Actinium emanation

In 1906 Professor Otto Hahn discovered radioactinium between actinium and actinium X (45). Actinium emanation, or actinon, which,... 

Rutherford debated the suggestion that the a-particle is a helium atom, but did not reach a definite conclusion. He mentions that Ramsay and Soddy had shown spectroscopically that radium emanation produces helium they did not mention the a-particle in 1903, but supposed that helium has some place in the sequence of radioactive changes. In 1904 Rutherford said he had no direct experimental evidence that the a-particle had a positive charge if it had it must have acquired it after its expulsion from the atom. Debierne and GieseR showed that actinium emanation forms helium. In 1906 Rutherford found that ejm for the a-particle from radium (1 5 x 10 e.s.u./g.) is half the value for the hydrogen atom, hence the a-particle could be H2+ or He++. 

Friedrich Ernst Dom in 1900. He used the same apparatus as Rutherford with thorium emanation and confirmed this. Using radium bromide he found a similar emanation, which did not penetrate aluminium as Rutherford (incorrectly) said thorium emanation did. Some doubts about the existence of radium emanation were removed by Rutherford and Soddy, who liquefied it by cooling in liquid air, and by Ramsay and Collie, who determined its spectrum. R. W. Gray and Ramsay determined its density by weighing on a microbalance and proposed for it the name m/on, shining . Actinium emanation was discovered by Debieme and by Giesel. The modem names thoron, radon, and actinon were proposed by W. Schmidt. ... 

Twenty isotopes are known. Radon-22, from radium, has a half-life of 3.823 days and is an alpha emitter Radon-220, emanating naturally from thorium and called thoron, has a half-life of 55.6 s and is also an alpha emitter. Radon-219 emanates from actinium and is called actinon. It has a half-life of 3.96 s and is also an alpha emitter. It is estimated that every square mile of soil to a depth of 6 inches contains about 1 g of radium, which releases radon in tiny amounts into the atmosphere. Radon is present in some spring waters, such as those at Hot Springs, Arkansas. 

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. 

May 14,1899 Aug. 16,1899 1899 1900 1900 Death of Nilson. Death of Bunsen. Debierne discovers actinium. Dorn discovers radon (radium emanation). Sir William Crookes discovers uranium Xj. 

ACTINON. The name of the isotope of radon (emanation), which occurs in the naturally occurring actinium, series being, produced by alpha-decay of actinium X, which is itself a radium isotope. Achnon has an atomic number of 86, a mass number of 219, and a half-life of 3.92 seconds, emitting an alpha particle to form polonium-215 (Actinium A). See also Chemical Elements and Radioactivity. 

A radioactive element is an element that disintegrates spontaneously with the emission of various rays and particles. Most commonly, the term denotes radioactive elements such as radium, radon (emanation), thorium, promethium, uranium, which occupy a definite place in the periodic table because of their atomic number. The term radioactive element is also applied to the various other nuclear species, (which arc produced by the disintegration of radium, uranium, etc.) including (he members of the uranium, actinium, thorium, and neptunium families of radioactive elements, which differ markedly in their stability, and are isotopes of elements from thallium (atomic number 81) to uranium (atomic number... 

Rn is formed by the alpha disintegration of 226Ra. Actinon, its isotope of mass number 219, is produced by alpha disintegration of 223 Ra (AcX) and is a member of the Actinium Series. Similarly, thoron, its isotope of mass number 220. is a member of the thorium senes. Since the name radon may be considered to be specific for the isotope of mass number 222 (from the radium series), the term emanation is sometimes used for element number 86 in general. Other isotopes of radon include those of mass numbers 209-218 and 221. 

Moseley then played with a problem concerning the life of an emanation of actinium, one of the radioactive elements. This period was so short that special, delicate devices had to be constructed to detect it. Together with the Polish scientist, K. Fajans, Professor of Chemistry at the University of Munich, he solved the question. The average life of the emanation was less than one five-hundredth of a second. 

Actinium was discovered a second time in 1902. German chemist Friedrich O. Giesel (1852-1927) had not heard of Debierne s earlier discovery. Giesel suggested the name emanium, from the word emanation, which means to give off rays. Debierne s name was adopted, however, because he discovered actinium first. 

Radon was discovered in 1899 by the McGill University professors Ernest Rutherford and Robert Owens, who found that radioactive thorium produced radioactive gas. They named this gaseous substance thorium emanation, later to become thoron. It was found that radium gave off a similar emanation (radon), as did actinium (actinon), in 1900 and 1904, respectively. Once the structure of the atom and the elemental transmutation process became better understood, it was determined that thoron, radon, and actinon were different isotopes of the same element (radon)— °Rn, Rn, and Rn, respectively. 

Rutherford sought for a similar gaseous emanation from radium compounds, but the quantity of these at his disposal was too small. Within a few months, however, Dorn detected the presence of the gas and three years later Debiernet found that actinium behaved likewise. The three emanations are now known as thoron of half-life 54 secs., radon 3 825 days, and actinon. 3 9 secs. 

By way of analogy, it was suggested that other radioactive elements could also evolve emanations. In 1900 the German physicist E. Dorn discovered the emanation of radium and three years later Debierne observed the emanation of actinium. Thus, two new radioactive elements were found, namely, radon and actinon. An important observation was that all the three emanations differed only in their half-lives—51.5 s for thoron, 3.8 days for radon, and 3.02 s for actinon. The longest-lived element is radon and therefore... 

Now it is clear that radioelements are just isotopes of natural radioactive elements. The three emanations are the isotopes of the radioactive element radon, the number 86 in the periodic system. The radioactive families consist of the isotopes of uranium, thorium, polonium, and actinium. Later many stable elements were found to have isotopes. An interesting observation may be made here. When a stable element was discovered this meant simultaneous discovery of all its isotopes. But in the cases of natural radioactive elements individual isotopes were discovered first. The discovery of radioelements was the discovery of isotopes. This was a significant difference between stable and radioactive elements in connection with the search for them in nature. No wonder that the periodic system was badly strained when accommodation had to be found for the multitude of radioelements,—it was a classification of elements, after all, not isotopes. The discovery of the displacement law and isotopy greatly clarified the situation and paved the way for future advances. 

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