Teasing out the measurement was a lot like “knowing you got this tiger by the tail,” Kent Paschke, a physicist at the University of Virginia and co-author of the new study, said. It took three months of intense runs of the laser, enduring power outages and round-the-clock monitoring of the system. The team wasn’t sure if they’d be able to complete the work in the three months they were given. But ultimately, the atomic-scale marathon turned up an exact measurement, one that redefines our understanding of the size of the neutron skin.