Last week, Iran made a deal with five other world powers about the future of its nuclear programs. But as President Obama made clear in his announcement of the deal, this agreement isn't based on trust: It'll be based on cold, hard evidence.

In order to hold Iran accountable, the International Atomic Energy Agency—the global nuclear weapons watchdog—has to be able to accurately monitor Iranian nuclear power reactors to track how much nuclear weapon-grade uranium and plutonium they have. But current techniques are far from foolproof. Right now, IAEA inspectors literally seal up equipment with tape and tag it with some sort of label. The idea is, anyone who tries to illicitly remove plutonium will disrupt the seal. Also, they might sample dust from near the reactor and take it to a lab to process.

So naturally, the inspectors would rather do all this remotely. But that's a science-trick no one quite knows how to pull off just yet. Even sensing gamma rays, for example—a byproduct of fission—requires getting up close, inside the reactor. (Some nuclear reactors need to be turned off before anyone can retrieve anything inside, a real maintenance hassle for inspectors.) But scientists are working on another possibility: hunting for antineutrinos, a subatomic particle released during fission.