The nature of point defects in hexagonal boron nitride (hBN) is of current interest for the potential to alter its optical and electrical properties. The strong interaction between neutrons and the boron-10 isotope makes neutron irradiation a controllable way to introduce point defects in hBN. In this study, we perform Raman spectroscopy, photoluminescence, electron paramagnetic resonance (EPR), and optically detected magnetic resonance (ODMR) characterization of neutron-irradiated monoisotopic (hBN with a single boron isotope) 10B-and 11B-enriched hBN crystalline flakes and a pyrolytic BN (pBN) reference sample. In h10BN and pBN, neutron irradiation produced two new Raman bands at 450 and 1335 cm-1, which could be associated with B-related vacancies or defects. The near-bandedge optical emission was also significantly impacted by the neutron irradiation. EPR measurements clarified the origin of a high-spin defect center due to negatively charged boron vacancies, which was recently reported for similar neutron-irradiated hBN crystals. The ODMR experiments further confirmed this assignment. High-Temperature annealing partially recovered some of the hBN vibrational and optical properties. Our results are helpful to identify the nature of defects in hBN and enable defect-engineered applications such as quantum information and sensing.