Plutonium-238 is a radioactive isotope used in radioisotope thermoelectric generators (RTGs) for deep-space missions, such as the Voyager space probes.
The table shows how the activity of a sample of plutonium-238 varies over time.
Time (years)04488132176220Activity (Bq)16001130800565400280 \begin{array}{|c|c|c|c|c|c|c|} \hline \textbf{Time (years)} & 0 & 44 & 88 & 132 & 176 & 220 \\ \hline \textbf{Activity (Bq)} & 1600 & 1130 & 800 & 565 & 400 & 280 \\ \hline \end{array} Time (years)Activity (Bq)0160044113088800132565176400220280(i) Explain step-by-step how a graph of activity (yyy-axis) against time (xxx-axis) is used to find the half-life of plutonium-238.
Use the data in the table directly to find the half-life of plutonium-238. Show your working.
The plutonium-238 is encased inside a solid titanium protective casing within the RTG.
(i) Plutonium-238 transfers thermal energy at a rate of 0.56 W0.56\text{ W}0.56 W for every gram of plutonium. Calculate the rate of thermal energy output from a plutonium-238 core with a mass of 24.2 g24.2\text{ g}24.2 g.
When plutonium-238 decays, it emits alpha particles. Explain why an operator can safely handle the outer titanium casing of the RTG without receiving a radiation dose from the alpha particles.
Remote deep-space probes must operate continuously for several decades in the outer solar system without maintenance.
Explain why it is essential to use a radioisotope with a long half-life like plutonium-238 rather than an isotope with a short half-life of a few weeks.
