Question

Why is plutonium, detected in trace amounts in natural uranium deposits, not likely to have been trapped at the time the solar system formed 4.7 × 10^9 years ago?

a) Plutonium has a very short half-life.
b) Plutonium is a synthetic element.
c) Plutonium is only formed in supernovae.
d) Plutonium is a decay product of uranium isotopes.

Answer 1

Plutonium found in uranium deposits is not from the solar system's formation because plutonium's half-life is too short, and it is mostly formed in nuclear reactors from U-238 capturing neutrons during U-235 fission. The correct option is a).

Step-by-step explanation:

The trace amounts of plutonium found in natural uranium deposits are not likely to have been trapped during the formation of the solar system 4.7 × 10^9 years ago due to the relatively short half-life of plutonium isotopes. Instead, the presence of plutonium can be attributed to the capture of neutrons by 238U nuclei.

In nuclear reactors, as U-235 undergoes fission, it releases additional neutrons, some of which are captured by 238U to form uranium-239, which then undergoes ß decay to form neptunium-239, and finally undergoes another ß decay to form plutonium-239.

This process is not something that would have occurred during the formation of the solar system and, given plutonium-239's half-life of 24,100 years, any plutonium existing from that time would have decayed long ago. Option a) is the correct one.