"Power."
A pretty powerful title, if we may say so ourselves.
We can't help but wonder, though, how the poem defines power in the first place. Is Rich talking about the power of knowledge? Of scientific discovery? Is she interested specifically in a gendered-female power? Is power something you have, or that has you? Can you control it, or does it control you? Is power always good? Is power something you must always struggle with? Or perhaps the poem is referring to a sort of scientific loss of power—the loss of power and energy that comes from the process of radioactive decay (which Curie herself discovered).
The poem raises all of these questions, but doesn't quite answer 'em. So pour yourself a nice glass of lemonade (or an old-school tonic, if that's what you need), and ponder the power.