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Chapter 21: Problem 78

Identify two of the most abundant radioactive elements that exist on Earth. Explain why they are still present. (You may need to consult a handbook of chemistry.)

Short Answer

Expert verified
The two most abundant radioactive elements on Earth are Uranium and Thorium. They are still present due to their long half-lives (4.5 billion years for Uranium-238 and 14 billion years for Thorium-232), which means they decay very slowly. The replenishment from processes like cosmic ray spallation and Earth's internal heat also contributes to their sustained presence.

Step by step solution

01

Identify the Most Abundant Radioactive Elements

The two most abundant radioactive elements on Earth are uranium (U) and thorium (Th). These elements are found in small amounts in the Earth's crust.
02

Understand the Concept of Half-Life

The half-life of a radioactive element is the time it takes for half of the atoms in a sample of that element to decay. It is a measure of how long the element will persist. Uranium-238, for example, has a half-life of about 4.5 billion years, and Thorium-232 has a half-life of about 14 billion years.
03

Explain Why Uranium and Thorium Are Still Present

Given their long half-lives, substantial amounts of uranium and thorium still remain, even though they were formed when Earth itself was formed. The long half-lives of these elements allow them to still exist in significant amounts, despite being in a constant state of decay. Moreover, these elements are continually replenished through the process of cosmic ray spallation, and also from the Earth's internal heat, from elements such as Potassium-40.

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Most popular questions from this chapter

The half-life of \({ }^{27} \mathrm{Mg}\) is \(9.50 \mathrm{~min}\). (a) Initially there were \(4.20 \times 10^{12}{ }^{27} \mathrm{Mg}\) nuclei present. How many \({ }^{27}\) Mg nuclei are left 30.0 min later? (b) Calculate the \({ }^{27} \mathrm{Mg}\) activities \((\) in \(\mathrm{Ci})\) at \(t=0\) and \(t=30.0 \mathrm{~min}\) (c) What is the probability that any one \({ }^{27} \mathrm{Mg}\) nucleus decays during a 1 -s interval? What assumption is made in this calculation?

Tritium contains one proton and two neutrons. There is no proton-proton repulsion present in the nucleus. Why, then, is tritium radioactive?

Fill in the blanks in these radioactive decay series: (a) \(^{232} \mathrm{Th} \stackrel{\alpha}{\longrightarrow}\) _______ \(\stackrel{\beta}{\longrightarrow}\) ________ \(\stackrel{\beta}{\longrightarrow}{ }^{228} \mathrm{Th}\) (b) \({ }^{235} \mathrm{U} \stackrel{\alpha}{\longrightarrow}\) ________ \(\stackrel{\beta}{\longrightarrow}\) _________ \(\stackrel{\alpha}{\longrightarrow}^{227} \mathrm{Ac}\) (c) _______ \(\stackrel{\alpha}{\longrightarrow}{ }^{233} \mathrm{~Pa} \stackrel{\beta}{\longrightarrow}\) ___________ \(\stackrel{\alpha}{\longrightarrow}\) ________.

Both barium (Ba) and radium (Ra) are members of Group \(2 \mathrm{~A}\) and are expected to exhibit similar chemical properties. However, \(\mathrm{Ra}\) is not found in barium ores. Instead, it is found in uranium ores. Explain.

What is the difference between radioactive decay and nuclear transmutation?
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