Question

Using the page from the Chart of the Nuclides, select a nuclide that is radioactive and decays (changes) to another nuclide by emitting an Alpha particle. Is the new element radioactive and if it is, how do you know that? If the new nuclide is radioactive, what does it decay to?

Do the same thing with a nuclide that emits a Beta particle.

If a rock contains 75% lead 206 (Pb206) and 25% uranium 238 (U238), how old is the rock? Explain how you determined the answer.

Is it possible to have a rock of that age on Earth, and what is the reason for your answer?

Answer 1

For a rock with a 75% Pb-206 to 25% U-238 ratio, the determined age would be approximately 13.5 billion years using uranium-lead dating, which is not possible given the age of Earth. U-238 decays to stable Pb-206 through alpha emissions, while Co-60 decays to Ni-60 by beta emission.

Step-by-step explanation:

When selecting a nuclide that is radioactive and decays by emitting an alpha particle, uranium-238 (U-238) is an example. It decays to thorium-234 (Th-234), and in a full decay series, it eventually becomes stable lead-206 (Pb-206). In the case of a beta particle emission, cobalt-60 (Co-60) decays to stable nickel-60 (Ni-60).

For a rock containing 75% lead-206 (Pb-206) and 25% uranium-238 (U-238), we determine the age based on the ratio of parent (U-238) to daughter (Pb-206) isotopes and the half-life of U-238, which is 4.5 billion years. Since the ratio indicates that three half-lives have passed, the rock would be approximately 13.5 billion years old. However, this exceeds the age of the Earth, which is about 4.54 billion years, so a rock of this age is not possible on Earth.