To get a graph like this, put the irradiated silicon sample in an EPR spectrometer and select a constant microwave frequency. Align the external magnetic field to an initial direction and start sweeping the field strength to find resonance peaks. From these, calculate the g-factors.
Then, rotate the crystal slightly, repeat the measurement, and continue this process over a full angular range. Plot the g-values versus angle to have a visualization of how the g-tensor changes with orientation. This helps identify the nature and symmetry of the defect.