Helium bubbles in molybdenum investigated by positron annihilation spectroscopy
作者:
P.M. G. Nambissan,
P. Sen,
B. Viswanathan,
期刊:
Radiation Effects and Defects in Solids
(Taylor Available online 1991)
卷期:
Volume 116,
issue 1-2
页码: 125-135
ISSN:1042-0150
年代: 1991
DOI:10.1080/10420159108221350
出版商: Taylor & Francis Group
关键词: Helium implantation;molybdenum;positron annihilation;helium bubbles
数据来源: Taylor
摘要:
Positron lifetime and Doppler broadening measurements have been performed in homogeneously helium implanted (715 appm) molybdenum. A new stage beyond the temperature range of stability of voids has been observed. The shorter lifetime componet τ1= 158 ± 2 ps of 60% intensity is assigned to the positron state in helium-decorated dislocation loops while the longer lifetime component τ2= 408 ± 5 ps of 40% intensity is explained in terms of positron trapping at voids with a small percentage of helium associated with them. Dissociation of helium from loops is observed in the range 300–800 K followed by loop annealing above 900 K. A sharp reduction of τ2around 1300 K is assigned to multiple helium occupancy of voids, resulting in their transformation into stable bubbles. Helium retention in bubbles is found stable up to the highest annealing temperature of 1700 K. The bubble parameters deduced from the positron lifetime results reveal that the pressure in the bubbles is maintained at the near-equilibrium value and that the vacancy mode of bubble growth is operative, in contrast to the reported growth of athermal bubbles in molybdenum following very low energy helium implantation where loop punching mechanism seems to control the excess pressure in bubbles. A brief comparison is also made between the observed behaviour of helium with that of hydrogen in molybdenum and the differences are discussed.
点击下载:
PDF (651KB)
返 回