## 3 Results and Discussion
### Raman Spectra of Neutron-Irradiated Diamonds
Rapid changes near the critical level of radiation damage of diamond in the spectral position of the \"1640\" band and the intensity of this band in comparison with the boson band (Figure 2) demonstrate the advantage of this technique over establishing the level of diamond critical damage based on the calculated value of vacancies [71] as deduced from the TRIM [72] computer code, the magnitude of mechanical stresses in the ion-implanted layer [73], or by the value of crystal lattice expansion [74]. The necessity of selecting diamonds for magnetic measurements is conditioned by different levels of radiation damage of diamond grains simultaneously irradiated in the fast reactor neutron flux (due to local variations of heat dissipation conditions). One of the goals of this work was to develop an algorithm for quantitative determination of the level of radiation damage of diamond. As a measure of radiation damage in ion implantation, the calculations of vacancy concentration using the SRIM computer algorithm are often used, which is based on the statistical Monte Carlo method, the pair collision approximation, and the semiempirical description of the potentials of the interaction of fast particles with electronic and atomic subsystems [75]. SRIM modeling correctly describes the distribution profiles of implanted impurity and radiation defects and gives in many respects a good agreement with experiment, but it has a number of limitations. Modeling according to SRIM algorithm does not take into account the crystalline nature of the bombarded substance (in particular, channeling), does not consider the interaction between defects and their diffusion, that is, it gives a \"frozen\" picture of primary point defects, and does not consider phenomena during the accumulation of radiation damage, including the so-called \"ballistic annealing\", when, at high implantation doses under conditions of a high concentration of defects, collision with an already knocked-out atom does not lead to the formation of a new defect and can even return the atom to the substituting position [76]. The concentrations of point defects calculated using SRIM should be used with great care at high levels of radiation damage, since under such conditions, the calculated concentration of vacancies can exceed the concentration of carbon atoms in diamond. In addition, SRIM modeling cannot predict the structure of the damaged material and its change during relaxation and annealing. The second problem in calculating the level of radiation damage is the irradiation conditions themselves: the temperature of irradiation and the content of impurities, primarily nitrogen [77]. A change in the microstructure of a material during radiation damage leads to its swelling due to a decrease in density. This phenomenon is observed in all materials, but in diamond, it is most pronounced and is accompanied by an increase in the crystal lattice parameter, determined by X-ray [74] and neutron [48] diffraction. Strong (up to 40 vol.%) swelling in radiation-damaged diamond is one of the evidences in favor of the hypothesis of the formation of an amorphous material with density of \(\approx\)2 g/cm\({}^{3}\)[77; 78; 79] and poorly manifested in X-ray diffraction. The value of swelling varies nonmonotonically during subsequent annealings [77], which in some cases does not allow the use of swelling as a quantitative measure of radiation damage. In the case of natural diamond crystallites with irregular geometric shapes, the comparison of sample sizes before and after irradiation is rather problematic. In this paper, to determine the degree of radiation damage, including critical damage, it is proposed to use Raman spectra. Figure 2 shows changes in the position of the maximum of the intense band \"1640\" in neutron-irradiated (with subcritical level of radiation damage) and ion-implanted (with the level of radiation damage above critical, annealing at 1400 \({}^{\circ}\)C led to continuous graphitization of ion-implanted layers) natural diamonds.