Plutonium-238 (
) is unstable and undergoes alpha decay.
Complete the equation to show the decay of plutonium-238.
The power source in a space probe contains 
of plutonium-238. Each nucleus of plutonium-238 that decays emits 
of energy. The half-life of plutonium-238 is 87.7 years.
Calculate the initial number 
of nuclei of plutonium-238 in the power source.
Determine the initial activity of the source. Give a unit with your answer.
Use your answer in (b)(ii) to determine the initial power output from the source due to the decay of plutonium-238.
The space probe will continue to function until the power output from the plutonium in the source decreases to 
of its initial value. Calculate the time, in years, for which the space probe will function.
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