A Natural Radioactive Decay Series

The radioactive elements in our environment are all undergoing radioactive decay. They are always present in our environment because they either have very long half-lives (billions of years) or they are continuously being formed by some 

The daughter nuclide, Th-234, is itself radioactive to Pa-234 with a half-life of 24.1 days. 

Suppose that you start with 1 million atoms of a particular radioactive isotope. How many half-lives would be required to reduce the number of imdecayed atoms to fewer than 1000  

6 Radiocarbon Dating Using Radioactivity to Measure the Age of Fossiis and Other Artifacts 

Archaeologists, geologists, antiiropologists, and odier scientists take advantage of the presence of natural radioactivity in our environment to estimate the ages of fossils and artifacts with a technique called radiocarbon dating. For example, in 

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

Uranium-238 is the parent of a natural radioactive decay series. 

Radioactive nuclei emit a particles, 13 particles, positrons, or y rays. The equation for a nuclear reaction includes the particles emitted, and both the mass numbers and the atomic numbers must balance. Uranium-238 is the parent of a natural radioactive decay series. A number of radioactive isotopes, such as and C, can be used to date objects. Artificially radioactive elements are created by the bombardment of other elements by accelerated neutrons, protons, or a particles. Nuclear fission is the splitting of a large nucleus into smaller nuclei plus neutrons. When these neutrons are captured efficiently by other nuclei, an uncontrollable chain reaction can occur. Nuclear reactors use the heat... 

FIGURE 8-2 A natural radioactive decay series. Alpha decay is shown by arrows that go down and to the left. Beta decay is shown by arrows to the right. The half-life is shown for each decay process. 

The stage was now set for the 1913 papers published independently by Fajans (1913b) and by Soddy (1913a). The paper by Fajans was published a couple of weeks prior to that by Soddy. Soddy has stated that he had not seen the Fajans paper at the time when he wrote his paper. Both papers try to generalize experimental observations on the chemical identities of decay products in the three natural radioactive decay series. 

Most of the known chemistry of polonium is based on the naturally occurring radioactive isotope polonium-210, which is a natural radioactive decay by-product of the uranium decay series. Its melting point is 254°C, its boiling point is 962°C, and its density is 9.32g/cm. ... 

Because all long natural radioactive decay series end up in lead, Pb made from different ores contain slightly different isotopic abundances of lead isotopes. An imusual use of this fact was made by Andrasko et. al. to identify smears and fragments from lead bullets used in a homicide case, so that the suspect could be bound to the case, as the isotopic composition of lead bullets can be identified not only by manufacturer but also by manufacturing date. 

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. 

Details of the natural radioactive decay series are particularly important for several radioactive dating methods (O Chap. 17 of this Volume). These methods depend on differences in chemical properties of chain components in a geological environment and ongrowth-and-decay among the components. See Chap. 7 in Vol. 1. 

Natural uranium is 99.28% which decays as we have described. However, the natural element also contains 0.72% This isotope starts a second radioactive decay series, which consists of a sequence of alpha and beta decays, ending with lead-207. The third naturally occurring radioactive decay series begins with thorium-232 and ends with lead-208. All three radioactive decay series found naturally end with an isotope of lead. 

The two disintegrations described in Equations 20.2 and 20.3 are only the first two of 14 steps that begin with 23 u. There are eight a-particle emissions and six /3-particle emissions, leading ultimately to a stable isotope of lead, 2° Pb. This entire natural radioactive decay series is described in Figure 20.11. There are two other natural disintegration series. One begins with 2 Th and ends with 2° Pb, and the other passes from 23 u to Pb. 

In addition to the natural radioactive decay series that begins with U-238 and ends with Pb-206, there are natural radioactive decay series that begin with U-235 and Th-232. Both of these series end with nuchdes of Pb. Predict the likely end product of each series and the number of a decay steps that occur. 

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 ... 

The last element of the group of metalloids is astatine. It has been estimated that the whole Earth s crust contains less than 44 mg astatine and this element with the atomic number 85 can thus be considered one of the rarest naturally occurring elements on Earth. All isotopes of this radioactive element have short half-lives and are products of several radioactive decay series. At (ti/2 = 54 s) occurs in one rare side branch of the decay series while At, one of the products of a side branch of the Po decay series, undergoes a very fast P decay (ti/2 = IxlO s). 

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. 

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. 

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. 

The noble gases occur as minor constituents of the atmosphere (Table 17-1). Helium is also found as a component (up to 7%) in certain natural hydrocarbon gases in the United States. This helium undoubtedly originated from decay of radioactive elements in rocks, and certain radioactive minerals contain occluded helium which can be released on heating. All isotopes of radon are radioactive and are occasionally given specific names (e.g., actinon, thoron) derived from their source in the radioactive decay series 222Rn is normally obtained by pumping off the gas from radium chloride solutions. Ne, Ar, Kr and Xe are obtainable as products of fractionation of liquid air. 

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