Half-life actinium

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. 

Gr. aktis, aktinos, beam or ray). Discovered by Andre Debierne in 1899 and independently by F. Giesel in 1902. Occurs naturally in association with uranium minerals. Actinium-227, a decay product of uranium-235, is a beta emitter with a 21.6-year half-life. Its principal decay products are thorium-227 (18.5-day half-life), radium-223 (11.4-day half-life), and a number of short-lived products including radon, bismuth, polonium, and lead isotopes. In equilibrium with its decay products, it is a powerful source of alpha rays. Actinium metal has been prepared by the reduction of actinium fluoride with lithium vapor at about 1100 to 1300-degrees G. The chemical behavior of actinium is similar to that of the rare earths, particularly lanthanum. Purified actinium comes into equilibrium with its decay products at the end of 185 days, and then decays according to its 21.6-year half-life. It is about 150 times as active as radium, making it of value in the production of neutrons. 

Each of the elements has a number of isotopes (2,4), all radioactive and some of which can be obtained in isotopicaHy pure form. More than 200 in number and mosdy synthetic in origin, they are produced by neutron or charged-particle induced transmutations (2,4). The known radioactive isotopes are distributed among the 15 elements approximately as follows actinium and thorium, 25 each protactinium, 20 uranium, neptunium, plutonium, americium, curium, californium, einsteinium, and fermium, 15 each herkelium, mendelevium, nobehum, and lawrencium, 10 each. There is frequently a need for values to be assigned for the atomic weights of the actinide elements. Any precise experimental work would require a value for the isotope or isotopic mixture being used, but where there is a purely formal demand for atomic weights, mass numbers that are chosen on the basis of half-life and availabiUty have customarily been used. A Hst of these is provided in Table 1. 

The final member of the group, actinium, was identified in uranium minerals by A. Debieme in 1899, the year after P. and M. Curie had discovered polonium and radium in the same minerals. However, the naturally occurring isotope, Ac, is a emitter with a half-life of 21.77 y and the intense y activity of its decay products makes it difficult to study. 

The actinoid elements (or actinides An) constitute a series of 14 elements which are formed by the progressive filling of the 5/ electron shell and follow actinium in the periodic table (atomic numbers 90-103). All of the isotopes of the actinide elements are radioactive and only four of the primordial isotopes, Th, and " " Pu, have a sufficient long half-life for there to be any of these left in nature. 

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. 

Strongly radioactive, short-lived element that can be found in tiny amounts in uranium ores. It arises fleetingly from 235U in its decay chain through actinium (227Ac). Is only of scientific value as it has a maximum half-life of about 22 minutes. Nevertheless, in its short existence it is the atom with the largest diameter (0.270 nm cesium 0.265 nm). 

Francium - the atomic number is 87 and the chemical symbol is Fr. The name derives from the country France , where the French physicist Marguerite Percy from the Curie Institute in Paris, France discovered it in 1939 in the alpha particle decay of actinium, Ac => He => Fr, which was known as actinium-K and has a half-life of 22 minutes. An earlier claim of discovery in 1930 with the element name Virginium was determined to be incorrect. A similar claim for discovery of the element with atomic number 87 and named moldavium was also determined to be incorrect. The longest half-life associated with this unstable element is 22 minute Fr. 

Actinium is the last (bottom) member of group 3 (IIIB) of elements in the periodic table and the first of the actinide series of metallic elements that share similar chemical and physical characteristics. Actinium is also closely related in its characteristics to the element lanthanum, which is located just above it in group 3. The elements in this series range from atomic number 89 (actinium) through 103 (lawrencium). Actiniums most stable isotope is actinium-227, with a half-life of about 22 years. It decays into Fr-223 by alpha decay and Th-227 through beta decay, and both of these isotopes are decay products from uranium-235. 

It was first identified and named brevium, meaning brief, by Kasimir Fajans and O. H. Gohring in 1913 because of its extremely short half-life. In 1918 Otto Hahn (1879—1968) and Lise Meitner (1878-1968) independently discovered a new radioactive element that decayed from uranium into (actinium). Other researchers named it uranium X2. It was not until 1918 that researchers were able to identify independently more of the elements properties and declare it as the new element 91 that was then named protactinium. This is another case in which several researchers may have discovered the same element. Some references continue to give credit for protactinium s discovery to Frederich Soddy (1877—1956) and John A. Cranston (dates unknown), as well as to Hahn and Meitner. 

Although in a strict sense not a member of the actinide series, actinium is included here for completeness as lanthanum is frequently included in the lanthanide series. The longest lived isotope of actinium is with a half-life of 21.8 years. It occurs in nature from the decay... 

In 1899, Andre Debierne added ammonium hydroxide to a solution of the U mineral pitchblende. When the lanthanoids precipitated as the hydroxides, a radioactive species was carried along. This element, which was a product of the radioactive decay of U-235 was named actinium. The species was Ac-227 (half life 21.77 years)... 

The actual discovery was made by Mile. Marguerite Perey at the Curie Institute in Paris. In 1939 she purified an actinium preparation by removing all the known decay products of this element. In her preparation she observed a rapid rise in beta activity which could not be due to any known substance. She was able to show that, while most of the actinium formed radioactinium, an isotope of thorium, by beta emission, 1.2 0.1 per cent of the disintegration of actinium occurred by alpha emission and gave rise to a new element, which she provisionally called actinium K, symbol AcK (35, 36). This decayed rapidly by beta emission to produce AcX, an isotope of radium, which was also formed by alpha emission from radioactinium. Thus AcK, with its short half-life, had been missed previously because its disintegration gave the same product as that from the more plentiful radioactinium. 

The failure to discover francium earlier is easy to understand when it is remembered that the half-life of the longest lived isotope is only 21 minutes. This gives the element the distinction of being the most unstable to radioactive disintegration of all elements up to number 98 (38). It is also noteworthy that this is the only element in the group discussed in this chapter which was not discovered by artificial preparation in the laboratory. Nevertheless, the rarity of actinium in nature is so great that this element is best prepared artificially when its properties or those of its daughter elements are to be studied. 

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. 

PROTACTINIUM. [CAS 7440-13-13], Chemical element, symbol Pa, at. no. 91, at. wt, 231.036, radioactive metal of the Actinide Series, mp is estimated at less than 1600°C, All isotopes arc radioactive. The most stable isotope is 23IPa with a half-life of 3,43 v 104 years, The latter is a second-generation daughter of a5U and a member of the actinium (2n + 3) decay series, See also Radioactivity, Electronic configuration... 

A tiny amount of a very unstable species (half-life, 21 minutes) has been detected among the decay products of actinium tracer experiments by Mile. M. Perey showed that this species has the same chemistry as that of cesium and is presumably the heaviest alkali metal. It is named francium after Mile. Perey s homeland. 

Both a 4n and a 4n + 3 series of heavy radioactive elements occur naturally. The 4n series is sometimes called the thorium series, since its long-lived parent is Th232 (half-life, 14,000,000,000 years), whereas the 4n + 3 series is the actinium series. The long-lived parent of the latter is U235 (half-life 707,000,000 years), but unlike the 4n + 2 series, one of its members is actinium (Ac227). Final members of both of these series are lead isotopes, Pb208 and Pb207. 

Up till a few years ago four elements were still missing from the roll-call, in fact 43, 61, 85, and 87, although their discovery had been announced repeatedly but always incorrectly. These elements have now all been prepared artificially and they have been found to be radioactive, while there are also grounds for assuming that stable isotopes of these elements cannot exist. These elements, if they have ever existed, have, at least as far as the first two are concerned, very probably died out on earth long ago, just as radium (half-life 1590 years) would also have remained unknown to us if it had not continually originated afresh from the extremely slowly decaying uranium (half-life 4.49 io9 years). The presence of 87 in extremely small quantities in the decomposition products of actinium was first dis-... 

The actinides are all radioactive elements. Actinium, thorium, protactinium, and uranium are the only four actinides that have been found in the environment the others are artificial, being produced through various nuclear reactions. It should be noted that at the creation of the universe some amount of Pu could have been formed however, with an 80 million year half-life, it would have fully decayed during the past 10 billion years. 

The great variety of radionuclides present in thorium and uranium ores are listed in Tables 4.1, 4.2 and 4.3. Whereas thorium has only one isotope with a very long half-life (- Th), uranium has two and giving ri.se to one decay scries for Th and two for U. In order to distinguish the two decay series of U, they were named after long-lived members of practical importance the uranium-radium series and the actinium series. The uranium-radium series includes the most important radium isotope ( Ra) and the actinium scries the most important actinium isotope ( Ac),... 

The natural radioelements are listed in Table 14.1. Isotopes of these elements are members of the uranium, actinium and thorium families (Table 1.2, and Tables 4.1 to 4.3). In the ores of U and Th the concentrations of natural radioelements are relatively high and proportional to the half-life. The average concentration of U in the earth s crust is about 2.9 mg/kg (ppm) and that of Th about 11 mg/kg (ppm). The... 

In the case of Th, the attainment of radioactive equilibrium with the daughter nuclides is very slow, because of the long half-life of Ra (q/2 = 5.75 y). Th can be determined directly by measuring its a radiation, but the measurement of Po is more sensitive (about 10 g Th can be determined in this way in 1 g of rock material). Other methods are based on the separation and measurement of Ra or Rn. In all determinations of Th, the possibility of the presence of radioactive impurities, mainly of members of the uranium and actinium families, has to be taken into account. 

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