. Independently of the work of George de Hevesy and Max Pahl, he discovered that the natural long-lived isotopes of samarium primarily decay by emission of alpha particles. Libby was appointed Instructor in the Department of Chemistry at the University of California, Berkeley, in 1933. He became an assistant professor of Chemistry there in 1938. He spent the 1930s building sensitive Geiger counters to measure weak natural and artificial radioactivity.
Willard Libby | Early life and career
Frances Pleasonton (1912–1990) was a Particle Physicist at the Oak Ridge National Laboratory. She was an active teacher and researcher, and a member of the team who first demonstrated neutron decay in 1951.
Frances Pleasonton | Introduction
When Fajans worked at the laboratory of Ernest Rutherford (with Henry G. Moseley) he was researching properties of the radioactive rows. He identified the half-lives of the uranium-actinium row and thorium nuclides. He discovered the phenomenon of the electrochemical branching of the radioactive rows. Afterwards Fajans was working on the electrochemical properties of elements as a result of the radioactive changes, and he formulated the law of the radioactive shifts which was later named the radioactive displacement law of Fajans and Soddy (Frederick Soddy received the Nobel Prize in chemistry in 1921 for his isotopic research). In 1913, together with Oswald Helmuth Göhring, he discovered the radionuclide of a new element, which was later called protactinium.
Kazimierz Fajans | Scientific work
Fanny Cook Gates (26 April 1872 – 24 February 1931) was an American physicist, an American Physical Society fellow and American Mathematical Society member. She made contributions to the research of radioactive materials, determining that radioactivity could not be destroyed by heat or ionization due to chemical reactions, and that radioactive materials differ from phosphorescent materials both qualitatively and quantitatively. More specifically, Gates showed that the emission of blue light from quinine was temperature dependent, providing evidence that the emitted light is produced from phosphorescence rather than radioactive decay. She also served as head of the Physics department at Goucher, Professor of Physics and Dean of Women at Grinnell College, and the Dean of Women at the University of Illinois.
Fanny Gates | Introduction
Rutherford named these fragments of ejected nucleus alpha particles. Rutherford realised that if an atom is losing protons, its identity is changing at the same time, since an atom's identity is governed by its proton number. Radioactive decay causes atoms of one element to transmute into atoms of a "different" element. He then sought to artificially engineer a specific transmutation.
Chemistry: A Volatile History | Ernest Rutherford explains radioactivity
In the 19th century, experimenters began to detect unexpected forms of radiation: Wilhelm Röntgen caused a sensation with his discovery of X-rays in 1895; in 1896 Henri Becquerel discovered that certain kinds of matter emit radiation on their own accord. In 1897, J. J. Thomson discovered the electron, and new radioactive elements found by Marie and Pierre Curie raised questions about the supposedly indestructible atom and the nature of matter. Marie and Pierre coined the term "radioactivity" to describe this property of matter, and isolated the radioactive elements radium and polonium. Ernest Rutherford and Frederick Soddy identified two of Becquerel's forms of radiation with electrons and the element helium.
History of physics | Radiation experiments
Bertram Borden Boltwood (July 27, 1870 Amherst, Massachusetts – August 15, 1927, Hancock Point, Maine) was an American pioneer of radiochemistry. He graduated from Yale University, and taught there 1897-1900. He established that lead was the final decay product of uranium, noted that the lead-uranium ratio was greater in older rocks and, acting on a suggestion by Ernest Rutherford, was the first to measure the age of rocks by the decay of uranium to lead, in 1907. He got results of ages of 400 to 2200 million years, the first successful use of radioactive decay by Pb/U chemical dating (isotopes not discovered yet).
Bertram Boltwood | Introduction
His 1932 doctoral thesis, written under the supervision of Rutherford and Charles Drummond Ellis, on "The Disintegration Electrons", subsequently published in the "Proceedings of the Royal Society", described relationship between the radioactive disintegration constants of beta particle-emitting radioisotopes and corresponding logarithms of their maximum beta particle energies. These plots are today known as "Sargent curves" or "Sargent diagrams". This was used by Enrico Fermi in developing his theory of beta decay. Sargent returned to Canada, where he became a lecturer and then an assistant professor at Queen's University. In 1941, he joined George Laurence of the National Research Council (NRC) in Ottawa to investigate nuclear energy, writing a report on "Uranium Fission in a Bulk of Carbon and Uranium Oxide".
Bernice Weldon Sargent | Biography
Alpha particles were first described in the investigations of radioactivity by Ernest Rutherford in 1899, and by 1907 they were identified as He ions. By 1928, George Gamow had solved the theory of alpha decay via tunneling. The alpha particle is trapped in a potential well by the nucleus. Classically, it is forbidden to escape, but according to the (then) newly discovered principles of quantum mechanics, it has a tiny (but non-zero) probability of "tunneling" through the barrier and appearing on the other side to escape the nucleus. Gamow solved a model potential for the nucleus and derived, from first principles, a relationship between the half-life of the decay, and the energy of the emission, which had been previously discovered empirically, and was known as the Geiger–Nuttall law.
Alpha decay | History
This was not in any probable decay chain, but it could have been contamination, as the Kaiser Wilhelm Institute for Chemistry had experimented with it. Hahn and Meitner demonstrated in 1919 that when actinium is treated with hydrofluoric acid, it remains in the insoluble residue. Since mesothorium II was an isotope of actinium, the substance was not mesothorium II; it was protactinium. Hahn was now confident enough that he had found something that he named his new isotope "uranium Z", and in February 1921, he published the first report on his discovery. Hahn determined that uranium Z had a half life of around 6.7 hours (with a two per cent margin of error) and that when uranium X1 decayed, it became uranium X2 about 99.75 per cent of the time, and uranium Z around 0.25 per cent of the time.
Otto Hahn | Discovery of nuclear isomerism
In 1898, Friedrich Ernst Dorn discovered a radioactive gas resulting from the radioactive decay of radium; Ramsay and Robert Whytlaw-Gray subsequently isolated radon in 1910. Astatine was synthesised in 1940 by Dale R. Corson, Kenneth Ross MacKenzie, and Emilio Segrè. They bombarded bismuth-209 with alpha particles in a cyclotron to produce, after emission of two neutrons, astatine-211.
Nonmetal | 20th century: Rn, (At)
He finished his doctoral thesis in 1913, and by 1914 he was considered by Rutherford as a leading researcher into beta decay, but he did no further work. He enlisted in the French army in 1914 and was killed in action near Cormicy.
Jan Kazimierz Danysz | Introduction
Around 1604, Vincenzo Casciarolo discovered a "lapis solaris" near Bologna, Italy. Once heated in an oxygen-rich furnace, it thereafter absorbed sunlight and glowed in the dark. The study of phosphorescent materials led to the discovery of radioactive decay.
Phosphorescence | Introduction
With the discovery of protactinium, most of the decay chains of uranium had been mapped. When Hahn returned to his work after the war, he looked back over his 1914 results, and considered some anomalies that had been dismissed or overlooked. He dissolved uranium salts in a hydrofluoric acid solution with tantalic acid. First the tantalum in the ore was precipitated, then the protactinium. In addition to the uranium X1 (thorium-234) and uranium X2 (protactinium-234), Hahn detected traces of a radioactive substance with a half life of between 6 and 7 hours. There was one isotope known to have a half life of 6.2 hours, mesothorium II (actinium-228).
Otto Hahn | Discovery of nuclear isomerism
Alpha, beta, and gamma are the first three letters of the Greek alphabet. In 1900, Becquerel measured the mass-to-charge ratio () for beta particles by the method of J.J. Thomson used to study cathode rays and identify the electron. He found that for a beta particle is the same as for Thomson's electron, and therefore suggested that the beta particle is in fact an electron. In 1901, Rutherford and Frederick Soddy showed that alpha and beta radioactivity involves the transmutation of atoms into atoms of other chemical elements. In 1913, after the products of more radioactive decays were known, Soddy and Kazimierz Fajans independently proposed their radioactive displacement law, which states that beta (i.e., ) emission from one element produces another element one place to the right in the periodic table, while alpha emission produces an element two places to the left.
Beta decay | Discovery and initial characterization
To ensure that their clean new laboratories stayed that way, Hahn and Meitner instituted strict procedures. Chemical and physical measurements were conducted in different rooms, people handling radioactive substances had to follow protocols that included not shaking hands, and rolls of toilet paper were hung next to every telephone and door handle. Strongly radioactive substances were stored in the old wood shop, and later in a purpose-built radium house on the institute grounds.
Otto Hahn | Discovery of radioactive recoil
But Hahn and Meitner had a sample from which they had regularly removed its mother isotope, mesothorium (), over a period of several years, allowing the radiothorium to decay away. Even then, it was still more difficult to work with because its induced decay products from neutron irradiation were isotopes of the same elements produced by thorium's own radioactive decay. What they found was three different decay series, all alpha emitters—a form of decay not found in any other heavy element, and for which Meitner once again had to postulate multiple isomers. They did find an interesting result: these (n, α) decay series occurred simultaneously when the energy of the incident neutrons was less than 2.5 MeV; when they had more, an (n, γ) reaction that formed was favoured.
Discovery of nuclear fission | Research
Niépce's superior, Michel Eugène Chevreul, recognized the phenomenon as a fundamental discovery (""une découverte capitale""), pointing out that uranium salts retained their power to expose photographic plates even after six months in the dark (""encore actif six mois après son insolation""). By 1861, Niépce stated frankly that uranium salts emitted some sort of radiation that was invisible to the human eye: "Original" : "" … cette activité persistante … ne peut mème pas être de la phosphorescence, car elle ne durerait pas si longtemps, d'après les expériences de M. Edmond Becquerel; il est donc plus probable que c'est un rayonnement invisible à nos yeux, comme le croit M.
Abel Niépce de Saint-Victor | Near-discovery of radioactivity
Bernice Weldon Sargent, (24 September 1906 – 17 December 1993) was a Canadian physicist who worked at the Manhattan Project's Montreal Laboratory during the Second World War as head of its nuclear physics division. In his 1932 doctoral thesis, he discovered the relationship between the radioactive disintegration constants of beta particle-emitting radioisotopes and corresponding logarithms of their maximum beta particle energies. These plots are known as "Sargent curves".
Bernice Weldon Sargent | Introduction
The discovery of radioactivity introduced another factor in the calculation. After Henri Becquerel's initial discovery in 1896, Marie and Pierre Curie discovered the radioactive elements polonium and radium in 1898; and in 1903, Pierre Curie and Albert Laborde announced that radium produces enough heat to melt its own weight in ice in less than an hour. Geologists quickly realized that this upset the assumptions underlying most calculations of the age of Earth. These had assumed that the original heat of the Earth and Sun had dissipated steadily into space, but radioactive decay meant that this heat had been continually replenished.
Age of Earth | Convective mantle and radioactivity
(In fact, it was an isotope of the known element thorium; the concept of an isotope, along with the term, was only coined in 1913, by the British chemist Frederick Soddy). Ramsay was enthusiastic when yet another new element was found in his institute, and he intended to announce the discovery in a correspondingly suitable way. In accordance with tradition this was done before the committee of the venerable Royal Society. At the session of the Royal Society on 16 March 1905 Ramsay communicated Hahn's discovery of radiothorium. The "Daily Telegraph" informed its readers: Hahn published his results in the "Proceedings of the Royal Society" on 24 March 1905.
Otto Hahn | Discovery of radio thorium, and other "new elements"
The discovery came after forty years of investigation into the nature and properties of radioactivity and radioactive substances. The discovery of the neutron by James Chadwick in 1932 created a new means of nuclear transmutation. Enrico Fermi and his colleagues in Rome studied the results of bombarding uranium with neutrons, and Fermi concluded that his experiments had created new elements with 93 and 94 protons, which his group dubbed ausonium and hesperium. Fermi won the 1938 Nobel Prize in Physics for his "demonstrations of the existence of new radioactive elements produced by neutron irradiation, and for his related discovery of nuclear reactions brought about by slow neutrons".
Discovery of nuclear fission | Introduction
Furthermore, the decay properties of all the nuclei in the decay chain of moscovium had not been previously characterized before the Dubna experiments, a situation which the JWP generally considers "troublesome, but not necessarily exclusive".
Moscovium | Discovery
While experimenting with the products of radioactive decay, in 1913 radiochemist Frederick Soddy discovered that there appeared to be more than one element at each position on the periodic table. The term isotope was coined by Margaret Todd as a suitable name for these elements. That same year, J. J. Thomson conducted an experiment in which he channeled a stream of neon ions through magnetic and electric fields, striking a photographic plate at the other end. He observed two glowing patches on the plate, which suggested two different deflection trajectories. Thomson concluded this was because some of the neon ions had a different mass.
Atomic theory | Discovery of isotopes
After switching from iron to graphene absorbers, the 1946 experiment dramatically showed that the negatively charged component of cosmic rays decayed radioactive rather than being captured by the graphite.
Marcello Conversi | Introduction
Pleasonton was an active researcher in neutron decay. There were several attempts to measure neutron half-life before the second world war, all of which failed due to the lack of availability of intense neutron sources. Arthur Snell and Leonard Miller built the Oak Ridge Graphite Reactor, which could focus beams of neutrons and allow scientists to observe their decay. They measured the half-life of a neutron in 1951. Pleasonton was supported by the United States Atomic Energy Commission and published broadly. In 1958 they examined the decay of helium-6, Pleasonton and Snell monitoring the directions of neutrinos and electrons. This result confirmed the electron-neutrino theory of beta decay.
Frances Pleasonton | Research
The calcium-48 beam was generated by chemically extracting the small quantities of calcium-48 present in naturally occurring calcium, enriching it 500 times. This work was done in the closed town of Lesnoy, Sverdlovsk Oblast, Russia. The experiment began in late July 2009. In January 2010, scientists at the Flerov Laboratory of Nuclear Reactions announced internally that they had detected the decay of a new element with atomic number 117 via two decay chains: one of an odd–odd isotope undergoing 6 alpha decays before spontaneous fission, and one of an odd–even isotope undergoing 3 alpha decays before fission. The obtained data from the experiment was sent to the LLNL for further analysis.
Tennessine | Discovery
When Hitchins first worked with Soddy, researchers were still searching for new chemical elements, and isotopes were not yet understood. As early as 1904, researchers had hypothesized that the decay of uranium resulted in the creation of radium, but how this occurred was not clear. In 1907, the American radiochemist Bertram Boltwood had isolated what he believed to be a new intermediate element in the decay chain between uranium and radium, "ionium". Researchers eventually determined that ionium was actually an isotope of thorium, Th. Soddy asked Hitchins to investigate ionium. She selectively extracted uranium from ore samples to create purified uranium preparations and established a half-life for ionium.
Ada Hitchins | Uranium and ionium
While at Repton he was awarded a doctorate from the University of London for a thesis in radioactive decay (the measurement of the half-period of Radium C).
Arthur W. Barton | Introduction
While experimenting with the products of radioactive decay, in 1913 radiochemist Frederick Soddy discovered that there appeared to be more than one type of atom at each position on the periodic table. The term isotope was coined by Margaret Todd as a suitable name for different atoms that belong to the same element. J. J. Thomson created a technique for isotope separation through his work on ionized gases, which subsequently led to the discovery of stable isotopes.
Atom | Discovery of isotopes
He reviewed medical records from survivors of the atomic bombings of Hiroshima and Nagasaki, as well as radiologists and patients exposed to X-rays. Lewis concluded that "health risks from radiation had been underestimated". Lewis published articles in "Science" and other journals and made a presentation to a Congressional committee on atomic energy in 1957. At the scientific level of the debate, the crucial question was whether the "threshold theory" was valid or whether, as Lewis insisted, the effects of radioactivity were "linear with no threshold", where every exposure to radiation had a long-term cumulative effect.
Edward B. Lewis | Career and research
William Henry Bragg and Richard Kleeman had noted that the alpha particles emitted from radioactive substances always had the same energy, providing a second way of identifying them, so Hahn set about measuring the alpha particle emissions of radiothorium. In the process, he found that a precipitation of thorium A (polonium-216) and thorium B (lead-212) also contained a short-lived "element", which he named thorium C (which was later identified as polonium-212). Hahn was unable to separate it, and concluded that it had a very short half life (it is about 300 ns). He also identified radioactinium (thorium-227) and radium D (later identified as lead-210).
Otto Hahn | Discovery of radio thorium, and other "new elements"
He found the equipment there primitive and the library bereft of modern physics literature, but his colleagues at Palermo included the mathematicians Michele Cipolla and Michele De Franchis, the mineralogist Carlo Perrier and the botanist . In 1936 he paid a visit to Ernest O. Lawrence's Berkeley Radiation Laboratory, where he met Edwin McMillan, Donald Cooksey, Franz Kurie, Philip Abelson and Robert Oppenheimer. Segrè was intrigued by the radioactive scrap metal that had once been part of the laboratory's cyclotron. In Palermo, this was found to contain a number of radioactive isotopes. In February 1937, Lawrence sent him a molybdenum strip that was emitting anomalous forms of radioactivity.
Emilio Segrè | Physics professor
Based on the radioactive displacement law of Fajans and Soddy, this was an isotope of the missing element, which they named "brevium" after its short half life. However, it was a beta emitter, and therefore could not be the mother isotope of actinium. This had to be another isotope of the same element. Hahn and Meitner set out to find the missing mother isotope. They developed a new technique for separating the tantalum group from pitchblende, which they hoped would speed the isolation of the new isotope. The work was interrupted by the First World War. Meitner became an X-ray nurse, working in Austrian Army hospitals, but she returned to the Kaiser Wilhelm Institute in October 1916.
Otto Hahn | Discovery of protactinium
At the start of the 20th century, the vigorous debate as to the existence of atoms had not yet been resolved. Philosophers such as Ernst Mach and Wilhelm Ostwald denied that atoms were real, viewing them as a convenient mathematical construct, while scientists such as Arnold Sommerfeld and Ludwig Boltzmann saw that physical theories required the existence of atoms. Radioactivity was discovered in 1896 by the French scientist Henri Becquerel, while working with phosphorescent materials. In 1898, Ernest Rutherford at Cavendish Laboratory distinguished two types of radioactivity, alpha rays and beta rays, which differed in their ability to penetrate, or travel into, ordinary objects or gases.
Discovery of the neutron | Discovery of radioactivity
Scientists at Los Alamos found traces in them of isotopes plutonium-246 and plutonium-244. Al Ghiorso at the University of California, Berkeley speculated that the filters might also contain atoms that had transformed, through radioactive decay, into the predicted but undiscovered elements 99 and 100. Ghiorso, Stanley Gerald Thompson and Glenn Seaborg obtained half a filter paper from the Ivy Mike test. They were able to detect the existence of the elements einsteinium and fermium, which had been produced by intensely concentrated neutron flux about the detonation site. The discovery was kept secret for several years, but the team was eventually given credit.
Ivy Mike | Scientific discoveries
As research on nuclear fission progressed in early 1939, Edwin McMillan at the Berkeley Radiation Laboratory of the University of California, Berkeley decided to run an experiment bombarding uranium using the powerful 60-inch (1.52 m) cyclotron that had recently been built at the university. The purpose was to separate the various fission products produced by the bombardment by exploiting the enormous force that the fragments gain from their mutual electrical repulsion after fissioning. Although he did not discover anything of note from this, McMillan did observe two new beta decay half-lives in the uranium trioxide target itself, which meant that whatever was producing the radioactivity had not violently repelled each other like normal fission products.
Neptunium | Discovery
The first information about the atomic nucleus was obtained at the beginning of the 20th century by studying radioactivity. For a long period of time only three kinds of nuclear decay modes (alpha, beta, and gamma) were known. They illustrate three of the fundamental interactions in nature: strong, weak, and electromagnetic. Spontaneous fission became better studied soon after its discovery in 1940 by Konstantin Petrzhak and Georgy Flyorov because of both the military and the peaceful applications induced fission. This was discovered circa 1939 by Otto Hahn, Lise Meitner, and Fritz Strassmann. There are many other kinds of radioactivity, e.g.
Cluster decay | History
The Paris group published their results in September 1938. Hahn dismissed the isotope with the 3.5-hour half-life as contamination, but after looking at the details of the Paris group's experiments and the decay curves, Strassmann was worried. He decided to repeat the experiment, using his more efficient method of separating radium. This time, they found what they thought was radium, which Hahn suggested resulted from two alpha decays: Meitner found this very hard to believe. In November, Hahn travelled to Copenhagen, where he met with Bohr and Meitner. They told him that they were very unhappy about the proposed radium isomers.
Discovery of nuclear fission | Eureka!
By 1931, the building which later became Pupin Hall was a leading research center. During this time Harold Urey (Nobel laureate in Chemistry) discovered deuterium and George B. Pegram was investigating the phenomena associated with the newly discovered neutron. In 1938, Enrico Fermi escaped fascist Italy after winning the Nobel prize for his work on induced radioactivity. In fact, he took his wife and children with him to Stockholm and immediately emigrated to New York. Shortly after arriving he began working at Columbia University with Dr. John Dunning. His work on nuclear fission, together with I. I. Rabi's work on atomic and molecular physics, ushered in a golden era of fundamental research at the university.
Pupin Hall | History
Radon was the fifth radioactive element to be discovered, in 1899 by Ernest Rutherford and Robert B. Owens at McGill University in Montreal, after uranium, thorium, radium, and polonium. In 1899, Pierre and Marie Curie observed that the gas emitted by radium remained radioactive for a month. Later that year, Rutherford and Owens noticed variations when trying to measure radiation from thorium oxide. Rutherford noticed that the compounds of thorium continuously emit a radioactive gas that remains radioactive for several minutes, and called this gas "emanation" (from , to flow out, and , expiration), and later "thorium emanation" ("Th Em").
Radon | History and etymology
It was the first of over 250 scientific publications of Otto Hahn in the field of radiochemistry. At the end of his time in London, Ramsay asked Hahn about his plans for the future, and Hahn told him about the job offer from Kalle & Co. Ramsay told him radiochemistry had a bright future, and that someone who had discovered a new radioactive element should go to the University of Berlin. Ramsay wrote to Emil Fischer, the head of the chemistry institute there, who replied that Hahn could work in his laboratory, but could not be a "Privatdozent" because radiochemistry was not taught there.
Otto Hahn | Discovery of radio thorium, and other "new elements"
In 1929, Feather took a year-long visit to Johns Hopkins University in Baltimore, USA. During his visit, he learned that Kelly Hospital used radon tubes in the treatment of cancers, and that the expired tubes were discarded after use. The expired radon tubes were a source of polonium, a source of energetic alpha particles. Since polonium was difficult to obtain and expensive at the time, Feather acquired a large number of the discarded radon tubes. The expired radon was to be used as a source of alpha particles for experiments in Cambridge. Indeed, the radioactive polonium source used by James Chadwick to discover the neutron in 1932 was derived from these radon tubes.
Norman Feather | Discovery of the Neutron
Harriet Brooks observed a radioactive recoil in 1904, but interpreted it wrongly. Hahn and Meitner succeeded in demonstrating the radioactive recoil incident to alpha particle emission and interpreted it correctly. Hahn pursued a report by Stefan Meyer and Egon Schweidler of a decay product of actinium with a half-life of about 11.8 days. Hahn determined that it was actinium X (radium-223). Moreover, he discovered that at the moment when a radioactinium (thorium-227) atom emits an alpha particle, it does so with great force, and the actinium X experiences a recoil. This is enough to free it from chemical bonds, and it has a positive charge, and can be collected at a negative electrode.
Otto Hahn | Discovery of radioactive recoil
Since these elements comprise a large percentage of fission products, Segrè and McMillan decided that the half-life must have been simply another fission product, titling the paper "An Unsuccessful Search for Transuranium Elements". However, as more information about fission became available, the possibility that the fragments of nuclear fission could still have been present in the target became more remote. McMillan and several scientists, including Philip H. Abelson, attempted again to determine what was producing the unknown half-life. In early 1940, McMillan realized that his 1939 experiment with Segrè had failed to test the chemical reactions of the radioactive source with sufficient rigor.
Neptunium | Discovery
A study in 1976 by a group of American researchers from several universities proposed that primordial superheavy elements, mainly livermorium, unbiquadium, unbihexium, and unbiseptium, could be a cause of unexplained radiation damage (particularly radiohalos) in minerals. This prompted many researchers to search for them in nature from 1976 to 1983. A group led by Tom Cahill, a professor at the University of California at Davis, claimed in 1976 that they had detected alpha particles and X-rays with the right energies to cause the damage observed, supporting the presence of these elements. In particular, the presence of long-lived (on the order of 10 years) unbiquadium and unbihexium nuclei, along with their decay products, at an abundance of 10 relative to their possible congeners uranium and plutonium, was conjectured.
Extended periodic table | Searches in nature
Hahn was thinking only of actinium, but on reading his paper, Meitner told him that he had found a new way of detecting radioactive substances. They set up some tests, and soon found actinium C (thallium-207) and thorium C (thallium-208). The physicist Walther Gerlach described radioactive recoil as "a profoundly significant discovery in physics with far-reaching consequences". In 1910, Hahn was appointed professor by the Prussian Minister of Culture and Education, August von Trott zu Solz. Two years later, Hahn became head of the Radioactivity Department of the newly founded Kaiser Wilhelm Institute for Chemistry in Berlin-Dahlem (in what is today the Hahn-Meitner-Building of the Free University of Berlin).
Otto Hahn | Discovery of radioactive recoil
Radioactivity Radionuclides Radiation by Joseph Magill and Jean Galy, Springer Verlag, 2005
Decay energy | References
At St Bartholomew's, Rotblat worked on the effects of radiation on living organisms, especially on ageing and fertility. This led him to an interest in nuclear fallout, especially strontium-90 and the safe limits of ionising radiation. In 1955, he demonstrated that the contamination caused by the fallout after the Castle Bravo nuclear test at Bikini Atoll by the United States had been far greater than that stated officially. Until then the official line had been that the growth in the strength of atomic bombs was not accompanied by an equivalent growth in radioactivity released. Japanese scientists who had collected data from a fishing vessel, the "Lucky Dragon", which had inadvertently been exposed to fallout, disagreed with this.
Joseph Rotblat | Nuclear fallout
The predicted half-lives were on the order of 10 years. Efforts to observe the process in laboratory date back to at least 1948 when Edward L. Fireman made the first attempt to directly measure the half-life of the isotope with a Geiger counter. Radiometric experiments through about 1960 produced negative results or false positives, not confirmed by later experiments. In 1950, for the first time the double beta decay half-life of was measured by geochemical methods to be 1.4 years, reasonably close to the modern value. This involved detecting the concentration in minerals of the xenon produced by the decay.
Double beta decay | History
She gave the phenomenon the name "radioactivity". Along with Pierre Curie and Gustave Bémont, she began investigating pitchblende, a uranium-bearing ore, which was found to be more radioactive than the uranium it contained. This indicated the existence of additional radioactive elements. One was chemically akin to bismuth, but strongly radioactive, and in July 1898 they published a paper in which they concluded that it was a new element, which they named "polonium". The other was chemically like barium, and in a December 1898 paper they announced the discovery of a second hitherto unknown element, which they called "radium". Convincing the scientific community was another matter.
Discovery of nuclear fission | Radioactivity
The new laboratories offered new opportunities, as the old ones had become too contaminated with radioactive substances to investigate feebly radioactive substances. They developed a new technique for separating the tantalum group from pitchblende, which they hoped would speed the isolation of the new isotope. The work was interrupted by the outbreak of the First World War in 1914. Hahn was called up into the German Army, and Meitner became a volunteer radiographer in Austrian Army hospitals. She returned to the Kaiser Wilhelm Institute in October 1916, when not only Hahn, but most of the students, laboratory assistants and technicians had been called up.
Discovery of nuclear fission | Protactinium
Initial experiments were carried out in September 1954. No alpha decay was seen from mendelevium atoms; thus, Ghiorso suggested that the mendelevium had all decayed by electron capture to fermium and that the experiment should be repeated to search instead for spontaneous fission events. The repetition of the experiment happened in February 1955. On the day of discovery, 19 February, alpha irradiation of the einsteinium target occurred in three three-hour sessions. The cyclotron was in the University of California campus, while the Radiation Laboratory was on the next hill. To deal with this situation, a complex procedure was used: Ghiorso took the catcher foils (there were three targets and three foils) from the cyclotron to Harvey, who would use aqua regia to dissolve it and pass it through an anion-exchange resin column to separate out the transuranium elements from the gold and other products.
Mendelevium | Discovery
Reasoning that interstellar gas contains a higher concentrations of shorter-lived radioactive nuclei than do the stars, Clayton invented in 1985 new mathematical solutions for the simplified differential equations of galactic abundance evolution that for the first time rendered these relationships understandable, ending decades of poor reasoning about radioactive abundances. Clayton then calculated an age of 13-15 billion years for the oldest galactic nuclei, which would necessarily approximate the long-sought age of our galaxy. More recently radioactive cosmochronology has diminished in importance because more precise techniques for determining the age of the Milky Way have been discovered in the cosmic microwave background.
Donald D. Clayton | Galactic abundance evolution of radioactive nuclei
The discovery of X‑rays by Wilhelm Röntgen in 1895 led to widespread experimentation by scientists, physicians, and inventors. Many people began recounting stories of burns, hair loss and worse in technical journals as early as 1896. In February of that year, Professor Daniel and Dr. Dudley of Vanderbilt University performed an experiment involving X-raying Dudley's head that resulted in his hair loss. A report by Dr. H.D. Hawks, of his suffering severe hand and chest burns in an X-ray demonstration, was the first of many other reports in "Electrical Review". Other experimenters, including Elihu Thomson and Nikola Tesla, also reported burns.
Radioactive decay | X-rays
Separating radium from the barium in the ore proved very difficult. It took three years for them to produce a tenth of a gram of radium chloride, and they never did manage to isolate polonium. In 1898, Ernest Rutherford noted that thorium gave off a radioactive gas. In examining the radiation, he classified Becquerel radiation into two types, which he called α (alpha) and β (beta) radiation. Subsequently, Paul Villard discovered a third type of Becquerel radiation which, following Rutherford's scheme, were called "gamma rays", and Curie noted that radium also produced a radioactive gas. Identifying the gas chemically proved frustrating; Rutherford and Frederick Soddy found it to be inert, much like argon.
Discovery of nuclear fission | Radioactivity
The first hypothesis for this alpha particle accumulation was contamination by uranium, which produces alpha-decay particles; analysis of alpha-decay particles ruled this out. Seaborg then postulated that a distinct alpha-producing element was being formed from element 93. In February 1941, Seaborg and his collaborators produced plutonium-239 through the bombardment of uranium. In their experiments bombarding uranium with deuterons, they observed the creation of neptunium, element 93. But it then underwent beta-decay, forming a new element, plutonium, with 94 protons. Plutonium is fairly stable, but undergoes alpha-decay, which explained the presence of alpha particles coming from neptunium. Thus, on March 28, 1941, Seaborg, physicist Emilio Segrè and Berkeley chemist Joseph W.
Glenn T. Seaborg | Pioneering work in nuclear chemistry
The existence of isotopes was first suggested in 1913 by the radiochemist Frederick Soddy, based on studies of radioactive decay chains that indicated about 40 different species referred to as "radioelements" (i.e. radioactive elements) between uranium and lead, although the periodic table only allowed for 11 elements between lead and uranium inclusive. Several attempts to separate these new radioelements chemically had failed. For example, Soddy had shown in 1910 that mesothorium (later shown to be Ra), radium (Ra, the longest-lived isotope), and thorium X (Ra) are impossible to separate. Attempts to place the radioelements in the periodic table led Soddy and Kazimierz Fajans independently to propose their radioactive displacement law in 1913, to the effect that alpha decay produced an element two places to the left in the periodic table, whereas beta decay emission produced an element one place to the right.
Isotope | Radioactive isotopes
Furthermore, these discoveries led to a principle known as the "conservation of strangeness", where in lightweight particles do not decay as quickly if they exhibit strangeness (because non-weak methods of particle decay must preserve the strangeness of the decaying baryon). In 1974 and 1975, an international team at the Fermilab that included scientists from Fermilab and seven European laboratories under the leadership of Eric Burhop carried out a search for a new particle, the existence of which Burhop had predicted in 1963. He had suggested that neutrino interactions could create short-lived (perhaps as low as 10 s) particles that could be detected with the use of nuclear emulsion.
Lambda baryon | Overview
With nuclear physicists' tenuous prediction of a "long-lived radioactive carbon isotope", Ruben and Kamen pursued several routes that could lead to identification of the carbon-14 isotope. After several failed attempts, Kamen collected the results of a 120-hour cyclotron bombardment of graphite and trudged in the rain with it to the “Rat House", adjacent both to the Chemistry Department and to the cyclotron, and Ruben's desk. At 8 AM, February 27, 1940, Ruben demonstrated unequivocally that the radioactivity was from carbon-14.
Sam Ruben | Research
Richard Daniel Kleeman (20 January 1875 – 10 October 1932) was an Australian physicist. With William Henry Bragg he discovered that the alpha particles emitted from particular radioactive substances always had the same energy, providing a new way of identifying and classifying them.
Richard Kleeman | Introduction
The Berlin group started by irradiating uranium salt with neutrons from a radon-beryllium source similar to the one that Fermi had used. They dissolved it and added potassium perrhenate, platinum chloride and sodium hydroxide. What remained was then acidified with hydrogen sulphide, resulting in platinum sulphide and rhenium sulphide precipitation. Fermi had noted four radioactive isotopes with the longest-lived having 13- and 90-minute half-lives, and these were detected in the precipitate. The Berlin group then tested for protactinium by adding protactinium-234 to the solution. When this was precipitated, it was found to be separated from the 13- and 90-minute half-life isotopes, demonstrating that von Grosse was incorrect, and they were not isotopes of protactinium.
Discovery of nuclear fission | Research
After Chadwick discovered the neutron in 1932, Irène Curie and Frédéric Joliot irradiated aluminium foil with alpha particles, and found that this results in a short-lived radioactive isotope of phosphorus. They noted that positron emission continued after the neutron emissions ceased. Not only had they discovered a new form of radioactive decay, they had transmuted an element into a hitherto unknown radioactive isotope of another, thereby inducing radioactivity where there had been none before. Radiochemistry was now no longer confined to certain heavy elements, but extended to the entire periodic table. Chadwick noted that being electrically neutral, neutrons could penetrate the atomic nucleus more easily than protons or alpha particles.
Lise Meitner | Transmutation
American chemist Bertram Boltwood proposed several decay chains linking these radioelements between uranium and lead. These were thought at the time to be new chemical elements, substantially increasing the number of known "elements" and leading to speculations that their discoveries would undermine the concept of the periodic table. For example, there was not enough room between lead and uranium to accommodate these discoveries, even assuming that some discoveries were duplicates or incorrect identifications. It was also believed that radioactive decay violated one of the central principles of the periodic table, namely that chemical elements could not undergo transmutations and always had unique identities.
History of the periodic table | Radioactivity, isotopes, and the Rutherford model
Alarmed, Hahn began to dismantle his experiments—but in a chance encounter, police discovered his activities, which triggered a Federal Radiological Emergency Response involving the FBI and the Nuclear Regulatory Commission. On June 26, 1995 the EPA, having designated Hahn's mother's property a Superfund hazardous materials cleanup site, dismantled the shed and its contents and buried them as low-level radioactive waste in Utah. Unknown to officials, his mother, fearful that she would lose her house if the full extent of the radiation were known, had already collected the majority of the radioactive material and thrown it away in the conventional garbage.
David Hahn | Creation of the neutron source
Along the way, Hahn determined that just as he was unable to separate thorium from radiothorium, so he could not separate mesothorium from radium. Hahn completed his habilitation in the spring of 1907, and became a "Privatdozent". A thesis was not required; the Chemical Institute accepted one of his publications on radioactivity instead. Most of the organic chemists at the Chemical Institute did not regard Hahn's work as real chemistry. Fischer objected to Hahn's contention in his habilitation colloquium that many radioactive substances existed in such tiny amounts that they could only be detected by their radioactivity, venturing that he had always been able to detect substances with his keen sense of smell, but soon gave in.
Otto Hahn | Discovery of mesothorium I
The Fernald School was the site of the 1946–53 joint experiments by Harvard University and MIT that exposed young male children to tracer doses of radioactive isotopes. Documents obtained in 1994 by the United States Department of Energy revealed the following details: The Advisory Committee on Human Radiation Experiments, reporting to the United States Department of Energy in 1994, reported on these experiments: In 1946, one study exposed seventeen subjects to radioactive iron. The second study, which involved a series of seventeen related subexperiments, exposed fifty-seven subjects to radioactive calcium between 1950 and 1953. It is clear that the doses involved were low and that it is extremely unlikely that any of the children who were used as subjects were harmed as a consequence.
Walter E. Fernald Developmental Center | Nuclear medicine research in children
McMillan realized that his 1939 work with Segrè had failed to test the chemical reactions of the radioactive source with sufficient rigor. In a new experiment, McMillan tried subjecting the unknown substance to HF in the presence of a reducing agent, something he had not done before. This reaction resulted in the sample precipitating with the HF, an action that definitively ruled out the possibility that the unknown substance was a rare earth. In May 1940, Philip Abelson from the Carnegie Institute in Washington, DC, who had independently also attempted to separate the isotope with the 2.3-day half-life, visited Berkeley for a short vacation, and they began to collaborate.
Edwin McMillan | Discovery of neptunium
In 1910, Auer von Welsbach reported a "mysterious observation", the induction of radioactivity in an inactive substance when exposed to a radioactive substance. Based on his report, it is possible that he may have been the first to observe neutron activation.
Carl Auer von Welsbach | Radium research