Chapter 21: Problem 15
How can the belt of stability be used to predict the probable decay mode of an unstable nuclide?
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Chapter 21: Problem 15
How can the belt of stability be used to predict the probable decay mode of an unstable nuclide?
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Explain how the product of \(\beta\) decay has a higher atomic number than the radio nuclide from which the product forms
Potassium- 40 is a radioactive isotope of potassium, a very common element in terrestrial rocks, which decays to \(^{40}\) Ar with a half-life of \(1.28 \times 10^{9}\) years. By measuring the ratio of \(^{40} \mathrm{Ar}\) to \(^{40} \mathrm{K},\) geologists can to determine the age of ancient rocks. a. Balance the nuclear equations for the decay of \(^{40} \mathrm{K}\) by identifying the missing isotope or particle.$$\begin{array}{l}^{40} \mathrm{K} \rightarrow^{40} \mathrm{Ar}+? \\\^{40} \mathrm{K} \rightarrow +_{-1}^{0} \beta\end{array}$$.b. Why might \(^{40} \mathrm{K}\) decay by two different pathways? c. Only about \(11 \%\) of the \(^{40} \mathrm{K}\) decays to \(^{40} \mathrm{Ar}\). If the ratio of \(^{40} \mathrm{Ar}\) to \(^{40} \mathrm{K}\) in a rock is found to be \(0.435,\) how old is the rock? d. Why don't geologists measure the \(^{40} \mathrm{Ca}:^{40} \mathrm{K}\) ratio instead?
What nuclide is produced in the core of a collapsing giant star by each of the following reactions? a. \({ }_{29}^{65} \mathrm{Cu}+3{ }_{0}^{1} \mathrm{n} \rightarrow ?+{ }_{-1}^{0} \boldsymbol{\beta}\) b. \({ }_{30}^{68} \mathrm{Zn}+2{ }_{0}^{1} \mathrm{n} \rightarrow ?+{ }_{-1}^{0} \beta\) c. \({ }_{38}^{88} \mathrm{Sr}+{ }_{0}^{1} \mathrm{n} \rightarrow ?+{ }_{-1}^{0} \beta\)
Dating Cave Paintings Cave paintings in Gua Saleh Cave in Borneo have been dated by measuring the amount of \(^{14} \mathrm{C}\) in calcium carbonate deposits that formed over the pigments used in the paint. The source of the carbonate ion was atmospheric \(\mathrm{CO}_{2}\).a. What is the ratio of the \(^{14} \mathrm{C}\) radioactivity in calcium carbonate that formed 9900 years ago to that in calcium carbonate formed today? b. The archaeologists also used a second method, uranium-thorium dating, to confirm the age of the paintings by measuring trace quantities of these elements present as contaminants in the calcium carbonate. Shown below are two candidates for the U-Th dating method. Which isotope of uranium do you suppose was chosen? Explain your answer. $$\begin{aligned} &t_{1 / 2}=^{233} \mathrm{U} \quad 7.04 \times 10^{8} \mathrm{yr} \quad^{231} \mathrm{Th} \quad \rightarrow \quad^{231} \mathrm{p}_{2} \quad 3 \quad \rightarrow \quad\\\ &t_{1 / 2}=^{234} \mathrm{U} \quad \begin{array}{rl}\rightarrow & ^{230} \mathrm{Th} \\ 2.44 \times 10^{5} \mathrm{yr} & 7.7 \times 10^{4} \mathrm{hr}\end{array} \quad \begin{array}{rl} 226 \mathrm{p}_{2} & \rightarrow \\\1600 & \mathrm{yr}\end{array}\end{aligned}$$
Strontium-90 in Milk In the years immediately following the explosion at the Chernobyl nuclear power plant, the concentration of \({ }^{90} \mathrm{Sr}\) in cow's milk in southern Europe was slightly elevated. Some samples contained as much as \(1.25 \mathrm{~Bq} / \mathrm{L}\) of \({ }^{90} \mathrm{Sr}\) radioactivity. The half-life of strontium-90 is 28.8 years. a. Write a balanced nuclear equation describing the decay of \({ }^{90} \mathrm{Sr}\). b. How many atoms of \({ }^{90} \mathrm{Sr}\) are in a \(200 \mathrm{~mL}\) glass of milk with \(1.25 \mathrm{~Bq} / \mathrm{L}\) of \({ }^{90} \mathrm{Sr}\) radioactivity? c. Why would strontium-90 be more concentrated in milk than other foods, such as grains, fruits, or vegetables?
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