Thorium natural, radioactivity

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. 

Rn-220 is another isotope of radon and belongs to the thorium decay series. Due to its short half life of 55.6 s, reports on its concentrations in those gases and in natural water are still scant. They are also important for a better estimate of our exposure to natural radioactivity and also for the geochemical study of the forma tion of those radon isotopes and their underground movement. 

Nuclear dating has been most helpful in establishing the history of the earth and of the moon and of the meteorites. The fact is, there is no other way of measuring their ages. Prior to the discovery of natural radioactivity in the late 19th century, indirect methods were used to estimate the age of the earth, but there were no real answers until the radioactivity of thorium, uranium, and potassium were discovered and we began to understand atomic structure and to realize that nuclear transformation was essentially independent of the chemical form. 

Although many nuclei are naturally radioactive, there are three main radioactive series in nature, all of which are relevant to a discussion of the isotopic composition of natural lead. These start with the elements uranium and thorium (238U, 235U and 232Th) and all end in one of the three stable isotopes... 

As thorium undergoes natural radioactive decay, a number of products, including gases, are emitted. These decay products are extremely dangerous radioactive poisons if inhaled or ingested. 

Linsalata P, Penna Franca E, Sachett I, et al. 1987. Radium, thorium, and the light rare earth elements in soils and vegetables grown in an area of high natural radioactivity. DOE Symp Ser 59 131-146. 

Thus it is evident that there are three natural radioactive isotopes of thallium, seven of lead, four of bismuth, seven elements in the polonium pleiad, three inert radioactive gases, four isotopes of radium, two of actinium, six of thorium, three eka-tantalums, and three uraniums. 

Thorium A naturally radioactive element with atomic number 90 and, as found in nature, an atomic weight of approximately 232. The fertile thorium 232 isotope is abundant and can be transmitted to fissionable uranium 233 by neutron irradiation. 

I he atomic wcighi varies because of natural variations in the isotopic composition of the element, caused by the various isotopes having different origins - I h is the end product of the thorium decay scries, while Ph and " Pb arise Irom uranium as end products of the actinium and radium series respectively. Lead-204 has no existing natural radioactive precursors. Electronic configuration l.v 2s lfc22/j"3v 3//,3i/l"4v- 4/, 4l/" 4/ IJ5v- 5/ "5t/l"bv />-. Ionic radius Pb I.IX A. Pb 1 0.7(1 A. Metallic radius 1.7502 A. Covalent radius (ip i 1.44 A. First ionization potential 7.415 cV second. 14.17 eV. Oxidation... 

It is of considerable interest to note that charge clusters can be formed in aqueous solutions and used to target dissolved radioactive materials. In experiments using low-level, naturally radioactive thorium, a considerable reduction of thorium from the solution has been achieved [6]. Charge clusters can be produced in air under various pressures [23]. However, not all arcs and sparks... 

Radium is a naturally-occurring silvery white radioactive metal that can exist in several forms called isotopes. It is formed when uranium and thorium (two other natural radioactive substances) decay (break down) in the environment. Radium has been found at very low levels in soil, water, rocks, coal, plants, and food. For example, a typical amount might be one picogram of radium per gram of soil or rock. This would be about one part of radium in one trillion (1,000,000,000,000) parts of soil or rock. These levels are not expected to change with time. 

Natural radioactivity The spontaneous disintegration of the nuclei of certain naturally occurring elements like uranium, thorium, polonium, radium, etc. is known as natural radioactivity. 

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- . ... 

One prominent and well-known kind of nuclear component is that which is produced by the decay of naturally occurring radionuclides (see Table 1). The best- and longest-known examples are He, produced by alpha decay of the natural isotopes of uranium and Th, and " Ar, produced in one branch of the beta decay of " K. (There are several other natural radionuclides which produce He by alpha decay, but whether because of low parent abundance and/or very slow decay, only in very unusual samples is the production of He not strongly dominated by uranium and thorium.) Since radioactive decay laws are well known, the ratio of daughter to parent isotope(s) in a closed system is a simple function of time, whence this phenomenon has been long and extensively exploited as a geochronometer (e.g., see Chapter 1.16). 

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... 

CAS 7439-92-1. Pb. Metallic element of atomic number 82, group IVA of the periodic table, aw 207.2, valences = 2,4, four stable isotopes. The isotopes are the end products of the disintegration of three series of natural radioactive elements uranium (206), thorium (208), and actinium (207). 

Of all impurity elements, in particular uranium and thorium contents must be extremely low. These naturally radioactive elements cause soft errors in memory circuits due to a-particle emission. 

Uranium undergoes natural radioactive decay, emitting an alpha particle, or helium nucleus, to become thorium-234. The thorium emits an electron and becomes protactinium. This nucleus continues to decay through a series of lighter and lighter isotopes of various elements until it finally reaches a stable state in the form of lead. The entire process involves fourteen distinct steps. 

Although short-lived radioactive nuclides disappear relatively quickly once they form, they are constantly being replenished because they are products of other radioactive decays. There are three long-lived radioactive nuclides (uranium-235, uranium-238, and thorium-232) that are responsible for many of the natural radioactive isotopes. 

Natural radioactivity is formed particularly by long-lived isotopes, i.e. by those with half-lives of 10 to 10 years. These isotopes are usually widely scattered in the soil. The activity level depends particularly on contents of uranium, thorium, radium and potassium the radiation energy of these elements represents as much as 98% of the total energy of radiation of all the natural radioactive elements in the soil. 

As previously noted, monazite usually contains significant amounts of thorium as well as uranium, and xenotime also contains uranium. Naturally radioactive minerals are, therefore, exposed to displacive radiation damage events over geological time scales. Accordingly, such minerals are frequently found in the metamict state, i.e. they can... 

As the detection technique for radioactivity has been refined, a number of long-lived radionuclides have been discovered in nature. The lightest have been motioned in 5.1. The heavier ones, not belonging to the natural radioactive decay series of uranium and thorium, are listed in Table 5.2. is the nuclide of lowest elemental specific activity ( 0.(XX)1 Bq/g) while the highest are Rb and Re (each —900 Bq/g). As our ability to make reliable measurements of low activities increases, the number of elem ts between potassium and lead with radioactive isotopes in nature can be expected to increase. 

Natural radioactivity provides tracers in a wide range of characteristic timescales and reactivities, which can be used as tools to study the rate of reaction and transport processes in the ocean. Apart from cosmogenic nuclides and the long-lived radioisotope K-40, the natural radioactivity in the ocean is primarily derived from the decay series of three radionuclides that were produced in the period of nucleosynthesis preceding the birth of our solar system Uranium-238, Thorium-232, and Uranium-235 (a fourth series, including Uranium-233, has already decayed away). The remaining activity of these so-called primordial nuclides in the Earth s crust, and the range of half-lives and reactivities of the elements in their decay schemes, control the present distribution of U-series nuclides in the ocean. 

Solar systems, or direct diabolic intervention, the writer feels that the exothermic argument is so strong that he, hesitantly, must look for other explanations such as collective hypnosis. Anyhow, for Crookes living 100 years ago, there was still enough of a connection with pre-scientific ideas that he suspected a maturation of the meta-elements in minerals. By the way, this is one of the rare cases of older history being optimistic and newer ideas pessimistic with exception of nuclear physics directed by human beings, the only transmutation of elements on Earth is the irreversible and uninfluenced natural radioactivity of which the chains mranium 238 to lead 206, thorium 232 to lead 208, and the rare isotope potassium 40 to argon 40 (1 percent of the atmosphere) and calcium 40 have a perceptible influence on the heat balance of the crust. 

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