Natural diamond detector (NDD) performance was studied up to a neutron fluence of 10 15 neutron/cm 2. The variations of the NDD spectrometric response to incident α-particles from 241Am source after exposure to fast neutron fluences up to 3×10 16 n/cm 2 were examined. No significant variations up to the level of 10 14 n/cm 2 were observed. Degradation of charge collection efficiency at higher fluences is reported. No remarkable increase of the NDD leakage current and count rate change had been observed up to a neutron fluence of 3×10 16 n/cm 2. The charge collection efficiency variations of neutron irradiated diamond spectrometer were studied ex situ under γ-rays, β-radiation and visible light excitation. Charge collection efficiency restoration up to 75% level and the NDD performance stabilization by extrinsic low-intensity visible light (550 nm< λ<800 nm) or intrinsic excitations have been demonstrated.