## 3 Model
### Strategy for Obtaining Better Smoothness of Cut Walls
#### 3.2.12. Modification Mechanism Preferable for Smooth Separation  
For the convenience of performing the necessary estimates in the proposed model, it is important to determine the predominant of the three mentioned above competing mechanisms of the modification zone formation. To simplify the modeling, we consider them as acting separately, not altogether. In such case, a mechanism which gives the maximum radius of the modification zone from the above radii \(R_{T}\), \(R_{TD}\)\(uR_{SW}\) should be considered as a dominant mechanism. It is also obvious that the smooth separation of interest can be realized in the case when the thermal (T) mechanism is dominant. Thus, to obtain a smooth separation, the condition must be met:  
\[R_{T}>R_{TD},\,R_{SW}. \tag{82}\]  
Indeed, in this case, we can hope for the formation of the impact zone without destruction in the form of scattered cracking in the solid material as a result of irradiation. As can be seen from Figure 6a, although the thermal deformation mechanism formally leads to cracking of the material directly inside the zone \(r\leq R_{TD}\), the boundary of which is conventionally designated by a zigzag circular contour, however, this zone completely and with excess is covered by the zone of action of the thermal mechanism \(r\leq R_{T}\). Therefore, although there is a cracking in the impact zone of the thermal deformation mechanism \(r\leq R_{TD}\), as a result of annealing in the larger zone \(r\leq R_{T}\) this cracking has no chance to occur when separation is completed. In the case of mechanical splitting following irradiation, a straight and smooth separation line is possible in this case, indicated as 1 in Figure 6a. However, the situation changes, and such annealing of the cracked material in the entire \(r\leq R_{TD}\) zone does not occur if the thermal deformation (TD) or the shock wave (SW) mechanisms are dominant. In this case (see Figure 6b) \(R_{T}<R_{TD}\) (or \(R_{T}<R_{SW}\)) and at radii \(r\), such that \(R_{T}<r\leq R_{TD}\) (or \(R_{T}<r\leq R_{SW}\)), there is a relatively large area of material cracking, characteristic for the thermal deformation (TD) or the shock wave (SW) mechanisms. This cracked area is not annealed, since it is not covered by a relatively small impact zone of the thermal mechanism \(r\leq R_{T}\). The surface of the mechanical splitting obtained in this case after irradiation (designated on the cross-section in Figure 6b as the line 2) passes through this cracking area. It has a zigzag-like, randomly changing direction since it passes through random numerous microcracks and boundaries between pieces of damaged material formed as a result of cracking in the indicated not annealed damage area. Such shape of the separation surface is rough and non-smooth. Moreover, on both halves of the sample obtained during the subsequent separation after irradiation, there will be a broken cracked (or microcracked) superficial layer corresponding to the area of damage on both sides of this rough separation surface 2 in this figure. The presence of such a cracked superficial layer has an extremely unfavourable effect on the mechanical strength of the material during its further operation after separation, since it serves as the nuclei of cracks that can occur and propagate with accidental or non-accidental mechanical impacts during subsequent use of the product. A comparison of situations (a) and (b) in Figure 6 shows that smoother separation becomes possible when the thermal mechanism dominates in the formation of the impact zone. Material parameters for fulfillment of the condition (82) for obtaining a smoother separation can be easily found, as all three modification radii are defined by formulas of the general type (23): (43) or (44) for \(R_{T}\), (45) for \(R_{TD}\) and (46) for \(R_{SW}\).