Radioactive series nuclear disintegration Radioactivity

We recognize that nuclear stability is determined largely by the neutron-to-proton raSo. For stable nuclei, this ratio increases with increasing atomic number. All nuclei with 84 or more protons are radioactive. Heavy nuclei gain stability by a series of nuclear disintegrations leading to stable nuclei. 

Some nuclei cannot gain stability by a single emission. Consequently, a series of successive emissions occurs as shown for uranium-238 in A FIGURE 21.3. Decay continues until a stable nucleus—lead-206 in this case—is formed. A series of nuclear reactions that begins with an unstable nucleus and terminates with a stable one is known as a radioactive series or a nuclear disintegration series. Three such series occur in nature uranium-238 to lead-206, uranium-235 to lead-207, and thorium-232 to lead-208. 

The radioactive noble gas radon has been much publicized in recent years as a potential risk to health. Radon-222 is a product of fire nuclear disintegration series of uranium-238 (Figure 21.4) and is continually generated as uranium in rocks and soil decays. As Figure 21.23 indicates, radon exposure is estimated to account for more fhan half the 360-mrem average annual exposure to ionizing radiation. 

Activity of a radioactive source the number of nuclear disintegrations per unit time occurring in a radioactive material. (21.3) Activity series a listing of the elements in order of their ease of losing electrons during reactions in aqueous solution. (4.5) Addition polymer a polymer formed by linking together many molecules by addition reactions. (25.1)... 

When the nucleus of a radioactive atom disintegrates, it emits various particles and so changes its own composition. When an alpha particle is lost then a new element is formed, which is two places to the left in the periodic table. When a beta particle is lost then a new element is formed which is one place to the right in the periodic table. Therefore, by a series of losses of alpha and beta particles, the element progressively changes. This is called decay , and the pattern it follows until a stable nuclear arrangement is reached (usually when the element lead is formed) is called the decay series (see Chapter 12). 

The Uranium Series o Radioactive Disintegrations. When an alpha particle (He++) is emitted by an atomic nucleus the nuclear charge decreases by two units the element hence is transmuted into the element two columns to the left in the periodic table. Its mass number (atomic weight) decreases by 4, the mass of the alpha particle. 

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. 

SECTION 21.2 The neutron-to-proton ratio is an important factor determining nuclear stability. By comparing a nuclide s neutron-to-proton ratio with those in the band of stability, we can predict the mode of radioactive decay. In general, neutron-rich nuclei tend to emit beta particles proton-rich nuclei tend to either emit positrons or im-dergo electron capture and heavy nuclei tend to emit alpha particles. The presence of magic numbers of nucleons and an even number of protons and neutrons also help determine the stability of a nucleus. A nuclide may undergo a series of decay steps before a stable nuclide forms. This series of steps is called a radioactive series or a nuciear disintegration series. 

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... 

As chemists write chemical equations to describe chemical changes, they write nuclear equations to describe nuclear changes. A nuclear equation shows the reactant nuclides or particles on the left and the product nuclides or particles on the right. The first step in the natural radioactive series observed by Becquerel is an alpha decay reaction. In it, a nucleus disintegrates, or decays, into a He nucleus (alpha particle) and a nucleus. The nuclear equation is... 

Write the nuclear equation for the changes that occur in the uranium-238 disintegration series when gfRa ejects an a-particle. Ra is the symbol for radium, one of the elements discovered by Pierre and Marie Curie in their study of radioactivity. 

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