We investigated in previous studies the electronic properties of three graphites and one pyrocarbon damaged by neutrons [1,2]. We have now extended this work to various other carbons and we present in this paper a unified presentation of the results and a quantitative evaluation of the damage in terms of positive hole concentration in the valence band vs irradiation dose. The materials tested and the electronic properties which were measured are listed in Table 1. Irradiations were performed at 35°C in conditions identical to those of previous studies [1,2] at the “Melusine” reactor of the Grenoble Nuclear Center. Doses D ranging from 10 17 to 4 × 10 20neutrons/cm 2 were recorded. The variation of the electrical resistivity at room temperature is shown in Figs. 1 and 2; of the Hall coefficient in Table 2 and of the magnetic mean susceptibility in Fig. 5. Figure 4 presents the relative transverse magnetoresistance ( i irradiated sample; o non irradiated). The paramagnetic susceptibility χ p was measured directly by EPR and its variation at 298°K with the neutron dose as shown in Fig. 6. Using the data on variation of χ p with temperature, the paramagnetic susceptibility is split[6] into contributions of the “localized paramagnetic centers” (Fig. 7) and of the conduction carriers (Fig. 8). The latter, χ deloc (Fig. 8) increases more slowly than the dose, while χ, loc (Fig. 7) increases first very rapidly, then much more slowly at high irradiation dose, when some recombination of point defects takes place. At higher doses when the Hall coefficient begins to decrease with increase of the dose, the data may be used to calculate the number N of positive holes created by irradiation: Figure 9 shows that approx. 4 holes/cm 2are produced by 1 neutron/.cm 2. Figure 10 shows that χ deloc of carriers is roughly proportional to √ N, as expected for the band structure of graphite. It is clear from Fig. 11 that N loc increases proportionally to N at low irradiation doses, but slower than N at high doses (recombination of vacancies). Although the radiation-induced changes in electronic properties differ widely for different carbons, it is possible to find some regularities in these results. We find that, in a given “class of carbons,” each unirradiated sample j may be characterized by an “equivalent neutron dose” Δ j p , Δ j p would be the dose needed to alter a property P of the most perfect material of the class from its value to the value equal to the unirradiated sample j. Then all the variations of P with ( D + Δ j p ) should be represented by a single curve for all the carbons of the same “class.” Such a parameter Δ j p can be useful only if Δ j p is independent from the nature of the property P: Δ j p = Δ j . Figure 12 shows the variation of the diamagnetic mean susceptibility −χ as a function of the “total dose” D + Δ j p ( D = real dose). There is indeed a single curve and the values of Δ j p . (arbitrarily set at zero for pyrocarbon or for PGCCL) are listed in Table 3. In the same way Fig. 13 shows the “single curve” for the Hall coefficient A and Table 3 lists the corresponding values of Δ j A . It may be seen that Δ j , is independent from the property P only for carbons belonging to the “class of graphites” or for those of the “class of pyrocarbons.” Papyex cannot be placed in any one of these classes, and there are not enough data for all the other carbons. For carbons in the same class, the value of Δ j , can be interpreted in terms of defect concentration prior to irradiation. Finally, from the “single curves” of Figs. 12 and 13, an “irradiation path” for each class of carbons can be drawn by plotting −χ vs A. Figure 14 shows that the irradiation and annealing paths of graphites are the same.