Uranium radioactive decay series

Each of the uranium isotopes is a member of one of the four possible radioactive decay series involving successive alpha and beta decay reactions. is the longest-lived member and the parent of the 4n -t- 2 series, which includes as a member. is the longest-lived member and the natural parent of the 4n + 3 series, decays by alpha emission to Th, the longest-lived member and natural parent of the 4n series, to be described in Chaps. 6 and 8. decays by alpha emission to Th, also a member of the 4n series. Problems arising from the radioactivity of and its daughters are discussed in Chap. 8. U decays by beta emission to Np, the longest-lived member of the 4n -I- 1 series, the only one not of natural occurrence. is an intermediate member of this series. 

Nuclide name Half-life Radiation uranium 

The daughters of of principal radiological concern in uranium mills and refineries are the long-lived nuclides Th and Ra (radium) and gaseous Rn (radon). The amount of these nuclides in uranium mills and tailings piles is discussed in Sec. 8.9 their occunence in uranium refineries is discussed in Secs. 9.2 and 9.7. 

This is only one-twenty-second of the activity of U and each of its dau ters. This small contribution to the activity of naturd uranium will be disregarded in the remainder of this chapter. 

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When uranium-238 decays it undergoes a series of 14 alpha and beta decays. This series of steps is known as the uranium radioactive decay series. Helium gas is released (due to the eight beta decays) and the final product is stable lead-206. For every uranium-238 atom that decays, one atom of lead-206 is produced at the end of the decay series. 

Polonium occurs three times in the course of the uranium radioactive decay series. Polonium-210 decays via alpha emission with a half-life of 138.4 days. Write an equation for its decay. 

Polonium, completing the elements of Group 16, is radioactive and one of the rarest naturally occurring elements (about 3 x 10 " % of the Earth s crust). The main natural source of polonium is uranium ores, which contain about lO g of Po per ton. The isotope 210-Po, occurring in uranium (and also thorium) minerals as an intermediate in the radioactive decay series, was discovered by M. S. Curie in 1898. 

Radon is a naturally occurring, chemically inert, radioactive gas. It is colorless, odorless, and tasteless. It is part of the uranium-238 decay series, the direct decay product of radium-226. Radon moves to the earth s surface through tiny openings and cracks in soil and rocks. High concentrations of radon can be found in soils derived from uranium-bearing rocks, such as pitchblende and some... 

Natural lead, a metallic element, is a mixture of the following four isotopes lead-204, lead-206, lead-207, and lead-208. Only lead-204 is a primordial isotope of nonradiogenic origin all the others are radiogenic, each isotope being the end product of one of the radioactive decay series of isotopes of thorium or uranium, namely, uranium-238, uranium-235, and thorium-232 the decay series of the uranium isotopes are listed in Figure 12 ... 

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. 

When thorium emits alpha particles, it disintegrates into other daughter radionuclides (radioactive materials), such as radium-226 and radon-222 (from thorium-230 in the uranium-238 decay series) or radium-228 and thoron (radon-220 from thorium-232 in the thorium decay series). It eventually decays to stable lead-208 or -206, which is not radioactive. More information about the decay of thorium can be found in Chapter 3. The toxicological characteristics of radon, radium, and lead are the subject of separate ATSDR Toxicological profiles. 

Radioactive decay usually does not immediately lead to a stable end product, but to other unstable nuclei that form a decay series (Kiefer 1990). The most important examples of unstable nuclei are started by very heavy, naturally occurring nuclei. Because the mass number changes only with a decay, all members of a series can be classified according to their mass numbers (see the uranium-238 decay series in Figure 32.2). A total of three natural decay series — formed at the birth of our planet — are named after their parent isotope Th, and (Figure 32.3). Several shorter decay series also exist. For example, Sr decays with a Tb 1/2 of 28 years by [3 emission to °Y, which in turn disintegrates (P emission) with a Tb 1/2 of 64 h to the stable °Zr (Kiefer 1990). Other examples of known radionuclides since the Earth s origin include " °K and Rb. In hazard assessments, all members of a decay series must be considered. 

Daughters of alpha emitters The recoil method can also be useful for the separation of daughter products produced by a decay of a parent. This technique has been applied to studies of short-lived daughters In the radioactive decay series of uranium, thorium, and actinium (175) ... 

One radioactive decay series that begins with uranium-235 and ends with lead-207 shows the partial sequence of emissions alpha, beta, alpha, beta, alpha, alpha, alpha, alpha, beta, beta, and alpha. Write an equation for each reaction in the series. 

A series of nuclear reactions that begins with an unstable nucleus and results in the formation of a stable nucleus is called a radioactive decay series. As you can see in Figure 25-11, uranium-238 first decays to thorium-235, which in turn decays to protactinium-234. Decay reactions continue until a stable nucleus, lead-206, is formed. 

Radioactive elements in rocks (see Section 2.8), most importantly potassium (K) and heavy elements such as radium (Ra), uranium (U) and thorium (Th), can release gases. Argon (Ar) arises from potassium decay and radon (Rn, a radioactive gas that has a half-life of 3.8 days) from radium decay. The uranium-thorium decay series results in the production of a particles, which are helium nuclei. Once these nuclei capture electrons, helium has effectively been added to the atmosphere. 

Th, U and U are the first members of radioactive decay series, forming other radioactive elements with atomic numbers 84-91, which are therefore present in small amounts in thorium and uranium ores. The 238U series is illustrated in Topic A. Fig. 1. Each series ends with a... 

Radium is element number 88, in which all of its isotopes are radioactive hence, what little radium is found on Earth is mostly as a trace element in uranium ores. The most common isotope has a mass number of 226 with a half-life of 1,604 years. The second longest-lived isotope is radium 228, with a half-life of 5.77 years. The other isotopes have much shorter half-lives ranging from microseconds to days. Radium is constantly being formed as part of the radioactive decay series of uranium and thorium. Because it decays so quickly, however, only minute quantities of radium ever exist at any one time. 

The disintegration of a radioactive nucleus is often the beginning of a radioactive decay series, which is a sequence of nuclear reactions that ultimately result in the formation of a stable isotope. Table 23.3 shows the decay series of naturally occurring uranium-238, which involves 14 steps. This decay scheme, known as the uranium decay series, also shows the half-lives of all the products. 

It is important to be able to balance the nuclear reaction for each of the steps in a radioactive decay series. For example, the first step in the uranium decay series is the decay of uranium-238 to thorium-234, with the emission of an a particle. Hence, the reaction is... 

Uranium-238 is the parent of a natural radioactive decay series that can be used to determine the ages of rocks. 

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. 

Another common method of dating U-minerals is by considering its content of lead isotopes. Lead has four stable isotopes of which three are end products of radioactive decay series. The fourth lead isotope, Pb, is foimd in lead minerals in about 1.4% isotopic abundance and has no radio-genetic origin. At the time of formation of the earth, all the Pb in nature must have been mixed with unknown amounts of the other lead isotopes. If a lead-containing mineral lacks Pb, it can be assumed that presence of the other lead isotopes together with uranium and/or thorium must be due to their formation in the decay... 

The accurate clocks provided by the uranium-thorium decay series enable us to extract rate information from the measurement of radioactive disequilibria in the ocean. Among the wide spectrum of available tracers, a mother-daughter pair with appropriate reactivities and half-lives can be found for a multitude of processes related to particle transport, water mass transport and mixing, and gas exchange (Table 5). 

Radon-222 is a direct decay product of radium-226, which is part of the decay series that begins with uranium-238 (see Chapter 3, Figure 3-1). Thorium-230 and thorium-234 are also part of this decay series. Uranium, thorium, and radium are the subjectof other ATSDR Toxicological Profiles. Other isotopes of radon, such as radon-219 and radon-220, are formed in other radioactive decay series. Flowever, radon-219 usually is not considered in the evaluation of radon-induced health effects because it is not abundant in the environment (Radon-219 is part of the decay chain of uranium-235, a relatively rare isotope) and has an extremely short half-life (4 seconds). Radon-220 is also usually not considered when evaluating radon-related health effects. While the average rate of production of radon-220 is about the same as radon-222, the amount of radon-220 entering the environment is much less than that of radon-222 because of the short half-life of radon-220 (56 seconds). All discussions of radon in the text refer to radon-222. 

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