<p>In this study, a comprehensive investigation was carried out to examine the effect of combined neutron and electron irradiation on the crystal structure and optical absorption spectra of colorless topaz, with the aim of obtaining a blue coloration. The topaz samples were subjected to sequential irradiation: first with fast neutrons at a fluence of approximately ~ 10¹⁸ cm^− 2 in a nuclear reactor, and then with an electron beam with energies of 3 ÷ 5&#xa0;MeV at doses of 60 and 150 MGy. The results show that irradiation with neutrons and electrons does not alter the orthorhombic crystal structure of topaz (space group <i>Pbnm</i>), but induces anisotropic changes in the unit cell parameters. The most significant increase in the lattice parameters <i>a</i> and <i>b</i> is observed after combined irradiation. Neutron irradiation caused pronounced degradation of the crystalline structure, leading to a decrease in the crystallite size to 42.4&#xa0;nm and an increase in the dislocation density. In the absorption spectra of the irradiated sample, a characteristic band around ~ 620&#xa0;nm is observed, which is responsible for the blue coloration and is associated with O⁻–Al centers. Quantitative analysis using the Smakula-Dexter method shows that the maximum concentration of color centers (~ 10¹⁷ cm^− 3) is achieved under neutron irradiation. In the case of combined neutron and electron irradiation, the concentration of centers is about 9.5 × 10¹⁶ cm^− 3, indicating that subsequent electron irradiation of the neutron-treated sample leads to partial annealing of defects and a reduction in the concentration of color centers.</p>