Predicting Which Nuclei Are Radioactive Which of the following nuclides would you expect to be stable, and which radioactive? (a) ^82As; (b) ^118Sn; (c) ^214Po. Analyze This question requires us to apply the rules of nuclear stability. We may also use Figure 25-7 to determine whether the nuclide

Question

Predicting Which Nuclei Are Radioactive

Which of the following nuclides would you expect to be stable, and which radioactive? (a) [latex]_{}^{82} ext{As}[/latex]; (b) [latex]_{}^{118} ext{Sn}[/latex]; (c) [latex]_{}^{214} ext{Po}[/latex].

Analyze
This question requires us to apply the rules of nuclear stability. We may also use Figure 25-7 to determine whether the nuclide lies within the belt of stability.

Accepted Answer

(a) Arsenic-82 has Z = 33 and N = 49. This is an odd-odd combination that is found in only four of the lighter elements. [latex]_{}^{82} ext{As}[/latex] is radioactive. (Note also that this nuclide is outside the belt of stability in Figure 25-7.)

(b) Tin has an atomic number of 50—a magic number. The neutron number is 68 in the nuclide [latex]_{}^{118} ext{Sn}[/latex]. This is an even-even combination, and we should expect the nucleus to be stable. Moreover, Figure 25-7 shows that this nuclide is within the belt of stability. [latex]_{}^{118} ext{Sn}[/latex] is a stable nuclide.

(c) [latex]_{}^{214} ext{Po}[/latex] has an atomic number of 84. All known atoms with Z > 83 are radioactive. [latex]_{}^{214} ext{Po}[/latex] is radioactive.

Assess
When considering whether a nuclide is radioactive, we must remember that all elements with Z > 83 are radioactive, and those with Z < 84 are radioactive if their Z and N form odd-odd combinations. A few exceptions exist to these rules, specifically when nuclides have atomic numbers that are one of the magic numbers.

Question 25.6: Predicting Which Nuclei Are Radioactive Which of the followi...

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