The thorium series

URANIUM compounds), Pb from the thorium series, and Pb from the actinium series (see Actinides and transactinides). The crystal stmcture of lead is face-centered cubic the length of the edge of the cell is 0.49389 nm the number of atoms per unit cell is four. Other properties are Hsted in Table 1. 

ISOTOPES There are 41 isotopes of polonium. They range from Po-188 to Po-219. All of them are radioactive with half-lives ranging from a few milliseconds to 102 years, the latter for its most stable isotope Po-209. Polonium is involved with several radioactive decay series, including the actinium series, Po-211 and Po-215 the thorium series, Po-212 and Po-216 and the uranium decay series, Po-210, Po-214, and Po-218. 

Joyet G. 1971. The thorium-series in cigarettes and lungs of smokers. Experientia 27 85-89. 

The thorium series is apparently independent of the three just named. In 1905 Otto Hahn, working under Sir William Ramsay s direction, discovered radiothorium in the residues from a Ceylon mineral called thorianite, and two years later he showed that mesothorium is an intermediate disintegration product (19, 35, 36). 

In 1902 Rutherford and Soddy added ammonium hydroxide to a thorium solution, filtered off the thorium hydroxide precipitate, and found that, after they evaporated the thorium-free filtrate to dryness and fumed off the ammonium salts, the residue was much more active than the original thorium salt (18). This observation led them to the discovery of a new member of the thorium series, which they called thorium X. 

The Thorium Series. This series commences with U2Th and ends with the stable isotope 3n Pb. The decay scheme is represented by ... 

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. 

In the early stages of dating by nuclear methods, the measurement of He formed by a decay in the natural decay series (9, 6 and 7 He atoms in the uranium series, the thorium series and the actinium series, respectively) has been applied. The preferred method was the U/He method which allows dating of samples with very low concentrations of U of the order of 1 mg/kg. Helium produced by a decay is driven out by heating and measured by sensitive methods, e.g. by MS. However, it is difficult to ensure the prerequisites of dating by the U/He method neither " He nor a-emitting members of the decay series must be lost and no " He atoms must be produced by other processes such as decay of Th and spallation processes in meteorites. 

Through the efforts of many investigators the chemistry of the radioactive elements of the uranium series and the thorium series was then unravelled. 

The Thorium Series. The third natural radioactive series begins with the long-lived naturally occurring isotope of thorium, Th, which has half-life 1.39 X years (Fig. 33-4). It leads to another stable isotope of lead, Pb- . ... 

The 4n series - the thorium series The 4n + 1 series — the neptunium series The 4n + 2 series = the uranium-radium series The 4n + 3 series - the uranium-actinium series... 

The series of Radioactive disintegrations the uranium-radium series, the uranium-actinium series, the thorium series, and the neptunium series. The age of the earth. The fundamental particles electron, proton, positron, neutron, positive, negative, and neutral mesons, neutrino. The photon (light quantum) the energy of a photon, hv. Planck s constant. The wave-particle duality of light and of matter. The wavelengths of electrons. 

A radionuclide, upon undergoing disintegration of a particular type, yields a specified nuclide. The original radionuclide is called the parent and the decay product is called the daughter. The daughter may also be a radionuclide. A succession of nuclides, each of which transforms by radioactive disintegration into the next until a stable nuclide results, is called a radioactive series. Examples of such series are the uranium series and the thorium series. 

High-purity detection systems having a very low background are suitable tools for the direct measurement of low-level radioactivity in environmental samples. The background features of the detection system are of considerable importance because they have to be known for one to obtain an estimate of the detection limit and of the minimum detectable activity (Curie, 1968). The natural radioactivity background originates from the uranium and the thorium series from K and from cosmic rays. Natural radioactivity is found in most materials, and it is necessary to shield the... 

The main source of terrestrial radiation is long-living isotopes of the uranium-radium series the thorium series ( Th) and the actinium series... 

FlC- 1-2, The three naturally occurring radioactive decay series and the man-made neptunium series. Although (which is the parent to the actinium series) and (which is the parent to the thorium series) have been discovered in nature, die decay series shown here begin with the most abundant Icmg-Uved nuclides. 

The half-lives T of a-partide emitters in the thorium series and the energy E of these o-partides are given in table 1 (Mattauch, Nudear physics tables , Intersdence, 1946). 

There are lour radiooc.livt, decay series lhat, by sequences of u and emissions, result in the eventual tormalion ot a stable isotope of lead or bismuth Members of each series have mass numbers which are exactly divisible by 4 (the thorium series, 4n), or alter being divided by lour leave remainders of I (the neptunium series, 4n i-1),... 

Th produces stable Pb after the emissions of six a particles and four P particles and constitutes the thorium series (A = 4n). The following expression summarizes these data ... 

The exponential laws of radioactive-series decay and growth of radionuclides were first formulated by Rutherford and Soddy in 1902, to explain their results (Rutherford and Soddy 1902,1903) on the thorium series of radionuclides. In 1910, Bateman (Bateman 1910) derived generalized mathematical expressions that were used to describe the decay and growth of the naturally occurring actinium, uranium, and thorium series until the discovery of nuclear fission and other new radioactive decay series were found in the 1940s. For the description of half-lives and decay constants, activities and number of radionuclides involved in the decay of two radionuclides, Friedlander et al. (1981) have given a representative overview (see also O Chap. 5 in Vol. 1). 

Once it became clear that radioactive elements were decaying to new elements, which were themselves radioactive, a great deal of effort was expended in working out the decay sequences. In most cases the new elements were at first obtained in quantities too small to be weighed and were distinguished from each other only by the type of decay they exhibited and the rate at which the decay occurred. Three decay series were elucidated the uranium series proceeded through radium and terminated with the stable radium G the thorium series ended in the stable thorium D and the actinium series ended in actinium D. Between them, these series contained around 25 new radioelements. 

Through the efforts of many investigators the chemistry of the radioactive elements of the uranium series and the thorium series was unraveled during the first two decades of the twentieth century, and that of the neptunium series during a few years from 1939 on. 

---