Due to its low solubility, He tends to cluster with vacancies to form bubbles in irradiated materials [1]. Previous studies showed that tuning the alloy chemical complexity in concentrated solid-solution alloys (CSAs) can be an effective approach to tailor defect energy landscapes and suppress He bubble growth [1,2]. In CSAs, multiple elements are randomly arranged in simple lattice structures, which generate extreme chemical complexity at the unit-cell level. A comprehensive understanding of how such chemical complexity affects defect generation and migration during irradiation is required. Here, atom probe tomography (APT) is used to accurately measure radiation-induced segregation near He bubbles, providing insight of defect energetics in CSAs. Four CSAs (NiFe, NiCo, NiCoCr, and NiCoFe) and Ni were irradiated by 200 keV He ions at 500°C to a fluence of 5×10 16 He/cm 2 . The size distributions of He bubbles were characterized using transmission electron microscopy (TEM). Field evaporation for APT was conducted in laser mode at 45 K with a pulse repetition rate of 200 kHz, a detection rate of 0.004 atoms per pulse, and a 70 pJ laser energy, such that more than twenty million ions were acquired from each sample for compositional analyses. A correlated TEM-APT study showed that He bubbles appeared as high-density regions in the APT reconstructions [3], so iso-density surfaces were used to locate the bubble positions in the APT reconstructions and elemental segregation to the bubble shell was measured using one-dimensional concentration profiles