Thorium isotope

Once uranium is incorporated into buried bone, shell, coral, or speleothems, the isotope uranium-235 decays, initially into the short-lived isotope (thorium-231) and then into long-lived protoactinium-231. Uranium-238, on the other hand, decays first into two successive short-lived isotopes (thorium-234 and protoactinium-234) and only then into a long-lived isotope, uranium-234 (see Fig. 12). The decay of uranium-235 to long-lived protoactinium-231 is used to date events up to 150,000 years in age that of uranium-234 (derived from uranium-238) to thorium-230 is of use for dating events within the time range 1000-500,000 years. 

More than 99% of natural thorium exists in the form (isotope) thorium-232. Besides this natural thorium isotope, there are more than 10 other different isotopes that can be artificially produced. In the environment, thorium-232 exists in various combinations with other minerals, such as silica. Most thorium compounds commonly found in the environment do not dissolve easily in water and do not evaporate from soil or water into the air. 

The transport of atmospherically deposited thorium from soil to plants is low. The soil to plant transfer coefficients (concentration in dry plant to concentration in dry soil) were estimated to be 10 to 7x10 by Garten (1978) and 0.6x10 for thorium-232 by Linsalata et al. (1989). The root systems of grasses and weeds adsorb thorium from the soil but the transport of thorium from the root to the aboveground parts of the plant is not very extensive, as indicated by 100-fold higher concentrations of all three isotopes (thorium-228, thorium-230, and thorium-232) in the root than in the aboveground parts of the plant (Taskayev et al. 1986). However, Ibrahim and Whicker (1988)... 

Environmental monitoring of nuclear contamination, including the determination of the concentration and isotope ratios of long-lived radionuchdes, such as uranium, plutonium isotopes, thorium, Np, Se, Sr, I and others, at trace and ultratrace levels, is a fast growing and fascinating application field for inorganic mass spectrometry." " Among the environmentally important radionuclides, I, Sr, uranium and transuranium elements are of special importance. For example, the natural I inventory in the atmosphere, hydrosphere and biosphere has been estimated to be about 263 kg. ... 

MeV. Natural isotope (Thorium-X, Thorium Series), T1 /2 = 3.6 days, decays to radioactive 220Rn by alphas of 5.7 MeV. Natural isotope 226Ra (Uranium Series), Tl/2 = 1600 years, decays to radioactive 222Ri by alphas of 4.8 MeV. Natural isotope 22SRa (Mesothorium = 1, Thorium Series), Tl/2 = 6.7 years, decays to radioactive 223. 0 by betas of 0.05 MeV. 

Many of the radioactive isotopes that occur in nature are related to each other. For example, when uranium-235 breaks apart, it forms a new isotope, thorium-231. But thorium-231 is radioactive also. It breaks apart to form protactinium-231. And protactinium-231 is also radioactive. It breaks apart to form actinium-227. This series goes on for 14 more steps until a stable isotope is finally formed. 

One of the earliest applications of radioactive tracer techniques to surface investigations is that of Paneth and Vorwerk/ who used the Pb isotope, thorium B, to determine the surface area of powdered PbS04 by exchange between the surface Pb ions of the solid and the radioactive Pb in solution. Since then a vast number of studies of catalytic systems involving the use of radioisotopes have been reported. As the earlier literature has been extensively reviewed by Campbell and Thomson, the present Report is mainly concerned with the literature published between 1970 and mid-1982, particular emphasis being placed on new developments in experimental methods. 

November 13, 1945. When power is produced in useful form the use of the U — U 3 conversion even when the conversion is less than unity becomes more attractive in that the non-fissionable isotope (thorium) will furnish the bulb energy with only a small loss of U in the 70 inlet tank connected to said inlet, each of said tanks hav-process. ing a wall in common with a portion of the wall of said... 

Similarly, natural thorium is a mononuclidic element, i.e., it has only one radioactive isotope thorium-232, parent radionuclide of the natural decay chain (4n), therefore, for a naturally occurring radioactive material containing a mass fraction of natural thorium, the specific activity of the parent radionuclide is given by ... 

The half-life of the radioactive isotope thorium-234 is 24.1 days. How long will it take for the mass of a sample of thorium-234 to decay from 84.5 milligrams to 20.9 milligrams ... 

As interest in the high-temperature reactor revived at the end of 1955, a working party was set up at Harwell. The new design was also intended to exploit what was described as the thorium cycle, whereby thorium 232 is converted to uranium 233, which is a fissile isotope. Thorium is both cheap and abundant, and this was seen as another way of stretching out the amount of uranium used, since uranium was then thought to be in short supply. 

FERTILE ISOTOPE. A fertile isotope or fertile material is a substance that is not itself fissionable by thermal neutrons but can be converted into fissfle material. This conversion is typically carried out by irradiation in a nuclear reactor. There are two basic fertile isotopes thorium-232 and uranium-238. When these fertile materials capture neutrons, they are converted into the fissile isotopes uranium-233 and plutonium-239, respectively. 

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