Targets of isotropic graphite and hexagonal boron nitride were exposed to short pulses of uranium ions with ∼1 GeV kinetic energy. The deposited power density of ∼3 MW/cm³ generates thermal stress in the samples leading to pressure waves. The velocity of the respective motion of the target surface was measured by laser Doppler vibrometry. The bending modes are identified as the dominant components in the velocity signal recorded as a function of time. With accumulated radiation damage, the bending mode frequency shifts towards higher values. Based on this shift, Young’s modulus of irradiated isotropic graphite is determined by comparison with ANSYS simulations. The increase of Young’s modulus up to 3 times the pristine value for the highest accumulated fluence of 3 × 10¹³ ions/cm² is attributed to the beam-induced microstructural evolution into a disordered structure similar to glassy carbon. Young’s modulus values deduced from microindentation measurements are similar, confirming the validity of the method. Beam-induced stress waves remain in the elastic regime, and no large-scale damage can be observed in graphite. Hexagonal boron nitride shows lower radiation resistance. Circular cracks are generated already at low fluences, risking material failure when applied in high-dose environment.

中文翻译：

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石墨和 h-BN 靶中短脉冲 GeV U 离子束引起的动态辐射效应

各向同性石墨和六方氮化硼的靶材暴露于具有约 1 GeV 动能的铀离子短脉冲。约 3 MW/cm³ 的沉积功率密度在样品中产生导致压力波的热应力。通过激光多普勒振动测量法测量目标表面的相应运动的速度。弯曲模式被确定为作为时间函数记录的速度信号中的主要成分。随着辐射损伤的累积，弯曲模式频率向更高的值移动。基于这种偏移，通过与 ANSYS 模拟进行比较来确定辐照各向同性石墨的杨氏模量。对于 3 × 10 ¹³离子/cm ²的最高累积注量，杨氏模量增加至原始值的 3 倍归因于光束诱导的微观结构演变成类似于玻璃碳的无序结构。从显微压痕测量推导出的杨氏模量值是相似的，证实了该方法的有效性。梁引起的应力波保持在弹性状态，在石墨中没有观察到大范围的损伤。六方氮化硼显示出较低的耐辐射性。圆形裂纹已经在低能量密度下产生，在高剂量环境中应用时存在材料失效的风险。