## 3 Results and Discussion  
Magnetic measurements were performed on the same block samples before and after neutron irradiation, on steel and cladded sides, respectively. In Figure 7, the \"Optimally chosen MAT descriptor\" is plotted as a function of neutron fluence. In this case, this descriptor is an element of \(Da\) matrix, characterized by \(h_{a}\) = \(-\)600 mA and \(h_{b}\) = 1200 mA. During evaluation, the \(Da\) matrix elements of irradiated samples were normalized by the corresponding \(Da\) matrix element of one of the reference (not irradiated, L44N36) samples. This is the meaning of \"Optimally chosen normalized MAT descriptor\". As is seen, the descriptors of reference samples are around 1, as they should be, but they scatter a lot. This means that the investigated samples behave differently from a magnetic point of view, even before neutron irradiation. Measurements were performed on the base material, both on top and bottom sides of the samples without cladding. After neutron irradiation, the top and bottom side received a different neutron fluence. Similar to the results reported previously on Charpy specimens [8], neutron irradiation caused measurable changes in the material properties. Neutron irradiation at low fluences generates a significant modification of the material properties [14], while a further increase of the neutron fluence causes a saturation for higher fluence levels. This means that the present results on RPV blocks are in good correlation with the expectation, based on previous measurement. Larger (15-25 \(\times\) 10\({}^{19}\) n/cm\({}^{2}\)) neutron fluence caused about 30-40% modification of the \"Optimally chosen MAT descriptors\" of the investigated material. However, it is also seen that the measured points scatter a lot (see Figure 7), much more than what can be explained by the measurement error of the magnetic measurements. This fact needs further analysis, which is out of the scope of this work, but will be done in our future work. Nevertheless, considering that magnetically the blocks were rather different even before irradiation, the scatter of points after irradiation is not so surprising any more. As mentioned previously, during neutron irradiation, some blocks had a uniform neutron fluence profile and some others were irradiated with an attenuation fluence profile. Since the studied MAT setup has a depth sensitivity profile, it is possible to consider the above presented results from this point of view, i.e., to see if this difference of irradiation caused any difference in the fluence dependent magnetic parameters. The results are shown in Figure 8. This figure contains the same points as Figure 7, but the two sets of samples are indicated by different symbols. Furthermore, for all the reference (not irradiated) samples, the magnetic parameter was taken as exactly equal to 1. It is seen that different irradiation conditions did not cause significant change in the magnetic descriptor vs. neutron fluence correlation. Magnetic measurements were also performed on the cladding side and included in Figures 7 and 8. In spite of the weak magnetic signal (see Figure 6), MAT evaluation resulted in a reasonable correlation between the magnetic parameters and the estimated neutron fluence. In other words, the influence of the neutron irradiation can be followed with acceptable signal-to-noise ratio by this technique. The tendency of the material degradation was found to be very similar as in the case of the hardness measurements performed directly on the base material. In case of MAT evaluation of cladding side measurements, the optimal MAT descriptor is an element of the reciprocal \(\mathbb{I}\alpha\) matrix, and is characterizedby \(h_{a}=150\) mA and \(h_{b}=1000\) mA field values. The results are shown in Figure 9. The sensitivity of the measurement is lower than when the measurements were performed on base material without cladding: 10-12% modification of magnetic behaviour of the investigated material was found.