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JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, vol.39, no.1, 2026 (SCI-Expanded, Scopus)
Nanocrystalline boron carbide (B4C) was probed by room-temperature X-band EPR before and after controlled neutron exposure to reveal irradiation-driven changes in defect populations and local symmetry. Pristine powders show a multi-component spectrum with an orthorhombic g-tensor. With increasing neutron fluence (10(15)-10(17) n center dot cm(-2)), the response converges to a stronger, more symmetric resonance near g approximate to 2.00 that exhibits clear peak-to-peak broadening (Delta B-pp). These trends are consistent with boron transmutation-dominantly B-10(n,alpha)Li-7 and, secondarily, B-11(n,gamma)-> B-12 -> C-12-creating vacancies and defect complexes, increasing spin concentration, enhancing dipolar interactions, and partially averaging g-anisotropy. Carbon channels are negligible at thermal energies. The results provide a concise, mechanism-anchored picture of defect evolution in irradiated B4C and establish g, Delta B-pp, and integrated intensity as practical spectral markers for monitoring neutron-induced changes in boron-rich ceramics.