The PREx-II collaboration, of which Gluckstern Professor Krishna Kumar is co-spokesperson, recently published exciting new findings detailing the size of the lead (Pb) nucleus. Neutrons in heavier nuclei tend to bulge out beyond the protons in the nucleus, forming a "skin". Prof. Kumar and his group played a key role in PREx, or Pb Radius Experiment, at Jefferson Laboratory in Virginia, that achieved a precise measurement of the thickness of this skin. Based on a paper by former UMass Prof. John Dubach and others, the technique exploits the neutral weak force, allowing the team to use electron scattering measurements to probe the structure of the nucleus. The picture at left shows UMass postdoc Chandan Ghosh assembling the PREX-II detectors at Jefferson Lab before the 2019 run. Read more about this path-breaking discovery on Science News, APS Physics, and UMass News, among others. Congratulations, KK and collaborators!