Interstitial Helium Diffusion in Metals

以获得间隙氦在金属中扩散的信息。测量了19keV He离子辐照高纯铝中氦的热脱附过程。照射温度为1×10~(-5)×10~(-5)×10~(-5)×10~(-5)He~(-2)。(1)几乎所有注入的氦原子都是在加热到熔点或更高温度时释放出来的。(2)氦的快速析出发生在熔点以下，与辐照剂量无关。(3)当辐照剂量大于5×10~(-5)~(-2)时，出现另一个演化速率峰，峰面积随辐照剂量的增加而显著增大，峰位向低温侧移动。特别是，结果(3)表明，出现在低温区的演化峰可能是由于包含大量氦原子的小空穴自发发射的氦的扩散和演化所致。在此基础上，根据阶梯加热温度突变前后的脱附速率，估算了低温区(10 0~2 0 0ﾟC)氦的析出活化能。得到的值约为0.3 eV。这一数值与铝中间隙氦扩散的计算结果(0.2-0.3 eV)非常接近。

In order to get information about the diffusion of interstitial helium in metals. Measurements have been made on the thermal desorption of helium from high purity aluminum irradiated with 19 keV He ions. The irradiation was performed at room temperature up to 1 x 10^<15> - 5 x 10^<16> He^+cm^<-2>.Remarkable features of the results are as follows. (1) Almost all helium atoms implanted are released released during heating up to the melting point or more. (2) A rapid helium evolution occurs just below the melting point, irrespective of irradiation dose. (3) For irradiation more than 5 x 10^<15> He^+cm^<-2>, another evolution rate peak appears ; the peak area is increased markedly with increasing irradiation dose, while the peak position is shifted to the lowler temperature side. In particular, the result (3) suggests that the evolution peak appearing in the lower temperature region may be due to diffusion and evolution of helium emitted spontaneously from small cavities containing a large number of helium atoms. According to the above, the activation energy for the helium evolution in the lower temperature region (100-200 ^ﾟC) was estimated from the desorption rates before and after the abrupt temperature chane during stepwise heating. The value obtained is about 0.3 eV. This value is very close to thouse (0.2-0.3 eV) calculated for interstitial helium diffusion in aluminum.