Radioactivity discover

The development of particle accelerators grew out of the discovery of radioactivity in uranium by Henri Becquerel in Paris in 1896. Some years later, due to the work of Ernest Rutherford and others, it was found that the radioactivity discovered by Becquerel was the emission o particles with kinetic energies o several MeV from uranium nuclei. Research using the emitted particles began shortly thereafter. It was soon realized that if scientists were to learn more about the properties of subatomic particles, they had to be accelerated to energies greater than those attained in natural radioactivity. 

Radioactivity discovered by H. Becquerel. Electron discovered by J. J. Thomson. Planck s radiation formula. Special Relativity. 

In the meantime, E. Rutherford (NLC 1908 ) studied the radioactivity discovered by Becquerel and the Curies. He determined that the emanations of radioactive materials include alpha particles (or rays) which are positively charged helium atoms, beta particles (or rays) which are negatively charged electrons, and gamma rays which are similar to x-rays. He also studied the radioactive decay process and deduced the first order rate law for the disappearance of a radioactive atom, characterized by the half-life, the time in which 50% of a given radioactive species disappears, and which is independent of the concentration of that species. 

He did some pioneer work in the field of radioactivity, discovering and characterizing alpha and beta particles — and received a Nobel Prize in chemistry for this work. But he s perhaps better known for his scattering experiments in which he realized that the atom was mostly empty space and that there had to be a dense, positive core at the center of the atom, which is now known as the nucleus. Inspired by Rutherford, many of his former students went on to receive their own Nobel Prizes. 

Curie, Marie Sklodowska (1867-1934) and Pierre Curie (1859-1906) Polish-bom chemist-physicist Marie was the first woman to teach at the University of Paris. She married French physicist-chemist Pierre Curie in 1895, and the couple collaborated on research into radioactivity, discovering the elements polonium and radium. She and her husband shared the 1903 Nobel Prize in Physics for their work she was the first woman so honored. After her husband died, she continued her research and received the 1911 Nobel Prize in Chemistry, the first person to receive the award in two different disciplines. She founded the Radium (later Curie) Institute. 

Spectroscope developed Bunsen and Kirchhoff 1869 Mendeleev s first periodic table organizes 63 known elements 1885 Balmer formula for visible H spectrum 1894 First "inert gas" discovered 1895 X rays discovered Roentgen 1896 Radioactivity discovered Becquerel 1874 Tetrahedral carbon atom Le Bel and van t Hoff 1884 Dissociation theory of electrolytes Arrhenius 1869 Chain theory of ammonates Blomstrand 1884 Amendments to chain theory Jorgensen 1892 Werner s dream about coordination compounds... 

Poland, native country of Mme. Curie) Polonium, also called Radium F, was the first element discovered by Mme. Curie in 1898 while seeking the cause of radioactivity of pitchblend from Joachimsthal, Bohemia. The electroscope showed it separating with bismuth. 

Thorium [7440-29-1], a naturally occurring radioactive element, atomic number 90, atomic mass 232.0381, is the second element of the actinide ( f) series (see Actinides AND transactinides Radioisotopes). Discovered in 1828 in a Norwegian mineral, thorium was first isolated in its oxide form. For the light actinide elements in the first half of the. series, there is a small energy difference between and 5/ 6d7 electronic configurations. Atomic spectra... 

Uranium [7440-61-17 is a naturally occurring radioactive element with atomic number 92 and atomic mass 238.03. Uranium was discovered in a pitchblende [1317-75-5] specimen ia 1789 by M. H. Klaproth (1) who named the element uranit after the planet Uranus, which had been recendy discovered. For 50 years the material discovered by Klaproth was thought to be metallic uranium. Pnligot showed that the uranit discovered by Klaproth was really uranium dioxide [1344-57-6] UO2, and obtained the tme elemental uranium as a black powder in 1841 by reduction of UCl [10026-10-5] with potassium (2). 

In 1896, Becquerel discovered that uranium was radioactive (3). Becquerel was studying the duorescence behavior of potassium uranyl sulfate, and observed that a photographic plate had been darkened by exposure to the uranyl salt. Further investigation showed that all uranium minerals and metallic uranium behaved in this same manner, suggesting that this new radioactivity was a property of uranium itself In 1934, Fermi bombarded uranium with neutrons to produce new radioactive elements (4). 

Edmond Becquerel was one of a family of scientists. His father, Antoine-Cesar, was professor of physics at the Museum d Histoire Naturelle, and his son, [Antoine-] Henri Becquerel, also a physicist, discovered the phenomenon of radioactivity (for which he received the Nobel Prize in 1903). 

Curie chose for her dissertation research the new topic of uranium rays, a phenomenon that had only recently been observed by Henri Becqiierel. The mystery was the source of the energy that allowed uranium salts to expose even covered photographic plates. Curie s first efforts in the field were systematic examinations of numerous salts to determine which salts might emit rays similar to those of Becquerel s uranium. After discovering that both thorium and uranium were sources of this radiation. Curie proposed the term radioactive to replace uranium rays. She also discovered that the intensity of the emissions depended not on the chemical... 

Although the Curies noted that one equivalent gram of radium released one hundred calorics of heat per hour, they were uninterested in the practical implications of this, as they were both devoted to pure scientific discovery. During their work with pitchblende in 1898, the Curies discovered two new radioactive elements, which they named polonium (in honor of Marie s homeland) and radium. By 1902 they had isolated a pure radium salt and made the first atomic weight determination. 

The most important contribution I lertz made in this inaugural lecture was his prediction, based on his estimates of the energy sources available, that ultimately the Earth was completely dependent on the Sun for the light and heat it needed to support life. Of course, this picture would change after Henri Becquerel discovered radioactivity in 1896, and thus introduced the nuclear age of physics. 

Marie and Irene Curie, and their husbands, Pierre Curie and Frederic Joliot. Marie Curie (1867-1934) was born Maria Sklodowska in Warsaw, Poland, then a part of the Russian empire. In 1891 she emigrated to Paris to study at the Sorbonne, where she met and married a French physicist, Pierre Curie (1859-1906). The Curies were associates of Henri Becquerel, the man who discovered that uranium salts are radioactive. They showed that thorium, like uranium, is radioactive and that the amount of radiation emitted is directly proportional to the amount of uranium or thorium in the sample. 

In 1921, Irene Curie (1897-1956) began research at the Radium Institute. Five years later she married Frederic Joliot (1900-1958). a brilliant young physicist who was also an assistant at the Institute. In 1931, they began a research program in nuclear chemistry that led to several important discoveries and at least one near miss. The Joliot-Curies were the first to demonstrate induced radioactivity. They also discovered the positron, a particle that scientists had been seeking for many years. They narrowly missed finding another, more fundamental particle, the neutron. That honor went to James Chadwick in England. In 1935,... 

Stanley G. Thompson joined my group on October 1, 1942 and it fell to his lot to discover the process that was chosen for use at Clinton Laboratories (in Tennessee) and the Hanford Engineer Works (in the state of Washington) for the separation of plutonium from uranium and the immense intensity of radioactive fission products with which it was produced in the nuclear chain reactors. Again I turn to my journal to tell the story ... 

Later experiments (4 ) were designed to determine a cell e.m.f. for the plutonium disproportionation system with a particular light source. Concentration quotients for the light and dark conditions, Qg and Qj, were determined, and an energy difference of 1.65 kcal (32 mV) was calculated by the relation -RTln C /Qd This reversible photochemical shift may be the only single-element system known at this time and certainly is the simplest such system. Even though the radioactive properties could prevent development and utilization of a plutonium photoconversion system, these studies certainly suggest that similar nonradioactive and more acceptable systems could be discovered and developed. 

FIGURE 17.2 Henri Becquerel discovered radioactivity when he noticed that an unexposed photographic plate left near some uranium oxide became fogged. This photograph shows one of his original plates annotated with his record of the event. 

The origin of the rays was initially a mystery, because the existence of the atomic nucleus was unknown at the time. However, in 1898, Ernest Rutherford took the first step to discover their origin when he identified three different types of radioactivity by observing the effect of electric fields on radioactive emissions (Fig. 17.4). Rutherford called the three types a (alpha), (3 (beta), and y (gamma) radiation. 

Polonium, completing the elements of Group 16, is radioactive and one of the rarest naturally occurring elements (about 3 x 10 " % of the Earth s crust). The main natural source of polonium is uranium ores, which contain about lO g of Po per ton. The isotope 210-Po, occurring in uranium (and also thorium) minerals as an intermediate in the radioactive decay series, was discovered by M. S. Curie in 1898. 

Shortly after Rutherford named those two emissions, a third one was discovered. It was named gamma, the third letter in the Greek alphabet. All of these names can be bewildering, but radioactive emissions actually come in only two fundamental forms electromagnetic radiation and particles. 

The first person to identify the hydrogen ion as a component of all atoms was Ernest Rutherford. Rutherford had his hand in virtually every aspect of atomic research. By 1919, he had discovered alpha and beta rays, found a new element (radon), won a Nobel Prize for his work with radioactive elements, and demonstrated that atoms had nuclei. For good measure, in 1914, he was knighted. However, still more discoveries and honors awaited him. 

The half-lives of the elements vary widely, as shown in Table 3.2. Some isotopes, nitrogen-14 for example, are stable and experience no natural radioactive decay. However, bombarding even a stable element with energetic alpha rays can cause transmutation. Rutherford discovered the proton when he created hydrogen from a stable isotope of nitrogen. 

The discovery of two new elements started a frenetic race to find more. Actinium was soon unearthed (Debierne 1900) and many other substances were isolated from U and Th which also seemed to be new elements. One of these was discovered somewhat fortuitously. Several workers had noticed that the radioactivity of Th salts seemed to vary randomly with time and they noticed that the variation correlated with drafts in the lab, appearing to reflect a radioactive emanation which could be blown away from the surface of the Th. This Th-emanation was not attracted by charge and appeared to be a gas, °Rn, as it turns out, although Rutherford at first speculated that it was Th vapor. Rutherford swept some of the Th-emanation into a jar and repeatedly measured its ability to ionize air in order to assess its radioactivity. He was therefore the first to report an exponential decrease in radioactivity with time, and his 1900 paper on the subject introduced the familiar equation dN/dt = - iN, as well as the concept of half-lives (Rutherford 1900a). His measured half-life for the Th emanation of 60 seconds was remarkably close to our present assessment of 55.6 seconds for °Rn. 

Were all of these newly discovered substances also new elements This question would not be answered for some years but there was a flurry of other major discoveries to keep the protagonists occupied. Pierre Curie discovered that radioactivity released large quantities of heat (Curie and Laborde 1903) which appeared mysterious—as if the heat was coming from nowhere. This discovery provided an extra heat source for the Earth and reconciled the estimates of a very old Earth, based on geological estimates, with the young age calculated by Lord Kelvin from cooling rates. The year 1903 also witnessed the first demonstration that a-decay released He (Ramsay and Soddy 1903). The build up of He was soon put to use to date geological materials, initially by Rutherford in 1905 who calculated the first ever radiometric age of 500 Myr for a pitchblende sample, and then by Strutt who examined a wide variety of minerals (Strutt... 

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