Temperature dependence of He trapping in niobium

The total amount and the depth distributions of 9 and 15 keV implanted ³He ions trapped in polycrystalline niobium have been studied using the ³He(d,p)⁴He reaction. The implantation target temperature was varied from 20 to 1000° C and subsequent anneal studies were carried out for temperatures up to 1600° C. For implantation temperatures below 400° C all ²He particles coming to rest in the target are trapped. Between 500°C and 1000°C the trapping probability decreases gradually with increasing temperature to a few percent. A greater amount of helium is always retained upon annealing of a lower temperature implant to a particular temperature than is retained for implantation at that temperature.