Plutonium-238 (94238Pu{}^{238}_{94}\text{Pu}94238Pu) is an alpha-emitting radioactive isotope used in Radioisotope Thermoelectric Generators (RTGs) to provide electrical power for deep-space robotic missions.
Describe the structure of a plutonium-238 nucleus.
Plutonium-238 decays by emitting an alpha particle to form uranium (U\text{U}U). Complete the balanced nuclear equation for this decay by finding the missing numbers and symbol:
94238Pu→……U+42……{}^{238}_{94}\text{Pu} \rightarrow \frac{\quad\dots\quad}{\quad\dots\quad}\text{U} + \frac{4}{2}\dots\dots94238Pu→……U+24……
In an RTG, the radiation must be completely absorbed by the surrounding thermal containment unit to generate heat, without exposing the spacecraft's delicate scientific instruments to damaging radiation. Explain why beta and gamma radiation are not suitable for this device.
The half-life of plutonium-238 is 87.7 years87.7\text{ years}87.7 years.
Explain what is meant by half-life.
Explain why a spacecraft powered by an RTG containing plutonium-238 experiences a gradual decline in the electrical power available to its instruments over its decades-long mission.
The table below shows data for two alpha-emitting radioactive isotopes:
| Source | Half-life | Radiation emitted |
|---|---|---|
| Plutonium-238 | 87.7 years87.7\text{ years}87.7 years | Alpha |
| Plutonium-239 | 24,100 years24,100\text{ years}24,100 years | Alpha |
Both sources start with the same number of radioactive nuclei. Which source presents a greater initial radiation hazard? Explain your answer.
A safety analyst says: 'There is virtually no risk to the health of the ground crew preparing the spacecraft on the launchpad from the active plutonium-238 source during normal pre-launch operations.'
Do you agree with this statement? Give two reasons for your answer.