Thorium radioactivity

Freshly purified natural thorium contains significant amounts of three radioactive nuclides long-lived Th, an equal activity of its daughter Th, and an amount of Th whose relative 

Thorium that has been irradiated in a nuclear reactor will contain much hi er concentrations of Th and its daughters than natural thorium because of the sequence of reactions 

This makes irradiated thorium much more toxic than natural thorium until it is separated from and stored sufficiently long (10 to 20 years) for the excess 1.91-year Th to decay (Prob. 6.1). 

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The air concentrations of thorium and other airborne radioactivity near a former thorium and rare-earth extraction facility in the United States were measured. The maximum radioactivity due to all three isotopes of thorium at a site about 450 feet from the primary waste pile was 0.66 fCi/m. Although the background thorium radioactivity was not reported, the total radioactivity at a site about 4000 feet south of the waste pile was about 3.5 times lower than a site 450 feet from the pile (Jensen et al. 1984). 

There is subterranean production of chlorine-36 and the world average chlorine contents of granite and basalt have been given as around 50 and 200 ppm, respectively. Sedimentary rocks have variable contents ranging from 10 ppm in sandstones to 20,000 ppm in deep-sea limestones. Rock outcrops are exposed to the cosmic neutron flux so that some chlorine-36 results from neutron capture by chlorine-35, but, below a few meters, it is ineffectual. Nonetheless, some chlorine-36 results from an in situ neutron flux in rock matrices caused by (a,n) reactions triggered by alpha particles from uranium and thorium radioactive decay systems. This flux may be of the order of 10 cm s (Kuhn et al. 1984). 

Table 22.2 shows some properties and compositions for the two end minerals. In minerals in the series some other metals can be present in varying contents calcium, rare earth metals, titanium, uranium, thorium. Radioactive elements present have an influence on the minerals, changing their originally lustrous, black surface to a dull brownish-black color. In this process the hardness decreases considerably. 

For some applications, such as submicron metallization of silicon with aluminum, extremely high purities are required and the allowable level may be very low for some materials. For example, the purity specified for alununum may be 99.999% pure with < lOppb (parts per billion) of uranium and thorium (radioactive materials). 

This is a radioactive element. It occurs in minute traces in barium and thorium minerals, but it can be produced by irradiation of bismuth in a nuclear reactor. (The study of its chemistry presents great difficulty because of its intense a radiation). 

Care must be taken in handling radon, as with other radioactive materials. The main hazard is from inhalation of the element and its solid daughters which are collected on dust in the air. Good ventilation should be provided where radium, thorium, or actinium is stored to prevent build-up of the element. Radon build-up is a health consideration in uranium mines. Recently radon build-up in homes has been a concern. Many deaths from lung cancer are caused by radon exposure. In the U.S. it is recommended that remedial action be taken if the air in homes exceeds 4 pCi/1. 

Cerium is a component of misch metal, which is extensively used in the manufacture of pyrophoric alloys for cigarette lighters. While cerium is not radioactive, the impure commercial grade may contain traces of thorium, which is radioactive. The oxide is an important constituent of incandescent gas mantles and is emerging as a hydrocarbon catalyst in self cleaning ovens. In this application it can be incorporated into oven walls to prevent the collection of cooking residues. 

Lead occurs naturally as a mixture of four non-radioactive isotopes, and Pb, as well as the radioactive isotopes ° Pb and Pb. All but Pb arise by radioactive decay of uranium and thorium. Such decay products are known as radiogenic isotopes. 

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. 

Argon-40 [7440-37-1] is created by the decay of potassium-40. The various isotopes of radon, all having short half-Hves, are formed by the radioactive decay of radium, actinium, and thorium. Krypton and xenon are products of uranium and plutonium fission, and appreciable quantities of both are evolved during the reprocessing of spent fuel elements from nuclear reactors (qv) (see Radioactive tracers). 

Radioactivity occurs naturally in earth minerals containing uranium and thorium. It also results from two principal processes arising from bombardment of atomic nuclei by particles such as neutrons, ie, activation and fission. Activation involves the absorption of a neutron by a stable nucleus to form an unstable nucleus. An example is the neutron reaction of a neutron and cobalt-59 to yield cobalt-60 [10198 0-0] Co, a 5.26-yr half-life gamma-ray emitter. Another is the absorption of a neutron by uranium-238 [24678-82-8] to produce plutonium-239 [15117 8-5], Pu, as occurs in the fuel of a nuclear... 

The same chemical separation research was done on thorium ores, leading to the discovery of a completely different set of radioactivities. Although the chemists made fundamental distinctions among the radioactivities based on chemical properties, it was often simpler to distinguish the radiation by the rate at which the radioactivity decayed. For uranium and thorium the level of radioactivity was independent of time. For most of the radioactivities separated from these elements, however, the activity showed an observable decrease with time and it was found that the rate of decrease was characteristic of each radioactive species. Each species had a unique half-life, ie, the time during which the activity was reduced to half of its initial value. 

By this time, the Periodic Table of elements was well developed, although it was considered a function of the atomic mass rather than atomic number. Before the discovery of radioactivity, it had been estabUshed that each natural element had a unique mass thus it was assumed that each element was made up of only one type of atom. Some of the radioactivities found in both the uranium and thorium decays had similar chemical properties, but because these had different half-Hves it was assumed that there were different elements. It became clear, however, that if all the different radioactivities from uranium and thorium were separate elements, there would be too many to fit into the Periodic Table. 

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... 

Historically the use of mona2ite, a thorium-containing mineral, as the principal lanthanide resource led to confusion regarding the relation between radioactivity and the lanthanides. Inadequate separations produced Th-contaminated Ln products. Modem processing technology results in products that meet all regulatory requirements. 

Uranium and thorium are the first members of natural radioactive chain which makes their determination in natural materials interesting from geochemical and radioecological aspect. They are quantitatively determined as elements by spectrophotometric method and/or their radioisotopes by alpha spectrometry. It is necessary to develop inexpensive, rapid and sensitive methods for the routine researches because of continuous monitoring of the radioactivity level. 

SI 1962/2710 Radioactive Substances (Uranium and Thorium) Exemption Order... 

SI 1962/2711 Radioactive Substances (Prepared Uranium and Thorium Compounds) Order... 

The bulk of both monazite and bastnaesite is made up of Ce, La, Nd and Pr (in that order) but, whereas monazite typically contains around 5-10% Th02 and 3% yttrium earths, these and the heavy lanthanides are virtually absent in bastnaesite. Although thorium is only weakly radioactive it is contaminated with daughter elements such as Ra which are more active and therefore require careful handling during the processing of monazite. This is a complication not encountered in the processing of bastnaesite. 

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... 

Spectral Gamma Ray Log. This log makes use of a very efficient tool that records the individual response to the different radioactive minerals. These minerals include potassium-40 and the elements in the uranium family as well as those in the thorium family. The GR spectrum emitted by each element is made up of easily identifiable lines. As the result of the Compton effect, the counter records a continuous spectrum. The presence of potassium, uranium and thorium can be quantitatively evaluated only with the help of a computer that calculates in real time the amounts present. The counter consists of a crystal optically coupled to a photomultiplier. The radiation level is measured in several energy windows. 

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. 

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