Smashing neutron-rich atoms together creates a proton-emitting cloud ten times larger than anyone predicted.
April 29, 2026
Original Paper
Large amplification of the isospin-dependence of proton emitting source size in radioactive heavy-ion collisions: a signal of n-p correlation
arXiv · 2604.25107
The Takeaway
Heavy-ion collisions involving radioactive isotopes show that the size of the proton-emitting source is highly dependent on the neutron count. Neutron-rich collisions produced source sizes 24 percent larger than neutron-deficient ones, which is a massive discrepancy. Current mean-field physics models cannot explain why this difference is an order of magnitude larger than the ground-state radii of the atoms. This suggests there is a hidden, dynamic interaction between protons and neutrons that only appears during the violent chaos of a collision. Solving this mystery will help physicists understand the extreme conditions found inside the cores of collapsing stars.
From the abstract
We report proton-proton correlation function measurements in central $^{132}$Sn+$^{124}$Sn and $^{108}$Sn+$^{112}$Sn collisions at 270 MeV/nucleon. The proton emitting source sizes are extracted for the systems by using femtoscopic imaging technique. The fast dynamic core radius for the neutron-rich system is found to be $2.22 \pm 0.13\ \text{(stat.)} \pm 0.07\ \text{(syst.)}$ fm, which is approximately 24\% larger than that for the neutron-deficient system, $1.74 \pm 0.08\ \text{(stat.)} \pm 0.